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pdfUNITED STATES OF AMERICA
BEFORE THE
FEDERAL ENERGY REGULATORY COMMISSION
North American Electric Reliability
Corporation
)
)
Docket No. _______
JOINT PETITION OF THE
NORTH AMERICAN ELECTRIC RELIABILITY CORPORATION AND
NORTHEAST POWER COORDINATING COUNCIL, INC. FOR APPROVAL OF
PROPOSED REGIONAL RELIABILITY STANDARD PRC-006-NPCC-2
Edward Schwerdt
President and CEO
Northeast Power Coordinating Council, Inc.
1040 Avenue of the Americas, 10th Floor
New York, NY 10018
(212) 840-1070
(212) 302-2782 – facsimile
[email protected]
President and CEO for the Northeast Power
Coordinating Council, Inc.
James McGrane
Senior Counsel
Lauren Perotti
Senior Counsel
North American Electric Reliability Corporation
1325 G Street, N.W., Suite 600
Washington, D.C. 20005
(202) 400-3000
(202) 644-8099– facsimile
[email protected]
[email protected]
Counsel for the North American Electric
Reliability Corporation
December 23, 2019
TABLE OF CONTENTS
I.
SUMMARY ............................................................................................................................ 2
II.
NOTICES AND COMMUNICATIONS ................................................................................ 3
III.
BACKGROUND ................................................................................................................. 3
A.
Regulatory Framework ..................................................................................................... 4
B.
NPCC Regional Reliability Standards Development Process.......................................... 5
C.
History of the PRC-006-NPCC Standard ......................................................................... 6
D.
Development of the Proposed Regional Reliability Standard.......................................... 7
IV.
JUSTIFICATION FOR APPROVAL.................................................................................. 8
A.
Overview of Proposed Modifications .............................................................................. 8
B.
Proposed Modifications to NPCC Regional Reliability Standard PRC-006-NPCC-2 .... 9
C.
Enforceability of Proposed Regional Reliability Standard ............................................ 16
V.
VI.
EFFECTIVE DATE .............................................................................................................. 16
CONCLUSION .................................................................................................................. 17
Exhibit A
Proposed Reliability Standard PRC-006-NPCC-2 – Automatic Underfrequency
Load Shedding
Exhibit B
Implementation Plan for Proposed Regional Reliability Standard PRC-006NPCC-2
Exhibit C
Order No. 672 Criteria for Proposed Regional Reliability Standard PRC-006NPCC-2
Exhibit D
Summary of Development History and Complete Record of Development
Exhibit E
NPCC Standard Drafting Team Roster
Exhibit F
Violation Risk Factor and Violation Severity Level Justification
i
UNITED STATES OF AMERICA
BEFORE THE
FEDERAL ENERGY REGULATORY COMMISSION
North American Electric Reliability
Corporation
)
)
Docket No. _______
JOINT PETITION OF THE
NORTH AMERICAN ELECTRIC RELIABILITY CORPORATION AND
NORTHEAST POWER COORDINATING COUNCIL, INC. FOR APPROVAL OF
PROPOSED REGIONAL RELIABILITY STANDARD PRC-006-NPCC-2
Pursuant to Section 215(d)(1) of the Federal Power Act (“FPA”) 1 and Section 39.5 2 of the
Federal Energy Regulatory Commission (“FERC” or “Commission”) regulations, the North
American Electric Reliability Corporation (“NERC”) 3 and the Northeast Power Coordinating
Council, Inc. (“NPCC”) hereby submit proposed Regional Reliability Standard PRC-006-NPCC2 – Automatic Underfrequency Load Shedding (“UFLS”) for Commission approval. Proposed
Regional Reliability Standard PRC-006-NPCC-2 establishes consistent and coordinated
requirements for the design, implementation, and analysis of automatic UFLS programs among all
NPCC applicable entities.
NERC and NPCC request that the Commission approve proposed Regional Reliability
Standard PRC-006-NPCC-2 (Exhibit A) as just, reasonable, not unduly discriminatory or
1
16 U.S.C. § 824o (2018).
2
18 C.F.R. § 39.5 (2019).
3
The Commission certified NERC as the electric reliability organization (“ERO”) in accordance with
Section 215 of the FPA. N. Am. Elec. Reliability Corp., 116 FERC ¶ 61,062 (2006) (“ERO Certification Order”).
Unless otherwise indicated, capitalized terms used in this Petition shall have the meaning set forth in the
Glossary of Terms Used in NERC Reliability Standards (“NERC Glossary”),
https://www.nerc.com/pa/Stand/Glossary%20of%20Terms/Glossary_of_Terms.pdf, or Appendix 2 to the NERC
Rules of Procedure, Definitions Used in the NERC Rules of Procedure,
https://www.nerc.com/AboutNERC/Pages/Rules-of-Procedure.aspx.
1
preferential, and in the public interest. NERC and NPCC also request approval of the associated
implementation plan (Exhibit B), and the associated Violation Risk Factors (“VRFs”) and
Violation Severity Levels (“VSLs”) (Exhibit F), and the retirement of Regional Reliability
Standard PRC-006-NPCC-1.
As required by Section 39.5(a) 4 of the Commission’s regulations, this Petition presents the
technical basis and purpose of the proposed Regional Reliability Standard, a summary of the
development history (Exhibit D), and a demonstration that the proposed Regional Reliability
Standard meets the criteria identified by the Commission in Order No. 672 5 (Exhibit C). Proposed
Regional Reliability Standard PRC-006-NPCC-2 was approved by the NPCC Board of Directors
on May 1, 2019. On September 5, 2019, the NPCC Board of Directors approved the correction of
an errata to the proposed Regional Reliability Standard. On November 5, 2019, the NERC Board
of Trustees adopted the proposed Regional Reliability Standard PRC-006-NPCC-2.
I.
SUMMARY
The purpose of proposed Regional Reliability Standard PRC-006-NPCC-2 is to establish
more stringent and specific NPCC underfrequency load shedding (“UFLS”) program requirements
than the NERC continent-wide PRC-006 standard, such that declining frequency is arrested and
recovered in accordance with established NPCC performance requirements. NPCC has revised
currently effective Regional Reliability Standard PRC-006-NPCC-1 to remove redundancies with
the currently effective continent-wide UFLS Reliability Standard PRC-006-3, clarify obligations
4
18 C.F.R. § 39.5(a).
5
The Commission specified in Order No. 672 certain general factors it would consider when assessing
whether a particular Reliability Standard is just and reasonable. See Rules Concerning Certification of the Electric
Reliability Organization; and Procedures for the Establishment, Approval, and Enforcement of Electric Reliability
Standards, Order No. 672, 114 FERC¶ 61,104, at PP 262, 321-37 (“Order No. 672”), order on reh’g, Order No.
672-A, 114 FERC ¶ 61,328 (2006).
2
for registered entities, improve communication of island boundaries to affected registered entities,
and provide entities with the flexibility to calculate net load shed for UFLS in certain situations.
For these reasons, and as discussed more fully herein, NERC and NPCC respectfully
request the Commission approve proposed Regional Reliability Standard PRC-006-NPCC-2, the
associated VRFs and VSLs, the Effective Date, and the retirement of currently effective
Regional Reliability Standard PRC-006-NPCC-1. The following petition presents the
justification for approval and supporting documentation.
II.
NOTICES AND COMMUNICATIONS
Notices and communications with respect to this filing may be addressed to the following: 6
Edward Schwerdt*
President and CEO
Northeast Power Coordinating Council, Inc.
1040 Avenue of the Americas, 10th Floor
New York, NY 10018
(212) 840-1070
[email protected]
III.
James McGrane*
Senior Counsel
Lauren Perotti*
Senior Counsel
North American Electric Reliability
Corporation
1325 G Street, N.W., Suite 600
Washington, D.C. 20005
202-400-3000
[email protected]
[email protected]
BACKGROUND
The following background information is provided below: (a) an explanation of the
regulatory framework for NERC and Regional Reliability Standards; (b) an explanation of the
NPCC Regional Reliability Standards development process; and (c) the history of development
of proposed Regional Reliability Standard PRC-006-NPCC-2.
6
Persons to be included on the Commission’s service list are identified by an asterisk. NERC respectfully
requests a waiver of Rule 203 of the Commission’s regulations, 18 C.F.R. § 385.203, to allow the inclusion of more
than two persons on the service list in this proceeding.
3
A.
Regulatory Framework
By enacting the Energy Policy Act of 2005, 7 Congress entrusted the Commission with the
duties of approving and enforcing rules to ensure the reliability of the Nation’s Bulk-Power System
(“BPS”), and with the duty of certifying an ERO that would be charged with developing and
enforcing mandatory Reliability Standards, subject to Commission approval. Section 215(b)(1) 8
of the FPA states that all users, owners, and operators of the BPS in the United States will be
subject to Commission-approved Reliability Standards. Section 215(d)(5) 9 of the FPA authorizes
the Commission to order the ERO to submit a new or modified Reliability Standard. Section
39.5(a) 10 of the Commission’s regulations requires the ERO to file with the Commission for its
approval each Reliability Standard that the ERO proposes should become mandatory and
enforceable in the United States, and each modification to a Reliability Standard that the ERO
proposes should be made effective.
The Commission has the regulatory responsibility to approve Reliability Standards that
protect the reliability of the BPS and to ensure that such Reliability Standards are just, reasonable,
not unduly discriminatory or preferential, and in the public interest. Pursuant to Section 215(d)(2)
of the FPA 11 and Section 39.5(c) 12 of the Commission’s regulations, the Commission will give
due weight to the technical expertise of the ERO with respect to the content of a Reliability
Standard.
7
16 U.S.C. § 824o.
8
Id. § 824o(b)(1).
9
Id. § 824o(d)(5).
10
18 C.F.R. § 39.5(a).
11
16 U.S.C. § 824o(d)(2).
12
18 C.F.R. § 39.5(c)(1).
4
Similarly, the Commission approves Regional Reliability Standards proposed by
Regional Entities if the Regional Reliability Standard is just, reasonable, not unduly
discriminatory or preferential, and in the public interest. 13 In addition, Order No. 672 requires
further criteria for Regional Reliability Standards. A regional difference from a continent-wide
Reliability Standard must either be: (1) more stringent than the continent-wide Reliability
Standard, or (2) necessitated by a physical difference in the BPS. 14 NPCC is not an
“interconnection-wide” Regional Entity and its standards are intended to apply only to that part
of the Eastern Interconnection within the NPCC geographical footprint and Québec.
B.
NPCC Regional Reliability Standards Development Process
The proposed Regional Reliability Standard was developed in an open and fair manner
and in accordance with the Commission-approved NPCC Regional Standard Processes Manual
(“RSPM”). 15 NPCC’s RSPM provides for reasonable notice and opportunity for public
comment, due process, openness, inclusiveness, balance of interests, transparency, and timeliness
in developing Reliability Standards and thus addresses certain of the criteria for approving
Reliability Standards. 16 The development process is “open to all persons and organizations that
are directly and materially affected by the reliability of the NPCC’s Bulk Electric System.” 17
NPCC considers the comments of all stakeholders, and a vote of stakeholders and the NPCC
13
Section 215(d)(2) of the FPA and 18 C.F.R. § 39.5(a).
14
Rules Concerning Certification of the Electric Reliability Organization; and Procedures for the
Establishment, Approval, and Enforcement of Electric Reliability Standards, Order No. 672 at 114 FERCP 291.
15
The currently-effective NPCC RSPM was approved by the Commission on December 23, 2014 (see N. Am.
Elec. Reliability Corp., RR14-7-000 (Dec. 23, 2014) (unpublished letter order)), and is available at
https://www.npcc.org/Standards/Regional%20Standards%20General/NPCC%20Regional%20%20Standard%20Proc
esses%20Manual_FERC_Approved_version_1_20141223.pdf.
16
Order Accepting ERO Compliance Filing, Accepting ERO/Regional Entity Delegation Agreements, and
Accepting Regional Entity 2007 Business Plans, 119 FERC ¶ 61,060, at P 17 (2007).
17
NPCC RSPM at 5.
5
Board of Directors is required to approve a Regional Reliability Standard. After approval by the
NPCC Board of Directors, NERC posts each proposed Regional Reliability Standard for an
additional comment period and must consider any comments received. The NERC Board of
Trustees must adopt the proposed Regional Reliability Standard before the proposed Regional
Reliability Standard is submitted to the Commission for approval.
C.
History of the PRC-006-NPCC Standard
The PRC-006-NPCC Standard was originally developed to “ensure[ ] the development of
an effective automatic [UFLS] program in order to preserve the security and integrity of the
[BPS] during declining system frequency events, in coordination with the NERC UFLS
reliability standard characteristics.” 18 The first version of the Regional Reliability Standard,
PRC-006-NPCC-1, became effective in 2015. 19 In approving Regional Reliability Standard
PRC-006-NPCC-1, the Commission stated,
“Regional Reliability Standard PRC-006-NPCC-1 is designed to operate in
conjunction with the NERC continent-wide UFLS Reliability Standard PRC-0061 by mitigating the consequences of underfrequency events, while
accommodating differences in system transmission and distribution topology
among NPCC planning coordinators. Regional Reliability Standard PRC-006NPCC-1 includes requirements that are not found in the corresponding NERC
Reliability Standard PRC-006-1 and that are more stringent than Reliability
18
Petition of the North American Electric Reliability Corporation for Approval of Proposed NPCC Regional
Reliability Standard PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding, Docket No. RM12-12-000, at
1 (May 4, 2012).
19
Regional Reliability Standard PRC-006-NPCC-1 was approved by the Commission in Order No. 775.
Regional Reliability Standard PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding, Order No. 775, 142
FERC ¶ 61,128 (2013).
6
Standard PRC-006-1 while accommodating differences in system transmission
and distribution topology among NPCC planning coordinators due to historical
design criteria, makeup of load demands, and generation resources.” 20
D.
Development of the Proposed Regional Reliability Standard
Following revisions to NERC’s PRC-006 Automatic Underfrequency Load Shedding and
PRC-024 Generator Frequency and Voltage Protective Relay Settings Standards, NPCC initiated
a project to review currently effective Regional Reliability Standard PRC-006-NPCC-1
requirements for potential revisions or retirements. As further described in Exhibit D hereto,
proposed Regional Reliability Standard PRC-006-NPCC-2 was developed in accordance with the
NPCC RSPM. On February 10, 2019, proposed Regional Reliability Standard PRC-006-NPCC2 was approved by the NPCC ballot body with a 95.9% percent affirmative vote at 80.0%
quorum. The NPCC Board of Directors approved the proposed Regional Reliability Standard on
May 1, 2019. NERC posted the Regional Reliability Standard for a 45-day comment period
concluding on June 21, 2019. The single commenter agreed that NPCC’s process was open,
inclusive, balanced, transparent, and that due process was followed. On August 6, 2019, prior to
adoption of the proposed Regional Reliability Standard by the NERC Board of Trustees, NPCC
was notified of an errata in the proposed Regional Reliability Standard and took steps pursuant to
Section 8 of the NPCC RSPM to correct the errata. On September 5, 2019, the NPCC Board of
Directors approved the correction of the errata to the proposed Regional Reliability Standard.
On November 5, 2019, the NERC Board of Trustees adopted proposed Regional Reliability
Standard PRC-006-NPCC-2.
20
Id. at P 11.
7
IV.
JUSTIFICATION FOR APPROVAL
As discussed below and in Exhibit C, proposed Regional Reliability Standard PRC-006-
NPCC-2 – Automatic Underfrequency Load Shedding is just, reasonable, not unduly
discriminatory or preferential, and in the public interest. As described more fully herein, the
proposed Regional Reliability Standard provides reliability benefits for the BPS in the NPCC
region by establishing more stringent and specific NPCC UFLS program requirements than the
NERC continent-wide PRC-006 Reliability Standard and ensuring that the program is designed
such that declining frequency is arrested and recovered in accordance with established NPCC
performance requirements stipulated in the proposed Regional Reliability Standard. The
remainder of this section of the petition addresses: (a) an overview of the proposed
modifications, (b) the proposed modifications to the proposed Regional Reliability Standard, and
(c) the enforceability of the proposed Regional Reliability Standard.
A.
Overview of Proposed Modifications
Proposed Regional Reliability Standard PRC-006-NPCC-2 makes the following changes
to the prior version:
•
removes redundancies with the most recent version of continent-wide NERC Reliability
Standard, PRC-006-3;
•
ensures UFLS island boundaries, once identified, are provided upon request to affected
entities;
•
removes a requirement for minimum time UFLS relay time delays and adds it to a table
in an Attachment;
•
adds the ability for a Transmission Owner or Distribution Provider to calculate net load
shed for UFLS if direct metering is not available;
8
•
makes a number of minor clarifications; and
•
clarifies that any compensatory load shedding for non-conformance with the
Underfrequency trip specification for generation (in service prior to July 1, 2015) must be
within the same island as the generator resides.
These changes resulted in a reduction in the number of Requirements from 23 in currently
enforceable Regional Reliability Standard PRC-006-NPCC-1, to 16 in proposed Regional
Reliability Standard PRC-006-NPCC-2. A detailed explanation of the changes in proposed
Regional Reliability Standard PRC-006-NPCC-2 is provided below. A Summary of Changes and
the NPCC mapping document are provided in Exhibit D.
B.
Proposed Modifications to NPCC Regional Reliability Standard PRC-006-
NPCC-2
This section discusses the modifications in proposed Regional Reliability Standard PRC006-NPCC-2.
1) Requirement R1
Proposed Requirement R1 requires each Planning Coordinator within the Eastern
Interconnection portion of NPCC to design a UFLS program, pertaining to islands wholly within
the NPCC region, having specific performance characteristics. Proposed Requirement R1
replaces in part currently effective PRC-006-NPCC-1 Requirement R2, the substance of which is
now addressed by proposed Requirements R1, R2, and R3.
2) Requirement R2
Proposed Requirement R2 requires each Planning Coordinator to provide UFLS island
boundaries, as identified per the NERC continent-wide PRC-006 Standard on UFLS, to
Distribution Providers, Generator Owners, and Transmission Owners within 30 calendar days of
9
receipt of a request. Proposed Requirement R2 ensures that the entities aggregating load are
aware of the island boundaries. Proposed Requirement R2 carries forward currently effective
PRC-006-NPCC-1 Requirement R3 largely unchanged, keeping the requirement to provide
information about UFLS island boundaries to affected entities while moving the requirements
regarding compensatory load shedding to proposed Requirement R13. Aspects of currently
effective PRC-006-NPCC-1 Requirements R1 and R2 were incorporated into proposed
Requirement R2 as well.
3) Requirement R3
Proposed Requirement R3 requires each Distribution Provider and Transmission Owner
in the Eastern Interconnection portion of NPCC to implement an automatic UFLS program
pursuant to more detailed requirements specified in Attachment C, Tables 1-3. Proposed
Requirement R3 also ensures that the entities aggregating load are aware of the island
boundaries. Proposed Requirement R3 replaces in part currently effective PRC-006-NPCC-1
Requirement R1, the substance of which is now addressed by proposed Requirements R2, R3,
and R13, and also replaces in part currently effective PRC-006-NPCC-1 Requirement R2, the
substance of which is now addressed by proposed Requirements R1, R2, and R3.
4) Requirement R4
Proposed Requirement R4 requires each Distribution Provider or Transmission Owner in
the Eastern Interconnection portion of NPCC or the Quebec Interconnection that cannot meet the
UFLS program parameters specified in Attachment C, Tables 1-3 or by its Planning Coordinator,
respectively, to notify its Planning Coordinator that it does not meet the UFLS program
parameters and either develop a Corrective Action Plan, provide its Planning Coordinator with a
technical study showing that the deviations from the program parameters will not result in failure
10
of UFLS performance criteria being met for any island, or provide its Planning Coordinator with
an analysis that no alternative load shedding solution is available that would allow the entity to
comply with Attachment C Table 2 or Table 3. Proposed Requirement R4 combines currently
effective PRC-006-NPCC-1 Requirements R4 and R5 into a single new requirement and clarifies
what registered entities must do in the event they are unable to meet the UFLS program
parameters specified in the Tables of Attachment C or by its Planning Coordinator, and in what
timeframe the registered entities must take the defined actions.
5) Requirement R5
Proposed Requirement R5 requires each Planning Coordinator to develop and review
settings for inhibit thresholds at least once per five calendar years to be utilized within its
region’s UFLS program. Proposed Requirement R5 carries forward currently effective PRC006-NPCC-1 Requirement R8 largely unchanged, but lengthens the periodicity of developing
and reviewing settings for inhibit thresholds from once per calendar year to once per five
calendar years. This timeframe coincides with the periodicity of UFLS studies and reduces the
administrative burden of developing and reviewing such settings on an annual basis as required
in currently effective PRC-006-NPCC-1 Requirement R8.
6) Requirement R6
Proposed Requirement R6 requires each Planning Coordinator to provide each
Transmission Owner and Distribution Provider within its Planning Coordinator area the
applicable inhibit thresholds within 30 calendar days of any changes. Proposed Requirement R6
carries forward currently effective PRC-006-NPCC-1 Requirement R9 substantively unchanged,
clarifying matters by removing language about each Planning Coordinator providing each
Transmission Owner and Distribution Provider within its Planning Coordinator area the
11
applicable inhibit thresholds within 30 days of the initial determination of those inhibit
thresholds, which is no longer needed because the initial determination of the inhibit thresholds
occurred as a consequence of the implementation of currently effective PRC-006-NPCC-1.
7) Requirement R7
Proposed Requirement R7 requires that each Distribution Provider and Transmission
Owner that receives a notification pursuant to proposed Requirement R6 develop and submit an
implementation plan with respect to inhibit thresholds for approval by the Planning Coordinator
within 90 calendar days of the request from the Planning Coordinator. Proposed Requirement
R7 carries forward currently effective PRC-006-NPCC-1 Requirement R11 substantively
unchanged, clarifying that the trigger for action is receipt of a notification pursuant to proposed
Requirement R6, and changing the requirement numbers that are referenced.
8) Requirement R8
Proposed Requirement R8 requires each Distribution Provider and Transmission Owner
to implement the inhibit thresholds provided by the Planning Coordinator in accordance with
proposed Requirement R6 and based on the Planning Coordinator approved implementation plan
in accordance with proposed Requirement R7. Proposed Requirement R8 carries forward
currently effective Requirement R10 substantively unchanged, updating the requirement
numbers referenced and adding clarification that the Planning Coordinator provides the inhibit
thresholds and approves the implementation plan.
9) Requirement R9
Proposed Requirement R9 requires each Transmission Owner and Distribution Provider
to annually provide documentation, with no more than 15 calendar months between updates, to
its Planning Coordinator of the actual net Load that would have been shed by the UFLS relays at
12
each UFLS stage. If measured data is unavailable, then calculated data may be used. Proposed
Requirement R9 revises currently effective PRC-006-NPCC-1 Requirement R12 by adding
language that allows the calculation of load from the nearest available metering rather than actual
metering. Currently effective PRC-006-NPCC-1 Requirement R12 had been placing undue
burden on registered entities to install metering when the actual net Load that would have been
shed by the UFLS relays at each UFLS stage could be accurately calculated as a cost-effective
alternative.
10) Requirement R10
Proposed Requirement R10 requires each Generator Owner to set each generator
underfrequency trip relay, if so equipped, on or below the appropriate generator underfrequency
trip protection setting threshold curve in Figure 2, except as otherwise exempted in proposed
Requirements R13 and R16. Proposed Requirement R10 carries forward currently effective
PRC-006-NPCC-1 Requirement R13 substantively unchanged, but clarifies that the
Underfrequency trip relay must be set to operate “on or below” the appropriate curve instead of
“below” the appropriate curve in order to clarify what settings are considered compliant under
the proposed Regional Reliability Standard.
11) Requirement R11
Proposed Requirement R11 requires each Generator Owner to transmit the generator
underfrequency trip setting and time delay within 45 calendar days of the Planning Coordinator’s
request. Proposed Requirement R11 carries forward currently effective PRC-006-NPCC-1
Requirement R14 substantively unchanged, updating only the numbering of the requirement.
12) Requirement R12
13
Proposed Requirement R12 requires each Generator Owner with a new generating unit,
or an existing generator increasing its net capacity by greater than 10% to design measures or
auxiliary systems or devices used for the control and protection of auxiliary systems such that the
generating unit will not trip for underfrequency conditions above the appropriate generator
underfrequency trip protection setting threshold curve in Figure 2. Proposed Requirement R12
carries forward currently effective PRC-006-NPCC-1 Requirement R15 substantively
unchanged, removing “on or after the effective date” language from the currently effective
Requirement because Version 1 of the Regional Reliability Standard has been in place and
transition and implementation concerns no longer need to be addressed in the proposed
Requirement, and also changes the numbers of Figures referenced in the currently effective
Requirement.
13) Requirement R13
Proposed Requirement R13 requires each Generator Owner with existing non-nuclear
units in service prior to July 1, 2015 that have underfrequency protections set to trip above the
appropriate curve in Figure 2 to set the underfrequency protection to operate at the lowest
frequency allowed by the plan design and licensing limitations and to transmit the existing
underfrequency settings and any changes to them along with the technical basis for the settings
to the Planning Coordinator. The proposed Requirement also requires each Planning Coordinator
to arrange for compensatory load shedding in accordance with Attachments A and B, depending
on geographic location, and as provided by a Distribution Provider or Transmission Owner that
is adequate to compensate for the loss of generator(s) due to early tripping that is within the
UFLS island identified by the Planning Coordinator in Requirement R2. Proposed Requirement
R13 carries forward currently effective PRC-006-NPCC-1 Requirement R16 substantively
14
unchanged, adding language to clarify that any compensatory load shedding must be within the
same island as the generating unit resides.
14) Requirement R14
Proposed Requirement R14 requires each Planning Coordinator in Ontario, Quebec, and
the Maritime provinces to apply the criteria described in Attachment A to determine the
compensatory load shedding that is required in Requirement R13.3 for generating units in its
respective NPCC area. Proposed Requirement R14 carries forward currently effective PRC-006NPCC-1 Requirement R17 substantively unchanged, updating only the numbering of the
requirement and the number of a referenced requirement.
15) Requirement R15
Proposed Requirement R15 requires each Planning Coordinator in the ISO-NE and
NYISO Planning Coordinator areas to apply the criteria described in Attachment B to determine
the compensatory load shedding that is required in Requirement R13.4 for generating units in its
respective NPCC area. Proposed Requirement R15 carries forward currently effective PRC-006NPCC-1 Requirement R18 substantively unchanged, updating only the numbering of the
requirement and the number of a referenced requirement.
16) Requirement R16
Proposed Requirement R16 requires each Generator Owner of existing nuclear generating
plans with units that have underfrequency relay threshold settings above the Eastern
Interconnection generator tripping curve in Figure 2 based on their licensing design to set the
underfrequency protection to operate at a frequency as low as possible in accordance with the
plan design and licensing limitations but not greater than 57.8 Hz, set the frequency trip setting
upper tolerance to no great than + 0.1 Hz, and transmit the initial frequency trip setting and any
15
changes to the setting and the technical basis for the setting to the Planning Coordinator.
Proposed Requirement R16 carries forward currently effective PRC-006-NPCC-1 Requirement
R19 substantively unchanged, updating only the numbering of the requirement and the number
of a Figure referenced in the requirement.
C.
Enforceability of Proposed Regional Reliability Standard
The proposed Regional Reliability Standard includes Measures that support each
requirement by clearly identifying what is required and how the requirement will be enforced.
These Measures help ensure that the requirements will be enforced in a clear, consistent, and
non-preferential manner and without prejudice to any party. 21 Additionally, the proposed
Regional Reliability Standard includes VRFs and VSLs. The VRFs and VSLs provide guidance
on the way that the requirements of the proposed Regional Reliability Standard will be enforced.
The VRFs and VSLs for the proposed Regional Reliability Standard continue to comport with
NERC and Commission guidelines related to their assignment. Exhibit F provides a detailed
review of the revised VRFs and VSLs, and the analysis of how the VRFs and VSLs were
determined using these guidelines.
V.
EFFECTIVE DATE
NERC respectfully requests that the Commission approve the proposed implementation
plan, provided in Exhibit B hereto. Under the proposed implementation plan, the proposed
Regional Reliability Standard would become effective on the first day of the first calendar
quarter following the applicable governmental and regulatory approvals. Applicable registered
entities would be required to comply with all proposed Requirements, except for proposed
Requirement R3, on that date. Proposed Requirement R3 would become enforceable on the first
21
Order No. 672 at P 327.
16
day of the first calendar quarter 12 months following applicable governmental and regulatory
approvals. Requirement R3 requires a 12 month implementation because entities need time to
modify their circuits (in terms of the percentage of load shed) in order to meet the attributes
described in Tables 1-3 of Attachment C due to the increasing penetration of Distributed Energy
Resources (“DERs”) in the NPCC region. Currently effective Regional Reliability Standard
PRC-006-NPCC-1 would be retired immediately prior to the effective date of proposed Regional
Reliability Standard PRC-006-NPCC-2.
VI.
CONCLUSION
For the reasons set forth above, NERC respectfully requests that the Commission approve:
•
•
•
•
proposed Regional Reliability Standard PRC-006-NPCC-2 in Exhibit A;
the other associated elements in the proposed Regional Reliability Standard in
Exhibit F, including the VRFs and VSLs;
the proposed Implementation Plan; included in Exhibit B; and
the retirement of Regional Reliability Standard PRC-006-NPCC-1.
Respectfully submitted,
/s/ James McGrane
Edward Schwerdt
President and CEO
Northeast Power Coordinating Council, Inc.
1040 Avenue of the Americas, 10th Floor
New York, NY 10018
(212) 840-1070
[email protected]
President and CEO for the Northeast Power
Coordinating Council, Inc.
James McGrane
Senior Counsel
Lauren Perotti
Senior Counsel
North American Electric Reliability
Corporation
1325 G Street, N.W., Suite 600
Washington, D.C. 20005
202-400-3000
[email protected]
[email protected]
Counsel for the North American Electric
Reliability Corporation
Date: December 23, 2019
17
Exhibit A
Proposed Reliability Standard
1
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Functional Entities:
4.1.1. Generator Owner
4.1.2. Planning Coordinator
4.1.3. Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
4.1.4. Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
5.
Effective Date: See Implementation Plan.
B. Requirements and Measures
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5
Hz for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent-wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
Page 1 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent-wide
PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1-3.
M3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1-3).
R4. Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified
by its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• Within 30 calendar days of determining that it does not meet the
specified parameters, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Page 2 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3.
M4. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
R5. Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and
time) to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M5. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
R6. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within
30 calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M6. Each Planning Coordinator shall provide evidence such as letters, emails or other
dated documentation that demonstrates that it meets Requirement R6.
R7. Each Distribution Provider and Transmission Owner that receives a notification
pursuant to Requirement R6 shall develop and submit an implementation plan with
respect to inhibit thresholds for approval by the Planning Coordinator within 90
calendar days of the request from the Planning Coordinator. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
M7. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
R8.
Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
M8. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
Page 3 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R9.
Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by
measuring or calculating Load through the switches that would disconnect load if
triggered by the UFLS relays. If measured data is unavailable then calculated data may
be used. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
R10. Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements
R13 and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
R11. Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
R12. Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
Page 4 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R13. For existing non-nuclear units in service prior to July 1, 2015, that have
underfrequency protections set to trip above the appropriate curve in Figure 2:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R13.
R14. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
R15. Each Generator Owner, Distribution Provider or Transmission Owner within the ISONE Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that
Page 5 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
is required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed
the methodology described in Attachment B and meets Requirement R15.
R16. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at a frequency setting that
is as low as possible in accordance with the plant design and licensing
limitations but not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and
dated documentation that demonstrates that it meets Requirement R16.
Page 6 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 1
Curve Data:
Overfrequency Requirements
t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
t > 30 s
f = 60.7 Hz
Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
NERC PRC-006-NPCC (Regional Standard on UFLS)
Page 7 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
Page 8 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority:
Northeast Power Coordinating Council
1.2. Evidence Retention:
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 2, 3, 4, 5, 8, and 9.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 6, and 7.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 15.
The Generator Owner shall keep evidence for three calendar years for Measures
10, 11, 12, 13, and 16.
1.3. Compliance Monitoring and Enforcement Program:
Compliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
Page 9 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Violation Severity Levels
Violation Severity Levels
R#
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator failed to
design an UFLS program having
performance characteristics that
prevent frequency from remaining
below 59.5 Hz in accordance with
Figure 1.
R2.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 30 calendar
days and up to and including 40
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 40 calendar
days but less than and including 50
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 50 calendar
days but less than and including 60
days following a request.
The Planning Coordinator failed to
provide its UFLS island boundaries,
as identified per the NERC
continent-wide PRC-006 Standard
on UFLS. within 60 calendar days
following a request.
R3.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%
or less of the relays identified as
included in the UFLS program, or
amount of load tripped is within
10% deviation from the required
amount of Load required to be
shed at each stage
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%40% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
20% deviation from the required
amount of Load required to be
shed at each stage m
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 40%60% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
30% deviation from the required
amount of Load required to be
shed at each stage.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on >
60% of the relays identified as
included in the UFLS program, or
amount of load tripped has a >
30% deviation from the required
amount of Load required to be
shed at each stage
R4.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
but exceeded the permissible
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program failed to meet all of items
in Requirement 5 within 60
Page 10 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items within a time
greater than 20 calendar days but
less than or equal to 30 calendar
days.
time frame for one or more of the
4 items within a time greater than
30 calendar days but less than or
equal to 60 calendar days.
calendar days of permissible time
for each item.
R5.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
100% but more than (and
including) 95% of relays within its
region’s UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
95% but more than (and including)
90% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and including)
85% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
85% of relays within its region’s
UFLS program.
R6.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 30 calendar days and up to
and including 40 calendar days of
any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 40 calendar days but less
than and including 50 calendar
days of any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar days but less
than and including 60 calendar
days of any changes.
R7.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 100 calendar days
and up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
R8.
Implemented the inhibit threshold
settings provided by the Planning
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
The Planning Coordinator failed to
provide to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds
within 60 calendar days after any
changes
The Distribution Provider or
Transmission Owner failed to
develop and submit its
implementation plan within 120
days following the request.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
Page 11 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
less than 100% but more than (and
including) 95% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 95% but more than (and
including) 90% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 90% but more than (and
including) 85% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 85% of UFLS relays.
R9.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 16 calendar
months but less than (and
including)17 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar
months but less than (and
including)18 calendar months
since last update.
The Distribution Provider or
Transmission Owner failed to
provide to its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 within 18 calendar months
since last update.
R10.
N/A
N/A
N/A
R11.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
45calendar days and less than (and
including) 55 calendar days of the
Planning Coordinator’s request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
55 calendar days and less than
(and including) 65 calendar days of
the Planning Coordinator’s
request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
65 calendar days and less than
(and including) 75 calendar days of
the Planning Coordinator’s
request.
The Generator Owner failed to
transmit the generator
underfrequency trip setting and
time delay within 75 calendar days
of the Planning Coordinator’s
request.
R12.
N/A
N/A
The Generator Owner with a new
generating unit, or an existing
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
The Generator Owner did not set
each generator underfrequency
trip relay, if so equipped, on or
below the appropriate generator
underfrequency trip protection
settings threshold curve in Figure
2, except as otherwise exempted.
Page 12 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
generator increasing its net
capability by greater than 10%:
Did not fulfill the obligation of
Requirement R12; Part 12.1
capability by greater than 10%, did
not fulfill the obligations of
Requirement R12, Part 12.1 and
Part 12.2.
OR
Did not fulfill the obligation of
Requirement R12, Part 12.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirement 13, Part 13.1
R13.
N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinatoras specified
in Requirement R13, Part 13.2.
R14.
N/A
N/A
N/A
The Planning Coordinator did not
apply the criteria described in
Attachment A to determine the
compensatory load shedding that
is required.
R15.
N/A
N/A
N/A
The Generator Owner, Distribution
Provider, or Transmission Owner
did not apply the criteria described
in Attachment B to determine the
compensatory load shedding that
is required.
R16.
N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis for
the settings to the Planning
The Generator Owner:
The Generator Owner did not
fulfill the obligations of
Requirement R16, Part 16.1 and
Part 16.2.
Failed to set the underfrequency
protection as specified in
Requirement R16; Part 16.1
The Planning Coordinator in
Ontario, Québec and the Maritime
Provinces or the Generator Owner
within the ISO-NE and in NYISO
Planning Coordinator areas failed
to arrange for compensatory load
shedding as specified in
Requirement R13, Part 13.3.
OR
Page 13 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Coordinator as specified in
Requirement R16, Part 16.3.
Failed to set the frequency trip
setting upper tolerance as
specified in Requirement R16, Part
16.2.
D. Regional Variances
None.
E. Associated Documents
Technical Rationale
Page 14 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Version History
Version
Date
Action
1
2-9-2012
Adopted by Board of Trustees
2
6-23-2015
RSAR Submitted
2
11-5-2019
Adopted by the NERC Board of Trustees
Change
Tracking
Page 15 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Standard Attachments
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (July 1, 2015 PRC-006-NPCC-1). The list must
indicate generating units, if any, that have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
Page 16 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage
(or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the electric system
for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
Page 17 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (July 1, 2015 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above
the appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip
above the appropriate curve in Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the same and smallest island identified by
the Planning Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet
the set points defined by the appropriate curve in Figure 2, the Generator Owner
shall arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
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PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facility.
Page 19 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2-3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing auxiliary relay
operating times, communication times, and the rated breaker interrupting time. The underfrequency relay operating
time is measured from the time when frequency passes through the frequency threshold setpoint, using a test rate of
frequency decay of 0.2 Hz per second. If the relay operating time is dependent on the rate of frequency decay, the
underfrequency relay operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear
frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the current
year.
Page 20 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
28 – 50
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing auxiliary relay
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the current
year.
operating times, communication times, and the rated breaker interrupting time. The underfrequency relay operating
time is measured from the time when frequency passes through the frequency threshold setpoint, using a test rate of
frequency decay of 0.2 Hz per second. If the relay operating time is dependent on the rate of frequency decay, the
underfrequency relay operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear
frequency decay of 0.2 Hz per second.
Page 21 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
• HVDC dynamic modeling
Rationale for Requirement R1: Figure 1 of this document shows the NPCC underfrequency
criteria for the Eastern Interconnection portion of NPCC. Figure 1 also shows the NERC criteria
as defined in the NERC PRC Standard on UFLS.
Rationale for Requirement R5: An inhibit function provides supervisory control over a UFLS
relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if the sensed
voltage decreases below an adjustable setting. An undervoltage inhibit function is intended to
prevent operation of a UFLS relay when the transmission supply is lost to distribution station
feeding many induction motors. Following loss of the transmission supply, motors may support
the voltage while the motors coast down in speed. The motors coasting down (ringing down)
will look like an underfrequency event to the relay. The inhibit setting is set to a voltage above
which the motor load is expected to sustain. This prevents the underfrequency relay from
Page 22 of 23
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
tripping and locking out distribution feeder breakers supplying the motor load, between the
time the transmission supply line trips and the time when the line recloses to restore the load.
Voltages sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower
than voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring down
voltages because of cable charging. Therefore, care must be taken so that the voltage inhibit
setting is not higher than the voltage at which UFLS relays are required to operate to meet UFLS
performance criteria.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the UFLS
program for every entity should perfectly match that prescribed in this Standard, for all phases
of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs. weekend vs. holidays),
daily (morning, noon, and night), etc. for all of the identified islands. Practically, however, this
is obviously not possible because the load cycles of the various areas and sub-areas within any
given island do not perfectly track the load cycle of the overall island. The UFLS program, on
the other hand, is designed based on peak conditions for the overall island. The percentages of
actual load shedding that would occur for any conditions other than peak, therefore, can only
approximate that prescribed in the Standard. To that end, Requirement R11 requires entities
to document measured loads in the UFLS program coincident with their own annual peak,
whether or not that peak occurs at the same time or in the same season as the peak of the
identified island in which their load resides. Using individual entity peaks vs. overall island
peaks provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
Page 23 of 23
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
A. Introduction
2.11. Title:
Automatic Underfrequency Load Shedding
2.22. Number:
PRC-006-NPCC-21
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2.33. Purpose: The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this documentTo provide a
regional reliability standard that ensures the development of an effective automatic
underfrequency load shedding (UFLS) program in order to preserve the security and
integrity of the bulk power system during declining system frequency events in
coordination with the NERC UFLS reliability standard characteristics.
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2.44. Applicability:
a.4.1.
Generator Owner
b.4.2.
Planning Coordinator
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c.4.3.
Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program established by
the Planning CoordinatorsDistribution Provider
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d.4.4.
Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program established by
the Planning CoordinatorsTransmission Owner
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2.55. Effective Date:
See Implementation PlanFor the Eastern Interconnection & Québec Interconnection
portions of NPCC excluding the Independent Electricity System Operator (IESO) Planning
Coordinator area of NPCC in Ontario, Canada:
The effective date for Requirements R1, R2, R3, R4, R5, R6, and R7 is the first day
of the first calendar quarter following applicable regulatory approval but no
earlier than January 1, 2016 The effective date for Requirements R8 through R23
is the first day of the first calendar quarter two years following applicable
governmental and regulatory approval.
For the Independent Electricity System Operator (IESO) Planning Coordinator’s area of
NPCC in Ontario, Canada:
All requirements are effective the first day of the first calendar quarter following
applicable governmental and regulatory approval but no earlier than April 1,
2017.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
B. Requirements and Measures
R1.
Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5 Hz
for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
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M1.
R2.
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
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Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
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M2.
R3.
Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
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Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent wide
PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
1.• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1-3.
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M3.
Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1-3).
R4.
M4.
R5.
Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified by
its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
• Within 30 calendar days of determining that it does not meet the
specified parameters, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3
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Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
R1
Each Planning Coordinator shall establish requirements for entities
aggregating their UFLS programs for each anticipated island and requirements for
compensatory load shedding based on islanding criteria (required by the NERC PRC
Standard on UFLS). [Violation Risk Factor: Medium] [Time Horizon: Long Term
Planning]
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Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and time)
to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M5.
R6.
Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
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Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon: Operations
Planning]
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M6.
R7.
Each Planning Coordinator shall provide evidence such as letters, emails or other dated
documentation that demonstrates that it meets Requirement R6.
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Each Distribution Provider and Transmission Owner that receives a notification pursuant
to Requirement R6 shall develop and submit an implementation plan with respect to
inhibit thresholds for approval by the Planning Coordinator within 90 calendar days of
the request from the Planning Coordinator. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
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M7.
R8.
Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
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Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
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M8.
Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
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R9.
Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by measuring
or calculating Load through the switches that would disconnect load if triggered by the
UFLS relays. If measured data is unavailable then calculated data may be used.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
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M9.
Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R10.
Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements R13
and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
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R11.
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Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation Risk
Factor: Lower] [Time Horizon: Operations Planning]
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M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
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R12.
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Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
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R2
Each Planning Coordinator shall, within 30 days of completion
of its system studies required by the NERC PRC Standard on UFLS, identify
to the Regional Entity the generation facilities within its Planning
Coordinator Area necessary to support the UFLS program performance
characteristics. [Violation Risk Factor: Medium] [Time Horizon: Long
Term Planning]
R3
Each Planning Coordinator shall provide to the Transmission
Owner, Distribution Provider, and Generator Owner within 30 days upon
written request the requirements for entities aggregating the UFLS
programs and requirements for compensatory load shedding program
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
derived from each Planning Coordinator’s system studies as determined by
Requirement R1. [Violation Risk Factor: Low] [Time Horizon: Long Term
Planning]
R4
Each Distribution Provider and Transmission Owner in the
Eastern Interconnection portion of NPCC shall implement an automatic
UFLS program reflecting normal operating conditions excluding outages for
its Facilities based on frequency thresholds, total nominal operating time and
amounts specified in Attachment C, Tables 1 through 3, or shall collectively
implement by mutual agreement with one or more Distribution Providers
and Transmission Owners within the same island identified in Requirement
R1 and acting as a single entity, provide an aggregated automatic UFLS
program that sheds their coincident peak aggregated net Load, based on
frequency thresholds, total nominal operating time and amounts specified in
Attachment C, Tables 1 through 3.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
Formatted: Font: Bold
R5
Each Distribution Provider or Transmission Owner that must
arm its load to trip on underfrequency in order to meet its requirements as
specified and by doing so exceeds the tolerances and/or deviates from the
number of stages and frequency set points of the UFLS program as specified
in the tables contained in Requirement R4 above, as applicable depending on
its total peak net Load shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
5.1
Inform its Planning Coordinator of the need to exceed the
stated tolerances or the number of stages as shown in UFLS Attachment C,
Table 1 if applicable and
Formatted: Font: Bold
5.2
Provide its Planning Coordinator with a technical study that
demonstrates that the Distribution Providers or Transmission Owners
specific deviations from the requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on the bulk power system.
5.3
Inform its Planning Coordinator of the need to exceed the
stated tolerances of UFLS Attachment C, Table 2 or Table 3, and in the case
of Attachment C, Table 2 only, the need to deviate from providing two stages
of UFLS, if applicable, and
5.4
Provide its Planning Coordinator with an analysis
demonstrating that no alternative load shedding solution is available that
would allow the Distribution Provider or Transmission Owner to comply
with UFLS Attachment C Table 2 or Attachment C Table 3.
Page 6 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R6 Each Distribution Provider and Transmission Owner in the
Québec Interconnection portion of NPCC shall implement an automatic
UFLS program for its Facilities based on the frequency thresholds, slopes,
total nominal operating time and amounts specified in Attachment C, Table
4 or shall collectively implement by mutual agreement with one or more
Distribution Providers and Transmission Owners within the same island,
identified in Requirement R1, an aggregated automatic UFLS program that
sheds Load based on the frequency thresholds, slopes, total nominal
operating time and amounts specified in Attachment C, Table 4. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
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R7
Each Distribution Provider and Transmission Owner shall set
each underfrequency relay that is part of its region’s UFLS program with the
following minimum time delay:
7.1
Eastern Interconnection – 100 ms
7.2
Québec Interconnection – 200 ms
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R8 Each Planning Coordinator shall develop and review once per
calendar year settings for inhibit thresholds (such as but not limited to
voltage, current and time) to be utilized within its region's UFLS program.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
Formatted: Font: 12 pt, Bold
R9
Each Planning Coordinator shall provide each Transmission
Owner and Distribution Provider within its Planning Coordinator area the
applicable inhibit thresholds within 30 days of the initial determination of
those inhibit thresholds and within 30 days of any changes to those
thresholds. [Violation Risk Factor: Medium] [Time Horizon: Operations
Planning]
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R10 Each Distribution Provider and Transmission Owner shall
implement the inhibit threshold settings based on the notification provided
by the Planning Coordinator in accordance with Requirement R9. [Violation
Risk Factor: High] [Time Horizon: Operations Planning]
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R11 Each Distribution Provider and Transmission Owner shall
develop and submit an implementation plan within 90 days of the request
from the Planning Coordinator for approval by the Planning Coordinator in
accordance with R9. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
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Page 7 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R12 Each Transmission Owner and Distribution Provider shall
annually provide documentation, with no more than 15 months between
updates, to its Planning Coordinator of the actual net Load that would have
been shed by the UFLS relays at each UFLS stage coincident with their
integrated hourly peak net Load during the previous year, as determined by
measuring actual metered Load through the switches that would be opened
by the UFLS relays. [Violation Risk Factor: Lower] [Time Horizon: Long
Term Planning]
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R13 Each Generator Owner shall set each generator
underfrequency trip relay, if so equipped, below the appropriate generator
underfrequency trip protection settings threshold curve in Figure 1, except
as otherwise exempted in Requirements R16 and R19. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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R14 Each Generator Owner shall transmit the generator
underfrequency trip setting and time delay to its Planning Coordinator
within 45 days of the Planning Coordinator’s request. [Violation Risk
Factor: High] [Time Horizon: Operations Planning]
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R15 Each Generator Owner with a new generating unit, scheduled
to be in service on or after the effective date of this Standard, or an existing
generator increasing its net capability by greater than 10% shall: [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
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15.1 Design measures to prevent the generating unit from tripping
directly or indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 1.
15.2 Design auxiliary system(s) or devices used for the control and
protection of auxiliary system(s), necessary for the generating unit operation
such that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip protection
settings threshold curve in Figure 1.
R16 Each Generator Owner of existing non-nuclear units in service
prior to the effective date of this standard that have underfrequency
Page 8 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
protections set to trip above the appropriate curve in Figure 1 shall:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
16.1 Set the underfrequency protection to operate at the lowest
frequency allowed by the plant design and licensing limitations.
16.2 Transmit the existing underfrequency settings and any changes
to the underfrequency settings along with the technical basis for the settings
to the Planning Coordinator.
16.3 Have compensatory load shedding, as provided by a
Distribution Provider or Transmission Owner that is adequate to
compensate for the loss of their generator due to early tripping.
R17 Each Planning Coordinator in Ontario, Quebec and the
Maritime provinces shall apply the criteria described in Attachment A to
determine the compensatory load shedding that is required in Requirement
R16.3 for generating units in its respective NPCC area. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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R18
Each Generator Owner, Distribution Provider or Transmission
Owner within the Planning Coordinator area of ISO-NE or the New York
ISO shall apply the criteria described in Attachment B to determine the
compensatory load shedding that is required in Requirement R16.3 for
generating units in its respective NPCC area. [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
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R19 Each Generator Owner of existing nuclear generating plants with units
that have underfrequency relay threshold settings above the Eastern
Interconnection generator tripping curve in Figure 1, based on their
licensing design basis, shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
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19.1
Set the underfrequency protection to operate at as low a
frequency as possible in accordance with the plant design and licensing
limitations but not greater than 57.8Hz.
19.2
0.1 Hz.
Set the frequency trip setting upper tolerance to no greater than +
19.3
Transmit the initial frequency trip setting and any changes to the
setting and the technical basis for the settings to the Planning Coordinator.
Page 9 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R20
The Planning Coordinator shall update its UFLS program
database as specified by the NERC PRC Standard on UFLS. This database
shall include the following information: [Violation Risk Factor: Lower]
[Time Horizon: Operations Planning]
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20.1
For each UFLS relay, including those used for compensatory load
shedding, the amount and location of load shed at peak, the corresponding
frequency threshold and time delay settings.
20.2
The buses at which the Load is modeled in the NPCC library
power flow case.
20.3
A list of all generating units that may be tripped for
underfrequency conditions above the appropriate generator underfrequency
trip protection settings threshold curve in Figure 1, including the frequency
trip threshold and time delay for each protection system.
20.4
The location and amount of additional elements to be switched for
voltage control that are coordinated with UFLS program tripping.
20.5 A list of all UFLS relay inhibit functions along with the corresponding
settings and locations of these relays.
R21
Each Planning Coordinator shall notify each Distribution
Provider, Transmission Owner, and Generator Owner within its Planning
Coordinator area of changes to load distribution needed to satisfy UFLS
program performance characteristics as specified by the NERC PRC
Standard on UFLS.[Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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R22
Each Distribution Provider, Transmission Owner and Generator
Owner shall implement the load distribution changes based on the
notification provided by the Planning Coordinator in accordance with
Requirement R21. [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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R23
Each Distribution Provider, Transmission Owner and Generator
Owner shall develop and submit an implementation plan within 90 days of
the request from the Planning Coordinator for approval by the Planning
Coordinator in accordance with Requirement R21. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
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Page 10 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
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R13.
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For existing non-nuclear units in service prior to July 1, 2015, that have underfrequency
protections set to trip above the appropriate curve in Figure 2: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
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the same style
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated documentation
demonstrating that it meets Requirement R13.
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R14.
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Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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Page 11 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
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R15.
Each Generator Owner, Distribution Provider or Transmission Owner within the ISO-NE
Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that is
required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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M15. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the NYISO shall provide evidence such as reports,
memorandum, or other documentation that demonstrates that it followed the
methodology described in Attachment B and meets Requirement R15.
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R16.
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Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1 Set the underfrequency protection to operate at a frequency setting that is as
low as possible in accordance with the plant design and licensing limitations but
not greater than 57.8 Hz.
16.2 Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3 Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and dated
documentation that demonstrates that it meets Requirement R16.
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Page 12 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Figure 1
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
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Formatted: Left
Figure 1
Page 13 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Formatted: List Number
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Formatted: Font: 8 pt, Bold
Formatted Table
Curve Data:
Overfrequency Requirements
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Source
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t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
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t > 30 s
f = 60.7 Hz
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NERC PRC-006 (Continent-Wide Standard on UFLS)
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Underfrequency Requirements
Source
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t≤2s
f = 58.0 Hz
NERC PRC-006 (Continent-Wide Standard on UFLS)
Formatted Table
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
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NERC PRC-006-NPCC (Regional Standard on UFLS)
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Formatted: Check spelling and grammar
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Page 14 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
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Page 15 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Measures
M1
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
M3 Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
M4 Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped, and the corresponding frequency thresholds,
on those circuits included in its UFLS program to achieve the individual and
cumulative percentages identified in Requirement R4. (Attachment C Tables 1-3).
M5 Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
M6 Each Distribution Provider and Transmission Owner in the Québec Interconnection
shall have evidence such as documentation or reports containing the location and
amount of load to be tripped and the corresponding frequency thresholds on those
circuits included in its UFLS program to achieve the load values identified in Table 4
of Requirement R6. (Attachment C Table 4).
Page 16 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M7 Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the
minimum time delay, in accordance with Requirement R7.
M8 Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R8.
M9 Each Planning Coordinator shall provide evidence such as letters, emails, or other
dated documentation that demonstrates that it meets Requirement R9.
M10 Each Distribution Provider and Transmission Owner shall provide evidence such as
test reports, data sheets or other documentation that demonstrates that it meets
Requirement R10.
M11 Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails or other dated documentation that demonstrates that it meets
Requirement R11.
M12 Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the frequency set point, the net amount of load shed and the
percentage of its peak load at each stage of its UFLS program coincident with the
integrated hourly peak of the previous year that demonstrates that it meets Requirement
R12.
M13 Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement R13.
M14 Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R14.
M15 Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R15.
M16 Each Generator Owner with existing non-nuclear units in service prior to the effective
date of this Standard which have underfrequency tripping that is not compliant with
Page 17 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Requirement R13 shall provide evidence such as reports, spreadsheets, memorandum
or dated documentation demonstrating that it meets Requirement R16.
M17 Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall
provide evidence such as emails, memorandum or other documentation that
demonstrates that it followed the methodology described in Attachment A and meets
Requirement R17.
M18 Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the New York ISO shall provide evidence
such as emails, memorandum, or other documentation that demonstrates that it
followed the methodology described in Attachment B and meets Requirement R18.
M19 Each Generator Owner of nuclear units that have been specifically identified by NPCC
as having generator trip settings above the generator trip curve in Figure 1 shall
provide evidence such as letters, reports and dated documentation that demonstrates
that it meets Requirement R19.
M20 Each Planning Coordinator shall provide evidence such as spreadsheets, system
studies, or other documentation that demonstrates that it meets the requirements of
Requirement R20.
M21 Each Planning Coordinator shall provide evidence such as emails, memorandum or
other dated documentation that it meets Requirement R21.
M22 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as reports, spreadsheets or other documentation that demonstrates that it
meets Requirement R22.
M23 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as letters, emails or other dated documentation that demonstrates it
meets Requirement 23.
C. Compliance
1.11. Compliance Monitoring Process
a.1.1.
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Compliance Enforcement Authority
Page 18 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Northeast Power Coordinating CouncilPCC Compliance Committee
a.
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Compliance Monitoring Period and Reset Time Frame
Not Applicable
b.1.2.
DataEvidence Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 24, 35, 46, 57, 810, and 119, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 3, 86, and 79, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall keep evidence
for three calendar years for Measure 17.
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The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 185, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
103, 114, 125, 136, and 169.
c.1.3.
Compliance Monitoring and Assessment Processes
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ComSelf -Certifications.
Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.pliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
d.
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Additional Compliance Information
None.
Page 19 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Page 20 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
1.2
Violation Severity Levels
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Violation Severity Levels
uiremen
tR#
Lower VSL
Moderate VSL
High VSL
Formatted Table
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator
failed to design an UFLS
program having performance
characteristics that prevent
frequency from remaining
below 59.5 Hz in accordance
with Figure 1.
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R2.
The Planning Coordinator
provided its UFLS island
boundaries, as identified per
the NERC continent-wide PRC006 Standard on UFLS but did
so more than 30 calendar days
and up to and including 40 days
following a request.
The Planning Coordinator
provided its UFLS island
boundaries, as identified per
the NERC continent-wide
PRC-006 Standard on UFLS
but did so more than 40
calendar days but less than
and including 50 days
following a request.
The Planning Coordinator
provided its UFLS island
boundaries, as identified per
the NERC continent-wide
PRC-006 Standard on UFLS
but did so more than 50
calendar days but less than
and including 60 days
following a request.
The Planning Coordinator
failed to provide its UFLS
island boundaries, as
identified per the NERC
continent-wide PRC-006
Standard on UFLS. within 60
calendar days following a
request.
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The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on
20% or less of the relays
identified as included in the
UFLS program, or amount of
load tripped is within 10%
deviation from the required
The Distribution Provider or
Transmission Owner failed
to apply appropriate
settings on 20%-40% of the
relays identified as included
in the UFLS program, or
amount of load tripped is
within 20% deviation from
The Distribution Provider or
Transmission Owner failed
to apply appropriate
settings on 40%-60% of the
relays identified as included
in the UFLS program, or
amount of load tripped is
within 30% deviation from
The Distribution Provider or
Transmission Owner failed
to apply appropriate
settings on > 60% of the
relays identified as included
in the UFLS program, or
amount of load tripped has
a > 30% deviation from the
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R3.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R4.
R5.
amount of Load required to be
shed at each stage
the required amount of
Load required to be shed at
each stage m
the required amount of
Load required to be shed at
each stage.
required amount of Load
required to be shed at each
stage
The Distribution Provider or
Transmission Owner that
cannot meet the tolerances
and/or number of stages and
frequency set points specified
in the UFLS Program fulfilled its
obligations for Requirement R5,
Parts %.1 through Part 5.4 but
exceeded the permissible time
frame for one or more of the 4
items by a period of up to 10
calendar days but less than or
equal to 20 calendar days.
The Distribution Provider or
Transmission Owner that
cannot meet the tolerances
and/or number of stages
and frequency set points
specified in the UFLS
Program fulfilled its
obligations for Requirement
R5, Parts %.1 through Part
5.4 but exceeded the
permissible time frame for
one or more of the 4 items
within a time greater than
20 calendar days but less
than or equal to 30 calendar
days.
The Distribution Provider or
Transmission Owner that
cannot meet the tolerances
and/or number of stages
and frequency set points
specified in the UFLS
Program fulfilled its
obligations but exceeded
the permissible time frame
for one or more of the 4
items within a time greater
than 30 calendar days but
less than or equal to 60
calendar days.
The Distribution Provider or
Transmission Owner that
cannot meet the tolerances
and/or number of stages
and frequency set points
specified in the UFLS
Program failed to meet all of
items in Requirement 5
within 60 calendar days of
permissible time for each
item.
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The Planning Coordinator
developed or reviewed settings
for inhibit thresholds at least
once per five calendar years,
for less than 100% but more
than (and including) 95% of
relays within its region’s UFLS
program.
The Planning Coordinator
developed or reviewed
settings for inhibit
thresholds at least once
per five calendar years, for
less than 95% but more
than (and including) 90% of
relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed
settings for inhibit
thresholds at least once per
five calendar years, for less
than 90% but more than
(and including) 85% of relays
within its region’s UFLS
program.
The Planning Coordinator
developed or reviewed
settings for inhibit
thresholds at least once per
five calendar years, for less
than 85% of relays within its
region’s UFLS program.
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Page 22 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R6.
R7.
R8.
The Planning Coordinator
provided to a Transmission
Owner or Distribution Provider
within its Planning Coordinator
area the applicable inhibit
thresholds more than 30
calendar days and up to and
including 40 calendar days of
any changes.
The Planning Coordinator
provided to a Transmission
Owner or Distribution
Provider within its Planning
Coordinator area the
applicable inhibit thresholds
more than 40 calendar days
but less than and including
50 calendar days of any
changes.
The Planning Coordinator
provided to a Transmission
Owner or Distribution
Provider within its Planning
Coordinator area the
applicable inhibit thresholds
more than 50 calendar days
but less than and including
60 calendar days of any
changes.
The Planning Coordinator
failed to provide to a
Transmission Owner or
Distribution Provider within
its Planning Coordinator
area the applicable inhibit
thresholds within 60
calendar days after any
changes
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The Distribution Provider or
Transmission Owner developed
and submitted its
implementation plan more
than 90 calendar days and up
to and including 100 calendar
days following the request.
The Distribution Provider or
Transmission Owner
developed and submitted its
implementation plan more
than 100 calendar days and
up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner
developed and submitted its
implementation plan more
than 110 calendar days and
up to and including 120
calendar days following the
request.
The Distribution Provider or
Transmission Owner failed
to develop and submit its
implementation plan within
120 days following the
request.
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Implemented the inhibit
threshold settings provided by
the Planning Coordinator in
accordance with the Planning
Coordinator approved
implementation plan for less
than 100% but more than (and
including) 95% of UFLS relays.
The Distribution Provider or
Transmission Owner
implemented the inhibit
threshold settings provided
by the Planning Coordinator
in accordance with the
Planning Coordinator
approved implementation
plan for less than 95% but
more than (and including)
90% of UFLS relays.
The Distribution Provider or
Transmission Owner
implemented the inhibit
threshold settings provided
by the Planning Coordinator
in accordance with the
Planning Coordinator
approved implementation
plan for less than 90% but
more than (and including)
85% of UFLS relays.
The Distribution Provider or
Transmission Owner
implemented the inhibit
threshold settings provided
by the Planning Coordinator
in accordance with the
Planning Coordinator
approved implementation
plan for less than 85% of
UFLS relays.
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Page 23 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9.
R10.
R11.
The Distribution Provider or
Transmission Owner provided
to its Planning Coordinator
documentation of the actual
net Load that would have been
shed by the UFLS relays at each
UFLS stage as described in
Requirement R11 more than 15
calendar months but less than
(and including) 16 calendar
months since last update.
The Distribution Provider or
Transmission Owner
provided to its Planning
Coordinator documentation
of the actual net Load that
would have been shed by
the UFLS relays at each UFLS
stage as described in
Requirement R11 more than
16 calendar months but less
than (and including)17
calendar months since last
update.
The Distribution Provider or
Transmission Owner
provided to its Planning
Coordinator documentation
of the actual net Load that
would have been shed by
the UFLS relays at each UFLS
stage as described in
Requirement R11 more than
17 calendar months but less
than (and including)18
calendar months since last
update.
The Distribution Provider or
Transmission Owner failed
to provide to its Planning
Coordinator documentation
of the actual net Load that
would have been shed by
the UFLS relays at each UFLS
stage as described in
Requirement R11 within 18
calendar months since last
update.
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N/A
N/A
N/A
The Generator Owner did
not set each generator
underfrequency trip relay, if
so equipped, on or below
the appropriate generator
underfrequency trip
protection settings
threshold curve in Figure 2,
except as otherwise
exempted.
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The Generator Owner failed
to transmit the generator
underfrequency trip setting
and time delay within 75
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The Generator Owner
transmitted the generator
underfrequency trip setting and
time delay more than
The Generator Owner
transmitted the generator
underfrequency trip setting
and time delay more than
The Generator Owner
transmitted the generator
underfrequency trip setting
and time delay more than
Page 24 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R12.
45calendar days and less than
(and including) 55 calendar
days of the Planning
Coordinator’s request.
55 calendar days and less
than (and including) 65
calendar days of the
Planning Coordinator’s
request.
65 calendar days and less
than (and including) 75
calendar days of the
Planning Coordinator’s
request.
calendar days of the
Planning Coordinator’s
request.
N/A
N/A
The Generator Owner with
a new generating unit, or
an existing generator
increasing its net capability
by greater than 10%:
The Generator Owner with a
new generating unit, or an
existing generator increasing
its net capability by greater
than 10%, did not fulfill the
obligations of Requirement
R12, Part 12.1 and Part 12.2.
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The Planning Coordinator in
Ontario, Québec and the
Maritime Provinces or the
Generator Owner within the
ISO-NE and in NYISO
Planning Coordinator areas
failed to arrange for
compensatory load
shedding as specified in
Requirement R13, Part 13.3.
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Did not fulfill the obligation
of Requirement R12; Part
12.1
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OR
Did not fulfill the obligation
of Requirement R12, Part
12.2.
R13.
N/A
The Generator Owner failed
to transmit the existing
underfrequency settings and
any changes to the
underfrequency settings
along with the technical
basis for the settings to the
Planning Coordinatoras
specified in Requirement
R13, Part 13.2.
The Generator Owner failed
to set the underfrequency
protection to operate at the
lowest frequency allowed by
the plant design and
licensing limitations a
specified in Requirement 13,
Part 13.1
Page 25 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R14.
R15.
R16.
N/A
N/A
N/A
N/A
N/A
The Generator Owner failed
to transmit the initial
frequency trip setting and
any changes to the setting
and the technical basis for
the settings to the Planning
Coordinator as specified in
Requirement R16, Part 16.3.
N/A
N/A
The Generator Owner:
Failed to set the
underfrequency protection
as specified in Requirement
R16; Part 16.1
The Planning Coordinator
did not apply the criteria
described in Attachment A
to determine the
compensatory load
shedding that is required.
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The Generator Owner,
Distribution Provider, or
Transmission Owner did not
apply the criteria described
in Attachment B to
determine the
compensatory load
shedding that is required.
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The Generator Owner did
not fulfill the obligations of
Requirement R16, Part 16.1
and Part 16.2.
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OR
Failed to set the frequency
trip setting upper tolerance
as specified in Requirement
R16, Part 16.2.
Page 26 of 42
Adopted by Board of Trustees: February 9, 2012
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Page 27 of 42
Adopted by Board of Trustees: February 9, 2012
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Standard Attachments
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PRC-006-NPCC-1 Attachment A
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Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
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The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operateThe Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible
for establishing the compensatory load shedding requirements for all existing non-nuclear units
in its NPCC area with underfrequency protections set to trip above the appropriate curve in
Figure 1. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure that
adequate compensatory load shedding is provided in all islands identified in Requirement R1 in
which the unit may operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (July 1, 2015 PRC-006-NPCC-1). The list must
indicate generating units, if any, that have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information for each unitThe Planning Coordinator
shall identify, compile and maintain an updated list of all existing non-nuclear generating
units in service prior to the effective date of this standard that have underfrequency
protections set to trip above the appropriate curve in Figure 1. The list shall include the
following information for each unit:
1.1.1
Generator name and generating capacity
2.1.2
Underfrequency protection trip settings, including frequency trip set
points and time delays
3.1.3
Physical and electrical location of the unit
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
4.1.4
All islands within which the unit may operate, as identified in
Requirement R1
5.2.
For each generating unit identified in (1) above, the Planning Coordinator shall
establish the requirements for compensatory load shedding based on criteria outlined
below:
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1.2.1
Arrange for a Distribution Provider or Transmission Owner that owns
UFLS relays within the island(s) identified by the Planning Coordinator within
which the generator may operate to provide compensatory load
sheddingArrange for a Distribution Provider or Transmission Owner that owns
UFLS relays within the island(s) identified by the Planning Coordinator in
Requirement R1 within which the generator may operate to provide compensatory
load shedding.
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2.2.2
In Ontario and in the Maritime provinces, Tthe compensatory load
shedding that is provided by the Distribution Provider or Transmission Owner
shall be in addition to the amount that the Distribution Provider or Transmission
Owner is required to shed as specified in Requirement R4..
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3.2.3
The compensatory load shedding shall be provided at the UFLS program
stage (or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2The compensatory load shedding shall be provided at the UFLS program
stage (or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 1 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 1 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest frequency
at which the subject generator will trip above the appropriate curve in Figure 1.
1.2.4
The amount of compensatory load shedding shall be equivalent
(±5%) to the average net generator megawatt output for the prior two calendar
years, as specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric systemThe amount of compensatory load shedding shall be equivalent
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0.75" + Tab after: 1" + Indent at: 1"
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
(±5%) to the average net generator megawatt output for the prior two calendar
years, as specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facilityIn the specific instance of
a generating unit that has been interconnected to the electric system for less than
two calendar years, the amount of compensatory load shedding shall be equivalent
(±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon
loss of the facility.
Page 30 of 42
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment B
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Compensatory Load Shedding Criteria for ISO-NE and NYISO:
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The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirementsThe Generator Owner in the New England states or New York State are
responsible for establishing a compensatory load shedding program for all existing non-nuclear
units with underfrequency protection set to trip above the appropriate curve in Figure 1 of this
standard. The Generator Owner shall follow the methodology below to determine compensatory
load shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (July 1, 2015 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above
the appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information associated with each unitThe Generator
Owner shall identify and compile a list of all existing non-nuclear generating units in
service prior to the effective date of this standard that has underfrequency protection set
to trip above the appropriate curve in Figure 1. The list shall include the following
information associated with each unit:
1.1.1
Generator name and generating capacity
2.1.2
Underfrequency protection trip settings, including frequency trip set
points and time delays
3.1.3
Physical and electrical location of the unit
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
4.1.4
Smallest island within which the unit may operate as identified by the
Planning Coordinator in Requirement R1 of this Standard.
5.2.
For each generating unit identified in (1) above, the Generator Owner shall
establish the requirements for compensatory load shedding based on criteria outlined
below:
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1.2.1
In cases where a Distribution Provider or Transmission Owner has
coordinated protection settings with the Generator Owner to cause the
generator to trip above the appropriate curve in Figure 2, the Distribution
Provider or Transmission Owner is responsible to provide the appropriate
amount of compensatory load to be shed within the same and smallest island
identified by the Planning Coordinator in Requirement R1 of this standardIn
cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 1, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the smallest island identified by the Planning Coordinator in
Requirement R1 of this standard.
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2.2.2
In cases where a Generator Owner has a generator that cannot physically
meet the set points defined by the appropriate curve in Figure 2, the Generator
Owner shall arrange for a Distribution Provider or Transmission Owner to
provide the appropriate amount of compensatory load to be shed within the
same and smallest island identified by the Planning Coordinator in Requirement
R1 of this standardIn cases where a Generator Owner has a generator that cannot
physically meet the set points defined by the appropriate curve in Figure 1, the
Generator Owner shall arrange for a Distribution Provider or Transmission Owner
to provide the appropriate amount of compensatory load to be shed within the
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
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3.2.3
The compensatory load shedding that is provided by the Distribution
Provider or Transmission Owner shall be in addition to the amount that the
Distribution Provider or Transmission Owner is required to shed as specified in
Requirement R4The compensatory load shedding that is provided by the
Distribution Provider or Transmission Owner shall be in addition to the amount
that the Distribution Provider or Transmission Owner is required to shed as
specified in Requirement R4.
4.2.4
The compensatory load shedding shall be provided at the UFLS program
stage with the frequency threshold setting at or closest to but above the
frequency at which the subject generator will trip The compensatory load
shedding shall be provided at the UFLS program stage with the frequency
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
threshold setting at or closest to but above the frequency at which the subject
generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric systemThe amount of compensatory load shedding shall be equivalent
(±5%) to the average net generator megawatt output for the prior two calendar
years, as specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facilityIn the specific instance of
a generating unit that has been interconnected to the electric system for less than
two calendar years, the amount of compensatory load shedding shall be equivalent
(±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon
loss of the facility.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
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PRC-006-NPCC-1 Attachment C
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW or more of peak net Load
shall implement a UFLS program with the following attributes:
Frequency
Threshold
(Hz)
Total Nominal
Operating
Time (s) 1
Load Shed at Stage as
% of TO or DP
Load
Cumulative Load Shed as % of
TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
27.5 – 28.5
59.5
10.0
2–3
1.
Formatted Table
– 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW or more and less than 100 MW
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating
Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW or more and less than 50 MW
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
Page 36 of 42
PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
UFLS Table 4: Quebec Interconnection
MW
at peak
Mvar
at peak
Total
Nominal
Operating
Time (s) 2
Rate
Frequency
(Hz)
(*Load must
be fixed at all
times when
above 60% of
peak load..)
Threshold Stage 1
–––
58.5
1000*
1000
0.30
Threshold Stage 2
–––
58.0
800*
800
0.30
Threshold Stage 3
–––
57.5
800
800
0.30
Threshold Stage 4
–––
57.0
800
800
0.30
–––
59.0
500
500
20.0
Slope Stage 1
-0.3 Hz/s
58.5
400
400
0.30
Slope Stage 2
-0.4 Hz/s
59.8
800*
800
0.30
Slope Stage 3
-0.6 Hz/s
59.8
800*
800
0.30
Slope Stage 4
-0.9 Hz/s
59.8
800
800
0.30
Threshold Stage 5
(anti-stall)
UFLS Table 1: Eastern Interconnection
Formatted: Font: +Body (Calibri)
MW2
Distribution Providers and Transmission Owners with 100
or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
TO or DP
% of TO or
Load
DP Load
2. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communications time, and the rated breaker interrupting time. The
underfrequency relay operating time shall be measured from the time when the frequency passes through the
frequency threshold set point.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
1
2
3
4
5
59.5
59.3
59.1
58.9
59.5
0.10
0.10
0.10
0.10
0.10
Operating
Time (s) 2
0.30
0.30
0.30
0.30
10.0
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6.5 – 7.5
6.5 – 7.5
6.5 – 7.5
6.5 – 7.5
2-3
6.5 – 7.5
13.5 – 14.5
20.5 – 21.5
27.5 – 28.5
29.5 – 31.5
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UFLS Table 2: Eastern Interconnection
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MW2
Distribution Providers and Transmission Owners with 50
or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
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UFLS Table 3: Eastern Interconnection
MW2
Formatted: Font: (Default) +Body (Calibri)
MW2
Distribution Providers and Transmission Owners with 25
or more and less than 50
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing auxiliary relay
operating times, communication times, and the rated breaker interrupting time. The underfrequency relay operating
time is measured from the time when frequency passes through the frequency threshold setpoint, using a test rate of
frequency decay of 0.2 Hz per second. If the relay operating time is dependent on the rate of frequency decay, the
underfrequency relay operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear
frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the current
year.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
1
59.5
1.
2.
0.10
Operating
Time (s) 1
0.30
TO or DP
Load
28 – 50
% of TO or
DP Load
28 – 50
The total nominal operating time includes the underfrequency relay operating time plus any interposing auxiliary relay
operating times, communication times, and the rated breaker interrupting time. The underfrequency relay operating
time is measured from the time when frequency passes through the frequency threshold setpoint, using a test rate of
frequency decay of 0.2 Hz per second. If the relay operating time is dependent on the rate of frequency decay, the
underfrequency relay operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear
frequency decay of 0.2 Hz per second.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the current
year.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Rationale Box:
Formatted: Font: Times New Roman
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
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PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Formatted: Font: +Body (Calibri)
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
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Rationale for Requirement R1: Figure 1 of this document shows the NPCC underfrequency
criteria for the Eastern Interconnection portion of NPCC. Figure 1 also shows the NERC criteria
as defined in the NERC PRC Standard on UFLS.
Rationale for Requirement R5: An inhibit function provides supervisory control over a UFLS
relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if the sensed
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
voltage decreases below an adjustable setting. An undervoltage inhibit function is intended to
prevent operation of a UFLS relay when the transmission supply is lost to distribution station
feeding many induction motors. Following loss of the transmission supply, motors may support
the voltage while the motors coast down in speed. The motors coasting down (ringing down)
will look like an underfrequency event to the relay. The inhibit setting is set to a voltage above
which the motor load is expected to sustain. This prevents the underfrequency relay from
tripping and locking out distribution feeder breakers supplying the motor load, between the
time the transmission supply line trips and the time when the line recloses to restore the load.
Voltages sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower
than voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring down
voltages because of cable charging. Therefore, care must be taken so that the voltage inhibit
setting is not higher than the voltage at which UFLS relays are required to operate to meet UFLS
performance criteria.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the UFLS
program for every entity should perfectly match that prescribed in this Standard, for all phases
of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs. weekend vs. holidays),
daily (morning, noon, and night), etc. for all of the identified islands. Practically, however, this
is obviously not possible because the load cycles of the various areas and sub-areas within any
given island do not perfectly track the load cycle of the overall island. The UFLS program, on
the other hand, is designed based on peak conditions for the overall island. The percentages of
actual load shedding that would occur for any conditions other than peak, therefore, can only
approximate that prescribed in the Standard. To that end, Requirement R11 requires entities
to document measured loads in the UFLS program coincident with their own annual peak,
whether or not that peak occurs at the same time or in the same season as the peak of the
identified island in which their load resides. Using individual entity peaks vs. overall island
peaks provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
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PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
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Page 42 of 42
Exhibit B
Implementation Plan
1
Implementation Plan
Regional Reliability Standard PRC-006-NPCC-2 – Automatic
Underfrequency Load Shedding
Applicable Standard(s)
•
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requested Retirement(s)
•
PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding
Applicable Entities
•
•
•
•
Generator Owners
Planning Coordinators
Distribution Providers that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Transmission Owners that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Background
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. To determine if the applicability of the standard needs to be revised in accordance with
Project 2014-01 Dispersed Generation Resources.
2. To determine if the performance requirements as contained in the criteria of NPCC
Directory#12 Sections 5.1.1 and 5.1.2 should be explicitly included in the requirements
of the Regional Standard and potential retirement of Directory 12 Automatic
Underfrequency Load Shedding Program.
3. Review Attachment C in PRC-006-NPCC-1 to address the implications of the design
assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. Review and revise Table 4 in Attachment C in accordance with the 2013 NPCC UFLS
Adequacy Assessment. Additionally, the applicability of Requirements R4 and R5 will be
reviewed to consider that Hydro Quebec is not part of the Eastern Interconnection.
Effective Date
All requirements with the exception of R3 will be enforceable on the first day of the first
calendar quarter following the applicable governmental and regulatory approvals.
R3 will be enforceable on the first day of the first calendar quarter 12 months following
the applicable governmental and regulatory approvals.
Retirement Date
The NPCC Regional Reliability Standard PRC-006-NPCC-1 shall be retired immediately
prior to the Effective Date of PRC-006-NPCC-2.
Exhibit C
Order No. 672 Criteria
Exhibit C
Order No. 672 Criteria
In Order No. 672, 1 the Commission identified a number of criteria it will use to analyze
Reliability Standards proposed for approval to ensure they are just, reasonable, not unduly
discriminatory or preferential, and in the public interest. The discussion below identifies these
factors and explains how the proposed Regional Reliability Standard meets or exceeds the
criteria.
1. Proposed Reliability Standards must be designed to achieve a specified reliability
goal and must contain a technically sound means to achieve that goal. 2
The purpose of proposed Regional Reliability Standard PRC-006-NPCC-2 is to establish
more stringent and specific NPCC UFLS program requirements than the NERC continent-wide
PRC-006 Standard. The program is designed such that declining frequency is arrested and
recovered in accordance with established NPCC performance requirements. The proposed
Regional Reliability Standard PRC-006-NPCC-2 is technically sound as it retains the reliabilityrelated content of the previously FERC-approved Regional Reliability Standard PRC-006NPCC-1, while updating the document to remove redundancies with the latest NERC continentwide PRC-006 Standard and clarify several points of confusion from the currently effective
Regional Reliability Standard.
1
Rules Concerning Certification of the Electric Reliability Organization; and Procedures for the
Establishment, Approval, and Enforcement of Electric Reliability Standards, Order No. 672, FERC Stats. & Regs. ¶
31,204, order on reh’g, Order No. 672-A, FERC Stats. & Regs. ¶ 31,212 (2006).
2
Order No. 672 at PP 321, 324.
1
2. Proposed Reliability Standards must be applicable only to users, owners and
operators of the BPS, and must be clear and unambiguous as to what is required
and who is required to comply. 3
The proposed Regional Reliability Standard is clear and unambiguous as to what is
required and who is required to comply, in accordance with Order No. 672. The proposed
Regional Reliability Standard applies to the following entities within the NPCC region:
Generator Owners; Planning Coordinators; Distribution Providers that are responsible for the
ownership, operation, or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators; and Transmission Owners that are responsible for the
ownership, operation, or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators. The proposed Regional Reliability Standard clearly
articulates the actions that such entities must take to comply with the Regional Reliability
Standard.
3. A proposed Reliability Standard must include clear and understandable
consequences and a range of penalties (monetary and/or non-monetary) for a
violation. 4
The Violation Risk Factors (“VRFs”) and Violation Severity Levels (“VSLs”) for the
proposed Reliability Standard comport with NERC and Commission guidelines related to their
assignment, as discussed further in Exhibit F. The assignment of the severity level for each VSL
is consistent with the corresponding requirement. The VSLs do not use any ambiguous
terminology, thereby supporting uniformity and consistency in the determination of similar
3
4
Order No. 672 at PP 322, 325.
Order No. 672 at P 326.
2
penalties for similar violations. Upon approval by the Commission, the ranges of penalties for
violations will continue to be based, in part, on the applicable VRF and VSL in accordance with
the sanctions table and the supporting penalty determination process described in the
Commission-approved NERC Sanction Guidelines, Appendix 4B to the NERC Rules of
Procedure. For these reasons, the proposed Reliability Standard includes clear and
understandable consequences and a range of penalties for a violation in accordance with Order
No. 672.
4. A proposed Reliability Standard must identify clear and objective criterion or
measure for compliance, so that it can be enforced in a consistent and nonpreferential manner. 5
The proposed Regional Reliability Standard contains measures that support the
requirements by clearly identifying what is required to demonstrate compliance. These measures
help provide clarity regarding the manner in which the requirements will be enforced and help
ensure that the requirements will be enforced in a clear, consistent, and non-preferential manner
and without prejudice to any party.
5. Proposed Reliability Standards should achieve a reliability goal effectively and
efficiently — but do not necessarily have to reflect “best practices” without regard
to implementation cost or historical regional infrastructure design. 6
The proposed Regional Reliability Standard achieves the reliability goals effectively and
efficiently in accordance with Order No. 672. The proposed Regional Reliability Standard builds
5
Order No. 672 at P 327.
6
Order No. 672 at P 328.
3
upon the BPS reliability protections provided by the NERC automatic UFLS standard by adding
more specificity for the NPCC region.
6. Proposed Reliability Standards cannot be “lowest common denominator,” i.e.,
cannot reflect a compromise that does not adequately protect BPS reliability.
Proposed Reliability Standards can consider costs to implement for smaller entities,
but not at consequences of less than excellence in operating system reliability. 7
The proposed Regional Reliability Standard does not reflect a “lowest common
denominator” approach that does not adequately protect BPS reliability.
7. Proposed Reliability Standards must be designed to apply throughout North
America to the maximum extent achievable with a single Reliability Standard while
not favoring one geographic area or regional model. It should take into account
regional variations in the organization and corporate structures of transmission
owners and operators, variations in generation fuel type and ownership patterns,
and regional variations in market design if these affect the proposed Reliability
Standard. 8
The proposed Regional Reliability Standard PRC-006-NPCC-2 is designed to work in
conjunction with NERC Reliability Standard PRC-006-3, while accommodating differences in
system transmission and distribution topology among NPCC planning coordinators and will be
enforceable for registered entities within the NPCC region.
7
Order No. 672 at P 329-30.
8
Order No. 672 at P 331.
4
8. Proposed Reliability Standards should cause no undue negative effect on
competition or restriction of the grid beyond any restriction necessary for
reliability. 9
The proposed Regional Reliability Standard has no undue negative impact on
competition and does not restrict the available transmission capability beyond what is necessary
for reliability.
9. The implementation time for the proposed Reliability Standard is reasonable. 10
The implementation plan for the proposed Regional Reliability Standard is just and
reasonable. Under the proposed implementation plan, the proposed Regional Reliability
Standard would become effective on the first day of the first calendar quarter following the
applicable governmental and regulatory approvals. Applicable registered entities would be
required to comply with all proposed Requirements, except for proposed Requirement R3, on
that date. Proposed Requirement R3 would become enforceable on the first day of the first
calendar quarter 12 months following the applicable governmental and regulatory approvals.
Requirement R3 requires a 12 month implementation because entities need time to modify their
circuits (in terms of the percentage of load shed) in order to meet the attributes described in
Tables 1-3 of Attachment C due to the increasing penetration of DERs in the NPCC region.
10. The Reliability Standard was developed in an open and fair manner and in
accordance with the Commission-approved Reliability Standard development
process. 11
9
Order No. 672 at P 332.
10
Order No. 672 at P 333.
11
Order No. 672 at P 334.
5
The proposed Regional Reliability Standard was developed in accordance with NERC’s
and NPCC’s Commission-approved processes for developing and approving Reliability
Standards. NPCC develops Regional Reliability Standards in accordance with the NPCC
Regional Standard Processes Manual. The development process is open to all persons and
organizations that are directly and materially affected by the reliability of the NPCC’s Bulk
Electric System. For more detail, please see the complete development history in Exhibit D.
11. NERC must explain any balancing of vital public interests in the development of
proposed Reliability Standards.12
NERC and NPCC have identified no competing vital public interests regarding the
request for approval of the proposed Regional Reliability Standard. No comments were received
that indicated the proposed Regional Reliability Standard conflicts with other vital public
interests.
12. Proposed Reliability Standards must consider any other appropriate factors. 13
No other negative factors relevant to whether the proposed Reliability Standard is just
and reasonable were identified.
12
Order No. 672 at P 335.
13
Order No. 672 at P 323.
6
Exhibit D
Summary of Development History and Complete Record of Development
1
Summary of Development History
1
Summary of Development History
The development record for proposed NPCC Regional Reliability Standard PRC-006NPCC-2 is summarized below.
I.
Overview of the Standard Drafting Team
When evaluating a proposed Reliability Standard, the Commission is expected to give
“due weight” to the technical expertise of the ERO. 1 The technical expertise of the ERO is
derived from the acceptance of qualified candidates for the Standard Drafting Team (“SDT”)
pursuant to Step 2.2 of the NPCC Regional Standard Processes Manual. 2 For this project, the
SDT consisted of industry experts, all with a diverse set of experiences. A roster of the Standard
Drafting Team members is included in Exhibit E.
II.
Standard Development History
A. Standard Authorization Request Development
On March 31, 2015, NPCC received a Regional Standard Authorization Request
(“RSAR”) to review “regional reliability standard PRC-006-NPCC-1 for potential revisions or
retirements made necessary by NERC’s PRC-006-1/PRC-006-2 Automatic Underfrequency
Load Shedding and PRC-024-1/PRC-024-2 Generator Frequency and Voltage Protective Relay
Settings standards.” 3 On June 26, 2015, the Regional Standards Committee accepted the RSAR
and authorized posting the RSAR, thereby starting the project to develop proposed Regional
Reliability Standard PRC-006-NPCC-2.
B. First Posting - Comment Period
1
Section 215(d)(2) of the Federal Power Act; 16 U.S.C. § 824o(d)(2) (2018).
2
The NPCC Regional Standard Processes Manual is available at
https://www.npcc.org/Standards/Regional%20Standards%20General/NPCC%20Regional%20%20Standard%20Proc
esses%20Manual_FERC_Approved_version_1_20141223.pdf.
3
See Exhibit D.
1
On September 1, 2017, NPCC posted proposed Regional Reliability Standard PRC-006NPCC-2 and a proposed implementation plan for a 45-day comment period, from September 1
through October 16, 2017. 4 Based on the comments received, the standard drafting team decided
to make substantive revisions to the proposed Regional Reliability Standard. Therefore, the
proposed Regional Reliability Standard was posted for an additional comment period.
C. Second Posting – Comment Period
On April 16, 2018, NPCC posted proposed Regional Reliability Standard PRC-006NPCC-2 and a proposed implementation plan for a 45-day comment period, from April 16, 2018
through May 31, 2018. Based on the comments received, the standard drafting team decided to
make substantive revisions to the proposed Regional Reliability Standard. Therefore, the
proposed Regional Reliability Standard was posted for an additional comment period.
D. Third Posting – Comment Period
On August 10, 2018, NPCC posted proposed Regional Reliability Standard PRC-006NPCC-2 and a proposed implementation plan for a 45-day comment period, from August 10,
2018 to September 25, 2018. Based on the comments received, the standard drafting team
decided to make substantive revisions to the proposed Regional Reliability Standard.
E. Final Ballot and NPCC Board of Directors Approval
Proposed Regional Reliability Standard PRC-006-NPCC-2 was posted for a 30-day preballot review and a subsequent 10-day ballot period through midnight December 22, 2018. Due
to a lack of quorum by the end of the ballot period, on January 9, 2019, NPCC issued a
notification that it was extending the ballot period until quorum was satisfied. On February 15,
4
Materials for this posting and subsequent postings are on the NPCC project page, available at
https://www.npcc.org/Standards/SitePages/DevStandardDetail.aspx?DevDocumentId=122.
2
2019, NPCC announced that the ballot for proposed Regional Reliability Standard PRC-006NPCC-2 and associated documents reached quorum at 80.95% of the total registered NPCC
General and Full Members Representatives, and receiving support from 76% of the voters. On
May 1, 2019, the NPCC Board of Directors approved the proposed Regional Reliability
Standard. On August 6, 2019, NPCC was notified of an errata and applied its Regional
Standards Development Process to address it. 5 On September 5, 2019, the NPCC Board of
Directors approved the correction of the errata to the proposed Regional Reliability Standard.
F. Board of Trustees Adoption
NERC posted proposed Regional Reliability Standard PRC-006-NPCC-2 for a 45 day
public comment period from May 8, 2019 to June 21, 2019. The NERC Board of Trustees
adopted proposed Regional Reliability Standard PRC-006-NPCC-2 on November 5, 2019. 6
5
The errata was in Figure 1 of the proposed Regional Reliability Standard. In the version of the proposed
Regional Reliability Standard that the NPCC Board of Directors approved on May 1, 2019, a performance curve had
an incorrect mathematical expression to describe it. Instead of “(0.1s - 1.1s; ≥58.0 Hz)”, the mathematical
expression should have read “(0.1s - 2.0s; ≥58.10 Hz)”.
6
NERC, November 2019 Board of Trustees Agenda Package, Agenda Item 5.c (PRC-006-NPCC-2 –
Automatic Underfrequency Load Shedding), available at
https://www.nerc.com/gov/bot/Agenda%20highlights%20and%20Mintues%202013/Board_Open_Meeting_Agenda
_Package_November_5_2019.pdf.
3
Complete Record of Development
1
Regional Standard:
PRC-006-NPCC
Automatic Underfrequency Load Shedding
Current Status:
Regional BOD Approved
View Supporting Documents
Approval & Implementation
Date
Action
09/05/19
Region BOD Approval
Ballot Period 11/12/2018 through 2/10/2019
Date
Action
02/10/19
Ballot Period Ended
12/12/18
Other Ballot Supporting Document posted publicly
56
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12/12/18
Other Ballot Supporting Document posted publicly
55
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12/12/18
Membership Ballot Document posted publicly
12/12/18
Membership Ballot Document posted publicly
12/12/18
Membership Ballot Document posted publicly
53
52
12/12/18
Membership Ballot Document posted publicly
51
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12/12/18
Membership Ballot Document posted publicly
50
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12/12/18
Ballot Period Started
11/12/18
Pre-Ballot Review Document posted publicly
57
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54
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View Ballot Submissions
11/12/18
49
Pre-Ballot Review Document posted publicly 48
47
Pre-Ballot Review Document posted publicly
11/12/18
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46
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11/12/18
Pre-Ballot Review Document posted publicly
45
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11/12/18
Pre-Ballot Review Document posted publicly
44
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11/12/18
RSC Posts for Pre-Ballot Review
11/12/18
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Comment Period 8/10/2018 through 9/24/2018
Date
Action
11/02/18
Comments Response Document posted publicly
11/02/18
43
Comments Response Document posted publicly 42
Comments Response Document posted publicly 41
11/02/18
Comments Response Document posted publicly
40
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11/02/18
Comments Response Document posted publicly
39
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09/25/18
Comment Period Ended
11/02/18
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38
08/10/18
Comments Template Document posted publicly
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08/10/18
Draft Standard Document (Redline) posted publicly
37
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08/10/18
Draft Standard Document (Redline) posted publicly
36
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08/10/18
Implementation Plan posted publicly
08/10/18
Draft Standard Document posted publicly
08/10/18
Comment Period Started
08/10/18
Comment Period Announcement posted publicly
35
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34
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33
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32
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Comment Period 4/16/2018 through 5/31/2018
Date
Action
08/09/18
Comments Response Document posted publicly
31
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07/24/18
Comments Response Document posted publicly
30
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07/24/18
Comments Response Document posted publicly
07/24/18
Comments Response Document posted publicly
07/24/18
Comments Response Document posted publicly
29
28
27
07/24/18
Comments Response Document posted publicly
26
07/24/18
Comments Response Document posted publicly
06/01/18
Comment Period Ended
05/01/18
Draft Standard Document (Redline) posted publicly
04/16/18
Draft Standard Document posted publicly 23
04/16/18
Comment Period Started
04/16/18
Other Commenting Supporting Document posted publicly
04/16/18
Implementation Plan posted publicly
04/16/18
Draft Standard Document (Redline) posted publicly
04/16/18
Comments Template Document posted publicly
18
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04/16/18
Comment Period Announcement posted publicly
17
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25
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24
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22
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20
21
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19
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Comment Period 9/1/2017 through 10/16/2017
Date
Action
01/30/18
Comments Response Document posted publicly
01/30/18
Comments Response Document posted publicly
16
01/30/18
15
Comments Response Document posted publicly 14
13
Comments Response Document posted publicly
01/30/18
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01/30/18
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12
11
01/30/18
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10
01/30/18
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01/30/18
Comments Response Document posted publicly 9
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01/30/18
Comments Response Document posted publicly
8
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10/16/17
Comment Period Ended
09/01/17
Comment Period Announcement posted publicly
7
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09/01/17
Comment Period Started
09/01/17
Implementation Plan posted publicly
09/01/17
Draft Standard Document (Redline) posted publicly
09/01/17
Draft Standard Document posted publicly
09/01/17
Comments Response Document posted publicly
6
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5
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4
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3
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2
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Project Initiation / Drafting Team Formation
Date
Action
06/26/15
RSC Accepts
06/26/15
RSAR Document posted publicly 1
View Document
Northeast Power Coordinating Council (NPCC)
Info
63
PRC-006-NPCC-2
Clean 62
Summary of
61
Changes
PRC-006-NPCC-2
Automatic
Underfrequency Load
Shedding
Implementation Plan
Standards in
Development
05/08/10 06/21/2019
60
Submit Comments
Unofficial Comment
Form (Word)
59
Comments Received
58
Information in a Regional Standard Authorization
Request (RSAR)
The tables below identify information to be submitted in a Regional Standard
Authorization Request to the NPCC Regional Standards Process Manager,
[email protected] . The NPCC Regional Standards Process Manager shall be
responsible for implementing and maintaining this form as needed to support the
information requirements of the standards process.
Regional Standard Authorization Request Form
Title of Proposed Standard :
PRC-006-NPCC-2
Request Date:
03-31-2015
RSAR Requester Information
Name:
Brian Robinson
Company:
NPCC
RSAR Type (Check box for one of these
selections.)
New Standard
Telephone: 802-241-1400
Revision to Existing Standard
Fax:
(866) 214-8632
Withdrawal of Existing Standard
Email:
[email protected]
Urgent Action
Purpose (Describe the purpose of the proposed standard – what the standard will achieve in
support of reliability.)
The purpose of the proposed RSAR is to review regional reliability standard PRC-006-NPCC-1
for potential revisions or retirements made necessary by NERC’s PRC-006-1/PRC-006-2
Automatic Underfrequency Load Shedding and PRC-024-1/PRC-024-2 Generator Frequency
and Voltage Protective Relay Settings standards.
PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard needs to be
revised in accordance with Project 2014-01 Dispersed Generation Resources.
PRC-006-NPCC-1 is to be reviewed in order to determine if the performance requirements as
contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2 should be explicitly
included in the requirements of the Regional Standard.
Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the design
assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not meeting the
program performance characteristics as identified in Requirement R3 of PRC-006-1/PRC-006-2.
PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in accordance
with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the applicability of
Requirements R4 and R5 will be reviewed to consider that Hydro Quebec is not part of the
Eastern Interconnection.
Retiring PRC-006-NPCC-1 is to be considered if it is determined that it can be retired without
sacrificing the ability to develop an effective underfrequency load shedding program.
Industry Need (Provide a detailed statement justifying the need for the proposed standard, along
with any supporting documentation.)
To enhance efficiencies and cost effectiveness, it must be determined if PRC-006-NPCC-1
requirements can be revised or retired to address the new NERC BES definition, Paragraph 81,
and eliminate redundancy leading to double jeopardy with PRC-006-1/PRC-006-2 and PRC024-1/PRC-024-2 requirements without sacrificing the ability to develop an effective
underfrequency load shedding program.
Brief Description: (Describe the proposed standard in sufficient detail to clearly define the
scope in a manner that can be easily understood by others.)
The requirements in PRC-006-NPCC-1 will be reviewed individually for revision or deletion
with respect to the new NERC BES definition, and Paragraph 81. In addition,
PRC-006-NPCC-1 will be reviewed against NERC’s PRC-006-1/PRC-006-2 and PRC-0241/PRC-024-2 2-2. PRC-006-1/PRC-006-2 mandates the establishment of design and
documentation requirements for automatic underfrequency load shedding (UFLS) programs.
PRC-024-1/PRC-024-2 mandate that Generator Owners set their generator protective relays such
that generating units remain connected during defined frequency and voltage excursions. These
“umbrellas” encompasses the relevant requirements in PRC-006-NPCC-1. However, the
relevant requirements in each of the standards are to be compared and the requirements of PRC006-NPCC-1, if so determined, are revised or deleted to eliminate redundancy and the
concomitant double jeopardy. The review will also ensure that NERC Rules of Procedure,
Section 312. Regional Reliability Standards, bullet 1that reads “Regional Entities may propose
Regional Reliability Standards that set more stringent reliability requirements than the NERC
Reliability Standard or cover matters not covered by an existing NERC Reliability Standard.”
will govern.
PRC-006-1/PRC-006-2 specifies in Requirement R4 that “Each Planning Coordinator shall
conduct and document a UFLS design assessment at least once every five years…” Revision to
Attachment C of PRC-006-NPCC-1 needs to be considered to address the circumstance
surrounding a design assessment that does not meet the performance characteristics as identified
in Requirement R3 of PRC-006-1/PRC-006-2.
Revise Table 4 Attachment C to reflect the modified Quebec UFLS program parameters as
recommended in the 2013 NPCC UFLS Adequacy Assessment and review the applicability of
Requirements R4 and R5 as they pertain to the Quebec Interconnection.
Additionally, as identified by SS38 there are aspects of the performance requirements in NERC
PRC-006-1 that are slightly more relaxed than the criteria in Directory#12 and these more
stringent attributes of the NPCC criteria were not incorporated into the regional standard.
Specifically, the NPCC criteria in Directory#12 (Sections 5.1.1 and 5.1.2) state that (1)
frequency decline is arrested at no less than 58.0 Hz for the portions of NPCC in the Eastern
Interconnection, and 56.0 Hz for the portion of NPCC in the Quebec Interconnection (2)
frequency should not remain below 59.5Hz for more than 30 seconds and should not remain
below 58.5 Hz. for more than 10 seconds. Review the need to include the performance criteria
presently in Directory#12 into PRC-006-NPCC-02, or whether the performance criteria included
in PRC-006-1/PRC-006-2 is sufficient.
Interpretations of PRC-006-NPCC-1 to be considered to clarify PRC-006-NPCC-2.
The review will include an assessment of the need to include language to address dispersed
generation resources.
PRC-006-NPCC-2 should be made to conform to the NERC Results Based Standard format.
After this review is completed, it will be determined if PRC-006-NPCC-1 should be revised, or
retired.
Reliability Functions
The Standard will Apply to the Following Functions (Check all applicable boxes.)
Reliability
Coordinator
The entity that is the highest level of authority who is responsible for the
reliable operation of the Bulk Electric System, has the Wide Area view of
the Bulk Electric System, and has the operating tools, processes and
procedures, including the authority to prevent or mitigate emergency
operating situations in both next-day analysis and real-time operations.
The Reliability Coordinator has the purview that is broad enough to enable
the calculation of Interconnection Reliability Operating Limits, which may
be based on the operating parameters of transmission systems beyond any
Transmission Operator’s vision.
Balancing
Authority
The responsible entity that integrates resource plans ahead of time,
maintains load-interchange-generation balance within a Balancing
Authority Area, and supports Interconnection frequency in real time.
Interchange
Authority
Authorizes valid and balanced Interchange Schedules.
Planning
Coordinator
The responsible entity that coordinates and integrates transmission facility
and service plans, resource plans, and protection systems.
Transmission The entity that administers the transmission tariff and provides
Service
Transmission Service to Transmission Customers under applicable
Provider
transmission service agreements.
Transmission The entity that owns and maintains transmission facilities.
Owner
Transmission The entity responsible for the reliability of its “local” transmission system,
Operator
and that operates or directs the operations of the transmission facilities.
Transmission The entity that develops a long-term (generally one year and beyond) plan
Planner
for the reliability (adequacy) of the interconnected bulk electric
transmission systems within its portion of the Planning Authority Area.
Resource
Planner
The entity that develops a long-term (generally one year and beyond) plan
for the resource adequacy of specific loads (customer demand and energy
requirements) within a Planning Authority Area.
Generator
Operator
The entity that operates generating unit(s) and performs the functions of
supplying energy and Interconnected Operations Services.
Generator
Owner
Entity that owns and maintains generating units.
PurchasingSelling
Entity
The entity that purchases or sells, and takes title to, energy, capacity, and
Interconnected Operations Services. Purchasing-Selling Entities may be
affiliated or unaffiliated merchants and may or may not own generating
facilities.
Distribution
Provider
Provides and operates the “wires” between the transmission system and the
customer.
LoadServing
Entity
Secures energy and transmission service (and related Interconnected
Operations Services) to serve the electrical demand and energy
requirements of its end-use customers.
Reliability and Market Interface Principles
Applicable Reliability Principles (Check all boxes that apply.)
1. Interconnected bulk power systems shall be planned and operated in a coordinated
manner to perform reliably under normal and abnormal conditions as defined in
the NERC Standards.
2. The frequency and voltage of interconnected bulk power systems shall be
controlled within defined limits through the balancing of real and reactive power
supply and demand.
3. Information necessary for the planning and operation of interconnected bulk
power systems shall be made available to those entities responsible for planning
and operating the systems reliably.
4. Plans for emergency operation and system restoration of interconnected bulk
power systems shall be developed, coordinated, maintained, and implemented.
5. Facilities for communication, monitoring, and control shall be provided, used, and
maintained for the reliability of interconnected bulk power systems.
6. Personnel responsible for planning and operating interconnected bulk power
systems shall be trained, qualified, and have the responsibility and authority to
implement actions.
7. The security of the interconnected bulk power systems shall be assessed,
monitored, and maintained on a wide-area basis.
Does the proposed Standard comply with all of the following Market Interface
Principles? (Select ‘yes’ or ‘no’ from the drop-down box.)
Recognizing that reliability is an Common Attribute of a robust North American economy:
1. A reliability standard shall not give any market participant an unfair competitive
advantage.Yes
2. A reliability standard shall neither mandate nor prohibit any specific market structure.
Yes
3. A reliability standard shall not preclude market solutions to achieving compliance with
that standard. Yes
4. A reliability standard shall not require the public disclosure of commercially sensitive
information. All market participants shall have equal opportunity to access
commercially non-sensitive information that is required for compliance with reliability
standards. Yes
Detailed Description (Provide enough detail so that an independent entity familiar with the
industry could draft a standard based on this description.)
Review and compare regional standard PRC-006-NPCC-1with continent-wide standards PRC006-1/PRC-006-2 and PRC-024-1/PRC-024-2 to determine if revisions are necessary, or
retirement of PRC-006-NPCC-01 possible.
Determine the necessity for including wording to address dispersed generation resources.
Consider incorporating more stringent aspects of Directory#12 in order to facilitate future
retirement of Directory#12.
Related Standards
Standard No.
Explanation
PRC-0061/PRC-006-2
NERC Automatic Underfrequency Load shedding
PRC-0241/PRC-024-2
NERC Generator Frequency and Voltage Protective Relay Settings
Related SARs or RSARs
SAR ID
Explanation
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Standard establishes more stringent and specific NPCC UFLS program requirements to
ensure that declining frequency is arrested and recovered in accordance with established
NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.3. Distribution Providers that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program.
4.4. Transmission Owners that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program.
5.
Effective Date:
The first day of the first calendar quarter following applicable governmental and
regulatory approvals.
B. Requirements
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Note that
Figure 1 also shows the NERC criteria as defined in the NERC PRC Standard on
UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design an
UFLS program having performance characteristics that prevents the frequency from
remaining below 59.5 Hz for greater than 30 seconds in accordance with Figure 1. [Violation
Risk Factor: Medium] [Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or realtime power flow data captured from actual system events and other dated documentation that
demonstrates it meets Requirement R1.
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC PRC Standard on UFLS, to Distribution Providers, Generator Owners, and
Transmission Owners within 30 days of receipt of a request. [Violation Risk Factor:
Medium] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
1
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R3. Each Planning Coordinator shall, within 30 days of completion of its UFLS system studies,
identify to the Regional Entity all non-BES generation facilities, within its Planning
Coordinator Area, that must not trip above the appropriate generator underfrequency trip
threshold curve in Figure 2 in order to support acceptable UFLS program performance.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
M3. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
R4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall implement an automatic UFLS program reflecting normal operating
conditions, excluding outages. The automatic UFLS program shall be implemented on an
island basis for each island identified per the NERC PRC Standard on UFLS. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
4.1. The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating times
and load shedding amounts specified in Attachment C, Tables 1 through 3.
4.2. Alternatively, the program can be implemented collectively by multiple Distribution
Providers or Transmission Owners with less than 100 MW of individual peak net Load,
as long they reside in the same UFLS Island identified by the Planning Coordinator per
R2. These multiple Distribution Providers or Transmission owners, via mutual
agreement, shall act as a single entity to provide an aggregated automatic UFLS
program that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time and amounts specified in
Attachment C, Tables 1 through 3.
M4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall have evidence such as documentation or reports containing the location and
amount of load to be tripped in their respective areas, and the corresponding frequency
thresholds, on those circuits included in its UFLS program identified in Requirement R4.
(Attachment C Tables 1-3).
R5. Each Distribution Provider or Transmission Owner that cannot meet the tolerances and/or
number of stages and frequency set points specified in the UFLS Program, shall notify its
Planning Coordinator within 30 days, and: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
5.1. Each Distribution Provider or Transmission Owner applicable to Attachment C,
Table 1, within 90 calendar days of informing of its Planning Coordinator that
2
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
tolerances cannot be met, determine if tolerances can be met through adjustments
and notify the Planning Coordinator of the determination and;
5.1.1. If adjustments are possible, make the adjustments within 180 calendar
days after determining that adjustments are possible and notify the Planning
Coordinator when complete, or;
5.1.2. If adjustments are not possible then provide its Planning Coordinator
with a technical study within 180 calendar days that demonstrates that the
Distribution Providers or Transmission Owners specific deviations from the
requirements of UFLS Attachment C, Table 1 will not have a significant
adverse impact on the bulk power system.
5.2. Each Distribution Provider or Transmission Owner applicable to Attachment C,
Table 2 or Table 3, within 90 calendar days after informing the Planning
Coordinator, determine if tolerances can be met through adjustments and notify the
Planning Coordinator of the determination, and;
5.2.1. If adjustments are possible, within 90 calendar days make the
adjustments of determining that adjustments are possible and notify the
Planning Coordinator when complete, or;
5.2.2. If adjustments are not possible, then within 90 calendar days
provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the
Distribution Provider or Transmission Owner to comply with UFLS
Attachment C Table 2 or Attachment C Table 3.
5.3. Each Distribution Provider or Transmission Owner in the Quebec Interconnection,
within 90 calendar days after informing the Planning Coordinator, determine if
tolerances can be met through adjustments and notify the Planning Coordinator of
the determination, and;
5.3.1. If adjustments are possible, within 180 calendar days make the
adjustments of determining that adjustments are possible and notify the
Planning Coordinator when complete, or;
5.3.2. If adjustments are not possible, then within 90 calendar days
provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the
Distribution Provider or Transmission Owner to comply with the UFLS
program.
M5. Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
Rationale for Requirement R6: Operation of underfrequency relays results directly in
load being shed, interrupting service to customers. The security of underfrequency
relays against misoperation is therefore paramount. The 100 ms minimum time delay
specified in R6 serves to prevent premature activation of these relays during shortlived transient frequency excursions that may occur on a localized basis in the absence
3
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
of a serious system event wherein UFLS would be appropriate. This intentional delay
helps to ensure that the relays activate only for frequency excursions that are due to
actual system events that require automatic UFLS to reestablish the balance of
generation to load.
R6. Each Distribution Provider and Transmission Owner shall set each underfrequency relay
that is part of its region’s UFLS program with a 100 ms minimum time delay. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
M6. Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the minimum
time delay, in accordance with Requirement R6.
R7. Each Planning Coordinator shall develop and review settings for inhibit thresholds at least
once per five calendar years (such as but not limited to voltage, current and time) to be
utilized within its region’s UFLS program. [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
M7. Each Planning Coordinator shall have evidence such as reports, system studies or analysis
that demonstrates that it meets Requirement R7.
R8. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
days of any changes to those thresholds. [Violation Risk Factor: Medium] [Time Horizon:
Operations Planning]
M8. Each Planning Coordinator shall provide evidence such as letters, emails, or other dated
documentation that demonstrates that it meets Requirement R8.
R9. Each Distribution Provider and Transmission Owner that receives a notification pursuant to
Requirement R8 shall develop and submit an implementation plan within 90 days of the
request from the Planning Coordinator for approval by the Planning Coordinator. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M9. Each Planning Coordinator shall provide evidence such as letters, emails, or other dated
documentation that demonstrates that it meets Requirement R9.
R10. Each Distribution Provider and Transmission Owner shall implement the inhibit threshold
settings provided by the Planning Coordinator in accordance with Requirement R8 and
based on the Planning Coordinator approved implementation plan in accordance with R9.
[Violation Risk Factor: High] [Time Horizon: Operations Planning]
M10. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that demonstrates that it
meets Requirement R10.
4
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Rationale for Requirement R11: It is recognized that, ideally, the amount of load to
be shed in each stage of the UFLS program for every entity should perfectly match
that prescribed in this Standard universally, for all phases of the load cycle, i.e.,
seasonal (summer vs. winter), weekly (weekday vs. weekend vs. holidays), daily
(morning, noon, and night), etc. for all of the identified islands. Practically, however,
this is obviously not possible because the load cycles of the various areas and subareas within any given island do not perfectly track the load cycle of the overall
island. The UFLS program, on the other hand, is designed based on peak conditions
for the overall island. The percentages of actual load shedding that would occur for
any conditions other than peak, therefore, can only approximate that prescribed in the
Standard. This being said, entities are required by R11 to document measured loads
in the UFLS program coincident with their own annual peak, whether or not that peak
occurs at the same time or in the same season as the peak of the identified island in
which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that
are responsible for designing and maintaining their UFLS programs.
R11. Each Transmission Owner and Distribution Provider shall annually provide documentation,
with no more than 15 months between updates, to its Planning Coordinator of the actual net
Load projected to be shed by the UFLS relays at each UFLS stage. The actual net Load shall
be coincident with the entity’s integrated hourly peak net Load during the previous year, as
determined by measuring actual metered Load through the switches that would disconnect
load if triggered by the UFLS relays. If there is no local metering of the load through said
switches, the load may be calculated from measurements made at the nearest available
metering. (e.g., upstream metering on the distribution feeder that supplies the load to be
shed). [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M11. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning Coordinator
that indicates the frequency set point, the net amount of load shed and the percentage of its
peak load at each stage of its UFLS program to demonstrate that it meets Requirement R11.
R12. Each Generator Owner shall set each generator underfrequency trip relay, if so equipped,
on or below the appropriate generator underfrequency trip protection settings threshold
curve in Figure 2, except as otherwise exempted in Requirements R15 and R18. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
M12. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets or
other documentation that demonstrates that it meets Requirement R12.
R13. Each Generator Owner shall transmit the generator underfrequency trip setting and time
delay to its Planning Coordinator within 45 days of the Planning Coordinator’s request.
[Violation Risk Factor: High] [Time Horizon: Operations Planning]
5
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
M13. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R13.
R14. Each Generator Owner with a new generating unit, or an existing generator increasing its
net capability by greater than 10% shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
14.1. Design measures to prevent the generating unit from tripping directly or indirectly
for underfrequency conditions above the appropriate generator tripping threshold
curve in Figure 2.
14.2. Design auxiliary system(s) or devices used for the control and protection of
auxiliary system(s), necessary for the generating unit operation such that they will
not trip the generating unit during underfrequency conditions above the appropriate
generator underfrequency trip protection settings threshold curve in Figure 2.
M14. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement R14.
R15. Each Generator Owner of existing non-nuclear units in service prior to the effective date of
this standard, as documented in accordance with Attachments A or B, that have
underfrequency protections set to trip above the appropriate curve in Figure 2 shall:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
15.1. Set the underfrequency protection to operate at the lowest frequency allowed by the
plant design and licensing limitations.
15.2. Transmit the existing underfrequency settings and any changes to the
underfrequency settings along with the technical basis for the settings to the
Planning Coordinator.
15.3. Have compensatory load shedding, as provided by a Distribution Provider or
Transmission Owner that is adequate to compensate for the loss of their generator
due to early tripping that is within the UFLS island identified by the Planning
Coordinator in Requirement R2.
M15. Each Generator Owner with existing non-nuclear units in service prior to the effective date
of this Standard which have underfrequency tripping that is not compliant with Requirement
R13 shall provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R15.
R16. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply the
criteria described in Attachment A to determine the compensatory load shedding that is
required in Requirement R15.3 for generating units in its respective NPCC area. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
6
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
M16. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall provide
evidence such as emails, memorandum or other documentation that demonstrates that it
followed the methodology described in Attachment A and meets Requirement R16.
R17. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the New York ISO shall apply the criteria described in
Attachment B to determine the compensatory load shedding that is required in Requirement
R15.3 for generating units in its respective NPCC area. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
M17. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the New York ISO shall provide evidence such as emails,
memorandum, or other documentation that demonstrates that it followed the methodology
described in Attachment B and meets Requirement R17.
R18. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator tripping
curve in Figure 2, based on their licensing design basis, shall: [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
18.1.
Set the underfrequency protection to operate at as low a frequency as possible in
accordance with the plant design and licensing limitations but not greater than
57.8 Hz.
18.2.
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
18.3.
Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
M18. Each Generator Owner of nuclear units that have been specifically identified by NPCC as
having generator trip settings above the generator trip curve in Figure 2 shall provide
evidence such as letters, reports and dated documentation that demonstrates that it meets
Requirement R18.
7
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 1
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
8
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
Time (sec)
9
1000
55.5
55
10000
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority
NPCC Compliance Committee
1.2. Compliance Monitoring Period and Reset Time Frame
Not Applicable
1.3. Data Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 4, 5, 6,7,10, 11, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 3, 8, 9, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall
keep evidence for three calendar years for Measure 17.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 18, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
13, 14, 15, 16, and 19.
1.4. Compliance Monitoring and Assessment Processes
Self -Certifications.
Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.
1.5. Additional Compliance Information
None.
10
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 2.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all UFLS islands in which the unit may operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units, in their Planning Coordinator area, in service prior to the
effective date of Version 1 of the regional Standard (April, 2017 PRC-006-NPCC-1).
The list must indicate generating units, if any, that have their underfrequency protections
set to trip above the appropriate curve in Figure 2. Generating Units not appearing on the
list as of the effective date of Version 1 of the regional standard, as shown above, must
have their Underfrequency protections set to trip on or below the appropriate curve in
Figure 2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS
relays within the island(s) identified by the Planning Coordinator within which
the generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that is
provided by the Distribution Provider or Transmission Owner shall be in addition
to the amount that the Distribution Provider or Transmission Owner is required to
shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 2 during an underfrequency event. If the highest
11
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
frequency at which the subject generator will trip above the appropriate curve in
Figure 2 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
12
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units in service prior to the effective date of Version 1 of the regional
Standard (April, 2017 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, that have their underfrequency protections set to trip above the
appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2. The
list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 2, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the smallest island identified by the Planning Coordinator in
Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 2, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
13
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
14
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
Frequency Threshold
(Hz)
Total Nominal
Operating
Time (s) 1
Load Shed at Stage as %
of TO or DP Load
Cumulative Load Shed as
% of TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
27.5 – 28.5
59.5
10.0
2
–3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
15
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating
Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50
MW2 of peak net Load shall implement a UFLS program with the following attributes:
16
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Guidelines and Technical Basis:
Standard PRC-006-2, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
•
•
•
•
•
•
•
•
•
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
Generator dynamic modeling (MOD-027-1 - Verification of Models and Data for
Turbine/Governor and Load Control or Active Power/Frequency Control Functions) or system
modeling (if variations in system response are detected under MOD-033 - Steady-State and
Dynamic System Model Validation)
17
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-21
3.
Purpose: To provide a regional reliability standard that ensures the development of
an effective automatic underfrequency load shedding (UFLS) program in order to
preserve the security and integrity of the bulk power system during declining system
frequency events in coordination with the NERC UFLS reliability standard
characteristics. The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Sstandard establishes more stringent and specific NPCC UFLS program requirements to
ensure that declining frequency is arrested and recovered in accordance with established
NPCC performance requirements stipulated in this document.
4.
Formatted: Font: Not Bold
Commented [DML1]: Dan to move to “purpose” section
Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.2. Distribution Providers that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program.
4.3.
4.4. Transmission Owners that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program.
Distribution Provider
4.3.
4.4. Transmission Owner
5.
Effective Date:
For the Eastern Interconnection & Québec Interconnection portions of NPCC
excluding the Independent Electricity System Operator (IESO) Planning Coordinator
area of NPCC in Ontario, Canada:
The effective date for Requirements R1, R2, R3, R4, R5, R6, and R7 is the first day of
the first calendar quarter following applicable regulatory approval but no earlier than
January 1, 2016 The effective date for Requirements R8 through R23 is the first day of
the first calendar quarter two years following applicable governmental and regulatory
approval.
Formatted: No bullets or numbering
Commented [RS2]: National Grid:
Should the Applicability List re-ordered to list:
4.1 Planning Coordinator
4.2 Distribution Provider
4.3 Transmission Owner
4.4 Generation Owner
The current NERC guidance regarding the applicability
ordering.
Formatted: Indent: First line: 0"
For the Independent Electricity System Operator (IESO) Planning Coordinator’s area
of NPCC in Ontario, Canada:
All requirements are effective tThe first day of the first calendar quarter following
applicable governmental and regulatory approvals. but no earlier than April 1, 2017.
B. Requirements
R1 R1
1
NPCC Under frequency Load Shedding Program - More Stringent Criteria
Commented [RS3]: National Grid:
Thought standards now need an Implementation Plan and
should say “See Implementation Plan”
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
The NPCC underfrequency Criteria are in addition to, or more stringent or more specific than
the NERC PRC Standard on UFLS, or any Regional Reliability standard requirements.
The intent of the NPCC automatic Under frequency Load Shedding program is to ensure that
declining frequency is arrested and recovered in accordance with established NPCC
performance requirements stipulated in this document.
Commented [DML4]: Dan to move to “purpose” section
Each Planning Coordinator shall design a UFLS program that meets the following
performance characteristics in simulations of underfrequency conditions resulting from
an imbalance scenario, where an imbalance = [(load — actual generation output) /
(load)], of up to 25 percent within the identified island(s).
Rationale for Requirement R1: Attachment 1Figure 1 of this document shows the
NPCC underfrequency criteria for the Eeastern Iinterconnection portion of NPCC.
Note that Attachment 1Figure 1 also shows the NERC criteria as defined in the NERC
PRC Standard on UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design an
UFLS program having performance characteristics that prevents the frequency from
remaining below 59.5 Hz for greater than 30 seconds in accordance with Figure 1.
Formatted Table
Formatted: Font: Italic
R1.1 Frequency decline is arrested at no less than 58.0 Hz for the portions of NPCC in the Eastern
Interconnection.
R1.2 Frequency does not remain below 58.5 Hz for greater than 10 seconds, and does not remain
below 59.5 Hz for greater than 30 seconds.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
Formatted: Normal, Indent: Left: 0", Hanging: 0.25"
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or realtime power flow data captured from actual system events and other dated documentation that
demonstrates it meets Requirement R1.
Formatted: Font: 12 pt
Attachment 1 of this document shows the NPCC underfrequency criteria for the eastern
interconnection portion of NPCC. Note that Attachment 1 also shows the NERC
criteria as defined in the NERC PRC Standard on UFLS. The Section below need to be
move to Rationale Box:
“Attachment 1 of this document shows the NPCC underfrequency criteria for the
eastern interconnection portion of NPCC. Note that Attachment 1 also shows the
NERC criteria as defined in the NERC PRC Standard on UFLS.”
Formatted: Indent: Left: 0", Hanging: 0.63"
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC PRC Standard on UFLS, to Distribution pProviders, Generator Owners, and
2
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Transmission Oowners within 30 days of receipt of a of a request. [Violation Risk Factor:
Medium] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
Formatted: Font: Italic
Formatted: Font: 12 pt
Do not change language of existing R2 but it becomes:
R3. Each Planning Coordinator shall, within 30 days of completion of its system studies
required by the NERC PRC Standard on UFLS, identify to the Regional Entity the
generation facilities within its Planning Coordinator Area necessary to support the UFLS
program performance characteristics. [Violation Risk Factor: Medium] [Time Horizon:
Long Term Planning]
Commented [DML5]: R3 language needs to be rewritten so
as to clarify intent. Confusing as is.
Rationale for Requirement R3: Demonstrate to the Regional Entity, via system
studies, that the UFLS program will not meet performance requirements if all nonBES generators identified in R3.1 trip above underfrequency trip threshold curve in
Figure 1
R3.
Each Planning Coordinator shall, within 30 days of completion of its UFLS system
studies, identify to the Regional Entity all non-BES generation facilities, within its Planning
Coordinator Area, that must not trip above the appropriate generator underfrequency trip
threshold curve in Figure 2 in order to support acceptable UFLS program performance.
R3.2 Demonstrate to the Regional Entity, via system studies, that the UFLS program will not
meet performance requirements if all non-BES generators identified in R3.1 trip above
underfrequency trip threshold curve in Figure 1.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
M3. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
Formatted: Requirement, Indent: Left: 0", Hanging: 0.31"
Commented [RS6]: From National Grid: Do we still need
rationale box if we have this?
Commented [RS7]: National Grid:
Appears to be an administrative requirement which would
qualify as a “P81” requirement.
Formatted: Font: Italic
Commented [RS8]: Potentially move to Rationale Box or
Dean Latulipe find a way to avoid putting it into rationale box
and put specifics into the requirement.
Formatted: Font: Italic
Formatted: Font: Italic
Each Planning Coordinator shall provide to the Transmission Owner, Distribution
Provider, and Generator Owner within 30 days upon written request the requirements
for entities aggregating the UFLS programs and requirements for compensatory load
shedding program derived from each Planning Coordinator’s system studies as
determined by Requirement R1. [Violation Risk Factor: Low] [Time Horizon: Long
Term Planning]
Formatted: Font: Not Bold, Italic
Formatted: Indent: First line: 0"
Formatted: Indent: First line: 0"
3
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
R4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall implement an automatic UFLS program reflecting normal operating
conditions, excluding outages. The automatic UFLS program shall be implemented on an
island basis for each island identified per the NERC PRC Standard on UFLS. for its
Facilities [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
Formatted: Font: Italic
4.1. The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according based toon the frequency thresholds, total nominal
operating times and load shedding amounts specified in Attachment C, Tables 1
through 3.,
Formatted: Font: Bold
4.2. Alternatively, the program can be implemented or shall collectively implement , by
mutual agreement by with multiple one or more Distribution Providers orand
Transmission Owners with less than 100 MW of individual peak net Load, as long they
reside in the same UFLS Island identified by the Planning Coordinator per R2. within
the same island per identified in. Requirement R1. These multiple Distribution
Providers or Transmission ownersand, via mutual agreement, shall acting as a single
entity to, provide an aggregated automatic UFLS program that sheds their coincident
peak aggregated net Load according to, based on the frequency thresholds, total
nominal operating time and amounts specified in Attachment C, Tables 1 through 3.
Formatted: Font: Bold
4.3.
Formatted: Font: Bold
Whether implemented collectively or individually, the automatic UFLS program
shall be implemented on an island basis. Each Distribution Provider and Transmission
Owner shall provide the required loadshedding amounts and frequency thresholds
specified in the Attachment C, Tables 1 through 3, within each island identified in R2.
Formatted: Indent: Left: 0.31", Hanging: 0.31"
Formatted: Indent: Left: 0", First line: 0"
M4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall have evidence such as documentation or reports containing the location and
amount of load to be tripped in their respective areas, and the corresponding frequency
thresholds, on those circuits included in its UFLS program to achieve the individual and
cumulative percentages identified in Requirement R4. (Attachment C Tables 1-3).
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
Formatted: Font: (Default) Times New Roman, Bold
Formatted: Indent: Left: 0", Hanging: 0.31"
Formatted: Indent: Left: 0", Hanging: 0.31"
Formatted: Indent: Left: 0", Hanging: 0.31"
R5.
If a Distribution Provider or Transmission Owner cannot meet the tolerances and/or number of
stages and frequency set points specified in Attachment C, Tables 1 through 3, such
Distribution Provider or Transmission Owner shall: .
4
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Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Each Distribution Provider or Transmission Owner that must arm its load to trip on
underfrequency in order to meet its requirements as specified and by doing so exceeds the
tolerances and/or deviates from the number of stages and frequency set points of the UFLS
program as specified in the tables contained in Requirement R4 above, as applicable
depending on its total peak net Load shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
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5.1. Inform its Planning Coordinator of the need to exceed the stated tolerances or the number of
stages as shown in UFLS Attachment C, Table 1 if applicable and5.1.1. and;5.1.2.
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keep with next
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5.2. Provide its Planning Coordinator with a technical study that demonstrates that the
Distribution Providers or Transmission Owners specific deviations from the requirements of
UFLS Attachment C, Table 1 will not have a significant adverse impact on the bulk power
system..1
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5.3. Inform its Planning Coordinator of the need to exceed the stated tolerances of UFLS
Attachment C, Table 2 or Table 3, and in the case of Attachment C, Table 2 only, the need
to deviate from providing two stages of UFLS, if applicable, and5.3.1.
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5.4. Provide its Planning Coordinator with an analysis demonstrating that no alternative load
shedding solution is available that would allow the Distribution Provider or Transmission
Owner to comply with UFLS Attachment C Table 2 or Attachment C Table 3..1
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M5. Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
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Rationale for Requirement R6: Operation of underfrequency relays results directly in
load being shed, interrupting service to customers. The security of underfrequency
relays against misoperation is therefore paramount. The 100 ms minimum time delay
specified in R6 serves to prevent premature activation of these relays during shortlived transient frequency excursions that may occur on a localized basis in the absence
of a serious system event wherein UFLS would be appropriate. This intentional delay
helps to ensure that the relays activate only for frequency excursions that are due to
actual system events that require automatic UFLS to reestablish the balance of
generation to load.
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R5. Each Distribution Provider or Transmission Owner that cannot meet the tolerances and/or
number of stages and frequency set points specified in the UFLS Program, shall notify its
5
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Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Planning Coordinator within 30 days, and: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
5.1. Each Distribution Provider or Transmission Owner applicable to Attachment C,
Table 1, within 90 calendar days of informing of its Planning Coordinator that
tolerances cannot be met, determine if tolerances can be met through adjustments
and notify the Planning Coordinator of the determination and;
5.1.1. If adjustments are possible, make the adjustments within 180 calendar
days after determining that adjustments are possible and notify the Planning
Coordinator when complete, or;
5.1.2. If adjustments are not possible then provide its Planning Coordinator
with a technical study within 180 calendar days that demonstrates that the
Distribution Providers or Transmission Owners specific deviations from the
requirements of UFLS Attachment C, Table 1 will not have a significant
adverse impact on the bulk power system.
5.2. Each Distribution Provider or Transmission Owner applicable to Attachment C,
Table 2 or Table 3, within 90 calendar days after informing the Planning
Coordinator, determine if tolerances can be met through adjustments and notify the
Planning Coordinator of the determination, and;
5.2.1. If adjustments are possible, within 90 calendar days make the
adjustments of determining that adjustments are possible and notify the
Planning Coordinator when complete, or;
5.2.2. If adjustments are not possible, then within 90 calendar days
provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the
Distribution Provider or Transmission Owner to comply with UFLS
Attachment C Table 2 or Attachment C Table 3.
5.3. Each Distribution Provider or Transmission Owner in the Quebec Interconnection,
within 90 calendar days after informing the Planning Coordinator, determine if
tolerances can be met through adjustments and notify the Planning Coordinator of
the determination, and;
5.3.1. If adjustments are possible, within 180 calendar days make the
adjustments of determining that adjustments are possible and notify the
Planning Coordinator when complete, or;
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5.3.2. If adjustments are not possible, then within 90 calendar days
provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the
Distribution Provider or Transmission Owner to comply with the UFLS
program.
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M5. Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
6
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Rationale for Requirement R6: Operation of underfrequency relays results directly in
load being shed, interrupting service to customers. The security of underfrequency
relays against misoperation is therefore paramount. The 100 ms minimum time delay
specified in R6 serves to prevent premature activation of these relays during shortlived transient frequency excursions that may occur on a localized basis in the absence
of a serious system event wherein UFLS would be appropriate. This intentional delay
helps to ensure that the relays activate only for frequency excursions that are due to
actual system events that require automatic UFLS to reestablish the balance of
generation to load.
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0.65", List tab
R6 Each Distribution Provider and Transmission Owner in the Québec Interconnection portion
of NPCC shall implement an automatic UFLS program for its Facilities based on the
frequency thresholds, slopes, total nominal operating time and amounts specified in
Attachment C, Table 4 or shall collectively implement by mutual agreement with one
or more Distribution Providers and Transmission Owners within the same island,
identified in Requirement R1, an aggregated automatic UFLS program that sheds Load
based on the frequency thresholds, slopes, total nominal operating time and amounts
specified in Attachment C, Table 4. [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
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tab
R6.7
Each Distribution Provider and Transmission Owner shall set each
underfrequency relay that is part of its region’s UFLS program with a 100 mswith the
following minimum time delay.:
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0.25", List tab
7.1
Eastern Interconnection – 100 ms
7.2
Québec Interconnection – 200 ms
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[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M6. Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the minimum
time delay, in accordance with Requirement R6.
Each Distribution Provider and Transmission Owner in the Québec Interconnection shall have
evidence such as documentation or reports containing the location and amount of load to be
tripped and the corresponding frequency thresholds on those circuits included in its UFLS
program to achieve the load values identified in Table 4 of Requirement R6. (Attachment C
Table 4).Rationale Box: Operation of underfrequency relays results directly in load being shed,
interrupting service to customers. The security of underfrequency relays against misoperation is
therefore paramount. The 100 ms minimum time delay specified in R6 serves to prevent
premature activation of these relays during short-lived transient frequency excursions that may
occur on a localized basis in the absence of a serious system event wherein UFLS would be
appropriate. This intentional delay helps to ensure that the relays activate only for frequency
excursions that are due to actual system events that require automatic UFLS to reestablish the
balance of generation to load.
7
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Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
R7.8 Each Planning Coordinator shall develop and review settings for inhibit thresholds at least
once per five calendar years (such as but not limited to voltage, current and time) to be
utilized within its region’s UFLS program.Each Planning Coordinator shall develop and
review once per calendar year settings for inhibit thresholds (such as but not limited to
voltage, current and time) of UFLS relays to be utilized within its region's UFLS program.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
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M87. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R87.
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R8.9
Each Planning Coordinator shall provide each Transmission Owner
and Distribution Provider within its Planning Coordinator area the applicable inhibit
thresholds within 30 days of the initial determination of those inhibit thresholds and within
30 days of any changes to those thresholds. [Violation Risk Factor: Medium] [Time
Horizon: Operations Planning]
M8. Each Planning Coordinator shall provide evidence such as letters, emails, or other dated
documentation that demonstrates that it meets Requirement R8.
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Commented [RS9]: National Grid:
Suggest to remove “…of the initial determination of those
inhibit thresholds and…” My guess is that all the PC’s have
made their initial determinations and we only need to consider
any changes to those thresholds.
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R9.10
Each Distribution Provider and Transmission Owner that receives a
notification pursuant to Requirement R8 shall develop and submit an implementation plan
within 90 days of the request from the Planning Coordinator for approval by the Planning
Coordinator. [Violation Risk Factor: Lower] [Time Horizon: Operations Planning]
M9.
Each Planning Coordinator shall provide evidence such as letters, emails, or other
dated documentation that demonstrates that it meets Requirement R9.
Commented [RS10]: National Grid:
Suggestion to re-word. Each Distribution Provider and
Transmission Owner that receives a notification pursuant to
Requirement R8 shall, develop and submit an implementation
plan within 90 days of the request…
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R 10. Each Distribution Provider and Transmission Owner shall implement the inhibit
threshold settings based on the notification provided by the Planning Coordinator in
accordance with Requirement R89. and based on the Planning Coordinator approved
implementation plan in accordance with R9. [Violation Risk Factor: High] [Time Horizon:
Operations Planning]
M10. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that demonstrates that it
meets Requirement R10.
8
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Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Rationale for Requirement R11: It is recognized that, ideally, the amount of load to
be shed in each stage of the UFLS program for every entity should perfectly match
that prescribed in this Standard universally, for all phases of the load cycle, i.e.,
seasonal (summer vs. winter), weekly (weekday vs. weekend vs. holidays), daily
(morning, noon, and night), etc. for all of the identified islands. Practically, however,
this is obviously not possible because the load cycles of the various areas and subareas within any given island do not perfectly track the load cycle of the overall
island. The UFLS program, on the other hand, is designed based on peak conditions
for the overall island. The percentages of actual load shedding that would occur for
any conditions other than peak, therefore, can only approximate that prescribed in the
Standard. This being said, entities are required by R11 to document measured loads
in the UFLS program coincident with their own annual peak, whether or not that peak
occurs at the same time or in the same season as the peak of the identified island in
which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that
are responsible for designing and maintaining their UFLS programs.
(The original R9 was swapped with R10)*****
R11 Each Distribution Provider and Transmission Owner shall develop and submit an
implementation plan within 90 days of the request from the Planning Coordinator for
approval by the Planning Coordinator in accordance with R9. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
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R 11. Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 months between updates, to its Planning Coordinator
of the actual net Load that would have beenprojected to be shed by the UFLS relays at each
UFLS stage. The actual net Load shall be coincident with the entity’s integrated hourly peak
net Load during the previous year, as determined by measuring actual metered Load through
the switches that would be openeddisconnect load if triggered by the UFLS relays. If there is
no local metering of the load through said switches, the load may be calculated from
measurements made at the nearest available metering. , (e.g., upstream metering on the
distribution feeder that supplies the load to be shed). [Violation Risk Factor: Lower] [Time
Horizon: Long Term Planning]
M121. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning Coordinator
that indicates the frequency set point, the net amount of load shed and the percentage of its
peak load at each stage of its UFLS program coincident with the integrated hourly peak of
the previous year thatto demonstrates that it meets Requirement R121.
9
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Commented [RS11]: National Grid:
Suggest to shorten. A technical writer may be able to help with
this and eliminate words as “on the other hand.”
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stops: 0.38", List tab
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Formatted: Measure, Tab stops: 0.31", Left + 0.38", List
tab
R12 Each Transmission Owner and Distribution Provider shall annually provide documentation, with
no more than 15 months between updates, to its Planning Coordinator of the actual net Load
that would have been shed by the UFLS relays at each UFLS stage coincident with their
integrated hourly peak net Load during the previous year, as determined by measuring actual
metered Load through the switches that would be opened by the UFLS relays. [Violation
Risk Factor: Lower] [Time Horizon: Long Term Planning]
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stops: 0.38", List tab
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RATIONALE BOX:
It is recognized that, ideally, the amount of load to be shed in each stage of the UFLS program for every
entity should perfectly match that prescribed in this Standard universally, for all phases of the
load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs. weekend vs. holidays), daily
(morning, noon, and night), etc. for all of the identified islands. Practically, however, this is
obviously not possible because the load cycles of the various areas and sub-areas within any
given island do not perfectly track the load cycle of the overall island. The UFLS program, on
the other hand, is designed based on peak conditions for the overall island. The percentages of
actual load shedding that would occur for any conditions other than peak, therefore, can only
approximate that prescribed in the Standard. This being said, entities are required by R12 to
document measured loads in the UFLS program coincident with their own annual peak, whether
or not that peak occurs at the same time or in the same season as the peak of the identified island
in which their load resides. Using individual entity peaks vs. overall island peaks provides a
consistent approach for accounting purposes among the very entities that are responsible for
designing and maintaining their UFLS programs.
R122. 3
Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection settings
threshold curve in Figure 1Figure 2, except as otherwise exempted in Requirements R165
and R198. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M12. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets or
other documentation that demonstrates that it meets Requirement R12.
R13. 4
Each Generator Owner shall transmit the generator underfrequency
trip setting and time delay to its Planning Coordinator within 45 days of the Planning
Coordinator’s request. [Violation Risk Factor: High] [Time Horizon: Operations Planning]
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M13. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R13.
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10
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
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R14. 5 Each Generator Owner with a new generating unit, scheduled to be in service on or after
the effective date of this Standard, or an existing generator increasing its net capability by
greater than 10% shall: [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
Formatted: Font: Italic
154.1. Design measures to prevent the generating unit from tripping directly or indirectly
for underfrequency conditions above the appropriate generator tripping threshold
curve in Figure 1Figure 2.
Formatted: Font: Bold
145.2. Design auxiliary system(s) or devices used for the control and protection of
auxiliary system(s), necessary for the generating unit operation such that they will
not trip the generating unit during underfrequency conditions above the appropriate
generator underfrequency trip protection settings threshold curve in Figure 1Figure
2.
M14. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement R14.
Formatted: Font: Bold
R15. 6
Each Generator Owner of existing non-nuclear units in service prior
to the effective date of this standard, as documented in accordance with Attachments A or
B, that have underfrequency protections set to trip above the appropriate curve in Figure
1Figure 2 shall: [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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156.1.
Set the underfrequency protection to operate at the lowest frequency
allowed by the plant design and licensing limitations.
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156.2.
Transmit the existing underfrequency settings and any changes to the
underfrequency settings along with the technical basis for the settings to the
Planning Coordinator.
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156.3.
Have compensatory load shedding, as provided by a Distribution
Provider or Transmission Owner that is adequate to compensate for the loss of their
generator due to early tripping that is within the UFLS island identified by the
Planning Coordinator in Requirement R2..
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M165. Each Generator Owner with existing non-nuclear units in service prior to the effective
date of this Standard which have underfrequency tripping that is not compliant with
Requirement R13 shall provide evidence such as reports, spreadsheets, memorandum or
dated documentation demonstrating that it meets Requirement R165.
11
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Commented [RS12]: From National Grid: Guy to tightening
up standard so that existing units that do meet curve, cant file
to not meet curve.
Commented [DML13]: Guy to tightening up standard so
that existing units that do meet curve, cant file to not meet
curve. Add dates to attachment A and B and remove from
R15.
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Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
R176.
Each Planning Coordinator in Ontario, Quebec and the Maritime
provinces shall apply the criteria described in Attachment A to determine the compensatory
load shedding that is required in Requirement R165.3 for generating units in its respective
NPCC area. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
Commented [RS14]: Update Attachment A per the
comments submitted by Vincent M. Replace his with its.
Commented [DML15]: Vincent to modify attachment A
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2.25", Left + Not at -2.5"
M176. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall provide
evidence such as emails, memorandum or other documentation that demonstrates that it
followed the methodology described in Attachment A and meets Requirement R176.
R17. 8
Each Generator Owner, Distribution Provider or Transmission Owner
within the Planning Coordinator area of ISO-NE or the New York ISO shall apply the
criteria described in Attachment B to determine the compensatory load shedding that is
required in Requirement R156.3 for generating units in its respective NPCC area. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
M187.
Each Generator Owner, Distribution Provider or Transmission Owner
within the Planning Coordinator area of ISO-NE or the New York ISO shall provide
evidence such as emails, memorandum, or other documentation that demonstrates that it
followed the methodology described in Attachment B and meets Requirement R187.
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Commented [DML16]: Leave as is.
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R18. 9 Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator tripping
curve in Figure 1Figure 2, based on their licensing design basis, shall: [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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189.1. Set the underfrequency protection to operate at as low a frequency as possible in
accordance with the plant design and licensing limitations but not greater than
57.8 Hz.
198.2. Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
Formatted: Font: Bold
189.3. Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
Formatted: Font: Bold
M198. Each Generator Owner of nuclear units that have been specifically identified by NPCC
as having generator trip settings above the generator trip curve in Figure 1Figure 2 shall
provide evidence such as letters, reports and dated documentation that demonstrates that it
meets Requirement R189.
12
Formatted: Indent: Left: 0.5"
Commented [DML17]: Leave as is
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
R. 20
M19.20 Each Planning Coordinator shall provide evidence such as
spreadsheets, system studies, or other documentation that demonstrates that it meets the
requirements of Requirement R2019.
. TThe Planning Coordinator shall update its UFLS program database
parameters as specified by the NERC PRC Standard on UFLS. This database shall
include the following information: [Violation Risk Factor: Lower] [Time
Horizon: Operations Planning]
20.1
For each UFLS relay, including those used for compensatory load
shedding, the amount and location of load shed at peak, the
corresponding frequency threshold and time delay settings.
20..2
The buses at which the Load is modeled in the NPCC library power flow
case.
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20..3 A list of all generating units that may be tripped for underfrequency
conditions above the appropriate generator underfrequency trip protection
settings threshold curve in Figure 1, including the frequency trip threshold
and time delay for each protection system.
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20..4
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The location and amount of additional elements to be switched for voltage
control that are coordinated with UFLS program tripping.
20..5 A list of all UFLS relay inhibit functions along with the corresponding
settings and locations of these relays.
Formatted: Font: Bold
M20. Each Planning Coordinator shall provide evidence such as spreadsheets, system studies, or
other documentation that demonstrates that it meets the additional UFLS program database
parameters of Requirement R20.
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R21
13
Each Planning Coordinator shall notify each Distribution Provider, Transmission
Owner, and Generator Owner within its Planning Coordinator area of changes to load
distribution needed to satisfy UFLS program performance characteristics as specified by the
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
NERC PRC Standard on UFLS.[Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
Commented [RS18]: This requirement is covered by PRC006-2 Automatic UFLS Continent Wide Standard Requirement
15.
R22
Each Distribution Provider, Transmission Owner and Generator Owner shall
implement the load distribution changes based on the notification provided by the Planning
Coordinator in accordance with Requirement R21. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
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R23
Each Distribution Provider, Transmission Owner and Generator Owner shall develop
and submit an implementation plan within 90 days of the request from the Planning
Coordinator for approval by the Planning Coordinator in accordance with Requirement R21.
[Violation Risk Factor: Lower] [Time Horizon: Operations Planning]
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14
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Figure 1
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
Time (sec)
15
1000
55.5
55
10000
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Attachment 1Figure 1
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
16
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of the same style
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Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
PRC-006-NPCC-2 Figure 1
Frequency (Hz)
Underfrequency Load Shedding Program - Eastern Interconnection
Design Performance Requirements
63
62
61
(30s - 100s;
≤60.7 Hz)
(0.1s - 4.0s; ≤61.8 Hz)
Frequency Must
Remain Between the Overfrequency and
Underfrequency Performance
Characteristic Curves
60
59
(0.1s - 1.1s;
≥58.0 Hz)
58
57
0.1
17
1
Time (sec)
10
NPCC UnderFrequency Requirements
NERC UnderFrequency Requirements (From PRC-006-2)
Combined NPCC + NERC UnderFrequency requirements
100
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Formatted: List Number
Formatted: List Number
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
18
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
C.
Measures
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M1
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
M3 Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
M4 Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped, and the corresponding frequency thresholds,
on those circuits included in its UFLS program to achieve the individual and
cumulative percentages identified in Requirement R4. (Attachment C Tables 1-3).
19
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
M5 Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
M6 Each Distribution Provider and Transmission Owner in the Québec Interconnection
shall have evidence such as documentation or reports containing the location and
amount of load to be tripped and the corresponding frequency thresholds on those
circuits included in its UFLS program to achieve the load values identified in Table 4
of Requirement R6. (Attachment C Table 4).
M7 Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the
minimum time delay, in accordance with Requirement R7.
M8 Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R8.
M9 Each Planning Coordinator shall provide evidence such as letters, emails, or other
dated documentation that demonstrates that it meets Requirement R9.
M10 Each Distribution Provider and Transmission Owner shall provide evidence such as
test reports, data sheets or other documentation that demonstrates that it meets
Requirement R10.
M11 Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails or other dated documentation that demonstrates that it meets
Requirement R11.
M12 Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the frequency set point, the net amount of load shed and the
percentage of its peak load at each stage of its UFLS program coincident with the
integrated hourly peak of the previous year that demonstrates that it meets Requirement
R12.
M13 Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement R13.
20
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
M14 Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R14.
M15 Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R15.
M16 Each Generator Owner with existing non-nuclear units in service prior to the effective
date of this Standard which have underfrequency tripping that is not compliant with
Requirement R13 shall provide evidence such as reports, spreadsheets, memorandum
or dated documentation demonstrating that it meets Requirement R16.
Formatted: Normal, Don't adjust space between Latin and
Asian text, Don't adjust space between Asian text and
numbers
M17 Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall
provide evidence such as emails, memorandum or other documentation that
demonstrates that it followed the methodology described in Attachment A and meets
Requirement R17.
Formatted: Indent: Left: 0.25", Hanging: 0.4"
M18 Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the New York ISO shall provide evidence
such as emails, memorandum, or other documentation that demonstrates that it
followed the methodology described in Attachment B and meets Requirement R18.
Formatted: Indent: Left: 0.25", Hanging: 0.4"
M19 Each Generator Owner of nuclear units that have been specifically identified by NPCC
as having generator trip settings above the generator trip curve in Figure 1 shall
provide evidence such as letters, reports and dated documentation that demonstrates
that it meets Requirement R19.
M20 Each Planning Coordinator shall provide evidence such as spreadsheets, system
studies, or other documentation that demonstrates that it meets the requirements of
Requirement R20.
M21 Each Planning Coordinator shall provide evidence such as emails, memorandum or
other dated documentation that it meets Requirement R21.
M22 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as reports, spreadsheets or other documentation that demonstrates that it
meets Requirement R22.
21
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
M23 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as letters, emails or other dated documentation that demonstrates it
meets Requirement 23.
Formatted: Indent: Left: 0", First line: 0"
D.C.
1.
Compliance
Compliance Monitoring Process
1.1. Compliance Enforcement Authority
NPCC Compliance Committee
1.2. Compliance Monitoring Period and Reset Time Frame
Not Applicable
1.3. Data Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 4, 5, 6,7,10, 11, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 3, 8, 9, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall
keep evidence for three calendar years for Measure 17.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 18, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
13, 14, 15, 16, and 19.
1.4. Compliance Monitoring and Assessment Processes
Self -Certifications.
Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.
1.5. Additional Compliance Information
None.
22
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
PRC-006-NPCC-12 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
1Figure 2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure that
adequate compensatory load shedding is provided in all UFLS islands identified in Requirement
R1 in which the unit may operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain an updated a list of all
existing non-nuclear generating units, in their Planning Coordinator area, in service prior
to the effective date of theVersion 1 of the regional Standard (April, 2017 PRC-006NPCC-1). The list must indicate generating units, if any, effective date of this standard
that have their underfrequency protections set to trip above the appropriate curve in
Figure 1Figure 2. Generating Units not appearing on the list as of the effective date of
Version 1 of the regional standard, as shown above, must have their Underfrequency
protections set to trip on or below the appropriate curve in Figure 1Figure 2. The list
shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate, as identified in Requirement R1
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS
relays within the island(s) identified by the Planning Coordinator in Requirement
R1 within which the generator may operate to provide compensatory load
shedding.
2.2 In Ontario and in the Maritime provinces, Tthe compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4..
23
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 1Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 1Figure 2 does not correspond to a specific UFLS program stage
threshold setting, the compensatory load shedding shall be provided at the UFLS
program stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 1Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
24
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 1Figure 2 of this
standard. The Generator Owner shall follow the methodology below to determine compensatory
load shedding requirements:
1. The Generator Owner shall identify, and compile, and maintain a list of all of its existing
non-nuclear generating units in service prior to the effective date of Version 1 of the
regional is sStandard (April, 2017 PRC-006-NPCC-1). The list must indicate the
Generator Owner’s generating units, if any, that has have their underfrequency
protections set to trip above the appropriate curve in Figure 1Figure 2. Generating Units
not appearing on the list as of the effective date of Version 1 of the regional standard, as
shown above, must have their Underfrequency protections set to trip on or below the
appropriate curve in Figure 1Figure 2. The list shall include the following information
associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 1Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the smallest island identified by the Planning
Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 1Figure 2, the Generator
Owner shall arrange for a Distribution Provider or Transmission Owner to
provide the appropriate amount of compensatory load to be shed within the
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
25
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
26
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
Frequency Threshold
(Hz)
Total Nominal
Operating
Time (s) 1
Load Shed at Stage as %
of TO or DP Load
Cumulative Load Shed as
% of TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
59.5
10.0
2
27.5 – 28.5
2–3
29.5 29.5 – 31.5
Formatted: Numbered + Level: 1 + Numbering Style: 1, 2,
3, … + Start at: 2 + Alignment: Left + Aligned at: 0.25" +
Indent at: 0.5"
Formatted: Left, Indent: Left: 0.25", Hanging: 0.4", No
bullets or numbering
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
27
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating
Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1.
1. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Formatted: Numbered + Level: 1 + Numbering Style: 1, 2,
3, … + Start at: 1 + Alignment: Left + Aligned at: 0.19" +
Indent at: 0.44"
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50
MW2 of peak net Load shall implement a UFLS program with the following attributes:
28
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1.
1. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Formatted: Numbered + Level: 1 + Numbering Style: 1, 2,
3, … + Start at: 1 + Alignment: Left + Aligned at: 0.19" +
Indent at: 0.44"
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Formatted: Indent: Left: 0", First line: 0"
Commented [DML19]: Quebec want this out of standard
UFLS Table 4: Quebec Interconnection
MW
at peak
Mvar
at peak
Total
Nominal
Operating
Time (s) 2
Rate
Frequency
(Hz)
(*Load must
be fixed at all
times when
above 60% of
peak load..)
Threshold Stage 1
–––
58.5
1000*
1000
0.30
Threshold Stage 2
–––
58.0
800*
800
0.30
Threshold Stage 3
–––
57.5
800
800
0.30
Threshold Stage 4
–––
57.0
800
800
0.30
–––
59.0
500
500
20.0
Slope Stage 1
-0.3 Hz/s
58.5
400
400
0.30
Slope Stage 2
-0.4 Hz/s
59.8
800*
800
0.30
Slope Stage 3
-0.6 Hz/s
59.8
800*
800
0.30
Slope Stage 4
-0.9 Hz/s
59.8
800
800
0.30
Threshold Stage 5
(anti-stall)
2. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communications time, and the rated breaker interrupting time. The
underfrequency relay operating time shall be measured from the time when the frequency passes through the
frequency threshold set point.
29
Standard PRC-006-NPCC-12 Automatic Underfrequency Load Shedding
Guidelines and Technical Basis:
Guidelines and Technical Basis
Standard PRC-006-2, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
Formatted: Font: (Default) Times New Roman
Formatted: Left
Formatted: Font: (Default) Times New Roman
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
•
•
•
•
•
•
•
•
•
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
Generator dynamic modeling (MOD-027-1 - Verification of Models and Data for
Turbine/Governor and Load Control or Active Power/Frequency Control Functions) or system
modeling (if variations in system response are detected under MOD-033 - Steady-State and
Dynamic System Model Validation)
30
Commented [RS20]: Did not find the relevant Standard
Implementation Plan
Regional Reliability Standard PRC-006-NPCC-2 – Automatic
Underfrequency Load Shedding
Applicable Standard(s)
•
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requested Retirement(s)
•
PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding
Applicable Entities
•
•
•
•
Generator Owner
Planning Coordinator
Distribution Provider that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Transmission Owners that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Background
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
Effective Date
The first day of the first calendar quarter 6 months following applicable governmental
and regulatory approvals.
Retirement Date
Regional Reliability Standard PRC-006-NPCC-1 shall be retired immediately prior to the
effective date of PRC-006-NPCC-2.
NYISO Comments
Regional Standard PRC-006-NPCC-02
October 16, 2017
The NYISO submits the following comments on the proposed Regional Standard for the drafting team’s
consideration:
With regards to R3
Each Planning Coordinator shall, within 30 days of completion of its UFLS system studies, identify to
the Regional Entity all non-BES generation facilities, within its Planning Coordinator Area, that must
not trip above the appropriate generator underfrequency trip threshold curve in Figure 2 in order to
support acceptable UFLS program performance.
-
It is not clear what is considered to be non-BES generation facilities:
o
Is it limited to generation that is modeled?
o
How should DER, behind the meter or load/netted generation be addressed?
o
What is the criteria for determining what Non-BES generation is not allowed to trip
-
What is the role of the Regional Entity, once this information is provided?
-
Who will have the obligation/authority to inform any identified non-BES generators that they
must adhere to the appropriate trip threshold?
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
PSEG offers the following comments to inform the instant drafting team of PSEG’s
concerns with the proposed standard and to memorialize our position for future
consideration.
a) Generator Compensatory Load Shedding:
PRC-006-NPCC-02 requirement R15 part 3 (R15.3) as proposed would retain PRC-006NPCC-01’s requirement R16.3 for compensatory load shedding by Generators in U.S.
portions of NPCC. However, like PRC-006-NPCC-01, PRC-006-NPCC-02 also does not
include an accompanying requirement in the revised standard that requires a distribution or
transmission entity to make appropriate load (i.e. “within the UFLS island identified by the
Planning Coordinator in Requirement R2”) available to the Generator to shed. And there
also are no applicable Tariffs etc., or other NERC or NPCC standards that require
distribution or transmission entities to make any load available to Generators for this
purpose. Consequently, a requirement for Generator compensatory load shedding in U.S.
portions of NPCC is now and potentially would remain non-implementable for GOs.PRC006-NPCC-02 requirement R15 part 3 (R15.3) and should therefore be removed from the
proposed standard.
b) Generator Underfrequency Trip Protection Settings
The revised standard retains PRC-006-NPCC-01’s Figure 1 generator underfrequency trip
protection settings threshold curve, as PRC-006-NPCC-02 Figure 2. PSEG does not believe
retention of that curve or inclusion of another PRC-006-NPCC-specific Generator UF
settings curve in PRC-006-NPCC-2 are necessary. All UFLS plans of NERC Registered
Entities to whom NERC reliability standard PRC-006-2 is, PRC-006-NPCC-01 is and PRC006-NPCC-02 would be applicable, must already now meet the design performance
requirements identified in Attachment 1 of PRC-006-2. PRC-006-2 Attachment 1 includes
and illustrates that the least-demanding/potentially damaging (the ‘Eastern Interconnection’)
generator underfrequency trip protection settings threshold curve for generating units,
directed and required by NERC reliability standard PRC-024-2 (see Attachment 1 of PRC024-2), coordinates with the UFLS plan performance requirements set out in PRC-006-2.
And that curve (Attachment 1 of PRC-024-2) would coordinate with the UFLS plan
performance requirements that would be set out in PRC-006-NPCC-2 as now proposed (see
PRC-006-NPCC-02 Figure 1). All of the curves in Attachment 1 of PRC-024-2, including
the ‘Eastern Interconnection’ curve, are considered adequate generator UF and OF
performance by NERC and FERC by virtue of being in NERC- and FERC- approved
reliability standard PRC-024-2. If PRC-006-NPCC-02 is to retain PRC-006-NPCC-02
Figure 2, or another PRC-006-NPCC-specific Generator UF settings curve, PSEG
recommends additional technical justification for doing so.
Generator underfrequency trip protection settings that will be directed and required by PRC006-NPCC-2 requirement R12 (i.e. that Generators meet the curve presented in PRC-006NPCC-02 Figure 2) also directly impact the burden and costs Generators now or could in
future (new units; unit uprate modifications) bear to meet other requirements in the
standard: R14; R15; R17 without a commensurate reliability benefit. Generators’ additional
burdens and costs to meet these other requirements should be better supported by additional
technical justification explaining why PRC-006-NPCC-02’s Figure 2 curve, or any other
generator UF settings curve that might alternatively be proposed, is required for PRC-006NPCC-2, over adoption of (direct or implicit) and reliance upon the ‘Eastern
Interconnection’ curve in Attachment 1 of PRC-024-2.
c) Applicability to Non-BES Generators
PRC-006-NPCC-02 requirement R3 appears designed to result in NPCC requiring otherwise
non-BES (i.e. not NERC registered) Generators, or Generators’ otherwise non-BES
generating units, to comply with the standard’s under-frequency ride-through requirements.
The result would be that, where it could otherwise be needed to save an island, load
shedding beyond that directed in Tables 1 to 3 in Attachment C of the proposed standard
would be avoided, at these Generators’ risk (NERC compliance) and expense. PSEG does
not support this. The NERC registration criteria have been developed to generally ensure
that entities needed to ensure BES reliability via the NERC reliability standards are
registered and thereby in the scope of those standards. Similarly, the BES Definition was
developed to generally ensure that facilities and equipment needed to ensure BES reliability
via the NERC reliability standards, are designated as part of the BES and thereby in the
scope of those standards. PSEG recommends additional technical and legal justification
explaining why the Generators indicated in R3 (“non-BES generation facilities”) need to be
registered and become subject to the standard’s under-frequency ride-through requirements,
versus developing and implementing alternatives options such as requiring implementation
of additional load shedding.
d) Adequacy of Required DP and TO Load Shedding
Requirements R4 and R5 direct how much load DPs and TOs must shed, at what frequency
thresholds. However, neither of these requirements, nor any others in PRC-006-NPCC-02,
address or identify what additional action these DPs and TOs, PCs subject to PRC-006NPCC-02 R1, or any other entities are required to take in the event that the amount of load
shed required by R4 and R5 (i.e. load shed schedule listed in PRC-006-NPCC-02
Attachment C) would not produce UFLS program performance meeting PRC-006-NPCC-02
Figure 1. PSEG recommends clarification of what additional actions would be required, and
by whom.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments: Effective date indicated in Section 5 is not consistent with date indicated in
Implementation plan document. PSEG suggests that Section 5 refer to or direct the same
schedule as the Implementation Plan.
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: As noted in our comments in response to Question 1, PSEG disagrees with
compensatory load shedding requirements. PSEG reiterates that PRC-006-NPCC-02
requirement R15 part 3 (R15.3) should be removed from the proposed standard.
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
Following on our comments provided in response to Question 1, PSEG does not find
requirement R12 cost-effective because it requires Generators to meet a generator
underfrequency trip protection settings threshold curve (PRC-006-NPCC-02 Figure 2) which
exceeds what is necessary i.e. beyond what is needed for NPCC entities’ UFLS program
performance to produce BES frequency outcomes that will conform to PRC-006-NPCC-02
Figure 1 limits. Without any commensurate improvement in BES reliability, this increases
costs to Generators. For example, new generators’ UF provisions/protections, replicating
standard designs that otherwise meet others’ UF requirements outside of NPCC, may require
review and potential modification from standard design. PSEG recommends that the ‘Eastern
Interconnection’ curve in Attachment 1 of PRC-024-2 be adopted for PRC-006-NPCC-02, to
replace PRC-006-NPCC-02 Figure 2. This would be accomplished implicitly by removing
PRC-006-NPCC-02 R12 in its entirety from PRC-006-NPCC-02, since Generators already
must comply with PRC-024-2. It could also be done explicitly by replacing the current PRC006-NPCC-02 Figure 2 with: (i) a copy of the ‘Eastern Interconnection’ curve in Attachment
1 of PRC-024-2; or (ii) explicit reference to that curve in PRC-006-NPCC-02; or (iii)
incorporating the curve into PRC-006-NPCC-02 Figure 1 (as PRC-006-NPCC-02 Figure 1
has done with the BES System Frequency element of Attachment 1 of PRC-006-2, and
Attachment 1 of PRC-006-2 itself has done with the ‘Eastern Interconnection’ curve in
Attachment 1 of PRC-024-2).
On the basis of our comments in response to Question 1, PSEG does not find requirement R3
cost-effective because it could impose significant additional risks and costs on otherwise
non-BES Generators, or Generators’ otherwise non-BES generating units, to the benefit
(avoided additional costs) to other already-NERC-registered BES entities (DPs, TOs) who
could implement one or more alternative solutions (e.g.: additional load shed capability;
strengthened transmission capability).
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: This draft version of NPCC Regional Standard PRC-006-NPCC-2 ‘Automatic
Underfrequency Load Shedding’ includes instances of unclear language, exposing risks of
alternative interpretations; see questions and proposed changes under item #7 below for details.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments: Please consider changing language under Effective Dates to state: “See
Implementation Plan.” Please consider changing the effective date to read as the first day of the
first calendar quarter 12 months following applicable governmental and regulatory approvals.
The change from 6 months to 12 months will provide additional time that may be needed to
accommodate automatic UFLS changes that may need to be made on an island basis, for each
identified island. Changes involving automatic UFLS are generally made on an annual
schedule.
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: See #7 below.
7. Provide any additional comments for the drafting team to consider, if desired.
Comments: Below please find our general questions and proposed (editorial) changes:
- Should the word island (as in UFLS Island) be capitalized throughout this document,
since it is a defined term in the NPCC Glossary of Terms? The term island’ is sometimes written
with a lower case “i” and sometimes with a capital “I”, please review to ensure consistency in
standard.
- Suggesting changing reference to NERC PRC-006-2 from ‘generic’ version (i.e., NERC
PRC Standard on UFLS) to a more formal language e.g., NERC Reliability Standard PRC-006.
- Please review lay-out, in particular related to spacing between Requirements and
Measures.
- Applicability. Please consider revision Sections 4.3 (Distribution Providers) and 4.4
(transmission Owners) to the terminology of ‘UFLS entities’ as used in NERC Reliability
Standard PRC-006-2.
- R3. How can non-BES generation facilities become part of a requirement? If so, should
there be lower thresholds for non-BES generation? Since Requirement R3 as presently written is
only a reporting requirement, it seems reasonable to consider this requirement as a candidate for
deletion per Paragraph 81 (i.e., providing little protection to the reliable operations of the BES).
- R4. Please ensure consistency in language of sub-Requirements R4.1 and R4.2., where
R4.1 uses a shall (strong) language and R4.2 seems to allow for an exception (‘Alternatively’),
where the present language seems to expose a significant risk of alternative interpretations. It is
our interpretation that the ‘shall’ language requires compliance with the requirement in 4.1
during all conditions, and the alternative in 4.2 never seems to become applicable as a
requirement.
- R4. Consider re-instating language “for its Facilities based on frequency thresholds”, as
used in PRC-006-NPCC-01, to clarify meaning of which outages are referred to in 4.1. F urther,
does the requirement to exclude outages only refer to outages within each identified island?
- R5. The language in sub-requirements 5.1.1., etc. lack clarity and could be
misinterpreted. Suggesting adding comma signs, where appropriate, to make requirement R5
clearer and more precise. In 5.1.1. consider adding a comma sign after “… after determining that
adjustments are possible”.
- R5. The language in 5.2.1. and 5.3.1. to “make the adjustments of determining that
adjustments are possible” is unclear if it refers to having the adjustments made or only
determining if the adjustments are possible; also missing a comma sign (for readability) as noted
above for 5.1.1.
- R5. The term “bulk power system” seems to refer to NPCC BPS definition, but this is not
clear.
- R5. The number of days in the different sub-requirements varies between 90 and 180
days. Is this variation for the different sub-requirements intentional? If so, what is the rationale?
Also, 90 days to make necessary adjustments (if that is the correct interpretation) seems very
short.
-
R8. The word ‘those’ should either be removed or explained (what it refers to).
- R9. Suggest to move ‘for approval by the Planning Coordinator’ to before ‘within 90
days’.
- R10. Are there any time requirements related to implementation of the inhibit
thresholds?
box.
Rationale for R11. Please explain or delete the word ‘universally’, used in this rationale
- R11. Should the time 15 months, be written as 15 calendar months (for improved
clarity)?
- R11. Delete the last sentence “If there is no local metering of the load through said
switches, the load may be calculated from measurements made at the nearest available metering.
(e.g., upstream metering on the distribution feeder that supplies the load to be shed).” Since it is
not drafted as a requirement. This text could be moved to the rationale box, if appropriate.
-
The last paragraph in the Guidelines and Technical Basis section seems to be unfinished.
-
RE:
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
Suggest changing ‘the NERC PRC standard on UFLS’ to ‘the NERC Standard PRC-006’ in the
Rationale Box for R1, R2 and R4 and Attachment A.
The timeframe identified in R 5.1.1 would be applicable only if there were a limited number of
setting changes that could be performed on existing relays with UFLS capability.
Recommend changing to:
“If adjustments are possible utilizing existing UFLS relays, …”
For R 5.1.2 Will the Planning Coordinator be maintaining detailed UFLS base cases for
immediate use when DP/TO has a need to perform a technical study?
Recommend a 1-1/2 year Technical Study duration based on developing detailed scope for
approval, developing base cases for the analysis, performing the analysis, review of results by
PC, performing any requested sensitivity/other analysis, review and approval of the final study
report.
For R 5.1.2: Need to address the impact if the Technical Study does identify a significant
adverse impact. The additional steps and associated timeline to address the existing out of
tolerance/adverse impact need to be defined.
The DP/TO will need to develop an implementation plan which would be challenging to do in the
proposed 180 days. Eversource recommends a two-year implementation period based on
engineering the project, attaining capital funding for the Project, ordering equipment, performing
scheduling requirements, and construction of the project.
If a new or redefined Island is determined in your area that is the result of a new UFLS study
performed by the Planning Coordinator or NPCC, how would your Company comply with
Compliance Reporting by Island?
A new island(s) or modified Island boundary can create significant effort, construction time, and
cost, to be Compliant on an Island basis. This issue should be addressed in detail. The
magnitude of the required load shift could be significant. If a DP/TO does not have the
capability to add additional UFLS to an Island by simply activating UFLS on existing station
relays, the DP/TO must identify new stations/circuits and develop Projects to add the capability.
If a DP/TO is out of tolerance with island balancing only (entity as a whole meets the PRC-006NPCC UFLS Requirements), can an additional alternative be introduced to hold off on
adjustments / technical studies until completion of a NPCC/SS-38 UFLS Assessment Study that
is planned to occur in the near term?
(This is currently what Eversource Eastern Mass is doing since the NPCC/SS-38 UFLS
Assessment Study is being advanced and the analysis may redefine islands. Eversource
Eastern Mass is at a point where finding additional load shed opportunities in the New England
Island will be labor intensive and costly. Eversource Eastern Mass does not want to pursue
significant changes that may not be necessary. Developing independent study cases and
pursuing a separate technical study that would be done in parallel with a Regional Study would
not make sense.)
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
Section 5 states that the effective date is ‘The first day of the first calendar quarter following
applicable governmental and regulatory approvals’ but the Implementation Plan states that
‘The first day of the first calendar quarter 6 months following applicable governmental
and regulatory approvals.’ So not sure which effective date the SDT is proposing.
However, even if the effective date is at least 6 months, we are concerned with non-compliance
due to the possibility of significant UFLS Program change requirements and the amount of time
required to develop, fund and implement/construct a change Project.
For many this may not be an issue, but if a TO/DP needs to make significant changes to be
compliant by Island, they would not meet this requirement on the effective date.
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
In reference to R2, “PC to Provide UFLS Island Boundaries…”: The requirement for an entity’s
UFLS Program attributes to be compliant by Island rather than entity-wide can potentially create
costly modifications/changes to a TO/DPs UFLS Program that can take significant time,
resources, and dollars to implement. The criteria and severity of contingencies used in
defining Islands should consider the potential impact resulting from the Island defining process.
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
Regarding Compensatory Load Shedding, we agree with the revisions of 15.3 as well as to
Attachment B. Consider adding the following to the end of 2.1 of Attachment B to ensure GOs
properly communicate changes to the DP/TO.
‘The GO shall communicate any required changes for Compensatory Load Shedding to the DP
or TO (or within 90 days of implementing the change).’
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
We believe there is a potential misalignment between the design performance requirement in the
NERC continent-wide standard PRC-006-2 and in the proposed regional standard PRC-006-2NPCC-2 and the existing NPCC Directory #12. The NERC continent-wide standard requires
that the under-frequency performance characteristic (Requirement R3, Part 3.10) remains
between 59.3 Hz and 60.7 Hz after 60 seconds (60 s / 59.3 Hz & 60 s / 60.7 Hz). Both the
regional standard and the directory have the under-frequency performance requirement remain
above 59.5 Hz after 30 seconds (30 s / 59.5 Hz).
Planning Coordinators that are not part of NPC region design their UFLS program according to
the NERC continent-wide standard and use the 60 s / 59.3 Hz performance characteristic.
Planning Coordinators in the NPCC region design their UFLS program using the 30 s / 59.5 Hz
performance characteristic.
There may be instances where portions of Planning Coordinators in the NPCC region may form
islands with portions of systems outside of the NPCC's footprint. This may pose a potential
non-compliance with their own performance characteristic of 30 s / 59.5 Hz.
Given that there is no technical justification for the existing NPCC performance characteristic of
30 s / 59.5 Hz, we propose that the regional standard and/or directory (depending on whether the
regional or the directory is retired) be aligned with the continent-wide standard’s performance
characteristic of 60 s / 59.3 Hz. Since the NPCC performance characteristic is more stringent
than that of the continent-wide standard, there should be no impact on the current UFLS
program for the Eastern Interconnection. An aligned performance characteristic is not expected
to result in non-compliance for the NPCC Planning Coordinators.
Furthermore, we propose that, in lieu of revising the regional standard to align with the
performance characteristic contained in continent-wide standard and retiring the directory, to
align the NPCC Directory #12 with the continent-wide standard and retire the regional standard.
We find that using the NPCC process for developing/revising/approving criteria would be less
onerous for the alignment than the NERC standard development process (i.e., limited to NPCC
members as opposed to the greater NERC industry stakeholders needed to build consensus).
Our proposal to retire the regional standard is consistent with the objective of revising selected
NERC standards to remove the “fill-in-the-blank” requirements that were established at earlier
versions of the NERC standards. Now that the NERC PRC-006-2 has been developed, with
Regional Variance for Quebec (and WECC), and in effect, we do not see any value of
maintaining this regional standard. The more stringent and/or more specific requirements, if
desired to be retained, should be stipulated in a Directory.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments: See Comments for Question 1.
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
7. Provide any additional comments for the drafting team to consider, if desired.
We submit the following comments for your consideration:
R1: See Comments for Question 1.
R2: We see this as an administrative requirement that does not address any reliability need.
It would be sufficient for the Planning Coordinators to notify the applicable UFLS entities of the
UFLS program.
R3: Similar with R2, we see this as an administrative requirement as it is not clear what
reliability need this requirement is meant to address.
R11: This requirement is a duplication of R8 of PRC-006-2. We propose to have R11 removed.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: Based on the regional standard PRC-006-NPCC-2 the UFLS will be initiated
earlier when compared to the continent wide standard PRC-006-3 to prevent frequency
collapsing on any potential island created as result of Grid disturbances. When referencing the
performance characteristic requirements, a higher frequency requirement for the same time
duration is better for grid reliability.
OPG believes that an analysis of potential islands survivability must be performed for all the
potential islands that do not belongs entirely to NPCC region and will contain generators from
entities that do not have to comply with the proposed performance characteristic requirements of
the regional standard PRC-006-2-NPCC-2. In these case of a newly created island the UFLS
associated with the portion of the island contained in the NPCC region would be the first to shed
load in an attempt to prevent the decline in frequency due to more stringent PRC-006-NPCC-2
performance characteristic requirements (30 s / 59.5 Hz vs. 60 s / 59.3 Hz as required by PRC006-3). While frequency will be the same in the entire island the load shedding contained only to
NPCC region can potentially affect the island dynamic and steady state stability due to power
swings and circuits overload.
This would not be an issue if dynamic UFLS can be achieved/implemented or exceptions
allowed for specific islands (where dual interactive regulatory requirements are present) for
survivability purposed.
The above analysis is no longer required if the discrepancy between regional and continent wide
standard is eliminated by using the same performance characteristic requirements; it does
however no longer justifies from this point of view the existence of a regional standard and
perhaps the case for regional variance is more justified (i.e. when establishing the compensatory
load shedding per attachment A/B)
If the NPCC Directory #12 UFLS requirements are perfectly aligned with the NPCC continentwide standard, then there is no increase in grid reliability and no justification for existence. The
regional standards are justified if they increase the grid reliability through more stringent,
justified, requirements or when dealing with technical constraints by minimizing the compliance
effort without affecting grid reliability.
In order to justify more stringent regional standard requirements the SDT should revalidate the
initial technical justification for the more stringent performance characteristics (i.e. revalidate
NPCC UFLS assessment for the current grid composition in terms of different representative
generator manufacturers in service and compilation of capabilities/ride through for generators).
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: OPG has requested previously the Standard Drafting Team to ensure that the
obligations stemming from requirement R15 part 15.3 are clearly removed from the compliance
obligation of the Generator Owner, since in Ontario the Planning Coordinator is responsible for
establishing the compensatory load shedding requirements. This is only captured in PRC-006NPCC-2 attachment A and because of differences between Ontario, Quebec, Maritime Provinces
and the ISO-NE, NYISO we have two different entities having regulatory obligations for the
same requirement R15. OPG is of the opinion that the wording used on the latest draft standard
revision of R15 is still confusing and recommends the following changes:
R15. Each Generator Owner of existing non-nuclear units in service prior to the effective date of
this standard, that have underfrequency protections set to trip above the appropriate curve in
Figure 2 shall: [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
…
15.3. The responsible entity, as documented in accordance with Attachments A or B, shall
have compensatory load shedding, as provided by a Distribution Provider or Transmission
Owner that is adequate to compensate for the loss of their generator due to early tripping
that is within the UFLS Island identified by the Planning Coordinator in Requirement R2.
This will result only in part 15.3 creating compliance obligation for different entities similar to
variances.
OPG also recommend to make the following changes to the requirement “15.3 The responsible
entity, as documented in accordance with Attachments A or B, shall have compensatory load
shedding, as provided by a Distribution Provider, Underfrequency Load Shedding (UFLS)-only
Distribution Provider (DP) or Transmission Owner that is adequate to compensate for the loss of
their generator due to early tripping that is within the UFLS island identified by the Planning
Coordinator in Requirement R2.”
SDT should include the newly approved FERC registration category, “Underfrequency Load
Shedding (UFLS)-only Distribution Provider (DP)” in the revision of the standard PRC-006-NPCC2 Automatic Underfrequency Load Shedding, to bring PRC-006-NPCC-02 standard in line with
the newly registered functional categories as per Project 2017-07 Standards Alignment with
Registration.
Now that we also have newly registered UFLS-only DP entity, can SDT comment on following
the same NERC compliance obligation approach per PRC-006-3, which requires UFLS entity to
provide load shedding as determined by the Planning Coordinator(s)?
“R9. Each UFLS entity shall provide automatic tripping of Load in accordance with the UFLS
program design and schedule for implementation, including any Corrective Action Plan, as
determined by its Planning Coordinator(s) in each Planning Coordinator area in which it owns
assets. [VRF: High][Time Horizon: Long-term Planning]”
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments: Directory 12 Automatic Underfrequency Load Shedding Program has
requirements pertaining to the following:
Automatic Underfrequency Load Shedding
Underfrequency trip settings of the protective relaying
The requirements pertaining to Automatic Underfrequency Load Shedding are translated
into PRC-006-NPCC-02 which is the regional standard for Automatic Underfrequency
Load Shedding.
OPG is of the opinion that Directory 12 should not be retired before a regional standard is
prepared (i.e. PRC-024-NPCC-01) or regional variance is included via revision of the
PRC-024-2 for translation of Underfrequency trip settings of the protective relaying,
contained in D12.
The following are the NPCC Directory #12 – Under frequency Protection Requirements that
should be translated to a new regional standard or variance before D12 retirement.
“5.4 Generator Under frequency Protection Requirements
Generators shall not be tripped for under-frequency conditions in the area above
the curve in Figure 1, except as provided for in Sections 5.4.1 and 5.4.2.
5.4.1 It is recognized that, in special cases, requirements may dictate
generator trip in the region above the curve. In those cases, the Generator
Owner shall so notify its Balancing Authority and shall ensure through
alternate arrangements, that automatic load shedding additional to the
amount set out in Section 5.2 and in Section 5.3, equivalent (+/- 5%) to the
amount of generation to be tripped, is provided. Such cases shall be
reviewed by the Task Force on Coordination of Operation
5.4.2 Generator Owners shall not increase the under frequency trip
settings or make other modifications to the existing exempt generators
(that trip above the curve in Figure 1) that may cause these generators to,
directly or indirectly, trip at a higher frequency.”
Additionally these Under Frequency Protection Requirements should be adequately
designed and coordinated with the Balancing Authorities (i.e. IESO for Ontario) and the
NERC PRC-024 existing requirement, to eliminate potential gaps.
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: All the requirements associated with the Underfrequency Trip Settings
associated and the Figure 2 of the PRC-006-NPCC-2 Underfrequency Load Shedding
Program – Thresholds for Setting Underfrequency Trip Protection for Generators should be
deleted from this regional standard and adequately addressed/included in a newly develop
regional standard PRC-024-NPCC-01, or revision of PRC-024-2 to include regional variance
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
OPG is of the opinion that although included in the Standard PRC-006-NPCC-1 Automatic
Underfrequency Load Shedding, the requirements for the Frequency Settings of the
Protective Relaying is better suited in a new regional standard PRC-024-NPCC-01 or a
newly revised PRC-024-3 that includes the required regional variance.
If the decision is taken to proceed with the development of a new regional standard then
coordination between regulators is required to eliminate potential gaps between the currently
applicable regulatory compliance requirements with respect to Generator Frequency
Protective Relay Settings:
NERC Standard PRC-024-2 — Generator Frequency and Voltage Protective
Relay Settings
IESO Market Rules - Chapter 4 - Grid Connection Requirements – Appendix 4.2
– Generation Facility Requirements
Market Manual 2: Market Administration Part 2.20: Performance Validation - 3.
Generator Requirements
NPCC Regional Reliability Reference Directory # 12 - Under frequency Load
Shedding Program Requirements
All these regulatory requirements should be coordinated to eliminate the potential for
inadvertent noncompliance. Although this requires a lot of effort and can be met with
resistance the better the effort put in the development of coordinated standards by
different regulators on the same technical issue, the higher Grid Reliability end result and
the least potential for inadvertent noncompliance due to misunderstandings.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: While in general agreement with the changes; the proposed text should be
modified for clarity and enforceability.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments: Consider allowing the flexibility to adopt immediately or adopt when the next
annual load review is carried out to address any changes that may only be incorporated during
the next review.
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: Specify that the requirement applies to only BES generators either in this
requirement or in the applicability section.
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments: Note that this requirement does not impact NB Power generation.
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: R3: Suggest rewording R3 such that the PC will provide data to RE within 30
days of request from the RE, where the data to be based on the most recent study. Also, for
clarity, identify the requirement(s) that define acceptable UFLS program performance.
The RE does not (to my knowledge) have a formal process for such data submission and is
not consistent in acknowledging such data submissions.
R5: Limiting mutual agreements to smaller entities could result in the unnecessary
installation of UFLS devices to meet load shedding thresholds.
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
Part 4, Applicability: Similar to PRC-006-2, the applicability of TO and DP should include
text to clarify that UFLS program as established by the Planning Coordinator.
Assuming the intent is to only include BES generators the applicability should clearly specify
otherwise the standard could be considered as applicable to all generation facilities owned by a
generation owner regardless if a BES facility or not. Another option is to replace “generator”
with “BES generator” in the relevant requirements.
Requirement 1: I would expect that this requirement is met through application of the UFLS
tables in standard attachment. If the tables in the attachment do not meet this requirement how
does the PC reconcile this requirement with the load shedding tables?
Requirement 3: Suggest rewording R3 such that the PC will provide the information to the
RE within 30 days of request from the RE, where the information supplied to the RE is based on
the most recent study as required by PRC-006-2 R4.
For clarity please identify the requirement(s) that define acceptable UFLS program
performance either in this standard or PRC-006-2
It is not clear on how the PC determines if a non-BES unit results in unacceptable UFLS
performance. Would the UFLS performance be based on a single generator misoperation or
multiple simultaneous misoperations?
Requirement 4: The general reference “the NERC PRC Standard on UFLS” should include
the standard number and the requirement for clarity.
To be more flexible, why limit mutual agreements to small entities but allow any entity to
participate in a mutual agreement though conditional on PC approval. Allowing more flexibility
could help resolve the scenario in R5 in some situations.
Requirement 5: Propose wording “…within 30 days of discovery” .
For R 5.1.2, I am concerned with the DP or TO carrying out a technical study to determine if
there is no significant impact on the bulk power system.
Requirement 6: If this requirement is not a critical component of the UFLS, and is simply
there to prevent load loss on significant frequency swings, recommend moving this requirement
to the guidance section.
Requirement 7: Please define or describe “inhibit thresholds”.
Requirement 11: Why are we limiting the approach in determining peak load values for a
given load? Approach should be broadened to allow for other reasonable methods. Also
question the situation where a meter data is unavailable. Another approach could also allow for
monthly meter readings reconciled with system peak. So recommend that “…or monthly meter
reading values reconciled with system hourly peak values. Also recommend broad wording
allowing other approaches that provide a reasonable calculation of a load’s peak load.
Requirement 12: The curve is not the same as off normal frequency capability curve PRC024 attachment 1 (Eastern Interconnection). To avoid uncertainty with generator owners that
have met compliance with PRC-024 a note could be added in this requirement identifying the
more stringent generator UFLS curve. In addition, the drafting team may consider a regional
variance on PRC-024 adding the new curve for generation or referencing applicable portions of
this regional standard.
R15.1 This sub-requirement would be more flexible if “plant design and licensing
limitations” was replaced with “plant design or licensing limitations” (replaced and with or) to
address those situations were licensing may not be effected though the plant design is.
Guidelines and Technical Basis: I agree with the approach taken. I assume that there are no
compliance implications on the factors that could initiate a new assessment. Do you agree?
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
If the R5.1 technical study shows that there are significant adverse
impacts on the system, then the standard doesn’t provide guidance on next steps. In
Figure 1, for clarity, move the label for the “combined NERC – NPCC curve” to the far
left in the legend and make it plainly the “NPCC Underfrequency Curve”
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
Absolutely. We agree with the retirement of any NPCC Directories
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
M9 – needs to be changed for applicability of R9 to DPs and TOs; In
several places, the term calendar days is used and in others simply days. Use one notation
for consistency; In the Guidelines and Technical Basis section the final sentence “Generator
dynamic modeling (MOD-027-1…)” should be made into a bullet.
11/26/2019
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Automatic Underfrequency Load Shedding
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Comment Period (9/1/2017 - 10/16/2017)
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10/16/2017
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10/16/2017
10/13/2017
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National Grid
View Attachment
10/13/2017
Comments: R4: R4 states, “The automatic UFLS program shall be implemented on an island basis for each island identified
per the NERC PRC Standard on UFLS” but the individual TO/DP will not have visibility or control for identified islands. The
islands may span a different area than the TO/DP service area. The individual TO/DP will not be able to demonstrate
compliance on an island basis; the individual TO/DP is limited to demonstrating compliance for its service area which may
nor may not align with the island. The requirement should be clarified to state that it applies to only the portion of the island
the TO/DP has control over. R11: Can the drafting team address the following two questions: What is the purpose of R11?
and What is the quantitative benefit of collecting and sharing this information? If the purpose and/or benefit is not
quantitative why not remove R11 altogether from the standard? Under the current version of PRC-006-NPCC, the TP (or DP)
provides historical data on load that would have been shed if the UFLS Program had operated at the actual peak from prior
year. The phrase “that would have been” shed is being replaced with “projected to be” shed. Under the proposed language,
the TP (or DP) is required to provide a projection of the amount of load that will be shed, at the projected peak load
conditions, if ULFS Program is actually triggered. This is already addressed by PRC-006-2 R8. However the second sentence
of the requirement does not align because it refers to the actual net load from the previous year. The “that would have
been” language in the first sentence should be retained, if the purpose and/or benefit is quantitative. Otherwise, R11 should
be removed from the standard. General comment: For Attachment C, Table 1, Footnote 1, include the following additional
sentence: “This total operating time may include a maximum deviation, for any load, limited to ±50 milliseconds.” Rationale
for Comment: Relay and circuit breaker operating times are rarely precisely repeatable. Thus it is not practicable to expect
zero deviation of a specified time-operating interval. This is probably the reason why NPCC Directory #12 Req. 5.2.1 which
refers to the same operating time requirement, included the maximum deviation allowance in its own Footnote (1). Note
this comment does not pertain to any changes brought about by the current revision, but to a deficiency in the previous
version. This -2 revision is an opportunity to correct the deficiency.
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10/13/2017
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09/28/2017
Independent Electricity System Operator
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https://www.npcc.org/Standards/SitePages/Comments.aspx?DevDocumentId=122&CommentPeriodId=244
1/1
September 1, 2017
Subject: Posting for Open Process Review of PRC-006-NPCC-2 Automatic Underfrequency
Load Shedding.
The clean and redlined versions of the revised NPCC Regional Standard PRC-006-NPCC-2
Automatic Underfrequency Load Shedding, have been posted on the NPCC Website for a 45-day
comment period through October 16, 2017, along with a proposed Implementation Plan.
This initial draft has been developed in accordance with the NPCC Regional Standard Process
Manual (RSPM) and within the scope of NPCC Regional Standard Authorization Request, which
was accepted by the NPCC Regional Standard Committee (RSC). The revisions are also
presented as mandated by the NERC Rules of Procedure. This initial draft does not include the
Violation Severity Levels, which will be developed for the next posting period.
Among the proposed changes included in the initial draft version of the Standard are:
• Modifications to Figures #1 and #2 in the Standard
• Added a Guidelines and Technical Basis section (NERC may request us to create a
separate document for this section and post it with the standard subsequent to approvals)
• Incorporated certain Criteria attributes from Directory #12 Automatic UFLS Program
Requirements which will facilitate the retirement of Directory #12
• Additional clarification of requirement language
• Proposed retirements of some of the Requirements that are redundant to the PRC-006-2
Continent-wide NERC standard
Also posted is a set of questions developed by the Regional Standard Drafting Team to solicit
comments on the draft standard and associated draft Implementation Plan for the Regional
Standard. Included in these questions is one on cost effectiveness of the requirements.
Comments on the posted materials may be submitted through the NPCC Open Process Portal,
which may be accessed through:
https://www.npcc.org/Standards/SitePages/DevStandardDetail.aspx?DevDocumentId=122
Subsequent to consideration of comments and revision, the standard is tentatively scheduled to
be posted for a second comment period in the first quarter of 2018 and then for a 30-day preballot review and 10-day ballot period following the conclusion of the review period.
Please contact me with any questions regarding this Standard.
Thank you.
Ruida Shu
Northeast Power Coordinating Council, Inc.
Senior Engineer, Reliability Standards and Criteria
Main: 212-840-1070
Direct: 917-934-7976
Fax: 212-302-2782
Email: [email protected]
R4:
R4 states, “The automatic UFLS program shall be implemented on an island basis for each island
identified per the NERC PRC Standard on UFLS” but the individual TO/DP will not have
visibility or control for identified islands. The islands may span a different area than the TO/DP
service area. The individual TO/DP will not be able to demonstrate compliance on an island
basis; the individual TO/DP is limited to demonstrating compliance for its service area which
may nor may not align with the island. The requirement should be clarified to state that it
applies to only the portion of the island the TO/DP has control over.
Drafting Team Response:
The Planning Coordinator is the responsible entity to determine UFLS program requirements on
an island basis.
The Transmission Owner and Distribution Provider are responsible to implement the appropriate
amount of load-shedding in accordance with Attachment C for each island in its service area.
R11:
Can the drafting team address the following two questions: What is the purpose of R11? and
What is the quantitative benefit of collecting and sharing this information? If the purpose and/or
benefit is not quantitative why not remove R11 altogether from the standard?
Under the current version of PRC-006-NPCC, the TP (or DP) provides historical data on load
that would have been shed if the UFLS Program had operated at the actual peak from prior year.
The phrase “that would have been” shed is being replaced with “projected to be” shed. Under the
proposed language, the TP (or DP) is required to provide a projection of the amount of load that
will be shed, at the projected peak load conditions, if ULFS Program is actually triggered. This is
already addressed by PRC-006-2 R8. However, the second sentence of the requirement does not
align because it refers to the actual net load from the previous year. The “that would have been”
language in the first sentence should be retained, if the purpose and/or benefit is quantitative.
Otherwise, R11 should be removed from the standard.
Drafting Team Response:
The drafting team decided to make modifications to requirement language of R11.
General comment:
For Attachment C, Table 1, Footnote 1, include the following additional sentence:
“This total operating time may include a maximum deviation, for any load, limited to ±50
milliseconds.”
Rationale for Comment: Relay and circuit breaker operating times are rarely precisely
repeatable. Thus, it is not practicable to expect zero deviation of a specified time-operating
interval. This is probably the reason why NPCC Directory #12 Req. 5.2.1 which refers to the
same operating time requirement, included the maximum deviation allowance in its own
Footnote (1).
Note this comment does not pertain to any changes brought about by the current revision, but to
a deficiency in the previous version. This “-2” revision is an opportunity to correct the
deficiency.
Drafting Team Response:
Action Item:
The drafting team will discuss the 300 ms total nominal operating time at a later time.
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
Suggest changing ‘the NERC PRC standard on UFLS’ to ‘the NERC Standard PRC-006’ in the
Rationale Box for R1, R2 and R4 and Attachment A.
The timeframe identified in R 5.1.1 would be applicable only if there were a limited number of
setting changes that could be performed on existing relays with UFLS capability.
Recommend changing to:
“If adjustments are possible utilizing existing UFLS relays, …”
For R 5.1.2 Will the Planning Coordinator be maintaining detailed UFLS base cases for
immediate use when DP/TO has a need to perform a technical study?
Recommend a 1-1/2 year Technical Study duration based on developing detailed scope for
approval, developing base cases for the analysis, performing the analysis, review of results by
PC, performing any requested sensitivity/other analysis, review and approval of the final study
report.
For R 5.1.2: Need to address the impact if the Technical Study does identify a significant
adverse impact. The additional steps and associated timeline to address the existing out of
tolerance/adverse impact need to be defined.
The DP/TO will need to develop an implementation plan which would be challenging to do in
the proposed 180 days. Eversource recommends a two-year implementation period based on
engineering the project, attaining capital funding for the Project, ordering equipment, performing
scheduling requirements, and construction of the project.
If a new or redefined Island is determined in your area that is the result of a new UFLS study
performed by the Planning Coordinator or NPCC, how would your Company comply with
Compliance Reporting by Island?
A new island(s) or modified Island boundary can create significant effort, construction time, and
cost, to be Compliant on an Island basis. This issue should be addressed in detail. The magnitude
of the required load shift could be significant. If a DP/TO does not have the capability to add
additional UFLS to an Island by simply activating UFLS on existing station relays, the DP/TO
must identify new stations/circuits and develop Projects to add the capability.
If a DP/TO is out of tolerance with island balancing only (entity as a whole meets the PRC-006NPCC UFLS Requirements), can an additional alternative be introduced to hold off on
adjustments / technical studies until completion of a NPCC/SS-38 UFLS Assessment Study that
is planned to occur in the near term?
(This is currently what Eversource Eastern Mass is doing since the NPCC/SS-38 UFLS
Assessment Study is being advanced and the analysis may redefine islands. Eversource Eastern
Mass is at a point where finding additional load shed opportunities in the New England Island
will be labor intensive and costly. Eversource Eastern Mass does not want to pursue significant
changes that may not be necessary. Developing independent study cases and pursuing a separate
technical study that would be done in parallel with a Regional Study would not make sense.)
Drafting Team Response:
In general specifics in regards to the NERC Standard numbers are avoided due to the possibility
of changes to the standard due to retirements or other standards superseding the existing
standard. In additional to clarification we will refer to the NERC standard references as continent
wide.
The drafting team does not agree with adding the language “utilizing existing UFLS relays” to
requirement 5, because it is not in the interest of reliability.
After reviewing all the comments for requirement 5 of the standard, the drafting team decided to
provide a rationale box to clarify the standard.
In regards to the new or modified islands per the study of SS38, it is covered by the requirement
3 and requirement 15 in the continent-wide standard.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
Section 5 states that the effective date is ‘The first day of the first calendar quarter following
applicable governmental and regulatory approvals’ but the Implementation Plan states that
‘The first day of the first calendar quarter 6 months following applicable governmental
and regulatory approvals.’ So not sure which effective date the SDT is proposing.
However, even if the effective date is at least 6 months, we are concerned with non-compliance
due to the possibility of significant UFLS Program change requirements and the amount of time
required to develop, fund and implement/construct a change Project.
For many this may not be an issue, but if a TO/DP needs to make significant changes to be
compliant by Island, they would not meet this requirement on the effective date.
Drafting Team Response:
The drafting team changed the language in section 5 to Refer to Implementation Plan”.
In the Implementation Plan drafting team increased the implementation period to 12 months for
R4 and keeping the remainder requirements to the first day of the first calendar quarter following
the applicable governmental and regulatory approvals.
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
In reference to R2, “PC to Provide UFLS Island Boundaries…”: The requirement for an
entity’s UFLS Program attributes to be compliant by Island rather than entity-wide can
potentially create costly modifications/changes to a TO/DPs UFLS Program that can take
significant time, resources, and dollars to implement. The criteria and severity of contingencies
used in defining Islands should consider the potential impact resulting from the Island defining
process.
Drafting Team Response:
The criteria and severity of contingencies used in defining Islands is beyond the scope of this
standard (PRC-006-NPCC-2). Criteria for determining islands is in part defined in the continent
–wide standard on UFLS in requirements R1 and R2 of PRC-006-3. The criteria and severity of
contingencies used to define Islands is at the discretion of the PC conducting the study to identify
islands. As a general comment however, the goal of the island identification analysis is to
identify coherent generation groups that define where and how the islands are formed.
Identification of these coherent generation groups may require the simulation of beyond extreme
contingencies (i.e. simulation of normal and extreme contingencies may not be adequate to
identify these coherent generation groups).
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
Regarding Compensatory Load Shedding, we agree with the revisions of 15.3 as well as to
Attachment B. Consider adding the following to the end of 2.1 of Attachment B to ensure GOs
properly communicate changes to the DP/TO.
‘The GO shall communicate any required changes for Compensatory Load Shedding to the DP
or TO (or within 90 days of implementing the change).’
Drafting Team Response:
Thank you for your comments.
The drafting team believes the current R15 addresses the concern.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
We believe there is a potential misalignment between the design performance requirement in the
NERC continent-wide standard PRC-006-2 and in the proposed regional standard PRC-006-2NPCC-2 and the existing NPCC Directory #12. The NERC continent-wide standard requires
that the under-frequency performance characteristic (Requirement R3, Part 3.10) remains
between 59.3 Hz and 60.7 Hz after 60 seconds (60 s / 59.3 Hz & 60 s / 60.7 Hz). Both the
regional standard and the directory have the under-frequency performance requirement remain
above 59.5 Hz after 30 seconds (30 s / 59.5 Hz).
Planning Coordinators that are not part of NPC region design their UFLS program according to
the NERC continent-wide standard and use the 60 s / 59.3 Hz performance characteristic.
Planning Coordinators in the NPCC region design their UFLS program using the 30 s / 59.5 Hz
performance characteristic.
There may be instances where portions of Planning Coordinators in the NPCC region may form
islands with portions of systems outside of the NPCC's footprint. This may pose a potential
non-compliance with their own performance characteristic of 30 s / 59.5 Hz.
Given that there is no technical justification for the existing NPCC performance characteristic of
30 s / 59.5 Hz, we propose that the regional standard and/or directory (depending on whether the
regional or the directory is retired) be aligned with the continent-wide standard’s performance
characteristic of 60 s / 59.3 Hz. Since the NPCC performance characteristic is more stringent
than that of the continent-wide standard, there should be no impact on the current UFLS
program for the Eastern Interconnection. An aligned performance characteristic is not expected
to result in non-compliance for the NPCC Planning Coordinators.
Furthermore, we propose that, in lieu of revising the regional standard to align with the
performance characteristic contained in continent-wide standard and retiring the directory, to
align the NPCC Directory #12 with the continent-wide standard and retire the regional standard.
We find that using the NPCC process for developing/revising/approving criteria would be less
onerous for the alignment than the NERC standard development process (i.e., limited to NPCC
members as opposed to the greater NERC industry stakeholders needed to build consensus).
Our proposal to retire the regional standard is consistent with the objective of revising selected
NERC standards to remove the “fill-in-the-blank” requirements that were established at earlier
versions of the NERC standards. Now that the NERC PRC-006-2 has been developed, with
Regional Variance for Quebec (and WECC), and in effect, we do not see any value of
maintaining this regional standard. The more stringent and/or more specific requirements, if
desired to be retained, should be stipulated in a Directory.
Drafting Team Response:
Thank you for your comments.
NPCC's Regional UFLS standard has been developed to meet the performance obligations
deemed necessary within the NPCC footprint. Currently, Directory 12, PRC-006-NPCC-1 and
PRC-006-3 have a slight miss-alignment in performance characteristics of the programs. The
SDT has endeavored to alleviate this issue with the inclusion of "Figure 1: PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz Design
Performance Requirements" which aligned the performance curves of PRC-006-3 and PRC-006NPCC-2. While the NPCC performance obligations continue to be more stringent, they are in
alignment with the continent-wide performance obligations.
The SDT is currently not aware of any instances of islanding which includes portions both within
and outside of NPCC. It is the SDT position that all portions of NPCC are to be planned and
programs implemented to meet the performance of the Figure 1 program specifications.
The SDT discussed the best course of action in deciding to retire Directory 12 in lieu of PRC006-NPCC and has decided that retirement of Directory 12 and enhancement of PRC-006-NPCC
is the most appropriate course of action. Directories within NPCC are only applicable to Full
Members of NPCC. This is a limited set of entities as compared to those applicable to the NERC
Reliability Standards. To meet the performance obligations as outlined in the standard broad
applicability, as required by the Regional Standard, is required.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments: See Comments for Question 1.
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
7. Provide any additional comments for the drafting team to consider, if desired.
We submit the following comments for your consideration:
R1: See Comments for Question 1.
R2: We see this as an administrative requirement that does not address any reliability need.
It would be sufficient for the Planning Coordinators to notify the applicable UFLS entities of the
UFLS program.
R3: Similar with R2, we see this as an administrative requirement as it is not clear what
reliability need this requirement is meant to address.
R11: This requirement is a duplication of R8 of PRC-006-2. We propose to have R11 removed.
Drafting Team Response:
Thank you for your comments, the drafting team decided that R2 is necessary to ensure the
island boundaries are clearly identified for the purposes of entities that may wish to aggregate
their load or for compensatory load shedding purposes.
R3 is still under development.
R11 has more specifics in regards to the data and it ensures the PCs are all seeking consistent
information regarding load that is measured and part of the UFLS program.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
If the R5.1 technical study shows that there are significant adverse
impacts on the system, then the standard doesn’t provide guidance on next steps. In
Figure 1, for clarity, move the label for the “combined NERC – NPCC curve” to the far
left in the legend and make it plainly the “NPCC Underfrequency Curve”
Drafting Team Response:
The drafting team will provide additional guidance on R5.1 with the rationale box as well
as modified the bottom legend of Figure 1 to reflect the comment.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
Absolutely. We agree with the retirement of any NPCC Directories
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
M9 – needs to be changed for applicability of R9 to DPs and TOs; In
several places, the term calendar days is used and in others simply days. Use one notation
for consistency; In the Guidelines and Technical Basis section the final sentence “Generator
dynamic modeling (MOD-027-1…)” should be made into a bullet.
Drafting Team Response:
The drafting team accepts these comments and will make changes accordingly.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: This draft version of NPCC Regional Standard PRC-006-NPCC-2 ‘Automatic
Underfrequency Load Shedding’ includes instances of unclear language, exposing risks of
alternative interpretations; see questions and proposed changes under item #7 below for details.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments: Please consider changing language under Effective Dates to state: “See
Implementation Plan.” Please consider changing the effective date to read as the first day of the
first calendar quarter 12 months following applicable governmental and regulatory approvals.
The change from 6 months to 12 months will provide additional time that may be needed to
accommodate automatic UFLS changes that may need to be made on an island basis, for each
identified island. Changes involving automatic UFLS are generally made on an annual
schedule.
Drafting Team Response:
The drafting team changed the language in section 5 to Refer to Implementation Plan”.
In the Implementation Plan drafting team increased the implementation period to 12 months for
R4 and keeping the remainder requirements to the first day of the first calendar quarter
following the applicable governmental and regulatory approvals.
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: See #7 below.
7. Provide any additional comments for the drafting team to consider, if desired.
Comments: Below please find our general questions and proposed (editorial) changes:
- Should the word island (as in UFLS Island) be capitalized throughout this document,
since it is a defined term in the NPCC Glossary of Terms? The term island’ is sometimes written
with a lower case “i” and sometimes with a capital “I”, please review to ensure consistency in
standard.
- Suggesting changing reference to NERC PRC-006-2 from ‘generic’ version (i.e., NERC
PRC Standard on UFLS) to a more formal language e.g., NERC Reliability Standard PRC-006.
- Please review lay-out, in particular related to spacing between Requirements and
Measures.
- Applicability. Please consider revision Sections 4.3 (Distribution Providers) and 4.4
(transmission Owners) to the terminology of ‘UFLS entities’ as used in NERC Reliability
Standard PRC-006-2.
- R3. How can non-BES generation facilities become part of a requirement? If so, should
there be lower thresholds for non-BES generation? Since Requirement R3 as presently written is
only a reporting requirement, it seems reasonable to consider this requirement as a candidate for
deletion per Paragraph 81 (i.e., providing little protection to the reliable operations of the BES).
- R4. Please ensure consistency in language of sub-Requirements R4.1 and R4.2., where
R4.1 uses a shall (strong) language and R4.2 seems to allow for an exception (‘Alternatively’),
where the present language seems to expose a significant risk of alternative interpretations. It is
our interpretation that the ‘shall’ language requires compliance with the requirement in 4.1
during all conditions, and the alternative in 4.2 never seems to become applicable as a
requirement.
- R4. Consider re-instating language “for its Facilities based on frequency thresholds”, as
used in PRC-006-NPCC-01, to clarify meaning of which outages are referred to in 4.1. F urther,
does the requirement to exclude outages only refer to outages within each identified island?
- R5. The language in sub-requirements 5.1.1., etc. lack clarity and could be
misinterpreted. Suggesting adding comma signs, where appropriate, to make requirement R5
clearer and more precise. In 5.1.1. consider adding a comma sign after “… after determining that
adjustments are possible”.
- R5. The language in 5.2.1. and 5.3.1. to “make the adjustments of determining that
adjustments are possible” is unclear if it refers to having the adjustments made or only
determining if the adjustments are possible; also missing a comma sign (for readability) as noted
above for 5.1.1.
- R5. The term “bulk power system” seems to refer to NPCC BPS definition, but this is not
clear.
- R5. The number of days in the different sub-requirements varies between 90 and 180
days. Is this variation for the different sub-requirements intentional? If so, what is the rationale?
Also, 90 days to make necessary adjustments (if that is the correct interpretation) seems very
short.
-
R8. The word ‘those’ should either be removed or explained (what it refers to).
- R9. Suggest to move ‘for approval by the Planning Coordinator’ to before ‘within 90
days’.
- R10. Are there any time requirements related to implementation of the inhibit
thresholds?
box.
Rationale for R11. Please explain or delete the word ‘universally’, used in this rationale
- R11. Should the time 15 months, be written as 15 calendar months (for improved
clarity)?
- R11. Delete the last sentence “If there is no local metering of the load through said
switches, the load may be calculated from measurements made at the nearest available metering.
(e.g., upstream metering on the distribution feeder that supplies the load to be shed).” Since it is
not drafted as a requirement. This text could be moved to the rationale box, if appropriate.
-
The last paragraph in the Guidelines and Technical Basis section seems to be unfinished.
-
RE:
Drafting Team Response:
The drafting team accepted the comments on changing “Islands” to “islands” and will made
updates to the documents accordingly.
For the sake of clarity, the drafting team will adopt the following reference throughout the
document: “NERC continent-wide UFLS standard”.
The drafting team will do a quality review of the entire document and make necessary layout
changes.
Section 4.3: Thank you for your comment. The drafting team decided the existing language is
sufficient and provides clarity.
R3 response: Non-BES generation facilities, although not subject to NERC requirements, could
be material to the performance to the UFLS program.
The requirement is directed to Planning Coordinator and supports regional UFLS study efforts
for reliability purposes.
R4 response: The drafting team reviewed the language and the team agreed that the existing
language is sufficiently clear and consistent. Use of the word “shall” does appear in both 4.1 and
4.2.
R5 response: The drafting team agrees with the comment and modified bulk power system to
BES since it is a NERC standard that focus on the NPCC region.
The drafting team agrees with the comment and modified 5.2.1 to 180 days. For 5.2.2 and 5.3.2,
since they are different analysis compared to 5.1.2 thus 90 days is suggested by the drafting
team.
R8 response: The drafting team accepted the comments and made modifications to the
requirement language accordingly.
R9 response: The drafting team accepted the comments and made modifications to the
requirement language accordingly.
R10 response: Thank you for your comments, please refer to the Implementation Plan in
accordance with R9.
R11 response: The drafting team accepted the comments and made modifications to the
requirement language accordingly.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: While in general agreement with the changes; the proposed text should be
modified for clarity and enforceability.
Drafting Team Response:
Standard is under revision.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments: Consider allowing the flexibility to adopt immediately or adopt when the next
annual load review is carried out to address any changes that may only be incorporated during
the next review.
Drafting Team Response:
Standard is under revision.
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: Specify that the requirement applies to only BES generators either in this
requirement or in the applicability section.
Drafting Team Response:
R15.3 is applicable to the BES generator that specify by your registration.
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments: Note that this requirement does not impact NB Power generation.
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: R3: Suggest rewording R3 such that the PC will provide data to RE within 30
days of request from the RE, where the data to be based on the most recent study. Also, for
clarity, identify the requirement(s) that define acceptable UFLS program performance.
The RE does not (to my knowledge) have a formal process for such data submission and is
not consistent in acknowledging such data submissions.
R5: Limiting mutual agreements to smaller entities could result in the unnecessary
installation of UFLS devices to meet load shedding thresholds.
Drafting Team Response:
The drafting team made modification to the R3 language and will develop a comment
question to ask the ISOs on this requirement in the next comment period.
For R5 please see the response provided by the drafting team in Question 7.
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
Part 4, Applicability: Similar to PRC-006-2, the applicability of TO and DP should include
text to clarify that UFLS program as established by the Planning Coordinator.
Assuming the intent is to only include BES generators the applicability should clearly specify
otherwise the standard could be considered as applicable to all generation facilities owned by a
generation owner regardless if a BES facility or not. Another option is to replace “generator”
with “BES generator” in the relevant requirements.
Requirement 1: I would expect that this requirement is met through application of the UFLS
tables in standard attachment. If the tables in the attachment do not meet this requirement how
does the PC reconcile this requirement with the load shedding tables?
Requirement 3: Suggest rewording R3 such that the PC will provide the information to the
RE within 30 days of request from the RE, where the information supplied to the RE is based on
the most recent study as required by PRC-006-2 R4.
For clarity please identify the requirement(s) that define acceptable UFLS program
performance either in this standard or PRC-006-2
It is not clear on how the PC determines if a non-BES unit results in unacceptable UFLS
performance. Would the UFLS performance be based on a single generator misoperation or
multiple simultaneous misoperations?
Requirement 4: The general reference “the NERC PRC Standard on UFLS” should include
the standard number and the requirement for clarity.
To be more flexible, why limit mutual agreements to small entities but allow any entity to
participate in a mutual agreement though conditional on PC approval. Allowing more flexibility
could help resolve the scenario in R5 in some situations.
Requirement 5: Propose wording “…within 30 days of discovery” .
For R 5.1.2, I am concerned with the DP or TO carrying out a technical study to determine if
there is no significant impact on the bulk power system.
Requirement 6: If this requirement is not a critical component of the UFLS, and is simply
there to prevent load loss on significant frequency swings, recommend moving this requirement
to the guidance section.
Requirement 7: Please define or describe “inhibit thresholds”.
Requirement 11: Why are we limiting the approach in determining peak load values for a
given load? Approach should be broadened to allow for other reasonable methods. Also
question the situation where a meter data is unavailable. Another approach could also allow for
monthly meter readings reconciled with system peak. So recommend that “…or monthly meter
reading values reconciled with system hourly peak values. Also recommend broad wording
allowing other approaches that provide a reasonable calculation of a load’s peak load.
Requirement 12: The curve is not the same as off normal frequency capability curve PRC024 attachment 1 (Eastern Interconnection). To avoid uncertainty with generator owners that
have met compliance with PRC-024 a note could be added in this requirement identifying the
more stringent generator UFLS curve. In addition, the drafting team may consider a regional
variance on PRC-024 adding the new curve for generation or referencing applicable portions of
this regional standard.
R15.1 This sub-requirement would be more flexible if “plant design and licensing
limitations” was replaced with “plant design or licensing limitations” (replaced and with or) to
address those situations were licensing may not be effected though the plant design is.
Guidelines and Technical Basis: I agree with the approach taken. I assume that there are no
compliance implications on the factors that could initiate a new assessment. Do you agree?
Drafting Team Response:
For part 4, drafting team accepted the comment and made modifications to the applicability
section of the standard.
The drafting team considered the applicability for the Generator is clear and concise. Thank you
for your comment.
The purpose of R1 is to establish performance criteria with Figure 1, this performance can be
met using table 1. If in the future, the performance criteria cannot be met using table 1, then the
PRC-006-NPCC-02 UFLS Regional Standard will need to be revised.
Thank you for your comment, the drafting team reviewed R3 and made a modification to specify
“acceptable” as being in accordance with PRC-006 standard requirements.
For R3, it will be up to the Planning Coordinator to determine its methodology in regards to nonBES units.
In response to R4, in general specifics in regards to the NERC Standard numbers are avoided due
to the possibility of changes to the standard due to retirements or other standards superseding the
existing standard.
The drafting team made modifications to R4 in regards to the mutual agreements.
For R5, the drafting team made modification to the requirement language.
The drafting team expects the Distribution Provider and Transmission Owner to perform the
analysis or to retain a consultant if necessary.
For R6, the drafting team reviewed the comments and decided the requirement is necessary for
the reliability services to the customers.
For R7, the drafting team will develop a rationale box to define inhibit threshold.
Action Item: Dean Latulipe will develop a rationale box to define inhibit threshold.
For R11, the drafting team made modifications to the requirement language.
For R12, the drafting team decided to add a note to clarify the differences between the Regional
UFLS standard vs PRC-024 in regards to the Figure 2.
At this time the drafting team decided it is impractical to pursue a NPCC regional variance.
For R15.1, the drafting team accepted the comment and made modification to the language.
The intent for Guidelines and Technical Basis is to provide additional guidance to the standard, it
is not intended to be audited.
NYISO Comments
Regional Standard PRC-006-NPCC-02
October 16, 2017
The NYISO submits the following comments on the proposed Regional Standard for the drafting
team’s consideration:
With regards to R3
Each Planning Coordinator shall, within 30 days of completion of its UFLS system studies,
identify to the Regional Entity all non-BES generation facilities, within its Planning Coordinator
Area, that must not trip above the appropriate generator underfrequency trip threshold curve in
Figure 2 in order to support acceptable UFLS program performance.
- It is not clear what is considered to be non-BES generation facilities:
o Is it limited to generation that is modeled?
o How should DER, behind the meter or load/netted generation be addressed?
o What is the criteria for determining what Non-BES generation is not allowed to
trip
- What is the role of the Regional Entity, once this information is provided?
- Who will have the obligation/authority to inform any identified non-BES generators that
they must adhere to the appropriate trip threshold?
Drafting Team Response:
The drafting team is considering removing or clarifying R3 and will draft a comment
question for the ISOs in the next comment period.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: Based on the regional standard PRC-006-NPCC-2 the UFLS will be initiated
earlier when compared to the continent wide standard PRC-006-3 to prevent frequency
collapsing on any potential island created as result of Grid disturbances. When referencing the
performance characteristic requirements, a higher frequency requirement for the same time
duration is better for grid reliability.
OPG believes that an analysis of potential islands survivability must be performed for all the
potential islands that do not belongs entirely to NPCC region and will contain generators from
entities that do not have to comply with the proposed performance characteristic requirements of
the regional standard PRC-006-2-NPCC-2. In these case of a newly created island the UFLS
associated with the portion of the island contained in the NPCC region would be the first to shed
load in an attempt to prevent the decline in frequency due to more stringent PRC-006-NPCC-2
performance characteristic requirements (30 s / 59.5 Hz vs. 60 s / 59.3 Hz as required by PRC006-3). While frequency will be the same in the entire island the load shedding contained only to
NPCC region can potentially affect the island dynamic and steady state stability due to power
swings and circuits overload.
This would not be an issue if dynamic UFLS can be achieved/implemented or exceptions
allowed for specific islands (where dual interactive regulatory requirements are present) for
survivability purposed.
The above analysis is no longer required if the discrepancy between regional and continent wide
standard is eliminated by using the same performance characteristic requirements; it does
however no longer justifies from this point of view the existence of a regional standard and
perhaps the case for regional variance is more justified (i.e. when establishing the compensatory
load shedding per attachment A/B)
If the NPCC Directory #12 UFLS requirements are perfectly aligned with the NPCC continentwide standard, then there is no increase in grid reliability and no justification for existence. The
regional standards are justified if they increase the grid reliability through more stringent,
justified, requirements or when dealing with technical constraints by minimizing the compliance
effort without affecting grid reliability.
In order to justify more stringent regional standard requirements the SDT should revalidate the
initial technical justification for the more stringent performance characteristics (i.e. revalidate
NPCC UFLS assessment for the current grid composition in terms of different representative
generator manufacturers in service and compilation of capabilities/ride through for generators).
Drafting Team Response:
It is true that PRC-006-NPCC-2 has more stringent performance requirements than PRC-006-3
for time frames greater than 30 seconds. Directory 12 does also.
It is not necessarily true that UFLS relays located in the NPCC region, would be the first to trip
in an island that straddles portions of NPCC and another NERC Region. Which UFLS relays
trip first would depend on the underfrequency trip settings of UFLS relays inside NPCC,
compared to the trip settings of UFLS relays in the neighboring region. Also, the associated time
delays of the UFLS relays will influence which relays trip first. The question of whether any
mismatch is UFLS relay trip times between Regions will cause the island to go unstable would
be answered by the simulations conducted to determine if the island meets underfrequency load
shedding performance requirements. If the island goes unstable, and collapses, then the island
would not meet UFLS performance requirements (either PRC-006-3 or PRC-006-NPCC-2). In
this case, the UFLS program in either portion of the island, or both, would need to be modified
such that the island meets the performance requirements.
Simulations for the island would still be required, even if the performance requirements of PRC006-3 and PRC-006-NPCC-2 were the same.
The drafting team disagrees, and maintains that PRC-006-NPCC-2 has more stringent
performance requirements than PRC-006-3 for time frames greater than 30 seconds. The
drafting team has no justification for lessening this stringency.
The drafting team did investigate this, and found no justification for lessening the stringency of
the PRC-006-NPCC-2 performance requirements.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: OPG has requested previously the Standard Drafting Team to ensure that the
obligations stemming from requirement R15 part 15.3 are clearly removed from the compliance
obligation of the Generator Owner, since in Ontario the Planning Coordinator is responsible for
establishing the compensatory load shedding requirements. This is only captured in PRC-006NPCC-2 attachment A and because of differences between Ontario, Quebec, Maritime Provinces
and the ISO-NE, NYISO we have two different entities having regulatory obligations for the
same requirement R15. OPG is of the opinion that the wording used on the latest draft standard
revision of R15 is still confusing and recommends the following changes:
R15. Each Generator Owner of existing non-nuclear units in service prior to the effective date of
this standard, that have underfrequency protections set to trip above the appropriate curve in
Figure 2 shall: [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
…
15.3. The responsible entity, as documented in accordance with Attachments A or B,
shall have compensatory load shedding, as provided by a Distribution Provider or
Transmission Owner that is adequate to compensate for the loss of their generator due to
early tripping that is within the UFLS Island identified by the Planning Coordinator in
Requirement R2.
This will result only in part 15.3 creating compliance obligation for different entities similar to
variances.
OPG also recommend to make the following changes to the requirement “15.3 The responsible
entity, as documented in accordance with Attachments A or B, shall have compensatory load
shedding, as provided by a Distribution Provider, Underfrequency Load Shedding (UFLS)-only
Distribution Provider (DP) or Transmission Owner that is adequate to compensate for the loss of
their generator due to early tripping that is within the UFLS island identified by the Planning
Coordinator in Requirement R2.”
SDT should include the newly approved FERC registration category, “Underfrequency Load
Shedding (UFLS)-only Distribution Provider (DP)” in the revision of the standard PRC-006NPCC-2 Automatic Underfrequency Load Shedding, to bring PRC-006-NPCC-02 standard in
line with the newly registered functional categories as per Project 2017-07 Standards Alignment
with Registration.
Now that we also have newly registered UFLS-only DP entity, can SDT comment on following
the same NERC compliance obligation approach per PRC-006-3, which requires UFLS entity to
provide load shedding as determined by the Planning Coordinator(s)?
“R9. Each UFLS entity shall provide automatic tripping of Load in accordance with the UFLS
program design and schedule for implementation, including any Corrective Action Plan, as
determined by its Planning Coordinator(s) in each Planning Coordinator area in which it owns
assets. [VRF: High][Time Horizon: Long-term Planning]”
Drafting Team Response:
The drafting team has revised requirement 15 for better consistency between compliance
obligations in R15.3 and Attachments A and B.
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments: Directory 12 Automatic Underfrequency Load Shedding Program has
requirements pertaining to the following:
Automatic Underfrequency Load Shedding
Underfrequency trip settings of the protective relaying
The requirements pertaining to Automatic Underfrequency Load Shedding are translated
into PRC-006-NPCC-02 which is the regional standard for Automatic Underfrequency
Load Shedding.
OPG is of the opinion that Directory 12 should not be retired before a regional standard is
prepared (i.e. PRC-024-NPCC-01) or regional variance is included via revision of the
PRC-024-2 for translation of Underfrequency trip settings of the protective relaying,
contained in D12.
The following are the NPCC Directory #12 – Under frequency Protection Requirements that
should be translated to a new regional standard or variance before D12 retirement.
“5.4 Generator Under frequency Protection Requirements
Generators shall not be tripped for under-frequency conditions in the area above
the curve in Figure 1, except as provided for in Sections 5.4.1 and 5.4.2.
5.4.1 It is recognized that, in special cases, requirements may dictate
generator trip in the region above the curve. In those cases, the Generator
Owner shall so notify its Balancing Authority and shall ensure through
alternate arrangements, that automatic load shedding additional to the
amount set out in Section 5.2 and in Section 5.3, equivalent (+/- 5%) to the
amount of generation to be tripped, is provided. Such cases shall be
reviewed by the Task Force on Coordination of Operation
5.4.2 Generator Owners shall not increase the under frequency trip
settings or make other modifications to the existing exempt generators
(that trip above the curve in Figure 1) that may cause these generators to,
directly or indirectly, trip at a higher frequency.”
Additionally these Under Frequency Protection Requirements should be adequately
designed and coordinated with the Balancing Authorities (i.e. IESO for Ontario) and the
NERC PRC-024 existing requirement, to eliminate potential gaps.
Drafting Team Response:
Underfrequency trip setting requirements for generators are already in Figure 1 of PRC-006NPCC-01. The drafting team merely re-numbered this Figure to #2 in PRC-006-NPCC-02. So
no changes to this requirement are proposed for PRC-006-NPCC-02.
The conditions under which the generator underfrequency protection requirements apply to are
already in PRC-006-NPCC-01 and were not changed for PRC-006-NPCC-02.
NERC BES Generators have to comply with NERC PRC-024 as well.
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: All the requirements associated with the Underfrequency Trip Settings
associated and the Figure 2 of the PRC-006-NPCC-2 Underfrequency Load Shedding
Program – Thresholds for Setting Underfrequency Trip Protection for Generators should be
deleted from this regional standard and adequately addressed/included in a newly develop
regional standard PRC-024-NPCC-01, or revision of PRC-024-2 to include regional variance
Drafting Team Response:
The drafting team believes that it is better to leave the Thresholds for Setting Underfrequency
Trip Protection for Generators in PRC-006-NPCC-2 on account of the fact that the low
frequency withstand capability of generation is a critical parameter in the development and
operation of any underfrequency load shedding program. The drafting team does not have
justification for reducing the margin and reliability.
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
OPG is of the opinion that although included in the Standard PRC-006-NPCC-1 Automatic
Underfrequency Load Shedding, the requirements for the Frequency Settings of the
Protective Relaying is better suited in a new regional standard PRC-024-NPCC-01 or a
newly revised PRC-024-3 that includes the required regional variance.
If the decision is taken to proceed with the development of a new regional standard then
coordination between regulators is required to eliminate potential gaps between the currently
applicable regulatory compliance requirements with respect to Generator Frequency
Protective Relay Settings:
NERC Standard PRC-024-2 — Generator Frequency and Voltage Protective
Relay Settings
IESO Market Rules - Chapter 4 - Grid Connection Requirements – Appendix 4.2
– Generation Facility Requirements
Market Manual 2: Market Administration Part 2.20: Performance Validation - 3.
Generator Requirements
NPCC Regional Reliability Reference Directory # 12 - Under frequency Load
Shedding Program Requirements
All these regulatory requirements should be coordinated to eliminate the potential for
inadvertent noncompliance. Although this requires a lot of effort and can be met with
resistance the better the effort put in the development of coordinated standards by
different regulators on the same technical issue, the higher Grid Reliability end result and
the least potential for inadvertent noncompliance due to misunderstandings.
Drafting Team Response:
The drafting team believes that it is better to leave the Thresholds for Setting Underfrequency
Trip Protection for Generators in PRC-006-NPCC-2 on account of the fact that the low
frequency withstand capability of generation is a critical parameter in the development and
operation of any underfrequency load shedding program.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from September 1, 2017 through October 16, 2017.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
PSEG offers the following comments to inform the instant drafting team of PSEG’s
concerns with the proposed standard and to memorialize our position for future
consideration.
a) Generator Compensatory Load Shedding:
PRC-006-NPCC-02 requirement R15 part 3 (R15.3) as proposed would retain PRC-006NPCC-01’s requirement R16.3 for compensatory load shedding by Generators in U.S.
portions of NPCC. However, like PRC-006-NPCC-01, PRC-006-NPCC-02 also does not
include an accompanying requirement in the revised standard that requires a distribution or
transmission entity to make appropriate load (i.e. “within the UFLS island identified by the
Planning Coordinator in Requirement R2”) available to the Generator to shed. And there
also are no applicable Tariffs etc., or other NERC or NPCC standards that require
distribution or transmission entities to make any load available to Generators for this
purpose. Consequently, a requirement for Generator compensatory load shedding in U.S.
portions of NPCC is now and potentially would remain non-implementable for GOs.PRC006-NPCC-02 requirement R15 part 3 (R15.3) and should therefore be removed from the
proposed standard.
b) Generator Underfrequency Trip Protection Settings
The revised standard retains PRC-006-NPCC-01’s Figure 1 generator underfrequency trip
protection settings threshold curve, as PRC-006-NPCC-02 Figure 2. PSEG does not believe
retention of that curve or inclusion of another PRC-006-NPCC-specific Generator UF
settings curve in PRC-006-NPCC-2 are necessary. All UFLS plans of NERC Registered
Entities to whom NERC reliability standard PRC-006-2 is, PRC-006-NPCC-01 is and PRC006-NPCC-02 would be applicable, must already now meet the design performance
requirements identified in Attachment 1 of PRC-006-2. PRC-006-2 Attachment 1 includes
and illustrates that the least-demanding/potentially damaging (the ‘Eastern Interconnection’)
generator underfrequency trip protection settings threshold curve for generating units,
directed and required by NERC reliability standard PRC-024-2 (see Attachment 1 of PRC024-2), coordinates with the UFLS plan performance requirements set out in PRC-006-2.
And that curve (Attachment 1 of PRC-024-2) would coordinate with the UFLS plan
performance requirements that would be set out in PRC-006-NPCC-2 as now proposed (see
PRC-006-NPCC-02 Figure 1). All of the curves in Attachment 1 of PRC-024-2, including
the ‘Eastern Interconnection’ curve, are considered adequate generator UF and OF
performance by NERC and FERC by virtue of being in NERC- and FERC- approved
reliability standard PRC-024-2. If PRC-006-NPCC-02 is to retain PRC-006-NPCC-02
Figure 2, or another PRC-006-NPCC-specific Generator UF settings curve, PSEG
recommends additional technical justification for doing so.
Generator underfrequency trip protection settings that will be directed and required by PRC006-NPCC-2 requirement R12 (i.e. that Generators meet the curve presented in PRC-006NPCC-02 Figure 2) also directly impact the burden and costs Generators now or could in
future (new units; unit uprate modifications) bear to meet other requirements in the
standard: R14; R15; R17 without a commensurate reliability benefit. Generators’ additional
burdens and costs to meet these other requirements should be better supported by additional
technical justification explaining why PRC-006-NPCC-02’s Figure 2 curve, or any other
generator UF settings curve that might alternatively be proposed, is required for PRC-006NPCC-2, over adoption of (direct or implicit) and reliance upon the ‘Eastern
Interconnection’ curve in Attachment 1 of PRC-024-2.
c) Applicability to Non-BES Generators
PRC-006-NPCC-02 requirement R3 appears designed to result in NPCC requiring otherwise
non-BES (i.e. not NERC registered) Generators, or Generators’ otherwise non-BES
generating units, to comply with the standard’s under-frequency ride-through requirements.
The result would be that, where it could otherwise be needed to save an island, load
shedding beyond that directed in Tables 1 to 3 in Attachment C of the proposed standard
would be avoided, at these Generators’ risk (NERC compliance) and expense. PSEG does
not support this. The NERC registration criteria have been developed to generally ensure
that entities needed to ensure BES reliability via the NERC reliability standards are
registered and thereby in the scope of those standards. Similarly, the BES Definition was
developed to generally ensure that facilities and equipment needed to ensure BES reliability
via the NERC reliability standards, are designated as part of the BES and thereby in the
scope of those standards. PSEG recommends additional technical and legal justification
explaining why the Generators indicated in R3 (“non-BES generation facilities”) need to be
registered and become subject to the standard’s under-frequency ride-through requirements,
versus developing and implementing alternatives options such as requiring implementation
of additional load shedding.
d) Adequacy of Required DP and TO Load Shedding
Requirements R4 and R5 direct how much load DPs and TOs must shed, at what frequency
thresholds. However, neither of these requirements, nor any others in PRC-006-NPCC-02,
address or identify what additional action these DPs and TOs, PCs subject to PRC-006NPCC-02 R1, or any other entities are required to take in the event that the amount of load
shed required by R4 and R5 (i.e. load shed schedule listed in PRC-006-NPCC-02
Attachment C) would not produce UFLS program performance meeting PRC-006-NPCC-02
Figure 1. PSEG recommends clarification of what additional actions would be required, and
by whom.
Drafting Team Response:
a) The settings are in place in order for the UFLS program to work. Those units identified
have already secure their compensatory load shedding. This allow the generator not able to
meet the performance curve due to design constraint and ability to meet the curve to secure
load shedding as an alternate need. New or upgraded units following the effective date of
the version 1 of this standard are not permitted to utilize compensatory load shedding
provisions therefore this requirement is not applicable to units that’s not already secured
compensatory load shedding.
b) The drafting team has reviewed and discussed this requirement extensively and have
concluded the fact that meeting the performance characteristics identified in Figure 2 is
necessary for reliability.
c) Pending
d) That situation is already covered by R15 in the continent wide standard (PRC-006-3). If
the planning coordinator determines that the UFLS program does not meet the performance
characteristics shall develop a Corrective Action Plan and a schedule for implementation by
the UFLS entities.
2. Do you agree with the proposed revisions to Section 5 of the document on Effective
Date? If not, please explain why and include any suggestions.
Yes
No
Comments: Effective date indicated in Section 5 is not consistent with date indicated in
Implementation plan document. PSEG suggests that Section 5 refer to or direct the same
schedule as the Implementation Plan.
Drafting Team Response:
The drafting team accepted the comments and made updates accordingly.
3. Do you agree with the proposed revisions to Requirement 15.3 on compensatory load
shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: As noted in our comments in response to Question 1, PSEG disagrees with
compensatory load shedding requirements. PSEG reiterates that PRC-006-NPCC-02
requirement R15 part 3 (R15.3) should be removed from the proposed standard.
Drafting Team Response:
Please refer to the drafting team response in question #1.
4. Do you agree with the drafting team on their proposal to keep Requirement 18 (old
Requirement 19) as is? If not, please explain why and include any suggestions.
Yes
No
Comments:
5. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
6. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
Following on our comments provided in response to Question 1, PSEG does not find
requirement R12 cost-effective because it requires Generators to meet a generator
underfrequency trip protection settings threshold curve (PRC-006-NPCC-02 Figure 2) which
exceeds what is necessary i.e. beyond what is needed for NPCC entities’ UFLS program
performance to produce BES frequency outcomes that will conform to PRC-006-NPCC-02
Figure 1 limits. Without any commensurate improvement in BES reliability, this increases
costs to Generators. For example, new generators’ UF provisions/protections, replicating
standard designs that otherwise meet others’ UF requirements outside of NPCC, may require
review and potential modification from standard design. PSEG recommends that the ‘Eastern
Interconnection’ curve in Attachment 1 of PRC-024-2 be adopted for PRC-006-NPCC-02, to
replace PRC-006-NPCC-02 Figure 2. This would be accomplished implicitly by removing
PRC-006-NPCC-02 R12 in its entirety from PRC-006-NPCC-02, since Generators already
must comply with PRC-024-2. It could also be done explicitly by replacing the current PRC006-NPCC-02 Figure 2 with: (i) a copy of the ‘Eastern Interconnection’ curve in Attachment
1 of PRC-024-2; or (ii) explicit reference to that curve in PRC-006-NPCC-02; or (iii)
incorporating the curve into PRC-006-NPCC-02 Figure 1 (as PRC-006-NPCC-02 Figure 1
has done with the BES System Frequency element of Attachment 1 of PRC-006-2, and
Attachment 1 of PRC-006-2 itself has done with the ‘Eastern Interconnection’ curve in
Attachment 1 of PRC-024-2).
On the basis of our comments in response to Question 1, PSEG does not find requirement R3
cost-effective because it could impose significant additional risks and costs on otherwise
non-BES Generators, or Generators’ otherwise non-BES generating units, to the benefit
(avoided additional costs) to other already-NERC-registered BES entities (DPs, TOs) who
could implement one or more alternative solutions (e.g.: additional load shed capability;
strengthened transmission capability).
Drafting Team Response:
For reliability purposes, the drafting team decided to retain the existing generator low frequency
requirement.
7. Provide any additional comments for the drafting team to consider, if desired.
Comments:
April 16, 2018
Subject: Posting for Open Process Review of PRC-006-NPCC-2 Automatic Underfrequency
Load Shedding.
The clean and redlined versions of the revised NPCC Regional Standard PRC-006-NPCC-2
Automatic Underfrequency Load Shedding, have been posted on the NPCC Website for a 45-day
comment period through May 31, 2018, along with a proposed Implementation Plan and
Mapping document.
This draft has been developed in accordance with the NPCC Regional Standard Process Manual
(RSPM) and within the scope of an NPCC Regional Standard Authorization Request, which was
accepted by the NPCC Regional Standard Committee (RSC). The revisions are also presented as
mandated by the NERC Rules of Procedure.
Among the proposed changes included in the updated draft version of the Standard are:
• Modifications to Figures #1 and #2 in the Standard
• Added a Guidelines and Technical Basis section (NERC may request us to create a
separate document for this section and post it with the standard subsequent to approvals)
• Incorporated certain Criteria attributes from Directory #12 Automatic UFLS Program
Requirements which will facilitate the retirement of Directory #12
• Additional clarification of requirement language
• Proposed retirements of some of the Requirements that are redundant to the PRC-006-2
Continent-wide NERC standard
Also posted is a set of questions developed by the Regional Standard Drafting Team to solicit
comments on the draft standard and associated draft Implementation Plan for the Regional
Standard. Included in these questions is one on cost effectiveness of the requirements.
Comments on the posted materials may be submitted through the NPCC Open Process Portal,
which may be accessed through:
https://www.npcc.org/Standards/SitePages/DevStandardDetail.aspx?DevDocumentId=122
Depending on comments received and if no revisions are deemed necessary by the Standard
Drafting Team, the standard is tentatively scheduled to be posted for a 30-day pre-ballot review
and 10-day ballot period towards third quarter of 2018.
Please contact me with any questions regarding this Standard.
Thank you.
Ruida Shu
Northeast Power Coordinating Council, Inc.
Senior Engineer, Reliability Standards and Criteria
Main: 212-840-1070
Direct: 917-934-7976
Fax: 212-302-2782
Email: [email protected]
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Standard establishes more stringent and specific NPCC UFLS program requirements to
ensure that declining frequency is arrested and recovered in accordance with established
NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.3. Distribution Providers that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program as established by the
Planning Coordinators.
4.4. Transmission Owners that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program as established by the
Planning Coordinators.
5.
Effective Date:
The first day of the first calendar quarter following applicable governmental and
regulatory approvals.
Reference to Implementation Plan.
B. Requirements
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Note that
Figure 1 also shows the NERC criteria as defined in the NERC PRC Standard on
UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design an
UFLS program having performance characteristics that prevents the frequency from
m remaining below 59.5 Hz for greater than 30 seconds in accordance with Figure 1.
[Violation Risk Factor: MediumHigh] [Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or real- time power flow data captured from actual system events and other dated documentation
that demonstrates it meets Requirement R1.
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC PRC Standard on UFLS, to Distribution Providers, Generator Owners, and
Transmission Owners within 30 dayscalendar days of receipt of a request. [Violation Risk
Facto
r: MediumLower] [Time Horizon: Long Term Planning]
1
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Planning Coordinator shall, within 30 dayscalendar days of completion of its UFLS
system studies, identify to the Regional Entity all non-BES generation facilities, within its
Planning Coordinator Area, that must not trip above the appropriate generator
underfrequency trip threshold curve in Figure 2 in order to support acceptable UFLS
program performance requirements. [Violation Risk Factor: Medium] [Time Horizon: Long
Term Planning]
M3.
Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
R4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall implement an automatic UFLS program, reflecting normal operating
conditions, excluding outages. The automatic UFLS program shall be implemented on an
island basis for each island identified per the NERC PRC Standard on UFLS. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
4.1. The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating times
and load shedding amounts specified in Attachment C, Tables 1 through 3 or,
.
4.2. Alternatively, tThe program can shall be implemented collectively by multiple
Distribution Providers or Transmission Owners with less than 100 MW of individual
peak net Load, as long as they reside in the same UFLS Island identified by the
Planning Coordinator per R2. These multiple Distribution Providers or Transmission
Oowners, via mutual agreement, shall act as a single entity to provide an aggregated
automatic UFLS program that sheds their coincident peak aggregated net Load
according to the frequency thresholds, total nominal operating time and amounts
specified in Attachment C, Tables 1 through 3.
M4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall have evidence such as documentation or reports containing the location and
amount of load to be tripped in their respective areas, and the corresponding frequency
thresholds, on those circuits included in its UFLS program identified in Requirement R4.
(Attachment C Tables 1-3).
R5. Each Distribution Provider or Transmission Owner that cannot meet the tolerances and/or
number of stages and frequency set points specified in the UFLS Program, shall notify its
Planning Coordinator within 30 days, and: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
2
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
5.1. Each Distribution Provider or Transmission Owner applicable to Attachment C, Table 1,
within 90 calendar days of informing of its Planning Coordinator that tolerances cannot be
met, determine if tolerances can be met through adjustments and notify the Planning
Coordinator of the determination and;
5.1.1. If adjustments are possible, make the adjustments within 180 calendar days after
determining that adjustments are possible and notify the Planning Coordinator when
complete, or;
5.1.2. If adjustments are not possible then provide its Planning Coordinator with a technical
study within 180 calendar days that demonstrates that the Distribution Providers or
Transmission Owners specific deviations from the requirements of UFLS Attachment C,
Table 1 will not have a significant adverse impact on the bulk power system.
5.2. Each Distribution Provider or Transmission Owner applicable to Attachment C, Table 2 or
Table 3, within 90 calendar days after informing the Planning Coordinator, determine if
tolerances can be met through adjustments and notify the Planning Coordinator of the
determination, and;
5.2.1. If adjustments are possible, within 90 calendar days make the adjustments of determining
that adjustments are possible and notify the Planning Coordinator when complete, or;
5.2.2. If adjustments are not possible, then within 90 calendar days provide its Planning
Coordinator with an analysis demonstrating that no alternative load shedding solution is
available that would allow the Distribution Provider or Transmission Owner to comply with
UFLS Attachment C Table 2 or Attachment C Table 3.
5.3. Each Distribution Provider or Transmission Owner in the Quebec Interconnection, within 90
calendar days after informing the Planning Coordinator, determine if tolerances can be met
through adjustments and notify the Planning Coordinator of the determination, and;
5.3.1. If adjustments are possible, within 180 calendar days make the adjustments of determining
that adjustments are possible and notify the Planning Coordinator when complete, or;
5.3.2. If adjustments are not possible, then within 90 calendar days provide its Planning
Coordinator with an analysis demonstrating that no alternative load shedding solution is
available that would allow the Distribution Provider or Transmission Owner to comply with
the UFLS program.Each Distribution Provider or Transmission Owner that cannot meet the
tolerances and/or number of stages and frequency set points specified in the UFLS Program,
shall: [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
5.1. Notify its Planning Coordinator within 30 calendar days of recognition.
5.2. Within the following 90 calendar days, determine if tolerances can be met through
adjustments and notify the Planning Coordinator.
5.3. If adjustments are possible, make the adjustments within 180 calendar days after
determining that adjustments are possible, and notify the Planning Coordinator
when complete, or,
5.4. If adjustments are not possible then:
5.4.1. Each Distribution Provider or Transmission Owner subject to Attachment C,
Table 1, shall within 180 calendar days, provide its Planning Coordinator with a
technical study that demonstrates that the Distribution Provider’s or Transmission
Owner’s specific deviations from the requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on the BES, or
3
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
5.4.2. Each Distribution Provider or Transmission Owner subject to Attachment C,
Table 2 or Table 3, or in the Quebec Interconnection, shall within 90 calendar days,
provide its Planning Coordinator with an analysis demonstrating that no alternative
load shedding solution is available that would allow the Distribution Provider or
Transmission Owner to comply with the UFLS program.
M5. Each Distribution Provider or Transmission Owner shall have evidence such as reports
, analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
Rationale for Requirement R6: Operation of underfrequency relays results directly
in load being shed, interrupting service to customers. The security of underfrequency
relays against misoperation is therefore paramount. The 100 ms minimum time delay
specified in R6 serves to prevent premature activation of these relays during shortlived transient frequency excursions that may occur on a localized basis in the absence
of a serious system event wherein UFLS would be appropriate. This intentional delay
helps to ensure that the relays activate only for frequency excursions that are due to
actual system events that require automatic UFLS to reestablish the balance of
generation to load.
R6. Each Distribution Provider and Transmission Owner shall set each underfrequency relay
that is part of its region’s UFLS program with a 100 ms minimum time delay. [Violation
Risk Factor: HighMedium] [Time Horizon: Long Term Planning]
M6. Each Distribution Provider and Transmission Owner shall have evidence such as
ddocumentation or reports that their underfrequency relays have been set with the
minimum
time delay, in accordance with Requirement R6.
Rationale for Requirement R7: An inhibit function provides supervisory control
over a UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay
operation if the sensed voltage decreases below an adjustable setting. An undervoltage
inhibit function is intended to prevent operation of a UFLS relay when the
transmission supply is lost to distribution station feeding many induction motors.
Following loss of the transmission supply, motors may support the voltage while the
motors coast down in speed. The motors coasting down (ringing down) will look like
an Underfrequency event to the relay. The inhibit setting is set to a voltage above
which the motor load is expected to sustain. This prevents the Underfrequency relay
from tripping and locking out distribution feeder breakers supplying the motor load,
between the time the transmission supply line trips and the time when the line recloses
to restore the load. Voltages sustained by motors that are coasting down (e.g. 0.70 pu)
are typically much lower than voltages at which the UFLS relays are required to
operate to meet UFLS performance criteria. However, motor loads supplied by cable
networks typically have higher ring down voltages because of cable charging.
Therefore, care must be taken so that the voltage inhibit setting is not higher than the
voltage at which UFLS relays are required to operate to meet UFLS performance
4
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
criteria.
R7. Each Planning Coordinator shall develop and review settings for inhibit thresholds at least
once per five calendar years (such as but not limited to voltage, current and time) to be
utilized within its region’s UFLS program. [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
M7. Each Planning Coordinator shall have evidence such as reports, system studies or analysis
that demonstrates that it meets Requirement R7.
R8. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
dayscalendar days of any changes to those thresholds. [Violation Risk Factor:
MediumLower] [Time Horizon: Operations
Planning]
M8. Each Planning Coordinator shall provide evidence such as letters, emails, or other dated
documentation that demonstrates that it meets Requirement R8.
R9.
Each Distribution Provider and Transmission Owner that receives a notification pursuant
to Requirement R8 shall develop and submit an implementation plan for approval by the
Planning Coordinator within 90 dayscalendar days of the request from the Planning
Coordinator for approval by the Planning Coordinator. [Violation Risk Factor: Lower]
[Time Horizon: Operations Planning]
M9. Each Planning Coordinator shall provide evidence such as letters, emails, or other dated
documentation that demonstrates that it meets Requirement R9Each Distribution Provider
and Transmission Owner shall provide evidence such as test reports, data sheets or other
letters, emails, or other dated documentation that demonstrates that it meets Requirement
R9.
R10. Each Distribution Provider and Transmission Owner shall implement the inhibit threshold
settings provided by the Planning Coordinator in accordance with Requirement R8 and
based on the Planning Coordinator approved implementation plan in accordance with R9.
[Violation Risk Factor: High] [Time Horizon: Operations Planning]
M10. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that demonstrates that
it meets Requirement R10.
Rationale for Requirement R11: It is recognized that, ideally, the amount of load to
be shed in each stage of the UFLS program for every entity should perfectly match
that prescribed in this Standard universally, for all phases of the load cycle, i.e.,
seasonal (summer vs. winter), weekly (weekday vs. weekend vs. holidaysdays), daily
(morning, noon, and night), etc. for all of the identified islands. Practically, however,
this is obviously not possible because the load cycles of the various areas and sub5
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
areas within any given island do not perfectly track the load cycle of the overall
island. The UFLS program, on the other hand, is designed based on peak conditions
for the overall island. The percentages of actual load shedding that would occur for
any conditions other than peak, therefore, can only approximate that prescribed in the
Standard. This being said, entities are required by R11 to document measured loads
in the UFLS program coincident with their own annual peak, whether or not that peak
occurs at the same time or in the same season as the peak of the identified island in
which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that
are responsible for designing and maintaining their UFLS programs.
R11. Each Transmission Owner and Distribution Provider shall annually provide documentation,
with no more than 15 calendar months between updates, to its Planning Coordinator of the
actual net Load projected to bethat would have been shed by the UFLS relays at each
UFLS stage. The
actual net Load shall be coincident with the entity’s integrated hourly peak net Load during
the previous year, as determined by measuring or calculating actual metered Load through
the switches
that would disconnect load if triggered by the UFLS relays. If there is no local metering of
the load through said switches, the load may be calculated from measurements made at the
nearest available metering. (e.g., upstream metering on the distribution feeder that supplies
the load to be shed). [Violation Risk Factor: Lower]
[Time Horizon: Long Term Planning]
M11. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning Coordinator
that indicates the frequency set point, the net amount of load shed and the percentage of its
peak load at each stage of its UFLS program to demonstrate that it meets Requirement
R11.
R12. Each Generator Owner shall set each generator underfrequency trip relay, if so equipped,
on or below the appropriate generator underfrequency trip protection settings threshold
curve in Figure 2, except as otherwise exempted in Requirements R15 and R18. [Violation
Risk Factor: HighMedium] [Time Horizon: Long Term Planning]
M12. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets or
other documentation that demonstrates that it meets Requirement R12.
R13. Each Generator Owner shall transmit the generator underfrequency trip setting and time
delay to its Planning Coordinator within 45 dayscalendar days of the Planning
Coordinator’s
request.
[Violation Risk Factor: HighLower] [Time Horizon: Operations Planning]
M13. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R13.
6
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R14. Each Generator Owner with a new generating unit, or an existing generator increasing its
net capability by greater than 10% shall: [Violation Risk Factor: HighMedium] [Time
Horizon:
Long Term Planning]
14.1. Design measures to prevent the generating unit from tripping directly or indirectly
for underfrequency conditions above the appropriate generator tripping threshold
curve in Figure 2.
14.2. Design auxiliary system(s) or devices used for the control and protection of
auxiliary system(s), necessary for the generating unit operation such that they will
not trip the generating unit during underfrequency conditions above the appropriate
generator underfrequency trip protection settings threshold curve in Figure 2.
M14. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement R14.
R15. For existing non-nuclear units in service prior to the effective date of this standard, as
documented in accordance with Attachments A or B, that have underfrequency protections
set to trip above the appropriate curve in Figure 2: [Violation Risk Factor: HighMedium]
[Time
Horizon: Long Term Planning]
15.1. Each Generator Owner shall set the underfrequency protection to operate at the
lowest frequency allowed by the plant design and licensing limitations.
15.2. Each Generator Owner shall transmit the existing underfrequency settings and any
changes to the underfrequency settings along with the technical basis for the
settings to the Planning Coordinator.
15.3. Each Planning Coordinator in Ontario, Québec and the Maritime Provinces in
accordance with Attachment A and each Generator Owner in the New-England
States and in New York State in accordance with Attachment B shall arrange for
compensatory load shedding, as provided by a Distribution Provider or
Transmission Owner that is adequate to compensate for the loss of generator(s) due
to early tripping that is within the UFLS island identified by the Planning
Coordinator in Requirement R2.
Each Generator Owner of existing non-nuclear units in service prior to the effective date of this
standard, as documented in accordance with Attachments A or B, that have underfrequency
protections set to trip above the appropriate curve in Figure 2 shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
15.1.
Set the underfrequency protection to operate at the lowest frequency allowed by the
plant design and licensing limitations.
15.2.
Transmit the existing underfrequency settings and any changes to the underfrequency
settings along with the technical basis for the settings to the Planning Coordinator.
15.3.
Have compensatory load shedding, as provided by a Distribution Provider or
Transmission Owner that is adequate to compensate for the loss of their generator due to
7
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
early tripping that is within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M15. Each Generator Owner with existing non-nuclear units in service prior to the effective date
of this Standard which have underfrequency tripping that is not compliant with
Requirement R123 shall provide evidence such as reports, spreadsheets, memorandum or
dated documentation demonstrating that it meets Requirement R15.
R16. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply the
criteria described in Attachment A to determine the compensatory load shedding that is
required in Requirement R15.3 for generating units in its respective NPCC area.
[Violation
Risk Factor: HighMedium] [Time Horizon: Long Term Planning]
M16. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall provide
evidence such as emailsreports, memorandum or other documentation that demonstrates
that it
followed the methodology described in Attachment A and meets Requirement R16.
R17. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the New York ISO shall apply the criteria described in
Attachment B to determine the compensatory load shedding that is required in
Requirement
R15.3 for generating units in its respective NPCC area. [Violation Risk Factor:
HighMedium]
[Time Horizon: Long Term Planning]
M17. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the New York ISO shall provide evidence such as
emailsreports,
memorandum, or other documentation that demonstrates that it followed the methodology
described in Attachment B and meets Requirement R17.
R18. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2, based on their licensing design basis, shall: [Violation Risk
Factor: HighMedium] [Time Horizon: Long Term Planning]
8
18.1.
Set the underfrequency protection to operate at as low a frequency as possible in
accordance with the plant design and licensing limitations but not greater than
57.8 Hz.
18.2.
18.3.
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
M18. Each Generator Owner of nuclear units that have been specifically identified by NPCC as
having generator trip settings above the generator trip curve in Figure 2 shall provide
evidence such as letters, reports and dated documentation that demonstrates that it meets
Requirement R18.
Figure 1
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
9
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
10
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
Time (sec)
C. Compliance
1.
11
Compliance Monitoring Process
1000
55.5
55
10000
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
1.1. Compliance Enforcement Authority
NPCC Compliance Committee
1.2. Compliance Monitoring Period and Reset Time Frame
Not Applicable
1.3. Data Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 4, 5, 6,7,10, 11, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 3, 8, 9, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall
keep evidence for three calendar years for Measure 17.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 18, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
13, 14, 15, 16, and 19.
1.4. Compliance Monitoring and Assessment Processes
Self -Certifications.
Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.
1.5. Additional Compliance Information
None.
2.
Violation Severity Levels
Requirement
R1
12
Lower VSL
N/A
Moderate VSL
N/A
High VSL
N/A
The P
to des
havin
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
chara
freque
59.5 H
1.
R2
The
Planning
Coordinator
provided its UFLS island
boundaries, as identified per the
NERC PRC Standard on UFLS
but did so more than 30 calendar
days and up to and including 40
days following a request.
The Planning Coordinator
provided its UFLS island
boundaries, as identified per the
NERC PRC Standard on UFLS
but did so more than 40 calendar
days but less than and including
50 days following a request.
The Planning Coordinator
provided its UFLS island
boundaries, as identified per the
NERC PRC Standard on UFLS but
did so more than 50 calendar days
but less than and including 60 days
following a request.
The P
to pro
bound
NERC
within
a requ
R3
The Planning Coordinator
identified to the Regional Entity
all non-BES the generation
facilities within its Planning
Coordinator Area that must not
trip above the appropriate
generator underfrequency trip
threshold curve in order
necessary to support the UFLS
program performance
requirements, but did so more
than 30 calendar days but less
than 41and up to and including
40 days after completion of the
system studies.
The Planning Coordinator
identified to the Regional Entity
all non-BES generation facilities
within its Planning Coordinator
Area that must not trip above the
appropriate generator
underfrequency trip threshold
curve in order to support the
UFLS program performance
requirements, but did so more
than 40 days but less than
calendar days but less than and
including 50 days after
completion of the system
studies.
The Planning Coordinator
identified to the Regional Entity all
non-BES generation facilities
within its Planning Coordinator
Area that must not trip above the
appropriate generator
underfrequency trip threshold
curve in order to support the UFLS
program performance
requirements,, but did so more than
50 calendar days but less than and
including 60 days after completion
of the system studies.
The P
identi
facilit
Coord
trip ab
gener
thresh
the U
requir
the R
calend
the sy
The P
identi
facilit
Coord
trip ab
gener
thresh
to sup
perfor
The D
Trans
imple
progr
specif
Part 4
R4
R5
13
OR
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations ir
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
ir Requirement R5, Parts %.1
through Part 5.4 but exceeded
the permissible time frame for
one or more of the 4 items
within a time greater than 20
calendar days but less than or
equal to 30 calendar days.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or number
of stages and frequency set points
specified in the UFLS Program
fulfilled its obligations but
exceeded the permissible time
frame for one or more of the 4
items within a time greater than
30 calendar days but less than or
equal to 60 calendar days.
The D
Trans
meet
numb
set po
Progr
items
60 ca
time f
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R6
The Distribution Provider or
Transmission Owner set less than
100% but more than (and
including) 95% of its
underfrequency relays that are
part of its region’s UFLS program
with a 100 ms minimum time
delay.
R7
The Planning Coordinator
developed or reviewed settings
for inhibit thresholds at least once
per five calendar years, for less
than 100% but more than (and
including) 95% of relays within
its region’s UFLS program.
R8
R9
The Distribution Provider or
Transmission Owner set less than
90% but more than (and including)
85% of its underfrequency relays
that are part of its region’s UFLS
program with a 100 ms minimum
time delay.
The D
Trans
than 8
relays
UFLS
minim
The Planning Coordinator
developed or reviewed settings
for inhibit thresholds at least
once per five calendar years,
for less than 95% but more
than (and including) 90% of
relays within its region’s UFLS
program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and
including) 85% of relays within its
region’s UFLS program.
The P
devel
for in
once p
less th
region
The Planning Coordinator
provided to a Transmission
Owner or Distribution Provider
within its Planning Coordinator
area the applicable inhibit
thresholds more than 30 calendar
days and up to and including 40
calendar days of any changes.
The Planning Coordinator
provided to a Transmission
Owner or Distribution Provider
within its Planning Coordinator
area the applicable inhibit
thresholds more than 40 calendar
daysbut less than and including
50 calendar days of any changes.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar daysbut less than
and including 60 calendar days of
any changes.
The P
to pro
Owne
within
area t
thresh
calend
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its
implementation plan more than
100 calendar days and up to and
including 110 calendar days
following the request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
The D
Trans
devel
imple
thanw
the re
R10
implemented the inhibit
threshold settings provided by
the Planning Coordinator in
accordance with the Planning
Coordinator approved
implementation plan for less
than 100% but more than (and
including) 95% of UFLS relays.
The Distribution Provider or
Transmission Owner
implemented the inhibit
threshold settings provided by
the Planning Coordinator in
accordance with the Planning
Coordinator approved
implementation plan for less
than 95% but more than (and
including) 90% of UFLS relays.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with the
Planning Coordinator approved
implementation plan for less than
90% but more than (and
including) 85 % of UFLS relays.
The D
Trans
imple
thresh
the Pl
accor
Coord
imple
than
R11
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each
UFLS stage as described in
Requirement R11 more than 16
calendar months but less than
(and including)17 calendar
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed by
the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar months
but less than (and including)18
calendar months since last update.
The D
Trans
provid
Coord
the ac
have b
relays
descri
within
last up
14
The Distribution Provider or
Transmission Owner set less
than 95% but more than (and
including) 90% of its
underfrequency relays that are
part of its region’s UFLS
program with a 100 ms
minimum time delay.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
months since last update.
R12
N/A
N/A
N/A
The G
each g
trip re
below
under
settin
Figur
exem
R13
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay to its
Planning Coordinator more than
45calendar days and less than
(and including) 55 calendar days
of the Planning Coordinator’s
request.
The Generator Owner
transmitted the generator
underfrequency trip setting and
time delay to its Planning
Coordinator more than 55
calendar days and less than (and
including) 65 calendar days of
the Planning Coordinator’s
request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay to its
Planning Coordinator more than 65
calendar days and less than (and
including) 75 calendar days of the
Planning Coordinator’s request.
The G
transm
under
time d
days o
Coord
R14
N/A
N/A
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
capability by greater than 10%:
The G
new g
existi
net ca
10%,
obliga
Part 1
Did not: fulfill the obligation of
Requirement R14; Part 14.1
OR
Did not fulfill the obligation of
Requirement R14, Part 14.2.
R15
N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinator.as
specified in Requirement R15,
Part 15.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirment 15, Part 15.1
The P
Ontar
Marit
Gener
Engla
State
comp
specif
Part 1
R16
N/A
N/A
N/A
The P
not ap
descri
determ
shedd
R17
N/A
N/A
N/A
The G
Distri
Trans
apply
15
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
in Att
the co
that is
R18
N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis
for the settings to the Planning
Coordinator as specified in
Requirement R18, Part 18.3.
The Generator Owner:
Failed to set the underfrequency
protection as specified in
Requirement R18; Part 18.1
OR
Failed to set the frequency trip
setting upper tolerance as specified
in Requirement R18, Part 18.2.
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 2.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all UFLS islands in which the unit may operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units, in their Planning Coordinator area, in service prior to the
effective date of Version 1 of the regional Standard (April, 2017 PRC-006-NPCC-1).
The list must indicate generating units, if any, that have their underfrequency protections
set to trip above the appropriate curve in Figure 2. Generating Units not appearing on the
list as of the effective date of Version 1 of the regional standard, as shown above, must
have their Underfrequency protections set to trip on or below the appropriate curve in
Figure 2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
16
The G
fulfill
Requi
Part 1
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS
relays within the island(s) identified by the Planning Coordinator within which
the generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that is
provided by the Distribution Provider or Transmission Owner shall be in addition
to the amount that the Distribution Provider or Transmission Owner is required to
shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 2 during an underfrequency event. If the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
17
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units in service prior to the effective date of Version 1 of the regional
Standard (April, 2017 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, that have their underfrequency protections set to trip above the
appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2. The
list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
18
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 2, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the smallest island identified by the Planning Coordinator in
Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 2, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
19
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment C
20
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load shall
implement a UFLS program with the following attributes:
Frequency Threshold
(Hz)
Total Nominal
Operating
Time (s)1
Load Shed at Stage as %
of TO or DP Load
Cumulative Load Shed as
% of TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
27.5 – 28.5
59.5
10.0
2
–3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100 MW2
of peak net Load shall implement a UFLS program with the following attributes:
21
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
22
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Guidelines and Technical Basis:
Standard PRC-006-32, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
23
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
Generator dynamic modeling
Dynamic VAR device modeling
HVDC dynamic modeling (MOD-027-1 - Verification of Models and Data for
Turbine/Governor and Load Control or Active Power/Frequency Control Functions) or
system modeling (if variations in system response are detected under MOD-033 - SteadyState and Dynamic System Model Validation)
Implementation Plan
Regional Reliability Standard PRC-006-NPCC-2 – Automatic
Underfrequency Load Shedding
Applicable Standard(s)
•
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requested Retirement(s)
•
PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding
Applicable Entities
•
•
•
•
Generator Owners
Planning Coordinators
Distribution Providers that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Transmission Owners that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Background
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. To determine if the applicability of the standard needs to be revised in accordance with
Project 2014-01 Dispersed Generation Resources.
2. To determine if the performance requirements as contained in the criteria of NPCC
Directory#12 Sections 5.1.1 and 5.1.2 should be explicitly included in the requirements
of the Regional Standard and potential retirement of Directory 12 Automatic
Underfrequency Load Shedding Program.
3. Review Attachment C in PRC-006-NPCC-1 to address the implications of the design
assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. Review and revise Table 4 in Attachment C in accordance with the 2013 NPCC UFLS
Adequacy Assessment. Additionally, the applicability of Requirements R4 and R5 will be
reviewed to consider that Hydro Quebec is not part of the Eastern Interconnection.
Effective Date
All requirements with the exception of R4 will be enforceable on the first day of the first
calendar quarter following the applicable governmental and regulatory approvals.
R4 will be enforceable on the first day of the first calendar quarter 12 months following
the applicable governmental and regulatory approvals.
Retirement Date
The NPCC Regional Reliability Standard PRC-006-NPCC-1 shall be retired immediately
prior to the Effective Date of PRC-006-NPCC-2.
Mapping Document
Draft NPCC Regional Automatic Underfrequency Load Shedding Standard
PRC-006-NPCC-2
NPCC’s regional standard PRC‐006‐NPCC‐2 “Automatic Underfrequency Load Shedding” (UFLS) was effective in the US in July 2015. The
standard is currently under revision to align with the continent‐wide PRC‐006‐2 UFLS standard which became effective on October 2015. The
draft of PRC‐006‐NPCC‐2 removes duplicity with the continent wide standard and adds specificity to allow retirement of the NPCC UFLS
Directory #12 containing more stringent UFLS performance criteria and harmonizes the requirements and criteria of all these documents.
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
PRC‐006‐NPCC‐1
Translation to New Standard or Other
Action
PRC‐006‐NPCC‐2
R1 Each Planning Coordinator shall establish R2. Each Planning Coordinator shall provide
requirements for entities aggregating their
UFLS island boundaries, as identified per
UFLS programs for each anticipated island and
the NERC PRC Standard on UFLS, to
requirements for compensatory load
Distribution Providers, Generator
shedding based on islanding criteria (required
Owners, and Transmission Owners
by the NERC PRC Standard on UFLS).
within 30 calendar days of receipt of a
[Violation Risk Factor: Medium] [Time
request. [Violation Risk Factor: Lower]
Horizon: Long Term Planning]
[Time Horizon: Long Term Planning]
R4. Each Distribution Provider and
Transmission Owner in the Eastern
Interconnection portion of NPCC shall
Description and Change Justification
The purpose of R1 in PRC‐006‐NPCC‐1 was
to ensure entities that aggregate their load
understand what the UFLS island
boundaries are and establish criteria for
compensatory load shedding. The revised
R2, R4, and R15 clearly address this in the
proposed PRC‐006‐NPCC‐2.
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
implement an automatic UFLS program,
reflecting normal operating conditions,
excluding outages. The automatic UFLS
program shall be implemented on an
island basis for each island identified per
the NERC PRC Standard on UFLS.
[Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
4.1. The UFLS program shall be
implemented by each Distribution
Provider and Transmission Owner
according to the frequency
thresholds, nominal operating
times and load shedding amounts
specified in Attachment C, Tables 1
through 3 or.
4.2. The program shall be implemented
collectively by multiple
Distribution Providers or
Transmission Owners , as long as
they reside in the same UFLS Island
identified by the Planning
Coordinator per R2. These multiple
Distribution Providers or
Transmission Owners, via mutual
Mapping Document
Project Number and Name | Month Year
2
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
agreement, shall act as a single
entity to provide an aggregated
automatic UFLS program that
sheds their coincident peak
aggregated net Load according to
the frequency thresholds, total
nominal operating time and
amounts specified in Attachment
C, Tables 1 through 3.
R15. For existing non‐nuclear units in
service prior to the effective date of
this standard, as documented in
accordance with Attachments A or B,
that have underfrequency protections
set to trip above the appropriate curve
in Figure 2: [Violation Risk Factor:
Medium] [Time Horizon: Long Term
Planning]
15.1. Each Generator Owner shall
set the underfrequency
protection to operate at the
lowest frequency allowed by
the plant design and licensing
limitations.
Mapping Document
Project Number and Name | Month Year
3
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
15.2. Each Generator Owner shall
transmit the existing
underfrequency settings and
any changes to the
underfrequency settings along
with the technical basis for the
settings to the Planning
Coordinator.
15.3. Each Planning Coordinator in
Ontario, Québec and the
Maritime Provinces in
accordance with Attachment A
and each Generator Owner in
the New‐England States and in
New York State in accordance
with Attachment B shall
arrange for compensatory load
shedding, as provided by a
Distribution Provider or
Transmission Owner that is
adequate to compensate for
the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Mapping Document
Project Number and Name | Month Year
4
Standard: PRC-006-NPCC-2
Translation to New Standard or Other
Action
Requirement in Approved Standard
Description and Change Justification
Planning Coordinator in
Requirement R2.
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R2 Each Planning Coordinator shall, within 30
days of completion of its system studies
required by the NERC PRC Standard on UFLS,
identify to the Regional Entity the generation
facilities within its Planning Coordinator Area
necessary to support the UFLS program
performance characteristics. [Violation Risk
Factor: Medium] [Time Horizon: Long Term
Planning]
R3. Each Planning Coordinator shall, within
30 calendar days of completion of its UFLS
system studies, identify to the Regional
Entity all non‐BES generation facilities,
within its Planning Coordinator Area, that
must not trip above the appropriate
generator underfrequency trip threshold
curve in Figure 2 in order to support UFLS
program performance requirements.
[Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
The original intent of R2 in Version 2 was to
ensure that the non‐BES units necessary to
support UFLS system performance were
subject to the standard with notification
going to NPCC to ensure they were
registered as being “material” per Appendix
5B of the NERC Rules of Procedure. Also
clarity was added that these generating
units must not trip above the appropriate
generator underfrequency trip threshold
curve in Figure 1. This was previously
implicit in the Version 1 of the standard and
NPCC will continue to have the PC identify
these units and pursue their registration.
The reliability intent of Version 1 R3 was to
R3 Each Planning Coordinator shall provide to R2. Each Planning Coordinator shall provide ensure that the entities aggregating load
the Transmission Owner, Distribution
UFLS island boundaries, as identified per were aware of the island boundaries. This is
covered in draft R2 of the proposed revision
Provider, and Generator Owner within 30
the NERC PRC Standard on UFLS, to
to the standard. Requirements regarding
Mapping Document
Project Number and Name | Month Year
5
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
days upon written request the requirements
Distribution Providers, Generator
for entities aggregating the UFLS programs
Owners, and Transmission Owners
and requirements for compensatory load
within 30 calendar days of receipt of a
shedding program derived from each Planning
request. [Violation Risk Factor: Lower]
Coordinator’s system studies as determined
[Time Horizon: Long Term Planning]
by Requirement R1. [Violation Risk Factor:
Low] [Time Horizon: Long Term Planning]
R15. For existing non‐nuclear units in
service prior to the effective date of
this standard, as documented in
accordance with Attachments A or B,
that have underfrequency protections
set to trip above the appropriate curve
in Figure 2: [Violation Risk Factor:
Medium] [Time Horizon: Long Term
Planning]
15.1. Each Generator Owner shall
set the underfrequency
protection to operate at the
lowest frequency allowed by
the plant design and licensing
limitations.
Description and Change Justification
compensatory load shedding have been
clarified and are covered through draft R15.
15.2. Each Generator Owner shall
transmit the existing
underfrequency settings and
any changes to the
Mapping Document
Project Number and Name | Month Year
6
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
underfrequency settings along
with the technical basis for the
settings to the Planning
Coordinator.
15.3. Each Planning Coordinator in
Ontario, Québec and the
Maritime Provinces in
accordance with Attachment A
and each Generator Owner in
the New‐England States and in
New York State in accordance
with Attachment B shall arrange
for compensatory load shedding,
as provided by a Distribution
Provider or Transmission Owner
that is adequate to compensate
for the loss of generator(s) due
to early tripping that is within
the UFLS island identified by the
Planning Coordinator in
Requirement R2.
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R4 Each Distribution Provider and
Transmission Owner in the Eastern
R4. Each Distribution Provider and
Transmission Owner in the Eastern
Mapping Document
Project Number and Name | Month Year
Added clarity and separated the
requirement into parts.
7
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Interconnection portion of NPCC shall
implement an automatic UFLS program
reflecting normal operating conditions
excluding outages for its Facilities based on
frequency thresholds, total nominal operating
time and amounts specified in Attachment C,
Tables 1 through 3, or shall collectively
implement by mutual agreement with one or
more Distribution Providers and Transmission
Owners within the same island identified in
Requirement R1 and acting as a single entity,
provide an aggregated automatic UFLS
program that sheds their coincident peak
aggregated net Load, based on frequency
thresholds, total nominal operating time and
amounts specified in Attachment C, Tables 1
through 3. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning
Mapping Document
Project Number and Name | Month Year
Translation to New Standard or Other
Action
Description and Change Justification
Interconnection portion of NPCC shall
implement an automatic UFLS program,
reflecting normal operating conditions,
excluding outages. The automatic UFLS
program shall be implemented on an
island basis for each island identified
per the NERC PRC Standard on UFLS.
[Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
4.1. The UFLS program shall be
implemented by each Distribution
Provider and Transmission Owner
according to the frequency
thresholds, nominal operating
times and load shedding amounts
specified in Attachment C, Tables 1
through 3 or.
4.2. The program shall be implemented
collectively by multiple
Distribution Providers or
Transmission Owners , as long as
they reside in the same UFLS Island
identified by the Planning
8
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
Coordinator per R2. These multiple
Distribution Providers or
Transmission Owners, via mutual
agreement, shall act as a single
entity to provide an aggregated
automatic UFLS program that
sheds their coincident peak
aggregated net Load according to
the frequency thresholds, total
nominal operating time and
amounts specified in Attachment
C, Tables 1 through 3.
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
Clarifications are proposed in the proposed
Version 2. Subrequirements have been
R5 Each Distribution Provider or Transmission R5. Each Distribution Provider or
Owner that must arm its load to trip on
Transmission Owner that cannot meet revised and separated out, timeframes have
underfrequency in order to meet its
the tolerances and/or number of stages been added.
requirements as specified and by doing so
and frequency set points specified in
exceeds the tolerances and/or deviates from
the UFLS Program, shall: [Violation Risk
the number of stages and frequency set
Factor: High] [Time Horizon: Long Term
points of the UFLS program as specified in the
Planning]
tables contained in Requirement R4 above, as 5.1. Notify its Planning Coordinator within
applicable depending on its total peak net
30 calendar days of recognition.
Load shall: [Violation Risk Factor: High] [Time 5.2. Within the following 90 calendar days,
Horizon: Long Term Planning]
determine if tolerances can be met
Mapping Document
Project Number and Name | Month Year
9
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
5.1 Inform its Planning Coordinator of the
need to exceed the stated tolerances or the
number of stages as shown in UFLS
Attachment C, Table 1 if applicable and
5.2 Provide its Planning Coordinator with a
technical study that demonstrates that the
Distribution Providers or Transmission
Owners specific deviations from the
requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on
the bulk power system.
5.3 Inform its Planning Coordinator of the
need to exceed the stated tolerances of UFLS
Attachment C, Table 2 or Table 3, and in the
case of Attachment C, Table 2 only, the need
to deviate from providing two stages of UFLS,
if applicable, and
5.4 Provide its Planning Coordinator with an
analysis demonstrating that no alternative
load shedding solution is available that would
allow the Distribution Provider or
Transmission Owner to comply with UFLS
Attachment C Table 2 or Attachment C Table
3.
Mapping Document
Project Number and Name | Month Year
Translation to New Standard or Other
Action
Description and Change Justification
through adjustments and notify the
Planning Coordinator.
5.3. If adjustments are possible, make the
adjustments within 180 calendar days
after determining that adjustments are
possible, and notify the Planning
Coordinator when complete, or,
5.4. If adjustments are not possible then:
5.4.1. Each Distribution Provider or
Transmission Owner subject to Attachment
C, Table 1, shall within 180 calendar days,
provide its Planning Coordinator with a
technical study that demonstrates that the
Distribution Provider’s or Transmission
Owner’s specific deviations from the
requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on
the BES, or
5.4.2. Each Distribution Provider or
Transmission Owner subject to Attachment
C, Table 2 or Table 3, or in the Quebec
Interconnection, shall within 90 calendar
days, provide its Planning Coordinator with
an analysis demonstrating that no
alternative load shedding solution is
10
Standard: PRC-006-NPCC-2
Translation to New Standard or Other
Action
Requirement in Approved Standard
Description and Change Justification
available that would allow the Distribution
Provider or Transmission Owner to comply
with the UFLS program.
PRC‐006‐NPCC‐1
The drafting team agreed to retire the
requirement.
PRC‐006‐NPCC‐2
R6 Each Distribution Provider and
Transmission Owner in the Québec
Interconnection portion of NPCC shall
implement an automatic UFLS program for its
Facilities based on the frequency thresholds,
slopes, total nominal operating time and
amounts specified in Attachment C, Table 4
or shall collectively implement by mutual
agreement with one or more Distribution
Providers and Transmission Owners within
the same island, identified in Requirement R1,
an aggregated automatic UFLS program that
sheds Load based on the frequency
thresholds, slopes, total nominal operating
time and amounts specified in Attachment C,
Table 4. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
PRC‐006‐NPCC‐1
Mapping Document
Project Number and Name | Month Year
11
Standard: PRC-006-NPCC-2
Translation to New Standard or Other
Action
Requirement in Approved Standard
Description and Change Justification
R7 Each Distribution Provider and
Transmission Owner shall set each
underfrequency relay that is part of its
region’s UFLS program with the following
minimum time delay: 7.1 Eastern
Interconnection – 100 ms 7.2 Québec
Interconnection – 200 ms [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
R6. Each Distribution Provider and
Transmission Owner shall set each
underfrequency relay that is part of its
region’s UFLS program with a 100 ms
minimum time delay. [Violation Risk
Factor: Medium] [Time Horizon: Long
Term Planning]
Elimnated Hydro Quebec Interconnection
minimum time delay of 200ms.
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
Periodicty of develop and review settings
has been increased from once per calendar
year to once per five calendar years. This
coincides with the the periodicity of UFLS
studies. Having a yearly “develop and
review” without taking any further action is
strictly administrative and does nothing for
reliability (P‐81 type of issue).
R8 Each Planning Coordinator shall develop R7. Each Planning Coordinator shall
and review once per calendar year settings for
develop and review settings for inhibit
inhibit thresholds (such as but not limited to
thresholds at least once per five
voltage, current and time) to be utilized
calendar years (such as but not limited
within its region's UFLS program. [Violation
to voltage, current and time) to be
Risk Factor: Medium] [Time Horizon: Long
utilized within its region’s UFLS
Term Planning]
program. [Violation Risk Factor:
Medium] [Time Horizon: Long Term
Planning]
NPCC‐006‐NPCC‐1
Mapping Document
Project Number and Name | Month Year
NPCC‐006‐NPCC‐2
12
Standard: PRC-006-NPCC-2
Translation to New Standard or Other
Action
Requirement in Approved Standard
Description and Change Justification
R9 Each Planning Coordinator shall provide
each Transmission Owner and Distribution
Provider within its Planning Coordinator area
the applicable inhibit thresholds within 30
days of the initial determination of those
inhibit thresholds and within 30 days of any
changes to those thresholds. [Violation Risk
Factor: Medium] [Time Horizon: Operations
Planning]
R8. Each Planning Coordinator shall
Clarified the language.
provide each Transmission Owner and
Distribution Provider within its Planning
Coordinator area the applicable inhibit
thresholds within 30 calendar days of
any changes. [Violation Risk Factor:
Lower] [Time Horizon: Operations
Planning]
NPCC‐006‐NPCC‐1
NPCC‐006‐NPCC‐2
R10 Each Distribution Provider and
Transmission Owner shall implement the
inhibit threshold settings based on the
notification provided by the Planning
Coordinator in accordance with Requirement
R9. [Violation Risk Factor: High] [Time
Horizon: Operations Planning]
R10. Each Distribution Provider and
Transmission Owner shall implement
Added clarification for Planning Coordinator
the inhibit threshold settings provided developes implementation plan.
by the Planning Coordinator in
accordance with Requirement R8 and
based on the Planning Coordinator
approved implementation plan in
accordance with R9. [Violation Risk
Factor: High] [Time Horizon: Operations
Planning]
NPCC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R11 Each Distribution Provider and
R9. Each Distribution Provider and
Transmission Owner shall develop and submit Transmission Owner that receives a
Mapping Document
Project Number and Name | Month Year
Same ‐ with changes to requirement
numbers referenced only.
Language clarifications and changes to
requirement numbers referenced.
13
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
an implementation plan within 90 days of the
request from the Planning Coordinator for
approval by the Planning Coordinator in
accordance with R9. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
notification pursuant to Requirement R8
shall develop and submit an
implementation plan for approval by the
Planning Coordinator within 90 calendar
days of the request from the Planning
Coordinator. [Violation Risk Factor: Lower]
[Time Horizon: Operations Planning]
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R12 Each Transmission Owner and
R11. Each Transmission Owner and
Distribution Provider shall annually provide
Distribution Provider shall annually
documentation, with no more than 15
provide documentation, with no more
months between updates, to its Planning
than 15 calendar months between
Coordinator of the actual net Load that would
updates, to its Planning Coordinator of
have been shed by the UFLS relays at each
the actual net Load that would have
UFLS stage coincident with their integrated
been shed by the UFLS relays at each
hourly peak net Load during the previous
UFLS stage. The actual net Load shall be
year, as determined by measuring actual
coincident with the entity’s integrated
metered Load through the switches that
hourly peak net Load during the
would be opened by the UFLS relays.
previous year, as determined by
[Violation Risk Factor: Lower] [Time Horizon:
measuring or calculating Load through
Long Term Planning]
the switches that would disconnect
load if triggered by the UFLS relays.
[Violation Risk Factor: Lower]
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Added language that allows calculation of
load from nearest available metering rather
than actual metering. The requirement as it
exists is placing undo burden to install
metering when it can be accurately
calculated as a cost effective alternative.
14
Standard: PRC-006-NPCC-2
Translation to New Standard or Other
Action
Requirement in Approved Standard
Description and Change Justification
[Time Horizon: Long Term Planning]
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R13 Each Generator Owner shall set each
generator underfrequency trip relay, if so
equipped, below the appropriate generator
underfrequency trip protection settings
threshold curve in Figure 1, except as
otherwise exempted in Requirements R16
and R19. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
Clarification was made that the
Underfrequency trip relay must to be set to
R12. Each Generator Owner shall set each
generator underfrequency trip relay, if operate “on or below” the appropriate
curve. In Version 1 it currently states below
so equipped, on or below the
and questions arose whether settings on
appropriate generator underfrequency
trip protection settings threshold curve the curve were considered in compliance.
in Figure 2, except as otherwise
exempted in Requirements R15 and
R18. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
NPCC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R14 Each Generator Owner shall transmit the R13. Each Generator Owner shall transmit
generator underfrequency trip setting and
the generator underfrequency trip
time delay to its Planning Coordinator within
setting and time delay within 45
45 days of the Planning Coordinator’s request.
calendar days of the Planning
[Violation Risk Factor: High] [Time Horizon:
Coordinator’s request. [Violation Risk
Operations Planning]
Factor: Lower] [Time Horizon:
Operations Planning]
No Change from Version 1 only requirement
numbering
PRC‐006‐NPCC‐1
Mapping Document
Project Number and Name | Month Year
PRC‐006‐NPCC‐2
15
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
R15 Each Generator Owner with a new
generating unit, scheduled to be in service on
or after the effective date of this Standard, or
an existing generator increasing its net
capability by greater than 10% shall:
[Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
15.1 Design measures to prevent the
generating unit from tripping directly or
indirectly for underfrequency conditions
above the appropriate generator tripping
threshold curve in Figure 1.
15.2 Design auxiliary system(s) or devices
used for the control and protection of
auxiliary system(s), necessary for the
generating unit operation such that they will
not trip the generating unit during
underfrequency conditions above the
appropriate generator underfrequency trip
protection settings threshold curve in Figure
1.
Mapping Document
Project Number and Name | Month Year
Translation to New Standard or Other
Action
R14. Each Generator Owner with a new
generating unit, or an existing
generator increasing its net capability
by greater than 10% shall: [Violation
Risk Factor: Medium] [Time Horizon:
Long Term Planning]
14.1. Design measures to prevent
the generating unit from
tripping directly or indirectly
for underfrequency conditions
above the appropriate
generator tripping threshold
curve in Figure 2.
Description and Change Justification
Removed language pertaining to the
Version 1 of the standard regarding on or
after the effective date. Version 1 has been
in place and transition/implementation
concerns need not be addressed in this
requirement.
14.2. Design auxiliary system(s) or
devices used for the control
and protection of auxiliary
system(s), necessary for the
generating unit operation such
that they will not trip the
generating unit during
underfrequency conditions
above the appropriate
generator underfrequency trip
16
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
protection settings threshold
curve in Figure 2.
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R16 Each Generator Owner of existing non‐
nuclear units in service prior to the effective
date of this standard that have
underfrequency protections set to trip above
the appropriate curve in Figure 1 shall:
[Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
R15. For existing non‐nuclear units in
service prior to the effective date of
this standard, as documented in
accordance with Attachments A or B,
that have underfrequency protections
set to trip above the appropriate curve
in Figure 2: [Violation Risk Factor:
Medium] [Time Horizon: Long Term
Planning]
15.1. Each Generator Owner shall set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations.
16.1 Set the underfrequency protection to
operate at the lowest frequency allowed by
the plant design and licensing limitations.
16.2 Transmit the existing underfrequency
settings and any changes to the
underfrequency settings along with the
technical basis for the settings to the Planning
Coordinator.
16.3 Have compensatory load shedding, as
provided by a Distribution Provider or
Transmission Owner that is adequate to
Mapping Document
Project Number and Name | Month Year
Addition made to R15.3 to clarify that any
compensatory load shedding must be in the
island the generating unit resides in.
15.2. Each Generator Owner shall
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
17
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
compensate for the loss of their generator
due to early tripping.
Translation to New Standard or Other
Action
Description and Change Justification
basis for the settings to the
Planning Coordinator.
15.3. Each Planning Coordinator in
Ontario, Québec and the Maritime
Provinces in accordance with
Attachment A and each Generator
Owner in the New‐England States
and in New York State in
accordance with Attachment B
shall arrange for compensatory
load shedding, as provided by a
Distribution Provider or
Transmission Owner that is
adequate to compensate for the
loss of generator(s) due to early
tripping that is within the UFLS
island identified by the Planning
Coordinator in Requirement R2.
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R17 Each Planning Coordinator in Ontario,
Quebec and the Maritime provinces shall
apply the criteria described in Attachment A
to determine the compensatory load
shedding that is required in Requirement
R16. Each Planning Coordinator in Ontario,
Quebec and the Maritime provinces
shall apply the criteria described in
Attachment A to determine the
compensatory load shedding that is
Mapping Document
Project Number and Name | Month Year
Same – numbering of requirements
changing
18
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
R16.3 for generating units in its respective
NPCC area. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
Translation to New Standard or Other
Action
Description and Change Justification
required in Requirement R15.3 for
generating units in its respective NPCC
area. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R18 Each Generator Owner, Distribution
Provider or Transmission Owner within the
Planning Coordinator area of ISO‐NE or the
New York ISO shall apply the criteria
described in Attachment B to determine the
compensatory load shedding that is required
in Requirement R16.3 for generating units in
its respective NPCC area. [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
R17. Each Generator Owner, Distribution
Provider or Transmission Owner within
the Planning Coordinator area of ISO‐
NE or the New York ISO shall apply the
criteria described in Attachment B to
determine the compensatory load
shedding that is required in
Requirement R15.3 for generating units
in its respective NPCC area. [Violation
Risk Factor: Medium][Time Horizon:
Long Term Planning]
PRC‐006‐NPCC‐1
PRC‐006‐NPCC‐2
R19 Each Generator Owner of existing
R18. Each Generator Owner of existing
nuclear generating plants with units that have
nuclear generating plants with units
underfrequency relay threshold settings
that have underfrequency relay
above the Eastern Interconnection generator
threshold settings above the Eastern
tripping curve in Figure 1, based on their
Interconnection generator tripping
licensing design basis, shall: [Violation Risk
curve in Figure 2, based on their
licensing design basis, shall: [Violation
Mapping Document
Project Number and Name | Month Year
Same – numbering of requirements
changing
Same – numbering of requirements
changing and Figure reference update
19
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Factor: High] [Time Horizon: Long Term
Planning]
19.1 Set the underfrequency protection to
operate at as low a frequency as possible in
accordance with the plant design and
licensing limitations but not greater than
57.8Hz.
19.2 Set the frequency trip setting upper
tolerance to no greater than + 0.1 Hz.
19.3 Transmit the initial frequency trip
setting and any changes to the setting and the
technical basis for the settings to the Planning
Coordinator.
Translation to New Standard or Other
Action
Description and Change Justification
Risk Factor: Medium] [Time Horizon:
Long Term Planning]
18.1. Set the underfrequency
protection to operate at as
low a frequency as possible
in accordance with the plant
design and licensing
limitations but not greater
than 57.8 Hz.
18.2. Set the frequency trip setting
upper tolerance to no greater
than + 0.1 Hz.
18.3. Transmit the initial frequency
trip setting and any changes
to the setting and the
technical basis for the
settings to the Planning
Coordinator.
PRC‐006‐NPCC‐1
PRC‐006‐2 (Existing in force continent‐wide The drafting team decided to remove
requirement 19 and 20 because they are
R20 The Planning Coordinator shall update its standard)
covered by the continent‐wide PRC‐006‐2
UFLS program database as specified by the
requirement 6.
NERC PRC Standard on UFLS. This database
R6. Each Planning Coordinator shall
shall include the following information:
maintain a UFLS database containing data
Mapping Document
Project Number and Name | Month Year
20
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
necessary to model its UFLS program for use The requirement 19 and 20 language will be
in event analyses and assessment of the
transferred over to new guideline
UFLS program at least once each calendar
document.
20.1 For each UFLS relay, including those
year, with no more than 15 months
used for compensatory load shedding, the
between maintenance activities. [VRF:
amount and location of load shed at peak, the
Lower][Time Horizon: Long‐term Planning]
corresponding frequency threshold and time
delay settings.
[Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
20.2 The buses at which the Load is modeled
in the NPCC library power flow case.
20.3 A list of all generating units that may be
tripped for underfrequency conditions above
the appropriate generator underfrequency
trip protection settings threshold curve in
Figure 1, including the frequency trip
threshold and time delay for each protection
system.
20.4 The location and amount of additional
elements to be switched for voltage control
that are coordinated with UFLS program
tripping.
20.5 A list of all UFLS relay inhibit functions
along with the corresponding settings and
locations of these relays.
Mapping Document
Project Number and Name | Month Year
21
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
PRC‐006‐NPCC‐1
R21 Each Planning Coordinator shall notify
each Distribution Provider, Transmission
Owner, and Generator Owner within its
Planning Coordinator area of changes to load
distribution needed to satisfy UFLS program
performance characteristics as specified by
the NERC PRC Standard on UFLS.[Violation
Risk Factor: High] [Time Horizon: Long Term
Planning]
Translation to New Standard or Other
Action
Description and Change Justification
PRC‐006‐2 (Existing in force continent‐wide
standard)
PRC‐006‐NPCC‐1 R21 is now redundant with
the NERC continent wide standard R3. This
R3. Each Planning Coordinator shall
requirement, R21 is proposed for
develop a UFLS program,
retirement under the P‐81 criteria.
including notification of and a
schedule for implementation by
UFLS entities within its area, that
meets the following performance
characteristics in simulations of
underfrequency conditions
resulting from an imbalance
scenario, where an imbalance =
[(load — actual generation
output) / (load)], of up to 25
percent within the identified
island(s). [VRF: High][Time
Horizon: Long‐term Planning]
3.1. Frequency shall remain above
the Underfrequency Performance
Characteristic curve in PRC‐006‐2
‐ Attachment 1, either for 60
seconds or until a steady‐state
condition between 59.3 Hz and
60.7 Hz is reached, and
Mapping Document
Project Number and Name | Month Year
22
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
3.2. Frequency shall remain below
the Overfrequency Performance
Characteristic curve in PRC‐006‐2
‐ Attachment 1, either for 60
seconds or until a steady‐state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.3. Volts per Hz (V/Hz) shall not
exceed 1.18 per unit for longer
than two seconds cumulatively
per simulated event, and shall not
exceed 1.10 per unit for longer
than 45 seconds cumulatively per
simulated event at each
generator bus and generator
step‐up transformer high‐side bus
associated with each of the
following:
Mapping Document
Project Number and Name | Month Year
Individual generating units
greater than 20 MVA (gross
nameplate rating) directly
connected to the BES
Generating plants/facilities
greater than 75 MVA (gross
23
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
aggregate nameplate rating)
directly connected to the BES
Facilities consisting of one or
more units connected to the
BES at a common bus with
total generation above 75
MVA gross nameplate rating.
PRC‐006‐NPCC‐1
PRC‐006‐2 (Existing in force continent‐wide PRC‐006‐NPCC‐1 R22 is now redundant with
the NERC continent wide standard R9 and
R22 Each Distribution Provider, Transmission standard)
Owner and Generator Owner shall implement R9. Each UFLS entity shall provide automatic this requirement, R22 is proposed for
retirement under the P‐81 criteria.
the load distribution changes based on the
tripping of Load in accordance with the
notification provided by the Planning
UFLS program design and schedule for
Coordinator in accordance with Requirement implementation, including any Corrective
R21. [Violation Risk Factor: High] [Time
Action Plan, as determined by its Planning
Horizon: Long Term Planning]
Coordinator(s) in each Planning Coordinator
area in which it owns assets. [VRF:
High][Time Horizon: Long‐term Planning]
PRC‐006‐NPCC‐1
PRC‐006‐2 (Existing in force continent‐wide PRC‐006‐NPCC‐1 states an implemention
plan for changes needs to be submitted to
R23 Each Distribution Provider, Transmission standard)
the PC for their approval within 90 days of
Owner and Generator Owner shall develop
R3. Each Planning Coordinator shall
the request. However in R22 of the regional
and submit an implementation plan within 90
develop a UFLS program,
standard it states that the changes shall be
days of the request from the Planning
including notification of and a
implemented based on the PC’s notification.
Coordinator for approval by the Planning
schedule for implementation by
Mapping Document
Project Number and Name | Month Year
24
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Coordinator in accordance with Requirement
R21. [Violation Risk Factor: Lower] [Time
Horizon: Operations Planning]
Translation to New Standard or Other
Action
UFLS entities within its area, that
meets the following performance
characteristics in simulations of
underfrequency conditions
resulting from an imbalance
scenario, where an imbalance =
[(load — actual generation
output) / (load)], of up to 25
percent within the identified
island(s). [VRF: High][Time
Horizon: Long‐term Planning]
Description and Change Justification
We believe this is fully covered in R3 and an
additional implementation plan beyond the
PC’s plan, which includes the notification
and schedule for the UFLS entities to follow
is now unnecessary in the regional standard.
We are recommending that R23 in the
regional standard be retired.
3.1. Frequency shall remain above
the Underfrequency Performance
Characteristic curve in PRC‐006‐2
‐ Attachment 1, either for 60
seconds or until a steady‐state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.2. Frequency shall remain below
the Overfrequency Performance
Characteristic curve in PRC‐006‐2
‐ Attachment 1, either for 60
seconds or until a steady‐state
Mapping Document
Project Number and Name | Month Year
25
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
condition between 59.3 Hz and
60.7 Hz is reached, and
3.3. Volts per Hz (V/Hz) shall not
exceed 1.18 per unit for longer
than two seconds cumulatively
per simulated event, and shall not
exceed 1.10 per unit for longer
than 45 seconds cumulatively per
simulated event at each
generator bus and generator
step‐up transformer high‐side bus
associated with each of the
following:
Individual generating units
greater than 20 MVA (gross
nameplate rating) directly
connected to the BES
Generating plants/facilities
greater than 75 MVA (gross
aggregate nameplate rating)
directly connected to the BES
Facilities consisting of one or more units
connected to the BES at a common bus with
Mapping Document
Project Number and Name | Month Year
26
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
total generation above 75 MVA gross
nameplate rating.
Mapping Document
Project Number and Name | Month Year
27
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 13, 2018 through May 29, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
X
Comments: We would like to reiterate a previous comment that we submitted concerning the
difference between the design performance requirement in the NERC continent-wide standard PRC006-2 and what is included in the proposed regional standard PRC-006-2-NPCC-2 and in the existing
NPCC Directory #12.
The NERC continent-wide standard requires that the system frequency be restored to between 59.3
Hz and 60.7 Hz in 60 seconds (60 s / 59.3 Hz & 60 s / 60.7 Hz), following an imbalance that results
in an under-frequency (Requirement R3, Part 3.10). However, both the regional standard and the
directory require the frequency to be restored to above 59.5 Hz in 30 seconds (30 s / 59.5 Hz).
Based on our experiences with the August 2003 Blackout and based on the UFLS assessment
completed by the SS-38 Working Group, Ontario could form islands with portions of the power
system that are not part of NPCC region. Given this and since there is no technical justification for
the existing NPCC performance characteristic of 30 s / 59.5 Hz, we believe the regional standard
should be aligned with the continent-wide standard’s performance characteristic of 60 s / 59.3 Hz.
This would eliminate any potential non-compliance risks that Ontario may face as a result of having
two different performance criteria apply to the same island.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes X
No
Comments: With respect to Sub-requirement 5.4.1., we are not certain that a Distribution
Provider or Transmission Owner will have the required data and capability to perform the
technical study to assess whether their specific deviations from the UFLS requirements will have
a significant adverse impact on the BES. The required data and capability to perform these
types of BES assessments are usually found with the Planning Coordinator.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes X
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes X
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
We are unable to find the rationale for changing the VRF from a HIGH to a MEDIUM for
various requirements (e.g. R12, R15-R18) addressing compensatory load shedding requirements
for generators that are set to trip above the applicable curves in Figure 2. Without knowing the
rationale, we do not support such changes since failing to shed load to compensate for the
additional loss of the tripped generation can lead to total collapse of the island. We recommend
the drafting team reconsider the reliability impact and reinstate these VRFs to HIGH, or provide
the technical justification for such changes.
National Grid Comments – PRC-006-NPCC-2
May 29, 2018
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: National Grid recommends that a technical writer review PRC-006-NPCC-2 for
possible improvements. Please ensure that all aspects of the regional standard conform with the
most recent NERC standards format.
Specific Comments:
Consider changing the Purpose to state: “To establish consistent and coordinated requirements
for the design, implementation, and analysis of automatic underfrequency load shedding (UFLS)
programs among all NPCC Region applicable entities.”
Consider changing the Applicability to state:
4.1 Planning Coordinators
4.2 UFLS entities shall mean all entities that are responsible for the ownership, operation, or
control of UFLS equipment as required by the UFLS program established by the Planning
Coordinators. Such entities may include one or more of the following:
4.2.1 Transmission Owners
4.2.2 Distribution Providers
4.2.3 UFLS-Only Distribution Providers
4.3 Generator Owners
This proposed applicability change will also be reflected in multiple requirements by replacing
Transmission Owners and Distribution Providers with UFLS entities.
Consider changing the Effective Date to state: “See Implementation Plan.”
Consider changing references for this standard from “NERC PRC Standard on UFLS” to “the
continent-wide PRC-006 standard.”
Consider changing from “greater than 30 seconds” to “more than 30 seconds” in Requirement
R1.
Consider consistent use of the comma. (e.g., missing in M1, R4.1, R4.2, etc.)
National Grid Comments – PRC-006-NPCC-2
May 29, 2018
Correct font type for “R4” in Requirement R4.
Please insert “for it Facilities” after the word ‘outage’ in requirement R4, to clarify type of
outages.
Consider changing capitalized “Island” to be lower case “island.” Island is not a NERC Glossary
Term. Please see requirement R4.2.
Consider improvements to the readability of sub-requirements, which are combined with ‘and’ or
‘or’ statements. Separate sub-requirements / alternatives in ‘and’ or ‘or’ statements by use of
semicolons, e.g., before the term “or” between R4.1 and R4.2.
Consider deleting “at least” in “at least once per five calendar years” in Requirement R7.
Consider changing capitalized “Underfrequency” to be lower case “underfrequency” in the
Rationale box for Requirement R7. Underfrequency is not a NERC Glossary defined term.
Consider revising R8 by changing the word “applicable” to “allowable”. As presently written it
appears as if the Planning Coordinator is responsible to develop (specific) settings for inhibit
thresholds.
Correct lay-out (break) in Requirement R13.
Consider ensuring the Compliance section of the standard is in conformance with other NERC
reliability standards. We suggest changing the Compliance Enforcement Authority to be NPCC
as the Regional Entity, instead of the NPCC Compliance Committee.
Consider removing the Guidelines and Technical Basis section in accordance with the NERC
Technical Rationale Transition Plan. A separate document may be required.
Consider adding a Version History section.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments: Consider consistent use of terms “technical study” as used in R5.4.1 and “system
studies” as used in Requirement R3, M1, M5, and M7. Are these terms referring to the same or
different studies?
National Grid Comments – PRC-006-NPCC-2
May 29, 2018
Consider improvements to the readability of sub-requirements, which are combined with ‘and’ or
‘or’ statements. Separate sub-requirements / alternatives in ‘and’ or ‘or’ statements by use of
semicolons, e.g., before the term “or” between R5.3 and R5.4, as well as between R5.4 and
R5.4.2.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments: National Grid recommends dividing R15.3 into two sub-requirements.
Recommended change:
15.3. Each Planning Coordinator in Ontario, Québec and the Maritime Provinces in
accordance with Attachment A shall arrange for compensatory load shedding, as provided by a
UFLS entity that is adequate to compensate for the loss of generator(s) due to early tripping that
is within the UFLS island identified by the Planning Coordinator in Requirement R2.
15.4. Each Generator Owner in the New-England States and in New York State in accordance
with Attachment B shall arrange for compensatory load shedding, as provided by a UFLS entity
that is adequate to compensate for the loss of generator(s) due to early tripping that is within the
UFLS island identified by the Planning Coordinator in Requirement R2.
Requirement R17 would also need to be revised to reference R15.4.
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
National Grid Comments – PRC-006-NPCC-2
May 29, 2018
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comments by Consolidated Edison Co. of New York
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: Con Edison agrees with the proposed revisions as posted. However, Con Edison
believes that, per the Guidelines and Technical Basis section in PRC-006-NPCC-2, “significant
variations” exist that impact the BES and mandate that an updated UFLS assessment be
conducted. The “significant variation” is the inability of generation to ride through high
frequency events. This issue has been highlighted by a NERC Industry Advisory, Turbine
Combustor Lean Blowout, issued June 26, 2008.
Con Edison recommends that a new UFLS assessment be conducted due to reliability concerns
of turbine-generator governor controls and the NPCC Under Frequency Load Shedding Study
results as discussed in this submittal.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments: See comments in section 6. The 1% UFLS tolerance specified in Attachment C
may not provide any additional benefit to the success of an UFLS system.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments: The lack of test performance standards provides no guarantee that turbinegenerators will remain synchronized to the system during a low frequency event. NPCC should
develop a more stringent requirement to test turbine-generators in a manner that verifies the
ability to ride through low frequency conditions, as well as high frequency conditions. This
testing is being developed worldwide. For example, National Grid in the United Kingdom has
Grid Code CO5 that verifies equipment performance and has developed frequency response
markets to provide performance incentives. Equipment testing is the only means of verifying
performance, and if this cannot be done, then assumptions on reliability of turbine-generators
should be more conservative.
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
An UFLS Standard is cost effective if it successfully islands a service area. On November 4th,
2006, Europe experienced an UFLS event and avoided a grid shutdown. The event resulted in
the European breaking up into 3 large grids. Post event, the grids were synchronized back
together in 39 minutes. Only a small percentage of customers were shutdown with minimal
economic impact on the European economy.
In the United States, the opposite occurred in 2003. A cascading outage initiated in the Midwest
caused the northeast portion of the Eastern Interconnection to isolate. The last line of defense
was the UFLS system, and it failed. The subsequent blackout caused a $6B economic impact per
the DOE. By implementing governor testing standards and improved UFLS studies, the
potential for a system wide blackout can be avoided. The money invested in this system is cost
effective as was seen in Europe in 2006.
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: Con Edison respectively adds the following comments.
(1) Requirement 1 references Figure 1 in PRC-006-NPCC. While this figure is based on the
NERC Standard from PRC-006, it is unrealistic. NPCC should develop a more stringent
requirement based on the documented performance of the governor during off frequency
conditions. Note that PRC-024 applies to protection relays, not governor controls. If the
governor controls reduce the fuel to cause flameout, or the steam turbine controls
increase the steam pressure to cause a drum level trip prior to the relay setting, then the
relay setting has minimal value except to protect the plant. If the governor controls work
properly, successful UFLS event is possible.
The figure below shows the response of large frame gas turbines during the 2/26/2008
FRCC System Disturbance. Per the FRCC report, the frequency excursion of 60.6 Hz
resulted in numerous lean blowouts of gas turbines. The NPCC Under Frequency Load
Shedding Study assumes gas turbines will operate reliably at 61.8Hz (1.2 Hz higher than
observed in the Florida event), which is unrealistic. Studies should include the loss of
generation at high frequencies, or limit the UFLS peak frequencies to a lower frequency.
Presently, large frame gas turbines-generators are base load generation commonly used in
combined cycle power plants. The loss of these combined cycle plants will result in a
system collapse and blackout. NPCC should develop more stringent governor test
requirements to support the performance requirements based on Figure 1. It is
recommended that advice from the original equipment manufacturers will provide
benefits; especially on the subject testing and modeling of governors in dynamic load
flows.
(2) PRC-006-NPCC Attachment C, Table 1 provides frequency thresholds, total operating
time, and percent load shed. The load shed tolerances may not be ideal for different
distribution system designs. All distribution systems consist of radial, loop and network
designs. Mandating a tolerance of 1% (7.5%-6.5%) may be appropriate for radial and
loop distribution systems because of the small customer load supply from single or two
area station supplies.
However, a 1% tolerance for network systems is much more challenging since the
customer load supply requires multiple area station supplies (greater than 2). For
example, if a service area has a 10,000MW peak load, with an average network size of
150MW; it is challenging to meet the 100MW tolerance (1% of peak).
DP’s and TO’s with network designs may have to change UFLS set points annually to
meet the 1% tolerance. More important, critical networks (high density populations,
hospitals, transportations hubs) may have to be included in the UFLS program merely to
meet a compliance target requiring a 1% tolerance.
The design basis for a 1% tolerance was the results of an SS38 study in which island
frequencies exceeded 61.8Hz. Since this high frequency is unrealistic as discussed
above, the 1% tolerance should be re-evaluated. More flexible tolerances should be
applied to accommodate different distribution systems. For example, the design change
can include system studies with more frequency thresholds and smaller load shedding
blocks.
3) Lastly, the Data Retention section C.1.3 needs to be updated to reflect the changes in this
latest revision. For example, R7 and M7 apply to Planning Coordinators, but in the Data
Retention section M7 is assigned to DP and TO.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: See question 2 comments
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments: R5.3 Presently states, “If adjustments are possible, make the adjustments
within 180 calendar days…”
Recommend drafting group address in wording direction on if adjustments are possible but it
will take longer than 180 days implement. What steps to take? Develop Implementation Plan
with PC? (This would be for the case where changes/”adjustments” are not just an existing relay
setting change, but may require installation of new relays where the time to implement will be
longer than 180 days (Project funding, design, purchase equipment, installation, testing, etc).
R5.4 presently states, “If adjustments are not possible then:” ………within 180 days provide
its PC with a technical study that demonstrates the deviations from the requirements will not
have a significant adverse impact on the BES.
Recommend drafting group address in wording: Steps if technical study demonstrates the
deviations from the requirements will have a significant adverse impact on the BES.
Should the TO then refer to R15 of the NERC Continent Wide PRC-006-3 Standard, and
develop a Corrective Action Plan and a schedule for implementation with the PC?
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: No comment
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: Proposed Implementation Plan Eversource comment to be provided for this
comment period: My understanding from discussions with the group during the review of
comments in October 2017, is that, If new UFLS Performance analysis identified significant
changes are required to a TO/DP’s UFLS Program (that will take longer than 12 months to
implement), the TO/DP will develop a Implementation Plan with the PC. The Implementation
Plan would fall under R15 of the continent-wide PRC-006 standard. During the review of
comments discussion in October, it was said drafting team will clarify this in 5.1.2, but 5.1.2 is
no longer exists.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
We have a concern with R3 because we are unsure of the rationale for the
requirement. Further, identifying which non-BES generators are critical for supporting the
frequency performance of an island in a non-discriminatory manner could be extremely
difficult, especially since non-BES generators tend to be smaller and potentially more
numerous. We recommend deleting this requirement. ISO New England requires non-BES
generation to meet underfrequency tripping requirements (or the procurement of
compensatory load shedding, if needed) through its tariff and operating procedures.
For R11, we suggest deleting the “or calculating” from the current language to make it read:
For R11, we suggest removing the “or calculating” wording in the requirement or adding “if
measured data is unavailable then calculated data may be used”. Also, the rational for the
requirement doesn’t seem quite right or it may be difficult to put into practice since different
islands may have peaks that occur at different times.
“Each Transmission Owner and Distribution Provider shall annually provide documentation,
with no more than 15 calendar months between updates, to its Planning Coordinator of the
actual net Load that would have been shed by the UFLS relays at each UFLS stage. The
actual net Load shall be coincident with the entity’s integrated hourly peak net Load during
the previous year, as determined by measuring or calculating Load through the switches that
would disconnect load if triggered by the UFLS relays. [Violation Risk Factor: Lower]
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments:
For the wording in Requirement 5, we recommend changing as follows:
“Each Distribution Provider or Transmission Owner that cannot does not meet the tolerances
and/or number of stages and frequency set points specified in the UFLS Program, shall:”
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: While agreeing with the overall proposed revisions there are still some changes
recommended by OPG via the answers to questions number 2, 4 and 6.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments: OPG is of the opinion that some distribution providers with assigned compliance
obligations as per R5 part 5.4 may not have the capability, nor the access to the required
information to perform a study to demonstrate that the specific deviations from the UFLS
requirements will not have a significant adverse impact on the BES. This exercise is more
suitable for the respective Transmission Planner and/or the Reliability Coordinator.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments: OPG is satisfied with R15 final revision, in accordance with the comments
previously provided for additional clarity with respect to the responsible entity for compensatory
load shedding.
Additional revisions of R15 may be required to incorporate the newly proposed revision for
R18, once accepted by the SDT.
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments: OPG is of the opinion that Directory 12 requirements pertaining to the
underfrequency trip settings of the protective relaying are better suited in a regional standard
(i.e. new PRC-024-NPCC-01) or in a regional variance of the standard PRC-024-2 — Generator
Frequency and Voltage Protective Relay Settings, and merely suggest SAR initiation.
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: It appears that for the existing BES the traditional UFLS based only on
frequency thresholds is cost effective for now. It may be possible that with the changes in the
mix of generating resources and grid evolution, in the future this method will no longer be
sufficient/reliable for emergency operating conditions and therefore new protective schemes,
based on frequency derivative, must be developed/implemented. Furthermore these type of
protections can possibly be dynamically adapted to grid configurations (i.e. coupled with widearea phasor measurements to limit or prevent the system from severe disturbances or even
collapses due to delayed response and over shedding).
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: OPG has the following comments:
Auxiliary power supplies located at the nuclear generating plants, driven by nonnuclear prime mover, that are connected to the grid only for the duration of testing,
should be considered non-nuclear units and should be subject to compliance with the
obligations spelled out in requirement # R15 (non-nuclear)
Existing Nuclear Generators that cannot satisfy the condition of maximum 57.8 Hz
imposed by R18 Part 18.1, due to extenuating equipment limitation circumstances, design
and licensing limitations, shall set the underfrequency protection to operate at the
lowest frequency allowed by the existing limitation factors, and communicate the
settings and technical basis to the Planning Coordinator
The standard should also be revised to include requirements for arrangements of adequate
compensatory load shedding, as per Attachment A or B, for the loss of nuclear
generator(s) due to early tripping that is within the UFLS island identified by the PC in
R2. Note This requirements is now missing
OPG believes the reasoning is obvious and is available to provide additional
information/justification if required.
OPG proposed language for R18 is as follows:
R18. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2, based on their licensing design basis, shall: [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
18.1. Set the underfrequency protection to operate at as low a frequency as
possible in accordance with the plant design and licensing limitations but not
greater than 57.8 Hz.
18.2. Each Generator Owner of existing nuclear generating plants that cannot
satisfy the condition of maximum 57.8 Hz imposed by 18.1, due to extenuating
circumstances such as equipment limitations or design and licensing limitations,
shall set the underfrequency protection to operate at the lowest frequency allowed
by the existing limiting factor. Auxiliary power supplies located at the nuclear
generating plants, driven by non-nuclear prime mover, that are connected to the
grid only for the duration of testing, are considered non-nuclear units and are
subject to compliance with the obligations spelled out in requirement # R15.
18.3.
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
18.4. Transmit the initial frequency trip setting, any subsequent changes to the
setting, and the technical basis for the settings to the Planning Coordinator.
18.5 Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces in accordance with Attachment A and each Generator Owner in the
New-England States and in New York State in accordance with Attachment B
shall arrange for compensatory load shedding, as provided by a Distribution
Provider or Transmission Owner that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified by the
Planning Coordinator in Requirement R2
12/6/2019
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PRC-006-NPCC
Regional Standards Committee
Automatic Underfrequency Load Shedding
NPCC BOD Approved
Comment Period (4/16/2018 - 5/31/2018)
Standards
Date
Organization
Non-Standards in Development
05/31/2018
Ontario Power Generation Inc.
View Attachment
Documents
05/31/2018
ISO-New England, Inc.
View Attachment
05/31/2018
Eversource Energy
View Attachment
05/30/2018
Consolidated Edison Company of New York, Inc.
View Attachment
05/30/2018
National Grid
View Attachment
05/29/2018
Independent Electricity System Operator
View Attachment
Standards in Development
05/29/2018
05/16/2018
View Attachment
Liberty Utilities (Granite State Electric), LLC
Comments: We recommend a change in the existing standard due to potential issues we have observed in meeting the
requirements in the past. Because of the site of the Granite States load it has been difficult to stay within the threshold. We
request that the drafting team consider a tolerance band of 5 to 10 MW for table 1. The current tolerance is too low for
entities that have load between 100 to 95. As an example, under table 2 an entity with 50 MW of load must shed in between
7 to 12.5 MW of load, which results in a tolerance band of 5.5 MW. An entity with 100 MW of load must shed 14 to 25 MW of
load, which results in a tolerance band of 11 MW. An entity with 101 MW of load fall under table 1. They must shed between
6.6 MW to 7.6 MW with a tolerance band of 1 MW. A tolerance band of 1 MW is way too tight. Below I provide a table that
shows loads at 50 MW increments to demonstrate the tolerance band. Table 1 (> 100 MW) Table 2 (50 to 100 MW) 0.065
0.075 0.14 0.25 Load MW Tolerance 50 7 12.5 5.50 101 6.57 7.58 1.01 14.14 25.25 11.11 150 9.75 11.25 1.50 21 37.5
16.50 200 13.00 15.00 2.00 28 50 22.00 250 16.25 18.75 2.50 35 62.5 27.50 300 19.50 22.50 3.00 42 75 33.00 350
22.75 26.25 3.50 49 87.5 38.50 400 26.00 30.00 4.00 56 100 44.00 450 29.25 33.75 4.50 63 112.5 49.50 500 32.50
37.50 5.00 70 125 55.00 550 35.75 41.25 5.50 77 137.5 60.50 600 39.00 45.00 6.00 84 150 66.00 650 42.25 48.75 6.50
91 162.5 71.50 700 45.50 52.50 7.00 98 175 77.00 750 48.75 56.25 7.50 105 187.5 82.50 800 52.00 60.00 8.00 112 200
88.00 850 55.25 63.75 8.50 119 212.5 93.50 900 58.50 67.50 9.00 126 225 99.00 950 61.75 71.25 9.50 133 237.5
104.50 1000 65.00 75.00 10.00 140 250 110.00 1050 68.25 78.75 10.50 147 262.5 115.50 1100 71.50 82.50 11.00 154
275 121.00 1150 74.75 86.25 11.50 161 287.5 126.50 1200 78.00 90.00 12.00 168 300 132.00 1250 81.25 93.75 12.50
175 312.5 137.50 1300 84.50 97.50 13.00 182 325 143.00 1350 87.75 101.25 13.50 189 337.5 148.50 1400 91.00 105.00
14.00 196 350 154.00 1450 94.25 108.75 14.50 203 362.5 159.50 1500 97.50 112.50 15.00 210 375 165.00 In addition,
the drafting team may consider clarifying foot note 2 to identify where peak net load is to be measured. Is it the peak net
load as seen by distribution provider or by transmission owner (highside or lowside of transformer)? The changes to section
4.2 implies that DPs and TO’s must coordinate their plan such that the entire plan meets the criteria identified in attachment
C. The rational for this change is not clear to me and therefore we are not sure that we agree with the drafting team.
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1/1
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Standard establishes more stringent and specific NPCC UFLS program requirements to
ensure that declining frequency is arrested and recovered in accordance with established
NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.3. Distribution Providers that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program as established by the
Planning Coordinators.
4.4. Transmission Owners that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program as established by the
Planning Coordinators.
5.
Effective Date:
Reference to Implementation Plan.
B. Requirements
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Note that
Figure 1 also shows the NERC criteria as defined in the NERC PRC Standard on
UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design an
UFLS program having performance characteristics that prevents the frequency from
remaining below 59.5 Hz for greater than 30 seconds in accordance with Figure 1.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or realtime power flow data captured from actual system events and other dated documentation
that demonstrates it meets Requirement R1.
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC PRC Standard on UFLS, to Distribution Providers, Generator Owners, and
Transmission Owners within 30 calendar days of receipt of a request. [Violation Risk Facto
Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
1
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R3. Each Planning Coordinator shall, within 30 calendar days of completion of its UFLS system
studies, identify to the Regional Entity all non-BES generation facilities, within its Planning
Coordinator Area, that must not trip above the appropriate generator underfrequency trip
threshold curve in Figure 2 in order to support UFLS program performance requirements.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
M3. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
R4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall implement an automatic UFLS program, reflecting normal operating
conditions, excluding outages. The automatic UFLS program shall be implemented on an
island basis for each island identified per the NERC PRC Standard on UFLS. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
4.1. The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating times
and load shedding amounts specified in Attachment C, Tables 1 through 3 or,
4.2. The program shall be implemented collectively by multiple Distribution Providers or
Transmission Owners, as long as they reside in the same UFLS Island identified by the
Planning Coordinator per R2. These multiple Distribution Providers or Transmission
Owners, via mutual agreement, shall act as a single entity to provide an aggregated
automatic UFLS program that sheds their coincident peak aggregated net Load
according to the frequency thresholds, total nominal operating time and amounts
specified in Attachment C, Tables 1 through 3.
M4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall have evidence such as documentation or reports containing the location and
amount of load to be tripped in their respective areas, and the corresponding frequency
thresholds, on those circuits included in its UFLS program identified in Requirement R4.
(Attachment C Tables 1-3).
R5. Each Distribution Provider or Transmission Owner that cannot meet the tolerances and/or
number of stages and frequency set points specified in the UFLS Program, shall: [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
5.1. Notify its Planning Coordinator within 30 calendar days of recognition.
5.2. Within the following 90 calendar days, determine if tolerances can be met through
adjustments and notify the Planning Coordinator.
5.3. If adjustments are possible, make the adjustments within 180 calendar days after
determining that adjustments are possible, and notify the Planning Coordinator
when complete, or,
5.4. If adjustments are not possible then:
2
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
5.4.1. Each Distribution Provider or Transmission Owner subject to Attachment C,
Table 1, shall within 180 calendar days, provide its Planning Coordinator with a
technical study that demonstrates that the Distribution Provider’s or Transmission
Owner’s specific deviations from the requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on the BES, or
5.4.2. Each Distribution Provider or Transmission Owner subject to Attachment C,
Table 2 or Table 3, or in the Quebec Interconnection, shall within 90 calendar days,
provide its Planning Coordinator with an analysis demonstrating that no alternative
load shedding solution is available that would allow the Distribution Provider or
Transmission Owner to comply with the UFLS program.
M5. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
Rationale for Requirement R6: Operation of underfrequency relays results directly
in load being shed, interrupting service to customers. The security of underfrequency
relays against misoperation is therefore paramount. The 100 ms minimum time delay
specified in R6 serves to prevent premature activation of these relays during shortlived transient frequency excursions that may occur on a localized basis in the absence
of a serious system event wherein UFLS would be appropriate. This intentional delay
helps to ensure that the relays activate only for frequency excursions that are due to
actual system events that require automatic UFLS to reestablish the balance of
generation to load.
R6. Each Distribution Provider and Transmission Owner shall set each underfrequency relay
that is part of its region’s UFLS program with a 100 ms minimum time delay. [Violation
Risk Factor: Medium] [Time Horizon: Long Term Planning]
M6. Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the minimum
time delay, in accordance with Requirement R6.
Rationale for Requirement R7: An inhibit function provides supervisory control
over a UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay
operation if the sensed voltage decreases below an adjustable setting. An undervoltage
inhibit function is intended to prevent operation of a UFLS relay when the
transmission supply is lost to distribution station feeding many induction motors.
Following loss of the transmission supply, motors may support the voltage while the
motors coast down in speed. The motors coasting down (ringing down) will look like
an Underfrequency event to the relay. The inhibit setting is set to a voltage above
which the motor load is expected to sustain. This prevents the Underfrequency relay
from tripping and locking out distribution feeder breakers supplying the motor load,
between the time the transmission supply line trips and the time when the line recloses
to restore the load. Voltages sustained by motors that are coasting down (e.g. 0.70 pu)
are typically much lower than voltages at which the UFLS relays are required to
3
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
operate to meet UFLS performance criteria. However, motor loads supplied by cable
networks typically have higher ring down voltages because of cable charging.
Therefore, care must be taken so that the voltage inhibit setting is not higher than the
voltage at which UFLS relays are required to operate to meet UFLS performance
criteria.
R7. Each Planning Coordinator shall develop and review settings for inhibit thresholds at least
once per five calendar years (such as but not limited to voltage, current and time) to be
utilized within its region’s UFLS program. [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
M7. Each Planning Coordinator shall have evidence such as reports, system studies or analysis
that demonstrates that it meets Requirement R7.
R8. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon: Operations
Planning]
M8. Each Planning Coordinator shall provide evidence such as letters, emails, or other dated
documentation that demonstrates that it meets Requirement R8.
R9. Each Distribution Provider and Transmission Owner that receives a notification pursuant to
Requirement R8 shall develop and submit an implementation plan for approval by the
Planning Coordinator within 90 calendar days of the request from the Planning Coordinator.
[Violation Risk Factor: Lower] [Time Horizon: Operations Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as letters,
emails, or other dated documentation that demonstrates that it meets Requirement R9.
R10. Each Distribution Provider and Transmission Owner shall implement the inhibit threshold
settings provided by the Planning Coordinator in accordance with Requirement R8 and
based on the Planning Coordinator approved implementation plan in accordance with R9.
[Violation Risk Factor: High] [Time Horizon: Operations Planning]
M10. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that demonstrates that
it meets Requirement R10.
Rationale for Requirement R11: It is recognized that, ideally, the amount of load to
be shed in each stage of the UFLS program for every entity should perfectly match
that prescribed in this Standard, for all phases of the load cycle, i.e., seasonal (summer
vs. winter), weekly (weekday vs. weekend vs. holidays), daily (morning, noon, and
night), etc. for all of the identified islands. Practically, however, this is obviously not
possible because the load cycles of the various areas and sub-areas within any given
island do not perfectly track the load cycle of the overall island. The UFLS program,
4
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
on the other hand, is designed based on peak conditions for the overall island. The
percentages of actual load shedding that would occur for any conditions other than
peak, therefore, can only approximate that prescribed in the Standard. This being
said, entities are required by R11 to document measured loads in the UFLS program
coincident with their own annual peak, whether or not that peak occurs at the same
time or in the same season as the peak of the identified island in which their load
resides. Using individual entity peaks vs. overall island peaks provides a consistent
approach for accounting purposes among the very entities that are responsible for
designing and maintaining their UFLS programs.
R11. Each Transmission Owner and Distribution Provider shall annually provide documentation,
with no more than 15 calendar months between updates, to its Planning Coordinator of the
actual net Load that would have been shed by the UFLS relays at each UFLS stage. The
actual net Load shall be coincident with the entity’s integrated hourly peak net Load during
the previous year, as determined by measuring or calculating Load through the switches
that would disconnect load if triggered by the UFLS relays. [Violation Risk Factor: Lower]
[Time Horizon: Long Term Planning]
M11. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning Coordinator
that indicates the frequency set point, the net amount of load shed and the percentage of its
peak load at each stage of its UFLS program to demonstrate that it meets Requirement
R11.
R12. Each Generator Owner shall set each generator underfrequency trip relay, if so equipped,
on or below the appropriate generator underfrequency trip protection settings threshold
curve in Figure 2, except as otherwise exempted in Requirements R15 and R18. [Violation
Risk Factor: Medium] [Time Horizon: Long Term Planning]
M12. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets or
other documentation that demonstrates that it meets Requirement R12.
R13. Each Generator Owner shall transmit the generator underfrequency trip setting and time
delay within 45 calendar days of the Planning Coordinator’s
request.
[Violation Risk Factor: Lower] [Time Horizon: Operations Planning]
M13. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R13.
R14. Each Generator Owner with a new generating unit, or an existing generator increasing its
net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time Horizon:
Long Term Planning]
5
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
14.1. Design measures to prevent the generating unit from tripping directly or indirectly
for underfrequency conditions above the appropriate generator tripping threshold
curve in Figure 2.
14.2. Design auxiliary system(s) or devices used for the control and protection of
auxiliary system(s), necessary for the generating unit operation such that they will
not trip the generating unit during underfrequency conditions above the appropriate
generator underfrequency trip protection settings threshold curve in Figure 2.
M14. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement R14.
R15. For existing non-nuclear units in service prior to the effective date of this standard, as
documented in accordance with Attachments A or B, that have underfrequency protections
set to trip above the appropriate curve in Figure 2: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
15.1. Each Generator Owner shall set the underfrequency protection to operate at the
lowest frequency allowed by the plant design and licensing limitations.
15.2. Each Generator Owner shall transmit the existing underfrequency settings and any
changes to the underfrequency settings along with the technical basis for the
settings to the Planning Coordinator.
15.3. Each Planning Coordinator in Ontario, Québec and the Maritime Provinces in
accordance with Attachment A and each Generator Owner in the New-England
States and in New York State in accordance with Attachment B shall arrange for
compensatory load shedding, as provided by a Distribution Provider or
Transmission Owner that is adequate to compensate for the loss of generator(s) due
to early tripping that is within the UFLS island identified by the Planning
Coordinator in Requirement R2.
M15. Each Generator Owner with existing non-nuclear units in service prior to the effective date
of this Standard which have underfrequency tripping that is not compliant with
Requirement R12shall provide evidence such as reports, spreadsheets, memorandum or
dated documentation demonstrating that it meets Requirement R15.
R16. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply the
criteria described in Attachment A to determine the compensatory load shedding that is
required in Requirement R15.3 for generating units in its respective NPCC area. [Violation
Risk Factor: Medium] [Time Horizon: Long Term Planning]
M16. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall provide
evidence such asreports, memorandum or other documentation that demonstrates that it
followed the methodology described in Attachment A and meets Requirement R16.
R17. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the New York ISO shall apply the criteria described in
Attachment B to determine the compensatory load shedding that is required in Requirement
6
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R15.3 for generating units in its respective NPCC area. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M17. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the New York ISO shall provide evidence such as reports,
memorandum, or other documentation that demonstrates that it followed the methodology
described in Attachment B and meets Requirement R17.
R18. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2, based on their licensing design basis, shall: [Violation Risk
Factor: Medium] [Time Horizon: Long Term Planning]
18.1.
18.2.
18.3.
Set the underfrequency protection to operate at as low a frequency as possible in
accordance with the plant design and licensing limitations but not greater than
57.8 Hz.
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
M18. Each Generator Owner of nuclear units that have been specifically identified by NPCC as
having generator trip settings above the generator trip curve in Figure 2 shall provide
evidence such as letters, reports and dated documentation that demonstrates that it meets
Requirement R18.
7
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 1
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
8
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
Time (sec)
9
1000
55.5
55
10000
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority
NPCC Compliance Committee
1.2. Compliance Monitoring Period and Reset Time Frame
Not Applicable
1.3. Data Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 4, 5, 6,7,10, 11, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 3, 8, 9, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall
keep evidence for three calendar years for Measure 17.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 18, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
13, 14, 15, 16, and 19.
1.4. Compliance Monitoring and Assessment Processes
Self -Certifications.
Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.
1.5. Additional Compliance Information
None.
2.
10
Violation Severity Levels
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Requirement
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1
N/A
N/A
N/A
The Plannning
Coordinator failed to
design an UFLS program
having performance
characteristics that
prevent frequency from
remaining below 59.5 Hz
in accordance with Figure
1.
R2
The
Planning
Coordinator provided
its
UFLS
island
boundaries,
as
identified per the
NERC PRC Standard
on UFLS but did so
more than 30 calendar
days and up to and
including 40 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC PRC Standard
on UFLS but did so
more than 40 calendar
days but less than and
including 50 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC PRC Standard
on UFLS but did so
more than 50 calendar
days but less than and
including 60 days
following a request.
The Planning Coordinator
failed to provide its UFLS
island boundaries, as
identified per the NERC
PRC Standard on UFLS.
within 60 calendar days
following a request.
R3
The Planning
Coordinator identified
to the Regional Entity
all non-BES
generation facilities
within its Planning
Coordinator Area that
must not trip above
the appropriate
generator
underfrequency trip
threshold curve in
order to support
UFLS program
performance
requirements, but did
so more than 30
calendar daysand up
to and including 40
days after completion
of the system studies.
The Planning
Coordinator identified
to the Regional Entity
all non-BES generation
facilities within its
Planning Coordinator
Area that must not trip
above the appropriate
generator
underfrequency trip
threshold curve in order
to support the UFLS
program performance
requirements, but did so
more than 40 days but
less than calendar days
but less than and
including 50 days after
completion of the
system studies.
The Planning
Coordinator identified
to the Regional Entity
all non-BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in
order to support the
UFLS program
performance
requirements,, but did
so more than 50
calendar days but less
than and including 60
days after completion
of the system studies.
The Planning Coordinator
identified all non-BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in order to
support the UFLS
program performance
requirements, but failed to
inform the Regional
Entity within 60 calendar
days after completion of
the system studies.
11
OR
The Planning Coordinator
did not identify the BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in order
to supportUFLS program
performance
requirements.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
The Distribution
Provider or Transmission
Owner failed to
implement the automatic
UFLS program on an
island basis as specified
by Requirement R4, Part
4.1 or Part 4.2.
R4
R5
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations ir
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the
4 items by a period of
up to 10 calendar days
but less than or equal
to 20 calendar days.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations ir
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the 4
items within a time
greater than 20 calendar
days but less than or
equal to 30 calendar
days.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations but
exceeded the
permissible time
frame for one or more
of the 4 items within
a time greater than 30
calendar days but less
than or equal to 60
calendar days.
The Distribution
Provider or Transmission
Owner that cannot meet
the tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program failed to meet
all of items in
Requirement 5 within 60
calendar days of
permissible time for each
item.
R6
The Distribution
Provider or
Transmission Owner
set less than 100% but
more than (and
including) 95% of its
underfrequency relays
that are part of its
region’s UFLS
program with a 100 ms
minimum time delay.
The Distribution
Provider or
Transmission Owner
set less than 95% but
more than (and
including) 90% of its
underfrequency relays
that are part of its
region’s UFLS program
with a 100 ms
minimum time delay.
The Distribution
Provider or
Transmission Owner
set less than 90% but
more than (and
including) 85% of its
underfrequency relays
that are part of its
region’s UFLS
program with a 100
ms minimum time
delay.
The Distribution
Provider or Transmission
Owner set less than 85%
ot its underfrequency
relays that are part of its
region’s UFLS program
with a 100 ms minimum
time delay.
R7
The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 100% but more
than (and including)
95% of relays within
its region’s UFLS
program.
The Planning
Coordinator
developed or reviewed
settings for inhibit
thresholds at least
once per five calendar
years, for less than
95% but more than
(and including) 90%
of relays within its
region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 90% but more
than (and including)
85% of relays within
its region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 85%
of relays within its
region’s UFLS program.
12
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R8
The Planning
Coordinator provided
to a Transmission
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds more
than 30 calendar days
and up to and
including 40 calendar
days of any changes.
The Planning
Coordinator provided to
a Transmission Owner
or Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds more than 40
calendar daysbut less
than and including 50
calendar days of any
changes.
The Planning
Coordinator provided
to a Transmission
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds
more than 50 calendar
daysbut less than and
including 60 calendar
days of any changes.
The Planning
Coordinator failed to
provide to a
Transmission Owner or
Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds within 60
calendar days after any
changes
R9
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 90 calendar
days and up to and
including 100
calendar days
following the request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 100 calendar
days and up to and
including 110 calendar
days following the
request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 110
calendar days and up
to and including 120
calendar days
following the request.
The Distribution
Provider or Transmission
Owner failed to develop
and submit its
implementation plan
within 120 days
following the request.
R10
implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 100%
but more than (and
including) 95% of
UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by the
Planning Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 95% but more
than (and including)
90% of UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 90% but
more than (and
including) 85 % of
UFLS relays.
The Distribution
Provider or Transmission
Owner implemented the
inhibit threshold settings
provided by the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 85 % of UFLS
relays.
R11
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 15 calendar
months but less than
The Distribution
Provider or
Transmission Owner
provided to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11 more
than 16 calendar
months but less than
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 17 calendar
months but less than
The Distribution
Provider or Transmission
Owner failed to provide
to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
within 18 calendar
months since last update.
13
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
(and including) 16
calendar months since
last update.
(and including)17
calendar months since
last update.
(and including)18
calendar months since
last update.
R12
N/A
N/A
N/A
The Generator Owner
did not set each
generator
underfrequency trip
relay, if so equipped, on
or below the appropriate
generator
underfrequency trip
protection settings
threshold curve in Figure
2, except as otherwise
exempted.
R13
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 45calendar
days and less than (and
including) 55 calendar
days of the Planning
Coordinator’s request.
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 55 calendar
days and less than (and
including) 65 calendar
days of the Planning
Coordinator’s request.
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 65 calendar
days and less than
(and including) 75
calendar days of the
Planning
Coordinator’s request.
The Generator Owner
failed to transmit the
generator
underfrequency trip
setting and time delay
within 75 calendar days
of the Planning
Coordinator’s request.
R14
N/A
N/A
The Generator Owner
with a new generating
unit, or an existing
generator increasing
its net capability by
greater than 10%:
The Generator Owner
with a new generating
unit, or an existing
generator increasing its
net capability by greater
than 10%, did not fulfill
the obligations of
Requirement R15, Part
15.1 and Part 15.2.
Did not: fulfill the
obligation of
Requirement R14;
Part 14.1
OR
Did not fulfill the
obligation of
Requirement R14,
Part 14.2.
R15
14
N/A
The Generator Owner
failed to transmit the
existing underfrequency
settings and any
changes to the
underfrequency settings
along with the technical
basis for the settings to
The Generator Owner
failed to set the
underfrequency
protection to operate at
the lowest frequency
allowed by the plant
design and licensing
limitations a specified
The Planning
Coordinator in Ontario,
Québec and the
Maritime Provinces or
the Generator Owner in
the New-England States
and in New York State
failed to arrange for
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
the Planning
Coordinator.as
specified in
Requirement R15, Part
15.2.
in Requirment 15, Part
15.1
compensatory load
shedding as specified in
Requirement R15, Part
15.3.
R16
N/A
N/A
N/A
The Planning
Coordinator did not
apply the methodology
described in Attachment
A to determine the
compensatory load
shedding that is required.
R17
N/A
N/A
N/A
The Generator Owner,
Distribution Provider, or
Transmission Owner did
not apply the
methodology described
in Attachment B to
determine the
compensatory load
shedding that is required.
R18
N/A
The Generator Owner
failed to transmit the
initial frequency trip
setting and any changes
to the setting and the
technical basis for the
settings to the Planning
Coordinator as
specified in
Requirement R18, Part
18.3.
The Generator Owner:
The Generator Owner
did not fulfill the
obligations of
Requirement R18, Part
18.1 and Part 18.2.
15
Failed to set the
underfrequency
protection as specified
in Requirement R18;
Part 18.1
OR
Failed to set the
frequency trip setting
upper tolerance as
specified in
Requirement R18, Part
18.2.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 2.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all UFLS islands in which the unit may operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units, in their Planning Coordinator area, in service prior to the
effective date of Version 1 of the regional Standard (April, 2017 PRC-006-NPCC-1).
The list must indicate generating units, if any, that have their underfrequency protections
set to trip above the appropriate curve in Figure 2. Generating Units not appearing on the
list as of the effective date of Version 1 of the regional standard, as shown above, must
have their Underfrequency protections set to trip on or below the appropriate curve in
Figure 2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS
relays within the island(s) identified by the Planning Coordinator within which
the generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that is
provided by the Distribution Provider or Transmission Owner shall be in addition
to the amount that the Distribution Provider or Transmission Owner is required to
shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 2 during an underfrequency event. If the highest
16
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
frequency at which the subject generator will trip above the appropriate curve in
Figure 2 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
17
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units in service prior to the effective date of Version 1 of the regional
Standard (April, 2017 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, that have their underfrequency protections set to trip above the
appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2. The
list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 2, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the smallest island identified by the Planning Coordinator in
Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 2, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
18
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
19
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
Frequency Threshold
(Hz)
Total Nominal
Operating
Time (s)1
Load Shed at Stage as %
of TO or DP Load
Cumulative Load Shed as
% of TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
27.5 – 28.5
59.5
10.0
2
–3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
20
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating
Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50
MW2 of peak net Load shall implement a UFLS program with the following attributes:
21
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Guidelines and Technical Basis:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
22
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
Generator dynamic modeling
Dynamic VAR device modeling
HVDC dynamic modeling
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-1
3.
Purpose: The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Standard establishes more stringent and specific NPCC UFLS program requirements to
ensure that declining frequency is arrested and recovered in accordance with established
NPCC performance requirements stipulated in this documentTo provide a regional
reliability standard that ensures the development of an effective automatic
underfrequency load shedding (UFLS) program in order to preserve the security and
integrity of the bulk power system during declining system frequency events in
coordination with the NERC UFLS reliability standard characteristics.
4.
Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.3. Distribution Provider that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program as established by the
Planning Coordinators.
4.4. Transmission Owner that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program as established by the Planning
Coordinators.
5.
Effective Date:
Reference to Implementation Plan For the Eastern Interconnection & Québec
Interconnection portions of NPCC excluding the Independent Electricity System
Operator (IESO) Planning Coordinator area of NPCC in Ontario, Canada:
The effective date for Requirements R1, R2, R3, R4, R5, R6, and R7 is the first
day of the first calendar quarter following applicable regulatory approval but no
earlier than January 1, 2016 The effective date for Requirements R8 through R23
is the first day of the first calendar quarter two years following applicable
governmental and regulatory approval.
For the Independent Electricity System Operator (IESO) Planning Coordinator’s area of
NPCC in Ontario, Canada:
All requirements are effective the first day of the first calendar quarter following
applicable governmental and regulatory approval but no earlier than April 1,
2017.
B. Requirements
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
1
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
underfrequency criteria for the Eastern Interconnection portion of NPCC. Note that
Figure 1 also shows the NERC criteria as defined in the NERC PRC Standard on
UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design an
UFLS program having performance characteristics that prevents the frequency from remaining
below 59.5 Hz for greater than 30 seconds in accordance with Figure 1. [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
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M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or realtime power flow data captured from actual system events and other dated documentation that
demonstrates it meets Requirement R1
R1
Each Planning Coordinator shall establish
requirements for entities aggregating their UFLS programs for each anticipated island and
requirements for compensatory load shedding based on islanding criteria (required by the NERC
PRC Standard on UFLS). [Violation Risk Factor: Medium] [Time Horizon: Long Term
Planning]
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R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC PRC Standard on UFLS, to Distribution Providers, Generator Owners, and Transmission
Owners within 30 calendar days of receipt of a request. [Violation Risk Factor Lower] [Time
Horizon: Long Term Planning]
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M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
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R2
Each Planning Coordinator shall, within 30 days of completion of its system studies
required by the NERC PRC Standard on UFLS, identify to the Regional Entity the generation
facilities within its Planning Coordinator Area necessary to support the UFLS program
performance characteristics. [Violation Risk Factor: Medium] [Time Horizon: Long Term
Planning]
R3. Each Planning Coordinator shall, within 30 calendar days of completion of its UFLS system
studies, identify to the Regional Entity all non-BES generation facilities, within its Planning
Coordinator Area, that must not trip above the appropriate generator underfrequency trip
threshold curve in Figure 2 in order to support UFLS program performance requirements.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
M3. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3
R4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall implement an automatic UFLS program, reflecting normal operating conditions,
excluding outages. The automatic UFLS program shall be implemented on an island basis for
2
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
each island identified per the NERC PRC Standard on UFLS. [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
4.1. The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating times
and load shedding amounts specified in Attachment C, Tables 1 through 3 or,
4.2. The program shall be implemented collectively by multiple Distribution Providers or
Transmission Owners, as long as they reside in the same UFLS Island identified by the
Planning Coordinator per R2. These multiple Distribution Providers or Transmission
Owners, via mutual agreement, shall act as a single entity to provide an aggregated
automatic UFLS program that sheds their coincident peak aggregated net Load
according to the frequency thresholds, total nominal operating time and amounts
specified in Attachment C, Tables 1 through 3
R3 Each Planning Coordinator shall provide to the Transmission Owner, Distribution
Provider, and Generator Owner within 30 days upon written request the requirements
for entities aggregating the UFLS programs and requirements for compensatory load
shedding program derived from each Planning Coordinator’s system studies as
determined by Requirement R1. [Violation Risk Factor: Low] [Time Horizon: Long
Term Planning]
M4. Each Distribution Provider and Transmission Owner in the Eastern Interconnection portion
of NPCC shall have evidence such as documentation or reports containing the location and
amount of load to be tripped in their respective areas, and the corresponding frequency
thresholds, on those circuits included in its UFLS program identified in Requirement R4.
(Attachment C Tables 1-3).R4
Each Distribution Provider and Transmission Owner in the
Eastern Interconnection portion of NPCC shall implement an automatic UFLS program
reflecting normal operating conditions excluding outages for its Facilities based on frequency
thresholds, total nominal operating time and amounts specified in Attachment C, Tables 1
through 3, or shall collectively implement by mutual agreement with one or more Distribution
Providers and Transmission Owners within the same island identified in Requirement R1 and
acting as a single entity, provide an aggregated automatic UFLS program that sheds their
coincident peak aggregated net Load, based on frequency thresholds, total nominal operating
time and amounts specified in Attachment C, Tables 1 through 3.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
R5. Each Distribution Provider or Transmission Owner that cannot meet the tolerances and/or
number of stages and frequency set points specified in the UFLS Program, shall: [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
5.1. Notify its Planning Coordinator within 30 calendar days of recognition.
5.2. Within the following 90 calendar days, determine if tolerances can be met through
adjustments and notify the Planning Coordinator.
3
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
5.3. If adjustments are possible, make the adjustments within 180 calendar days after
determining that adjustments are possible, and notify the Planning Coordinator
when complete, or,
5.4. If adjustments are not possible then:
5.4.1. Each Distribution Provider or Transmission Owner subject to Attachment C,
Table 1, shall within 180 calendar days, provide its Planning Coordinator with a
technical study that demonstrates that the Distribution Provider’s or Transmission
Owner’s specific deviations from the requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on the BES, or
5.4.2. Each Distribution Provider or Transmission Owner subject to Attachment C,
Table 2 or Table 3, or in the Quebec Interconnection, shall within 90 calendar days,
provide its Planning Coordinator with an analysis demonstrating that no alternative
load shedding solution is available that would allow the Distribution Provider or
Transmission Owner to comply with the UFLS program.
M5. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets Requirement
R5.
R5
Each Distribution Provider or Transmission Owner that must arm its load to trip on
underfrequency in order to meet its requirements as specified and by doing so exceeds the
tolerances and/or deviates from the number of stages and frequency set points of the UFLS
program as specified in the tables contained in Requirement R4 above, as applicable depending
on its total peak net Load shall: [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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0"
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Rationale for Requirement R6: Operation of underfrequency relays results directly
in load being shed, interrupting service to customers. The security of underfrequency
relays against misoperation is therefore paramount. The 100 ms minimum time delay
specified in R6 serves to prevent premature activation of these relays during shortlived transient frequency excursions that may occur on a localized basis in the absence
of a serious system event wherein UFLS would be appropriate. This intentional delay
helps to ensure that the relays activate only for frequency excursions that are due to
actual system events that require automatic UFLS to reestablish the balance of
generation to load.
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R6. Each Distribution Provider and Transmission Owner shall set each underfrequency relay
that is part of its region’s UFLS program with a 100 ms minimum time delay. [Violation
Risk Factor: Medium] [Time Horizon: Long Term Planning]
M6. Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the minimum
4
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
time delay, in accordance with Requirement R6.5.1 Inform its Planning Coordinator of the need
to exceed the stated tolerances or the number of stages as shown in UFLS Attachment C,
Table 1 if applicable and
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5.2
Provide its Planning Coordinator with a technical study that
demonstrates that the Distribution Providers or Transmission Owners specific deviations from
the requirements of UFLS Attachment C, Table 1 will not have a significant adverse impact on
the bulk power system.
5.3
Inform its Planning Coordinator of the need to exceed the stated tolerances of UFLS
Attachment C, Table 2 or Table 3, and in the case of Attachment C, Table 2 only, the need to
deviate from providing two stages of UFLS, if applicable, and
5.4
Provide its Planning Coordinator with an analysis demonstrating that no alternative load
shedding solution is available that would allow the Distribution Provider or Transmission Owner
to comply with UFLS Attachment C Table 2 or Attachment C Table 3.
R6 Each Distribution Provider and Transmission Owner in the Québec Interconnection portion
of NPCC shall implement an automatic UFLS program for its Facilities based on the frequency
thresholds, slopes, total nominal operating time and amounts specified in Attachment C, Table 4
or shall collectively implement by mutual agreement with one or more Distribution Providers
and Transmission Owners within the same island, identified in Requirement R1, an aggregated
automatic UFLS program that sheds Load based on the frequency thresholds, slopes, total
nominal operating time and amounts specified in Attachment C, Table 4. [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
Rationale for Requirement R7: An inhibit function provides supervisory control
over a UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay
operation if the sensed voltage decreases below an adjustable setting. An undervoltage
inhibit function is intended to prevent operation of a UFLS relay when the
transmission supply is lost to distribution station feeding many induction motors.
Following loss of the transmission supply, motors may support the voltage while the
motors coast down in speed. The motors coasting down (ringing down) will look like
an Underfrequency event to the relay. The inhibit setting is set to a voltage above
which the motor load is expected to sustain. This prevents the Underfrequency relay
from tripping and locking out distribution feeder breakers supplying the motor load,
between the time the transmission supply line trips and the time when the line recloses
to restore the load. Voltages sustained by motors that are coasting down (e.g. 0.70 pu)
are typically much lower than voltages at which the UFLS relays are required to
operate to meet UFLS performance criteria. However, motor loads supplied by cable
5
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
networks typically have higher ring down voltages because of cable charging.
Therefore, care must be taken so that the voltage inhibit setting is not higher than the
voltage at which UFLS relays are required to operate to meet UFLS performance
criteria.
R7. Each Planning Coordinator shall develop and review settings for inhibit thresholds at least
once per five calendar years (such as but not limited to voltage, current and time) to be utilized
within its region’s UFLS program. [Violation Risk Factor: Medium] [Time Horizon: Long Term
Planning]
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M7. Each Planning Coordinator shall have evidence such as reports, system studies or analysis
that demonstrates that it meets Requirement R7.
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R8. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon: Operations
Planning]
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M8. Each Planning Coordinator shall provide evidence such as letters, emails, or other dated
documentation that demonstrates that it meets Requirement R8.
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R9. Each Distribution Provider and Transmission Owner that receives a notification pursuant to
Requirement R8 shall develop and submit an implementation plan for approval by the Planning
Coordinator within 90 calendar days of the request from the Planning Coordinator. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as letters,
emails, or other dated documentation that demonstrates that it meets Requirement R9.
R7
Each Distribution Provider and Transmission Owner shall set each
underfrequency relay that is part of its region’s UFLS program with the following minimum
time delay:
7.1
Eastern Interconnection – 100 ms
7.2
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Québec Interconnection – 200 ms
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R8 Each Planning Coordinator shall develop and review once per calendar year settings for
inhibit thresholds (such as but not limited to voltage, current and time) to be utilized within
its region's UFLS program. [Violation Risk Factor: Medium] [Time Horizon: Long Term
Planning]
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Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9 Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30 days
of the initial determination of those inhibit thresholds and within 30 days of any changes to
those thresholds. [Violation Risk Factor: Medium] [Time Horizon: Operations Planning]
R10. Each Distribution Provider and Transmission Owner shall implement the inhibit threshold
settings provided by the Planning Coordinator in accordance with Requirement R8 and based on
the Planning Coordinator approved implementation plan in accordance with R9.
[Violation Risk Factor: High] [Time Horizon: Operations Planning]
M10. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that demonstrates that it
meets Requirement R10.
R10 Each Distribution Provider and Transmission Owner shall implement the inhibit
threshold settings based on the notification provided by the Planning Coordinator in accordance
with Requirement R9. [Violation Risk Factor: High] [Time Horizon: Operations Planning]
Rationale for Requirement R11: It is recognized that, ideally, the amount of load to
be shed in each stage of the UFLS program for every entity should perfectly match
that prescribed in this Standard, for all phases of the load cycle, i.e., seasonal (summer
vs. winter), weekly (weekday vs. weekend vs. holidays), daily (morning, noon, and
night), etc. for all of the identified islands. Practically, however, this is obviously not
possible because the load cycles of the various areas and sub-areas within any given
island do not perfectly track the load cycle of the overall island. The UFLS program,
on the other hand, is designed based on peak conditions for the overall island. The
percentages of actual load shedding that would occur for any conditions other than
peak, therefore, can only approximate that prescribed in the Standard. This being
said, entities are required by R11 to document measured loads in the UFLS program
coincident with their own annual peak, whether or not that peak occurs at the same
time or in the same season as the peak of the identified island in which their load
resides. Using individual entity peaks vs. overall island peaks provides a consistent
approach for accounting purposes among the very entities that are responsible for
designing and maintaining their UFLS programs.
R11. Each Transmission Owner and Distribution Provider shall annually provide documentation,
with no more than 15 calendar months between updates, to its Planning Coordinator of the
actual net Load that would have been shed by the UFLS relays at each UFLS stage. The
actual net Load shall be coincident with the entity’s integrated hourly peak net Load during
the previous year, as determined by measuring or calculating Load through the switches
that would disconnect load if triggered by the UFLS relays. [Violation Risk Factor: Lower]
7
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
[Time Horizon: Long Term Planning]R11
Each Distribution Provider and
Transmission Owner shall develop and submit an implementation plan within 90 days
of the request from the Planning Coordinator for approval by the Planning Coordinator
in accordance with R9. [Violation Risk Factor: Lower] [Time Horizon: Operations
Planning]
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M11. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning Coordinator
that indicates the frequency set point, the net amount of load shed and the percentage of its
peak load at each stage of its UFLS program to demonstrate that it meets Requirement
R11.
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R12. Each Generator Owner shall set each generator underfrequency trip relay, if so equipped,
on or below the appropriate generator underfrequency trip protection settings threshold
curve in Figure 2, except as otherwise exempted in Requirements R15 and R18. [Violation
Risk Factor: Medium] [Time Horizon: Long Term Planning]
M12. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets or
other documentation that demonstrates that it meets Requirement R12.
R13. Each Generator Owner shall transmit the generator underfrequency trip setting and time
delay within 45 calendar days of the Planning Coordinator’s
request. [Violation Risk Factor: Lower] [Time Horizon: Operations Planning]
R12 Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 months between updates, to its Planning
Coordinator of the actual net Load that would have been shed by the UFLS relays at
each UFLS stage coincident with their integrated hourly peak net Load during the
previous year, as determined by measuring actual metered Load through the switches
that would be opened by the UFLS relays. [Violation Risk Factor: Lower] [Time
Horizon: Long Term Planning]
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M13. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R13.
R14. Each Generator Owner with a new generating unit, or an existing generator increasing its
net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time Horizon:
Long Term Planning]
14.1. Design measures to prevent the generating unit from tripping directly or indirectly for
underfrequency conditions above the appropriate generator tripping threshold curve in
Figure 2.
14.2. Design auxiliary system(s) or devices used for the control and protection of auxiliary
system(s), necessary for the generating unit operation such that they will not trip the
generating unit during underfrequency conditions above the appropriate generator
underfrequency trip protection settings threshold curve in Figure 2.R13 Each
Generator Owner shall set each generator underfrequency trip relay, if so equipped,
8
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
below the appropriate generator underfrequency trip protection settings threshold curve
in Figure 1, except as otherwise exempted in Requirements R16 and R19. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
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R14 Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay to its Planning Coordinator within 45 days of the Planning Coordinator’s
request. [Violation Risk Factor: High] [Time Horizon: Operations Planning]
M14. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement R14.
R15. For existing non-nuclear units in service prior to the effective date of this standard, as
documented in accordance with Attachments A or B, that have underfrequency protections
set to trip above the appropriate curve in Figure 2: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
15.1. Each Generator Owner shall set the underfrequency protection to operate at the
lowest frequency allowed by the plant design and licensing limitations.
15.2. Each Generator Owner shall transmit the existing underfrequency settings and any
changes to the underfrequency settings along with the technical basis for the
settings to the Planning Coordinator.
15.3. Each Planning Coordinator in Ontario, Québec and the Maritime Provinces in
accordance with Attachment A and each Generator Owner in the New-England
States and in New York State in accordance with Attachment B shall arrange for
compensatory load shedding, as provided by a Distribution Provider or
Transmission Owner that is adequate to compensate for the loss of generator(s) due
to early tripping that is within the UFLS island identified by the Planning
Coordinator in Requirement R2
M15. Each Generator Owner with existing non-nuclear units in service prior to the effective date
of this Standard which have underfrequency tripping that is not compliant with
Requirement R12shall provide evidence such as reports, spreadsheets, memorandum or
dated documentation demonstrating that it meets Requirement R15.R15
Each
Generator Owner with a new generating unit, scheduled to be in service on or after the
effective date of this Standard, or an existing generator increasing its net capability by
greater than 10% shall: [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
15.1 Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate generator
tripping threshold curve in Figure 1.
9
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
15.2 Design auxiliary system(s) or devices used for the control and protection of
auxiliary system(s), necessary for the generating unit operation such that
they will not trip the generating unit during underfrequency conditions
above the appropriate generator underfrequency trip protection settings
threshold curve in Figure 1.
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R16 Each Generator Owner of existing non-nuclear units in service prior to the effective
date of this standard that have underfrequency protections set to trip above the
appropriate curve in Figure 1 shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
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16.1 Set the underfrequency protection to operate at the lowest frequency allowed by the
plant design and licensing limitations.
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16.2 Transmit the existing underfrequency settings and any changes to the underfrequency
settings along with the technical basis for the settings to the Planning Coordinator.
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16.3 Have compensatory load shedding, as provided by a Distribution Provider or
Transmission Owner that is adequate to compensate for the loss of their generator due
to early tripping.
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R17 Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R16.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R16. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply the
criteria described in Attachment A to determine the compensatory load shedding that is
required in Requirement R15.3 for generating units in its respective NPCC area. [Violation
Risk Factor: Medium] [Time Horizon: Long Term Planning]
M16. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall provide
evidence such asreports, memorandum or other documentation that demonstrates that it
followed the methodology described in Attachment A and meets Requirement R16.
R17. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the New York ISO shall apply the criteria described in
Attachment B to determine the compensatory load shedding that is required in Requirement
R15.3 for generating units in its respective NPCC area. [Violation Risk Factor: Medium]
10
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
[Time Horizon: Long Term Planning]
M17. Each Generator Owner, Distribution Provider or Transmission Owner within the Planning
Coordinator area of ISO-NE or the New York ISO shall provide evidence such as reports,
memorandum, or other documentation that demonstrates that it followed the methodology
described in Attachment B and meets Requirement R17.
R18. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2, based on their licensing design basis, shall: [Violation Risk
Factor: Medium] [Time Horizon: Long Term Planning]
18.1.
18.2.
18.3.
Set the underfrequency protection to operate at as low a frequency as possible in
accordance with the plant design and licensing limitations but not greater than
57.8 Hz.
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
M18. Each Generator Owner of nuclear units that have been specifically identified by NPCC as
having generator trip settings above the generator trip curve in Figure 2 shall provide
evidence such as letters, reports and dated documentation that demonstrates that it meets
Requirement R18.
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R18 Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the New York ISO shall apply the criteria
described in Attachment B to determine the compensatory load shedding that is
required in Requirement R16.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
R19 Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 1, based on their licensing design basis, shall: [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
19.1
Set the underfrequency protection to operate at as low a frequency as
possible in accordance with the plant design and licensing limitations but
not greater than 57.8Hz.
19.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
11
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
19.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
R20 The Planning Coordinator shall update its UFLS program database as specified by the
NERC PRC Standard on UFLS. This database shall include the following
information: [Violation Risk Factor: Lower] [Time Horizon: Operations Planning]
20.1
For each UFLS relay, including those used for compensatory load
shedding, the amount and location of load shed at peak, the corresponding
frequency threshold and time delay settings.
20.2
The buses at which the Load is modeled in the NPCC library power flow
case.
20.3
A list of all generating units that may be tripped for underfrequency
conditions above the appropriate generator underfrequency trip protection
settings threshold curve in Figure 1, including the frequency trip threshold
and time delay for each protection system.
20.4
The location and amount of additional elements to be switched for voltage
control that are coordinated with UFLS program tripping.
20.5
A list of all UFLS relay inhibit functions along with the corresponding
settings and locations of these relays.
R21 Each Planning Coordinator shall notify each Distribution Provider, Transmission
Owner, and Generator Owner within its Planning Coordinator area of changes to load
distribution needed to satisfy UFLS program performance characteristics as specified
by the NERC PRC Standard on UFLS.[Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
R22 Each Distribution Provider, Transmission Owner and Generator Owner shall
implement the load distribution changes based on the notification provided by the
Planning Coordinator in accordance with Requirement R21. [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
R23 Each Distribution Provider, Transmission Owner and Generator Owner shall develop
and submit an implementation plan within 90 days of the request from the Planning
Coordinator for approval by the Planning Coordinator in accordance with Requirement
R21. [Violation Risk Factor: Lower] [Time Horizon: Operations Planning]
12
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Figure 1
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
Figure 1
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
13
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Formatted: List Number
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
14
Adopted by Board of Trustees: February 9, 2012
Frequency (Hz)
60
59.5
59
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Formatted: List Number
C. Measures
15
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M1
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
M3 Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
M4 Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped, and the corresponding frequency thresholds,
on those circuits included in its UFLS program to achieve the individual and
cumulative percentages identified in Requirement R4. (Attachment C Tables 1-3).
M5 Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
M6 Each Distribution Provider and Transmission Owner in the Québec Interconnection
shall have evidence such as documentation or reports containing the location and
amount of load to be tripped and the corresponding frequency thresholds on those
circuits included in its UFLS program to achieve the load values identified in Table 4
of Requirement R6. (Attachment C Table 4).
M7 Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the
minimum time delay, in accordance with Requirement R7.
M8 Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R8.
M9 Each Planning Coordinator shall provide evidence such as letters, emails, or other
dated documentation that demonstrates that it meets Requirement R9.
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M10 Each Distribution Provider and Transmission Owner shall provide evidence such as
test reports, data sheets or other documentation that demonstrates that it meets
Requirement R10.
M11 Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails or other dated documentation that demonstrates that it meets
Requirement R11.
M12 Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the frequency set point, the net amount of load shed and the
percentage of its peak load at each stage of its UFLS program coincident with the
integrated hourly peak of the previous year that demonstrates that it meets Requirement
R12.
M13 Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement R13.
M14 Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R14.
M15 Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R15.
M16 Each Generator Owner with existing non-nuclear units in service prior to the effective
date of this Standard which have underfrequency tripping that is not compliant with
Requirement R13 shall provide evidence such as reports, spreadsheets, memorandum
or dated documentation demonstrating that it meets Requirement R16.
M17 Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall
provide evidence such as emails, memorandum or other documentation that
demonstrates that it followed the methodology described in Attachment A and meets
Requirement R17.
M18 Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the New York ISO shall provide evidence
such as emails, memorandum, or other documentation that demonstrates that it
followed the methodology described in Attachment B and meets Requirement R18.
17
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M19 Each Generator Owner of nuclear units that have been specifically identified by NPCC
as having generator trip settings above the generator trip curve in Figure 1 shall
provide evidence such as letters, reports and dated documentation that demonstrates
that it meets Requirement R19.
M20 Each Planning Coordinator shall provide evidence such as spreadsheets, system
studies, or other documentation that demonstrates that it meets the requirements of
Requirement R20.
M21 Each Planning Coordinator shall provide evidence such as emails, memorandum or
other dated documentation that it meets Requirement R21.
M22 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as reports, spreadsheets or other documentation that demonstrates that it
meets Requirement R22.
M23 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as letters, emails or other dated documentation that demonstrates it
meets Requirement 23.
D.C.
1.
Compliance
Compliance Monitoring Process
1.1. Compliance Enforcement Authority
NPCC Compliance Committee
1.2. Compliance Monitoring Period and Reset Time Frame
Not Applicable
1.3. Data Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 4, 5, 6,7,10, 11, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 3, 8, 9, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall
keep evidence for three calendar years for Measure 17.
18
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 18, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
13, 14, 15, 16, and 19.
1.4. Compliance Monitoring and Assessment Processes
Self -Certifications.
Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.
1.5. Additional Compliance Information
None.
19
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
2.
Violation Severity Levels
Requirement
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1
N/A
N/A
N/A
The Plannning
Coordinator failed to
design an UFLS program
having performance
characteristics that
prevent frequency from
remaining below 59.5 Hz
in accordance with Figure
1.
R2
The
Planning
Coordinator provided
its
UFLS
island
boundaries,
as
identified per the
NERC PRC Standard
on UFLS but did so
more than 30 calendar
days and up to and
including 40 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC PRC Standard
on UFLS but did so
more than 40 calendar
days but less than and
including 50 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC PRC Standard
on UFLS but did so
more than 50 calendar
days but less than and
including 60 days
following a request.
The Planning Coordinator
failed to provide its UFLS
island boundaries, as
identified per the NERC
PRC Standard on UFLS.
within 60 calendar days
following a request.
R3
The Planning
Coordinator identified
to the Regional Entity
all non-BES
generation facilities
within its Planning
Coordinator Area that
must not trip above
the appropriate
generator
underfrequency trip
threshold curve in
order to support
The Planning
Coordinator identified
to the Regional Entity
all non-BES generation
facilities within its
Planning Coordinator
Area that must not trip
above the appropriate
generator
underfrequency trip
threshold curve in order
to support the UFLS
program performance
The Planning
Coordinator identified
to the Regional Entity
all non-BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in
order to support the
UFLS program
The Planning Coordinator
identified all non-BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in order to
support the UFLS
program performance
requirements, but failed to
inform the Regional
20
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
UFLS program
performance
requirements, but did
so more than 30
calendar daysand up
to and including 40
days after completion
of the system studies.
requirements, but did so
more than 40 days but
less than calendar days
but less than and
including 50 days after
completion of the
system studies.
performance
requirements,, but did
so more than 50
calendar days but less
than and including 60
days after completion
of the system studies.
OR
The Planning Coordinator
did not identify the BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in order
to supportUFLS program
performance
requirements.
The Distribution
Provider or Transmission
Owner failed to
implement the automatic
UFLS program on an
island basis as specified
by Requirement R4, Part
4.1 or Part 4.2.
R4
R5
Entity within 60 calendar
days after completion of
the system studies.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations ir
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations ir
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
21
Adopted by Board of Trustees: February 9, 2012
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations but
exceeded the
permissible time
frame for one or more
The Distribution
Provider or Transmission
Owner that cannot meet
the tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program failed to meet
all of items in
Requirement 5 within 60
calendar days of
permissible time for each
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
permissible time frame
for one or more of the
4 items by a period of
up to 10 calendar days
but less than or equal
to 20 calendar days.
permissible time frame
for one or more of the 4
items within a time
greater than 20 calendar
days but less than or
equal to 30 calendar
days.
of the 4 items within
a time greater than 30
calendar days but less
than or equal to 60
calendar days.
R6
The Distribution
Provider or
Transmission Owner
set less than 100% but
more than (and
including) 95% of its
underfrequency relays
that are part of its
region’s UFLS
program with a 100 ms
minimum time delay.
The Distribution
Provider or
Transmission Owner
set less than 95% but
more than (and
including) 90% of its
underfrequency relays
that are part of its
region’s UFLS program
with a 100 ms
minimum time delay.
The Distribution
Provider or
Transmission Owner
set less than 90% but
more than (and
including) 85% of its
underfrequency relays
that are part of its
region’s UFLS
program with a 100
ms minimum time
delay.
The Distribution
Provider or Transmission
Owner set less than 85%
ot its underfrequency
relays that are part of its
region’s UFLS program
with a 100 ms minimum
time delay.
R7
The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 100% but more
than (and including)
95% of relays within
its region’s UFLS
program.
The Planning
Coordinator
developed or reviewed
settings for inhibit
thresholds at least
once per five calendar
years, for less than
95% but more than
(and including) 90%
of relays within its
region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 90% but more
than (and including)
85% of relays within
its region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 85%
of relays within its
region’s UFLS program.
R8
The Planning
Coordinator provided
to a Transmission
Owner or Distribution
Provider within its
Planning Coordinator
The Planning
Coordinator provided to
a Transmission Owner
or Distribution Provider
within its Planning
Coordinator area the
The Planning
Coordinator provided
to a Transmission
Owner or Distribution
Provider within its
Planning Coordinator
The Planning
Coordinator failed to
provide to a
Transmission Owner or
Distribution Provider
within its Planning
22
Adopted by Board of Trustees: February 9, 2012
item.
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9
R10
R11
area the applicable
inhibit thresholds more
than 30 calendar days
and up to and
including 40 calendar
days of any changes.
applicable inhibit
thresholds more than 40
calendar daysbut less
than and including 50
calendar days of any
changes.
area the applicable
inhibit thresholds
more than 50 calendar
daysbut less than and
including 60 calendar
days of any changes.
Coordinator area the
applicable inhibit
thresholds within 60
calendar days after any
changes
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 90 calendar
days and up to and
including 100
calendar days
following the request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 100 calendar
days and up to and
including 110 calendar
days following the
request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 110
calendar days and up
to and including 120
calendar days
following the request.
The Distribution
Provider or Transmission
Owner failed to develop
and submit its
implementation plan
within 120 days
following the request.
implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 100%
but more than (and
including) 95% of
UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by the
Planning Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 95% but more
than (and including)
90% of UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 90% but
more than (and
including) 85 % of
UFLS relays.
The Distribution
Provider or Transmission
Owner implemented the
inhibit threshold settings
provided by the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 85 % of UFLS
relays.
The Distribution
Provider or
Transmission Owner
The Distribution
Provider or
Transmission Owner
The Distribution
Provider or Transmission
Owner failed to provide
The Distribution
Provider or
Transmission Owner
23
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 15 calendar
months but less than
(and including) 16
calendar months since
last update.
provided to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11 more
than 16 calendar
months but less than
(and including)17
calendar months since
last update.
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 17 calendar
months but less than
(and including)18
calendar months since
last update.
to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
within 18 calendar
months since last update.
R12
N/A
N/A
N/A
The Generator Owner
did not set each
generator
underfrequency trip
relay, if so equipped, on
or below the appropriate
generator
underfrequency trip
protection settings
threshold curve in Figure
2, except as otherwise
exempted.
R13
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 45calendar
days and less than (and
including) 55 calendar
days of the Planning
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 55 calendar
days and less than (and
including) 65 calendar
days of the Planning
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 65 calendar
days and less than
(and including) 75
calendar days of the
The Generator Owner
failed to transmit the
generator
underfrequency trip
setting and time delay
within 75 calendar days
of the Planning
Coordinator’s request.
24
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R14
Coordinator’s request.
Coordinator’s request.
N/A
N/A
Planning
Coordinator’s request.
The Generator Owner
with a new generating
unit, or an existing
generator increasing
its net capability by
greater than 10%:
Did not: fulfill the
obligation of
Requirement R14;
Part 14.1
The Generator Owner
with a new generating
unit, or an existing
generator increasing its
net capability by greater
than 10%, did not fulfill
the obligations of
Requirement R15, Part
15.1 and Part 15.2.
OR
Did not fulfill the
obligation of
Requirement R14,
Part 14.2.
R15
N/A
The Generator Owner
failed to transmit the
existing underfrequency
settings and any
changes to the
underfrequency settings
along with the technical
basis for the settings to
the Planning
Coordinator.as
specified in
Requirement R15, Part
15.2.
The Generator Owner
failed to set the
underfrequency
protection to operate at
the lowest frequency
allowed by the plant
design and licensing
limitations a specified
in Requirment 15, Part
15.1
The Planning
Coordinator in Ontario,
Québec and the
Maritime Provinces or
the Generator Owner in
the New-England States
and in New York State
failed to arrange for
compensatory load
shedding as specified in
Requirement R15, Part
15.3.
R16
N/A
N/A
N/A
The Planning
Coordinator did not
apply the methodology
described in Attachment
A to determine the
25
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
compensatory load
shedding that is required.
R17
N/A
N/A
N/A
The Generator Owner,
Distribution Provider, or
Transmission Owner did
not apply the
methodology described
in Attachment B to
determine the
compensatory load
shedding that is required.
R18
N/A
The Generator Owner
failed to transmit the
initial frequency trip
setting and any changes
to the setting and the
technical basis for the
settings to the Planning
Coordinator as
specified in
Requirement R18, Part
18.3.
The Generator Owner:
The Generator Owner
did not fulfill the
obligations of
Requirement R18, Part
18.1 and Part 18.2.
26
Adopted by Board of Trustees: February 9, 2012
Failed to set the
underfrequency
protection as specified
in Requirement R18;
Part 18.1
OR
Failed to set the
frequency trip setting
upper tolerance as
specified in
Requirement R18, Part
18.2.
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 1.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all islands identified in Requirement R1 in which the
unit may operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements:
1. The Planning Coordinator shall identify, compile and maintain an updated list of all
existing non-nuclear generating units in service prior to the effective date of this standard
that have underfrequency protections set to trip above the appropriate curve in Figure 1.
The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate, as identified in Requirement R1
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS
relays within the island(s) identified by the Planning Coordinator in Requirement
R1 within which the generator may operate to provide compensatory load
shedding.
2.2 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4..
2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 1 during an underfrequency event. If the highest
27
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
frequency at which the subject generator will trip above the appropriate curve in
Figure 1 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 1.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
28
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 1 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify and compile a list of all existing non-nuclear
generating units in service prior to the effective date of this standard that has
underfrequency protection set to trip above the appropriate curve in Figure 1. The list
shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 1, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the smallest island identified by the Planning Coordinator in
Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 1, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
29
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
30
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Formatted: List Number, Centered, Indent: Left: 0", Don't
keep with next
PRC-006-NPCC-1 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW or more of peak net Load shall
implement a UFLS program with the following attributes:
Frequency
Threshold
(Hz)
Total Nominal
Operating
Time (s) 1
Load Shed at Stage as
% of TO or DP
Load
Cumulative Load Shed as % of
TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
59.5
10.0
2–3
27.5 – 28.5
29.5
–
31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW or more and less than 100 MW
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
Formatted: List Number, Centered, Indent: Left: 0", Don't
keep with next
1. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the frequency
threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating time is
dependent on the rate of frequency decay, the underfrequency relay operating time and any subsequent testing of
the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
31
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW or more of peak net Load shall
implement a UFLS program with the following attributes:
Frequency
Threshold
(Hz)
Total Nominal
Operating
Time (s) 2
Load Shed at Stage as
% of TO or DP
Load
Cumulative Load Shed as % of
TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
59.5
10.0
2–3
27.5 – 28.5
29.5
–
31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW or more and less than 100 MW
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the frequency
threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating time is
dependent on the rate of frequency decay, the underfrequency relay operating time and any subsequent testing of
the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
32
Formatted Table
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW or more and less than 50 MW of
peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the frequency
threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating time is
dependent on the rate of frequency decay, the underfrequency relay operating time and any subsequent testing of
the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
33
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 4: Quebec Interconnection
MW
at peak
Mvar
at peak
Total
Nominal
Operating
Time (s) 2
Rate
Frequency
(Hz)
(*Load must
be fixed at all
times when
above 60% of
peak load..)
Threshold Stage 1
–––
58.5
1000*
1000
0.30
Threshold Stage 2
–––
58.0
800*
800
0.30
Threshold Stage 3
–––
57.5
800
800
0.30
Threshold Stage 4
–––
57.0
800
800
0.30
–––
59.0
500
500
20.0
Slope Stage 1
-0.3 Hz/s
58.5
400
400
0.30
Slope Stage 2
-0.4 Hz/s
59.8
800*
800
0.30
Slope Stage 3
-0.6 Hz/s
59.8
800*
800
0.30
Slope Stage 4
-0.9 Hz/s
59.8
800
800
0.30
Threshold Stage 5
(anti-stall)
Formatted: Indent: Left: 0", First line: 0"
Guidelines and Technical Basis:
2. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communications time, and the rated breaker interrupting time. The
underfrequency relay operating time shall be measured from the time when the frequency passes through the
frequency threshold set point.
34
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
•
•
•
•
•
•
•
•
•
•
•
•
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
Generator dynamic modeling
Dynamic VAR device modeling
HVDC dynamic modeling
Formatted: List Paragraph, Space After: 10 pt, Bulleted +
Level: 1 + Aligned at: 0.25" + Indent at: 0.5", Don't keep
with next
Formatted: Font: Bold, Font color: Custom
Color(RGB(31,73,125)), English (United States)
Formatted: Font: Bold
35
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: See question 2 comments
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments: R5.3 Presently states, “If adjustments are possible, make the adjustments
within 180 calendar days…”
Recommend drafting group address in wording direction on if adjustments are possible but it
will take longer than 180 days implement. What steps to take? Develop Implementation Plan
with PC? (This would be for the case where changes/”adjustments” are not just an existing relay
setting change, but may require installation of new relays where the time to implement will be
longer than 180 days (Project funding, design, purchase equipment, installation, testing, etc).
R5.4 presently states, “If adjustments are not possible then:” ………within 180 days provide
its PC with a technical study that demonstrates the deviations from the requirements will not
have a significant adverse impact on the BES.
Recommend drafting group address in wording: Steps if technical study demonstrates the
deviations from the requirements will have a significant adverse impact on the BES.
Should the TO then refer to R15 of the NERC Continent Wide PRC-006-3 Standard, and
develop a Corrective Action Plan and a schedule for implementation with the PC?
Drafting Team Response:
The drafting team made modifications to the Requirement 5 according to the comment.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: No comment
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: Proposed Implementation Plan Eversource comment to be provided for this
comment period: My understanding from discussions with the group during the review of
comments in October 2017, is that, If new UFLS Performance analysis identified significant
changes are required to a TO/DP’s UFLS Program (that will take longer than 12 months to
implement), the TO/DP will develop a Implementation Plan with the PC. The Implementation
Plan would fall under R15 of the continent-wide PRC-006 standard. During the review of
comments discussion in October, it was said drafting team will clarify this in 5.1.2, but 5.1.2 is
no longer exists.
Drafting Team Response:
The drafting team made modifications to the Requirement 5 according to the comment.
We recommend a change in the existing standard due to potential issues we have observed in meeting
the requirements in the past. Because of the site of the Granite States load it has been difficult to stay
within the threshold. We request that the drafting team consider a tolerance band of 5 to 10 MW for
table 1. The current tolerance is too low for entities that have load between 100 to 95. As an example,
under table 2 an entity with 50 MW of load must shed in between 7 to 12.5 MW of load, which results in
a tolerance band of 5.5 MW. An entity with 100 MW of load must shed 14 to 25 MW of load, which
results in a tolerance band of 11 MW. An entity with 101 MW of load fall under table 1. They must shed
between 6.6 MW to 7.6 MW with a tolerance band of 1 MW. A tolerance band of 1 MW is way too
tight. Below I provide a table that shows loads at 50 MW increments to demonstrate the tolerance
band.
Table 1 (> 100 MW)
0.065
Table 2 (50 to 100 MW)
0.075
Load
MW
0.14
0.25
7
12.5
5.50
Tolerance
50
101
6.57
7.58
1.01
14.14
25.25
11.11
150
9.75
11.25
1.50
21
37.5
16.50
200
13.00
15.00
2.00
28
50
22.00
250
16.25
18.75
2.50
35
62.5
27.50
300
19.50
22.50
3.00
42
75
33.00
350
22.75
26.25
3.50
49
87.5
38.50
400
26.00
30.00
4.00
56
100
44.00
450
29.25
33.75
4.50
63
112.5
49.50
500
32.50
37.50
5.00
70
125
55.00
550
35.75
41.25
5.50
77
137.5
60.50
600
39.00
45.00
6.00
84
150
66.00
650
42.25
48.75
6.50
91
162.5
71.50
700
45.50
52.50
7.00
98
175
77.00
750
48.75
56.25
7.50
105
187.5
82.50
800
52.00
60.00
8.00
112
200
88.00
850
55.25
63.75
8.50
119
212.5
93.50
900
58.50
67.50
9.00
126
225
99.00
950
61.75
71.25
9.50
133
237.5
104.50
1000
65.00
75.00
10.00
140
250
110.00
1050
68.25
78.75
10.50
147
262.5
115.50
1100
71.50
82.50
11.00
154
275
121.00
1150
74.75
86.25
11.50
161
287.5
126.50
1200
78.00
90.00
12.00
168
300
132.00
1250
81.25
93.75
12.50
175
312.5
137.50
1300
84.50
97.50
13.00
182
325
143.00
1350
87.75
101.25
13.50
189
337.5
148.50
1400
91.00
105.00
14.00
196
350
154.00
1450
94.25
108.75
14.50
203
362.5
159.50
In addition, the drafting team may consider clarifying foot note 2 to identify where peak net load is to be
measured. Is it the peak net load as seen by distribution provider or by transmission owner (high side or
low side of transformer)?
The changes to section 4.2 implies that DPs and TO’s must coordinate their plan such that the entire
plan meets the criteria identified in attachment C. The rational for this change is not clear to me and
therefore we are not sure that we agree with the drafting team.
Drafting Team Response:
Thank you for your comments, the drafting team made modifications to Requirement 5 where an
entity can develop and implement a Corrective Action Plan that is mutually agreed upon with the
Planning Coordinator.
The drafting team believes that in order to make modifications to Table 1, 2 and 3 additional
technical justification is required.
The drafting team believes that the footnote #2 is sufficient enough for entities to determine
where they calculate or measure the load.
The drafting team believes that the current requirement 4.2 allows more flexibility to different
size utilities to aggregate their UFLS if they choose.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 13, 2018 through May 29, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
X
Comments: We would like to reiterate a previous comment that we submitted concerning the
difference between the design performance requirement in the NERC continent-wide standard PRC006-2 and what is included in the proposed regional standard PRC-006-2-NPCC-2 and in the existing
NPCC Directory #12.
The NERC continent-wide standard requires that the system frequency be restored to between 59.3
Hz and 60.7 Hz in 60 seconds (60 s / 59.3 Hz & 60 s / 60.7 Hz), following an imbalance that results
in an under-frequency (Requirement R3, Part 3.10). However, both the regional standard and the
directory require the frequency to be restored to above 59.5 Hz in 30 seconds (30 s / 59.5 Hz).
Based on our experiences with the August 2003 Blackout and based on the UFLS assessment
completed by the SS-38 Working Group, Ontario could form islands with portions of the power
system that are not part of NPCC region. Given this and since there is no technical justification for
the existing NPCC performance characteristic of 30 s / 59.5 Hz, we believe the regional standard
should be aligned with the continent-wide standard’s performance characteristic of 60 s / 59.3 Hz.
This would eliminate any potential non-compliance risks that Ontario may face as a result of having
two different performance criteria apply to the same island.
Drafting Team Response:
The drafting team changed the language of Requirement 1 to make 59.5Hz requirement only
applicable to islands wholly within the NPCC Region.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes X
No
Comments: With respect to Sub-requirement 5.4.1., we are not certain that a Distribution
Provider or Transmission Owner will have the required data and capability to perform the
technical study to assess whether their specific deviations from the UFLS requirements will have
a significant adverse impact on the BES. The required data and capability to perform these
types of BES assessments are usually found with the Planning Coordinator.
Drafting Team Response:
The drafting team believes there are enough technical consultants available to perform necessary
study for the TO or DP and PC will readily provide data for such study so the requirement need
not be modified. The PC, TP or RC could also serve as technical consultants to perform the
necessary studies.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes X
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes X
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
We are unable to find the rationale for changing the VRF from a HIGH to a MEDIUM for
various requirements (e.g. R12, R15-R18) addressing compensatory load shedding requirements
for generators that are set to trip above the applicable curves in Figure 2. Without knowing the
rationale, we do not support such changes since failing to shed load to compensate for the
additional loss of the tripped generation can lead to total collapse of the island. We recommend
the drafting team reconsider the reliability impact and reinstate these VRFs to HIGH, or provide
the technical justification for such changes.
Drafting Team Response:
The drafting team agreed with the comment and made VRF modifications to Requirement 12,
15-18.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
We have a concern with R3 because we are unsure of the rationale for the
requirement. Further, identifying which non-BES generators are critical for supporting the
frequency performance of an island in a non-discriminatory manner could be extremely
difficult, especially since non-BES generators tend to be smaller and potentially more
numerous. We recommend deleting this requirement. ISO New England requires non-BES
generation to meet underfrequency tripping requirements (or the procurement of
compensatory load shedding, if needed) through its tariff and operating procedures.
For R11, we suggest deleting the “or calculating” from the current language to make it read:
For R11, we suggest removing the “or calculating” wording in the requirement or adding “if
measured data is unavailable then calculated data may be used”. Also, the rational for the
requirement doesn’t seem quite right or it may be difficult to put into practice since different
islands may have peaks that occur at different times.
“Each Transmission Owner and Distribution Provider shall annually provide documentation,
with no more than 15 calendar months between updates, to its Planning Coordinator of the
actual net Load that would have been shed by the UFLS relays at each UFLS stage. The
actual net Load shall be coincident with the entity’s integrated hourly peak net Load during
the previous year, as determined by measuring or calculating Load through the switches that
would disconnect load if triggered by the UFLS relays. [Violation Risk Factor: Lower]
Drafting Team Response:
For Requirement 3, the drafting team decided to remove the requirement since there are
mechanisms in place for PC to collect the data (Tariffs etc.) and it does not create a reliability
gap because the performance characteristics UFLS program must still be met.
For Requirement 11, the drafting team accepted the comment and made modifications to the
requirement language accordingly.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments:
For the wording in Requirement 5, we recommend changing as follows:
“Each Distribution Provider or Transmission Owner that cannot does not meet the tolerances
and/or number of stages and frequency set points specified in the UFLS Program, shall:”
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments:
Drafting Team Response:
The drafting team made modifications to the requirement according to the comment.
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: While agreeing with the overall proposed revisions there are still some changes
recommended by OPG via the answers to questions number 2, 4 and 6.
Drafting Team Response:
Thank you for your comment.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments: OPG is of the opinion that some distribution providers with assigned compliance
obligations as per R5 part 5.4 may not have the capability, nor the access to the required
information to perform a study to demonstrate that the specific deviations from the UFLS
requirements will not have a significant adverse impact on the BES. This exercise is more
suitable for the respective Transmission Planner and/or the Reliability Coordinator.
Drafting Team Response:
The drafting team believes there are enough technical consultants available to perform necessary
study for the TO or DP and PC will readily provide data for such study so the requirement need
not be modified. The PC, TP or RC could also serve as technical consultants to perform the
necessary studies.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments: OPG is satisfied with R15 final revision, in accordance with the comments
previously provided for additional clarity with respect to the responsible entity for compensatory
load shedding.
Additional revisions of R15 may be required to incorporate the newly proposed revision for
R18, once accepted by the SDT.
Drafting Team Response:
Thank you for your comment, please see response to question 6.
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments: OPG is of the opinion that Directory 12 requirements pertaining to the
underfrequency trip settings of the protective relaying are better suited in a regional standard
(i.e. new PRC-024-NPCC-01) or in a regional variance of the standard PRC-024-2 — Generator
Frequency and Voltage Protective Relay Settings, and merely suggest SAR initiation.
Drafting Team Response:
Thank you for your comment. The drafting team would recommend you submit a SAR during
the NERC Periodic Review.
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: It appears that for the existing BES the traditional UFLS based only on
frequency thresholds is cost effective for now. It may be possible that with the changes in the
mix of generating resources and grid evolution, in the future this method will no longer be
sufficient/reliable for emergency operating conditions and therefore new protective schemes,
based on frequency derivative, must be developed/implemented. Furthermore these type of
protections can possibly be dynamically adapted to grid configurations (i.e. coupled with widearea phasor measurements to limit or prevent the system from severe disturbances or even
collapses due to delayed response and over shedding).
Drafting Team Response:
Thank you for your comment.
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: OPG has the following comments:
Auxiliary power supplies located at the nuclear generating plants, driven by nonnuclear prime mover, that are connected to the grid only for the duration of testing,
should be considered non-nuclear units and should be subject to compliance with the
obligations spelled out in requirement # R15 (non-nuclear)
Existing Nuclear Generators that cannot satisfy the condition of maximum 57.8 Hz
imposed by R18 Part 18.1, due to extenuating equipment limitation circumstances, design
and licensing limitations, shall set the underfrequency protection to operate at the
lowest frequency allowed by the existing limitation factors, and communicate the
settings and technical basis to the Planning Coordinator
The standard should also be revised to include requirements for arrangements of adequate
compensatory load shedding, as per Attachment A or B, for the loss of nuclear
generator(s) due to early tripping that is within the UFLS island identified by the PC in
R2. Note This requirements is now missing
OPG believes the reasoning is obvious and is available to provide additional
information/justification if required.
OPG proposed language for R18 is as follows:
R18. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2, based on their licensing design basis, shall: [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
18.1. Set the underfrequency protection to operate at as low a frequency as
possible in accordance with the plant design and licensing limitations but not
greater than 57.8 Hz.
18.2. Each Generator Owner of existing nuclear generating plants that cannot
satisfy the condition of maximum 57.8 Hz imposed by 18.1, due to extenuating
circumstances such as equipment limitations or design and licensing limitations,
shall set the underfrequency protection to operate at the lowest frequency allowed
by the existing limiting factor. Auxiliary power supplies located at the nuclear
generating plants, driven by non-nuclear prime mover, that are connected to the
grid only for the duration of testing, are considered non-nuclear units and are
subject to compliance with the obligations spelled out in requirement # R15.
18.3.
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
18.4. Transmit the initial frequency trip setting, any subsequent changes to the
setting, and the technical basis for the settings to the Planning Coordinator.
18.5 Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces in accordance with Attachment A and each Generator Owner in the
New-England States and in New York State in accordance with Attachment B
shall arrange for compensatory load shedding, as provided by a Distribution
Provider or Transmission Owner that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified by the
Planning Coordinator in Requirement R2
Drafting Team Response:
Thank you for your comments. The drafting team recognize the importance of protecting nuclear
generation however does not agree to have compensatory load shedding. The SDT believes that
the proposed change requested by the comment has a potential adverse reliability impact. The
SDT believes more information is needed to determine if this is a broader issue. The commenter
believes that there is currently no non-compliance however, going forward there could be a
scenario that may restrict utilization of nuclear assets. Sufficient justification was not provided
so the SDT decided not make the change at this time.
National Grid Comments – PRC-006-NPCC-2
May 29, 2018
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: National Grid recommends that a technical writer review PRC-006-NPCC-2 for
possible improvements. Please ensure that all aspects of the regional standard conform with the
most recent NERC standards format.
Specific Comments:
Consider changing the Purpose to state: “To establish consistent and coordinated requirements
for the design, implementation, and analysis of automatic underfrequency load shedding (UFLS)
programs among all NPCC Region applicable entities.”
Consider changing the Applicability to state:
4.1 Planning Coordinators
4.2 UFLS entities shall mean all entities that are responsible for the ownership, operation, or
control of UFLS equipment as required by the UFLS program established by the Planning
Coordinators. Such entities may include one or more of the following:
4.2.1 Transmission Owners
4.2.2 Distribution Providers
4.2.3 UFLS-Only Distribution Providers
4.3 Generator Owners
This proposed applicability change will also be reflected in multiple requirements by replacing
Transmission Owners and Distribution Providers with UFLS entities.
Consider changing the Effective Date to state: “See Implementation Plan.”
Consider changing references for this standard from “NERC PRC Standard on UFLS” to “the
continent-wide PRC-006 standard.”
Consider changing from “greater than 30 seconds” to “more than 30 seconds” in Requirement
R1.
Consider consistent use of the comma. (e.g., missing in M1, R4.1, R4.2, etc.)
National Grid Comments – PRC-006-NPCC-2
May 29, 2018
Correct font type for “R4” in Requirement R4.
Please insert “for it Facilities” after the word ‘outage’ in requirement R4, to clarify type of
outages.
Consider changing capitalized “Island” to be lower case “island.” Island is not a NERC Glossary
Term. Please see requirement R4.2.
Consider improvements to the readability of sub-requirements, which are combined with ‘and’ or
‘or’ statements. Separate sub-requirements / alternatives in ‘and’ or ‘or’ statements by use of
semicolons, e.g., before the term “or” between R4.1 and R4.2.
Consider deleting “at least” in “at least once per five calendar years” in Requirement R7.
Consider changing capitalized “Underfrequency” to be lower case “underfrequency” in the
Rationale box for Requirement R7. Underfrequency is not a NERC Glossary defined term.
Consider revising R8 by changing the word “applicable” to “allowable”. As presently written it
appears as if the Planning Coordinator is responsible to develop (specific) settings for inhibit
thresholds.
Correct lay-out (break) in Requirement R13.
Consider ensuring the Compliance section of the standard is in conformance with other NERC
reliability standards. We suggest changing the Compliance Enforcement Authority to be NPCC
as the Regional Entity, instead of the NPCC Compliance Committee.
Consider removing the Guidelines and Technical Basis section in accordance with the NERC
Technical Rationale Transition Plan. A separate document may be required.
Consider adding a Version History section.
Drafting Team Response:
Thank you for your comments but the drafting team slightly modified the Purpose language.
The quality review will be done prior to the next posting.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments: Consider consistent use of terms “technical study” as used in R5.4.1 and “system
studies” as used in Requirement R3, M1, M5, and M7. Are these terms referring to the same or
different studies?
National Grid Comments – PRC-006-NPCC-2
May 29, 2018
Consider improvements to the readability of sub-requirements, which are combined with ‘and’ or
‘or’ statements. Separate sub-requirements / alternatives in ‘and’ or ‘or’ statements by use of
semicolons, e.g., before the term “or” between R5.3 and R5.4, as well as between R5.4 and
R5.4.2.
Drafting Team Response:
Thank you for your comments. The quality review will be done prior to the next posting.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments: National Grid recommends dividing R15.3 into two sub-requirements.
Recommended change:
15.3. Each Planning Coordinator in Ontario, Québec and the Maritime Provinces in
accordance with Attachment A shall arrange for compensatory load shedding, as provided by a
UFLS entity that is adequate to compensate for the loss of generator(s) due to early tripping that
is within the UFLS island identified by the Planning Coordinator in Requirement R2.
15.4. Each Generator Owner in the New-England States and in New York State in accordance
with Attachment B shall arrange for compensatory load shedding, as provided by a UFLS entity
that is adequate to compensate for the loss of generator(s) due to early tripping that is within the
UFLS island identified by the Planning Coordinator in Requirement R2.
Requirement R17 would also need to be revised to reference R15.4.
Drafting Team Response:
Thank you for your comments, the drafting team decided to keep the requirement as it is.
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
National Grid Comments – PRC-006-NPCC-2
May 29, 2018
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from April 16, 2018 through May 31, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comments by Consolidated Edison Co. of New York
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments: Con Edison agrees with the proposed revisions as posted. However, Con Edison
believes that, per the Guidelines and Technical Basis section in PRC-006-NPCC-2, “significant
variations” exist that impact the BES and mandate that an updated UFLS assessment be
conducted. The “significant variation” is the inability of generation to ride through high
frequency events. This issue has been highlighted by a NERC Industry Advisory, Turbine
Combustor Lean Blowout, issued June 26, 2008.
Con Edison recommends that a new UFLS assessment be conducted due to reliability concerns
of turbine-generator governor controls and the NPCC Under Frequency Load Shedding Study
results as discussed in this submittal.
Drafting Team Response:
The concern is dully noted and it has been transferred to the appropriate NPCC groups.
2. Do you agree with the proposed revisions to Requirement 5? If not, please explain why
and include any suggestions.
Yes
No
Comments: See comments in section 6. The 1% UFLS tolerance specified in Attachment C
may not provide any additional benefit to the success of an UFLS system.
3. Do you agree with the proposed revisions to Requirement 15? If not, please explain why
and include any suggestions.
Yes
No
Comments: The lack of test performance standards provides no guarantee that turbinegenerators will remain synchronized to the system during a low frequency event. NPCC should
develop a more stringent requirement to test turbine-generators in a manner that verifies the
ability to ride through low frequency conditions, as well as high frequency conditions. This
testing is being developed worldwide. For example, National Grid in the United Kingdom has
Grid Code CO5 that verifies equipment performance and has developed frequency response
markets to provide performance incentives. Equipment testing is the only means of verifying
performance, and if this cannot be done, then assumptions on reliability of turbine-generators
should be more conservative.
Drafting Team Response:
The drafting team recognizes the importance of the issue however the drafting team recommend
Con Edison submit a SAR to NERC to the appropriate standard. PRC-006-NPCC-2 is consistent
with PRC-024-2 NERC standard.
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
An UFLS Standard is cost effective if it successfully islands a service area. On November 4th,
2006, Europe experienced an UFLS event and avoided a grid shutdown. The event resulted in
the European breaking up into 3 large grids. Post event, the grids were synchronized back
together in 39 minutes. Only a small percentage of customers were shutdown with minimal
economic impact on the European economy.
In the United States, the opposite occurred in 2003. A cascading outage initiated in the Midwest
caused the northeast portion of the Eastern Interconnection to isolate. The last line of defense
was the UFLS system, and it failed. The subsequent blackout caused a $6B economic impact per
the DOE. By implementing governor testing standards and improved UFLS studies, the
potential for a system wide blackout can be avoided. The money invested in this system is cost
effective as was seen in Europe in 2006.
Drafting Team Response:
Thank you for your comment.
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: Con Edison respectively adds the following comments.
(1) Requirement 1 references Figure 1 in PRC-006-NPCC. While this figure is based on the
NERC Standard from PRC-006, it is unrealistic. NPCC should develop a more stringent
requirement based on the documented performance of the governor during off frequency
conditions. Note that PRC-024 applies to protection relays, not governor controls. If the
governor controls reduce the fuel to cause flameout, or the steam turbine controls
increase the steam pressure to cause a drum level trip prior to the relay setting, then the
relay setting has minimal value except to protect the plant. If the governor controls work
properly, successful UFLS event is possible.
The figure below shows the response of large frame gas turbines during the 2/26/2008
FRCC System Disturbance. Per the FRCC report, the frequency excursion of 60.6 Hz
resulted in numerous lean blowouts of gas turbines. The NPCC Under Frequency Load
Shedding Study assumes gas turbines will operate reliably at 61.8Hz (1.2 Hz higher than
observed in the Florida event), which is unrealistic. Studies should include the loss of
generation at high frequencies, or limit the UFLS peak frequencies to a lower frequency.
Presently, large frame gas turbines-generators are base load generation commonly used in
combined cycle power plants. The loss of these combined cycle plants will result in a
system collapse and blackout. NPCC should develop more stringent governor test
requirements to support the performance requirements based on Figure 1. It is
recommended that advice from the original equipment manufacturers will provide
benefits; especially on the subject testing and modeling of governors in dynamic load
flows.
(2) PRC-006-NPCC Attachment C, Table 1 provides frequency thresholds, total operating
time, and percent load shed. The load shed tolerances may not be ideal for different
distribution system designs. All distribution systems consist of radial, loop and network
designs. Mandating a tolerance of 1% (7.5%-6.5%) may be appropriate for radial and
loop distribution systems because of the small customer load supply from single or two
area station supplies.
However, a 1% tolerance for network systems is much more challenging since the
customer load supply requires multiple area station supplies (greater than 2). For
example, if a service area has a 10,000MW peak load, with an average network size of
150MW; it is challenging to meet the 100MW tolerance (1% of peak).
DP’s and TO’s with network designs may have to change UFLS set points annually to
meet the 1% tolerance. More important, critical networks (high density populations,
hospitals, transportations hubs) may have to be included in the UFLS program merely to
meet a compliance target requiring a 1% tolerance.
The design basis for a 1% tolerance was the results of an SS38 study in which island
frequencies exceeded 61.8Hz. Since this high frequency is unrealistic as discussed
above, the 1% tolerance should be re-evaluated. More flexible tolerances should be
applied to accommodate different distribution systems. For example, the design change
can include system studies with more frequency thresholds and smaller load shedding
blocks.
3) Lastly, the Data Retention section C.1.3 needs to be updated to reflect the changes in this
latest revision. For example, R7 and M7 apply to Planning Coordinators, but in the Data
Retention section M7 is assigned to DP and TO.
Drafting Team Response:
Thank you for your comment.
The drafting team made appropriate changes to the standard based on the comments.
August 10, 2018
Subject: Posting for Open Process Review of PRC-006-NPCC-2 Automatic Underfrequency
Load Shedding.
The clean and redlined versions of the revised NPCC Regional Standard PRC-006-NPCC-2
Automatic Underfrequency Load Shedding, have been posted on the NPCC Website for a 45-day
comment period through September 25, 2018, along with a proposed Implementation Plan.
This draft has been developed in accordance with the NPCC Regional Standard Process Manual
(RSPM) and within the scope of an NPCC Regional Standard Authorization Request, which was
accepted by the NPCC Regional Standard Committee (RSC). The revisions are also presented as
mandated by the NERC Rules of Procedure.
Among the proposed changes included in the updated draft version of the Standard are:
• Modifications to Figures #1 and #2 in the Standard
• Added a Guidelines and Technical Basis section (NERC may request us to create a
separate document for this section and post it with the standard subsequent to approvals)
• Incorporated certain Criteria attributes from Directory #12 Automatic UFLS Program
Requirements which will facilitate the retirement of Directory #12
• Additional clarification of requirement language
• Proposed retirements of some of the Requirements that are redundant to the PRC-006-2
Continent-wide NERC standard
Also posted is a set of questions developed by the Regional Standard Drafting Team to solicit
comments on the draft standard and associated draft Implementation Plan for the Regional
Standard. Included in these questions is one on cost effectiveness of the requirements.
Comments on the posted materials may be submitted through the NPCC Open Process Portal,
which may be accessed through:
https://www.npcc.org/Standards/SitePages/DevStandardDetail.aspx?DevDocumentId=122
Depending on comments received and if no revisions are deemed necessary by the Standard
Drafting Team, the standard is tentatively scheduled to be posted for a 30-day pre-ballot review
and 10-day ballot period towards fourth quarter of 2018.
Please contact me with any questions regarding this Standard.
Thank you.
Ruida Shu
Northeast Power Coordinating Council, Inc.
Senior Engineer, Reliability Standards and Criteria
Main: 212-840-1070
Direct: 917-934-7976
Fax: 212-302-2782
Email: [email protected]
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes X
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes X
No
Comments:
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes X
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes X
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes
No
Comments: We believe that the language could be enhanced by adding some wording as
follows to clarify that a determination has been made:
Each Distribution Provider or Transmission Owner in the Eastern Interconnection portion of
NPCC that determines that it does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec…
Within 30 calendar days of determining that it does not meet the specified parameters, notify its
Planning Coordinator that it does not meet the UFLS program parameters; and
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: We suggest providing the curve definitions for Figure 1 (these are included in
the continent wide version and should make it easier for entities to determine if they are meeting
the curves). We also suggest deleting the red line showing the NERC underfrequency
requirements (continent wide standard on UFLS) since entities within NPCC must meet the
NPCC performance.
There is a typographical error in Attachment B, PRC-006-NPCC-1 was effective July 1,
2015. Revise to:
The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (April, 2017 July 1, 2015 PRC-006-NPCC-1).
For Attachment B, 2.1 and 2.2, compensatory load shedding must be in both the same and
smallest island as the generator (for example, there may be a unit that’s in the NE and CT
islands. We would need to make sure that the compensatory load shedding was in the CT
island., revise as follows:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated protection
settings with the Generator Owner to cause the generator to trip above the appropriate curve in
Figure 2, the Distribution Provider or Transmission Owner is responsible to provide the
appropriate amount of compensatory load to be shed within the smallest island as identified by
the Planning Coordinator in Requirement R1 of this standard that contains the generator.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the set points
defined by the appropriate curve in Figure 2, the Generator Owner shall arrange for a
Distribution Provider or Transmission Owner to provide the appropriate amount of
compensatory load to be shed within the smallest island as identified by the Planning
Coordinator in Requirement R1 of this standard that contains the generator.
11/26/2019
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Automatic Underfrequency Load Shedding
NPCC BOD Approved
Comment Period (8/10/2018 - 9/24/2018)
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Non-Standards in Development
09/24/2018
ISO-New England, Inc.
View Attachment
Documents
09/19/2018
Independent Electricity System Operator
View Attachment
09/06/2018
Talen Energy Supply, LLC
Standards in Development
Comments: The Fig. 2 disturbance ride-through requirements greatly exceed those of the continent-wide standard (PRC024-2) as well as the damage prevention limits set by many turbine OEMs. PRC-024 grandfathers units that cannot meet its
ride-out criteria, but PRC-006-NPCC-2 does so (in R13) only for units that were in service prior to July 1, 2015. R12
consequently is likely to preclude ever uprating our NPCC-area plants by 10% or more. This restriction is not new; it exists
in R15 of the current version of the standard (PRC-006-NPCC-1), but we believe that this circumstance does not prevent us
from using the present opportunity to request removal of this requirement, particularly since turbine OEM limits are not the
only issue causing the standard to be impractical. The disturbance magnitudes in Fig. 2 are extreme, making it impossible to
ensure that units will not suffer indirect trips (e.g. CTG flame-out, steam drum level high/low), especially since such
frequency excursions are likely to be accompanied by upsets to voltage and (due to governor action) MW output. Limits on
frequency relay settings are easy to implement, but, "shall not trip," requirements can lead to unsolvable frequency-vsother cause quandaries. R13 of PRC-006-NPCC-2 is also a concern, in that GOs with Fig. 2 conflicts for existing units in the
ISO-NE and NYISO areas must, “ arrange for compensatory load shedding, in accordance with Attachment B and as
provided by a Distribution Provider or Transmission Owner, that is adequate to compensate for the loss of generator(s) due
to early tripping that is within the UFLS island identified by the Planning Coordinator in Requirement R2.” The term,
“arrange for” seems to imply that there exists a market for compensatory load shedding (there is none) or that ISOs will
cooperate in this respect (the standard does not appear to require them to do so). Once again this is an existing problem, in
R16 of PRC-006-NPCC-1, not something new for Rev. 2 of the standard. R16 of PRC-006-NPCC-2 (R19 of PRC-006-NPCC-1)
is unreasonable as well, in that the allowance for OEM restrictions is cut off at 57.8 Hz. Units that can’t run this low are
evidently forced to retire or to set their relays in a fashion contradicting good engineering practice (i.e. allowing equipment
to be damaged).
08/24/2018
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1/1
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes
No
Comments: For the sake of clarity consider the following language, which spells out what
we want: “Set the underfrequency protection to operate at a frequency setting that is as low as
possible in accordance with the plant design”
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: The requirements are cost-effective as written
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: The purpose paragraph notes that the standard establishes more stringent
program requirements. It is unclear what we are comparing against. Are we comparing this
standard against Directory 12, the NERC PRC-006-3 standard, the previous NPCC PRC-006NPCC-01? Consider clarifying the purpose with something like:
“The NPCC Automatic Underfrequency Load Shedding (UFLS) regional Reliability Standard
establishes specific NPCC UFLS program requirements that are more stringent than those of
prior NPCC standards to ensure that declining frequency is arrested and recovered in
accordance with established NPCC performance requirements stipulated in this document.”
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Standard Development Timeline
This section is maintained by the drafting team during the development of the standard and will
be removed when the standard is adopted by the NERC Board of Trustees (Board).
Description of Current Draft
Completed Actions
Regional Standards Committee approved Regional Standard
Authorization Request (RSAR) for posting
Anticipated Actions
Date
June 23, 2015
Date
1st 45-day Formal Comment Period
September 1, 2017 October 18, 2017
2nd 45-day Formal Comment Period
April 16, 2018 –
June 1, 2018
30-day Pre-ballot Period
10-day ballot Period
Board adoption
PRC-006-NPCC-2
Page 1 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Upon Board adoption, the rationale boxes will be moved to the Supplemental Material Section.
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements to ensure that declining frequency is arrested and recovered in
accordance with established NPCC performance requirements stipulated in this
document.
4.
Applicability:
4.1. Functional Entities:
4.1.1. Generator Owner
4.1.2. Planning Coordinator
4.1.3. Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
4.1.4. Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
5.
Effective Date: See Implementation Plan.
B. Requirements and Measures
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1 also
shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5
Hz for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
PRC-006-NPCC-2
Page 2 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent wide
PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1-3.
M3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1-3).
R4. Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified
by its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• Within 30 calendar days, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
PRC-006-NPCC-2
Page 3 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3.
M4. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit
function is intended to prevent operation of a UFLS relay when the transmission supply is
lost to distribution station feeding many induction motors. Following loss of the
transmission supply, motors may support the voltage while the motors coast down in
speed. The motors coasting down (ringing down) will look like an underfrequency event
to the relay. The inhibit setting is set to a voltage above which the motor load is expected
to sustain. This prevents the underfrequency relay from tripping and locking out
distribution feeder breakers supplying the motor load, between the time the transmission
supply line trips and the time when the line recloses to restore the load. Voltages
sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower than
voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring
down voltages because of cable charging. Therefore, care must be taken so that the
voltage inhibit setting is not higher than the voltage at which UFLS relays are required to
operate to meet UFLS performance criteria.
R5. Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and
time) to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M5. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
PRC-006-NPCC-2
Page 4 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R6. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within
30 calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M6. Each Planning Coordinator shall provide evidence such as letters, emails or other
dated documentation that demonstrates that it meets Requirement R6.
R7. Each Distribution Provider and Transmission Owner that receives a notification
pursuant to Requirement R6 shall develop and submit an implementation plan with
respect to inhibit thresholds for approval by the Planning Coordinator within 90
calendar days of the request from the Planning Coordinator. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
M7. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
R8.
Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
M8. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the
UFLS program for every entity should perfectly match that prescribed in this Standard, for
all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
various areas and sub-areas within any given island do not perfectly track the load cycle
of the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would
occur for any conditions other than peak, therefore, can only approximate that
prescribed in the Standard. To that end, Requirement R11 requires entities to document
measured loads in the UFLS program coincident with their own annual peak, whether or
not that peak occurs at the same time or in the same season as the peak of the identified
island in which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
R9.
Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
PRC-006-NPCC-2
Page 5 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by
measuring or calculating Load through the switches that would disconnect load if
triggered by the UFLS relays. If measured data is unavailable then calculated data may
be used. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
R10. Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements
R13 and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
R11. Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
R12. Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
PRC-006-NPCC-2
Page 6 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R13. For existing non-nuclear units in service prior to July 1, 2015, that have
underfrequency protections set to trip above the appropriate curve in Figure 2:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R13.
R14. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
R15. Each Generator Owner, Distribution Provider or Transmission Owner within the ISONE Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that
is required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
PRC-006-NPCC-2
Page 7 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed
the methodology described in Attachment B and meets Requirement R15.
R16. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at as a low frequency as
possible in accordance with the plant design and licensing limitations but
not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and
dated documentation that demonstrates that it meets Requirement R16.
PRC-006-NPCC-2
Page 8 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 1
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
PRC-006-NPCC-2
Page 9 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
PRC-006-NPCC-2
Page 10 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority:
Northeast Power Coordinating Council
1.2. Evidence Retention:
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 2, 3, 4, 5, 8, and 9.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 6, and 7.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 15.
The Generator Owner shall keep evidence for three calendar years for Measures
10, 11, 12, 13, and 16.
1.3. Compliance Monitoring and Enforcement Program:
Compliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
PRC-006-NPCC-2
Page 11 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Violation Severity Levels
Violation Severity Levels
R#
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator failed to
design an UFLS program having
performance characteristics that
prevent frequency from remaining
below 59.5 Hz in accordance with
Figure 1.
R2.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
wide PRC-006 Standard on UFLS
but did so more than 30 calendar
days and up to and including 40
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
wide PRC-006 Standard on UFLS
but did so more than 40 calendar
days but less than and including 50
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
wide PRC-006 Standard on UFLS
but did so more than 50 calendar
days but less than and including 60
days following a request.
The Planning Coordinator failed to
provide its UFLS island boundaries,
as identified per the NERC
continent wide PRC-006 Standard
on UFLS. within 60 calendar days
following a request.
R3.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%
or less of the relays identified as
included in the UFLS program, or
amount of load tripped is within
10% deviation from the required
amount of Load required to be
shed at each stage
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%40% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
20% deviation from the required
amount of Load required to be
shed at each stage m
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 40%60% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
30% deviation from the required
amount of Load required to be
shed at each stage.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on >
60% of the relays identified as
included in the UFLS program, or
amount of load tripped has a >
30% deviation from the required
amount of Load required to be
shed at each stage
R4.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
but exceeded the permissible
PRC-006-NPCC-1
July 2018
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program failed to meet all of items
in Requirement 5 within 60
Page 12 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items within a time
greater than 20 calendar days but
less than or equal to 30 calendar
days.
time frame for one or more of the
4 items within a time greater than
30 calendar days but less than or
equal to 60 calendar days.
calendar days of permissible time
for each item.
R5.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
100% but more than (and
including) 95% of relays within its
region’s UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
95% but more than (and including)
90% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and including)
85% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
85% of relays within its region’s
UFLS program.
R6.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 30 calendar days and up to
and including 40 calendar days of
any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 40 calendar days but less
than and including 50 calendar
days of any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar days but less
than and including 60 calendar
days of any changes.
R7.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 100 calendar days
and up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
R8.
Implemented the inhibit threshold
settings provided by the Planning
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
PRC-006-NPCC-1
July 2018
The Planning Coordinator failed to
provide to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds
within 60 calendar days after any
changes
The Distribution Provider or
Transmission Owner failed to
develop and submit its
implementation plan within 120
days following the request.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
Page 13 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
less than 100% but more than (and
including) 95% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 95% but more than (and
including) 90% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 90% but more than (and
including) 85% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 85% of UFLS relays.
R9.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 16 calendar
months but less than (and
including)17 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar
months but less than (and
including)18 calendar months
since last update.
The Distribution Provider or
Transmission Owner failed to
provide to its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 within 18 calendar months
since last update.
R10.
N/A
N/A
N/A
R11.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
45calendar days and less than (and
including) 55 calendar days of the
Planning Coordinator’s request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
55 calendar days and less than
(and including) 65 calendar days of
the Planning Coordinator’s
request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
65 calendar days and less than
(and including) 75 calendar days of
the Planning Coordinator’s
request.
The Generator Owner failed to
transmit the generator
underfrequency trip setting and
time delay within 75 calendar days
of the Planning Coordinator’s
request.
R12.
N/A
N/A
The Generator Owner with a new
generating unit, or an existing
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
PRC-006-NPCC-1
July 2018
The Generator Owner did not set
each generator underfrequency
trip relay, if so equipped, on or
below the appropriate generator
underfrequency trip protection
settings threshold curve in Figure
2, except as otherwise exempted.
Page 14 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
generator increasing its net
capability by greater than 10%:
Did not fulfill the obligation of
Requirement R12; Part 12.1
capability by greater than 10%, did
not fulfill the obligations of
Requirement R12, Part 12.1 and
Part 12.2.
OR
Did not fulfill the obligation of
Requirement R12, Part 12.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirement 13, Part 13.1
R13.
N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinatoras specified
in Requirement R13, Part 13.2.
R14.
N/A
N/A
N/A
The Planning Coordinator did not
apply the criteria described in
Attachment A to determine the
compensatory load shedding that
is required.
R15.
N/A
N/A
N/A
The Generator Owner, Distribution
Provider, or Transmission Owner
did not apply the criteria described
in Attachment B to determine the
compensatory load shedding that
is required.
R16.
N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis for
the settings to the Planning
The Generator Owner:
The Generator Owner did not
fulfill the obligations of
Requirement R16, Part 16.1 and
Part 16.2.
PRC-006-NPCC-1
July 2018
Failed to set the underfrequency
protection as specified in
Requirement R16; Part 16.1
The Planning Coordinator in
Ontario, Québec and the Maritime
Provinces or the Generator Owner
within the ISO-NE and in NYISO
Planning Coordinator areas failed
to arrange for compensatory load
shedding as specified in
Requirement R13, Part 13.3.
OR
Page 15 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Coordinator as specified in
Requirement R16, Part 16.3.
Failed to set the frequency trip
setting upper tolerance as
specified in Requirement R16, Part
16.2.
D. Regional Variances
None.
E. Associated Documents
Technical Rationale
PRC-006-NPCC-1
July 2018
Page 16 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Version History
Version
Date
Action
1
2-9-2012
Adopted by Board of Trustees
2
6-23-2015
RSAR Submitted
PRC-006-NPCC-1
July 2018
Change
Tracking
Page 17 of 24
AAA-000-0 Supplemental Material
Standard Attachments
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (April, 2017 PRC-006-NPCC-1). The list must
indicate generating units, if any, that have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
Draft Number of Standard
Month Year
Page 18 of 24
AAA-000-0 Supplemental Material
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage
(or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the electric system
for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
Draft Number of Standard
Month Year
Page 19 of 24
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (April, 2017 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above
the appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip
above the appropriate curve in Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the smallest island identified by the
Planning Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet
the set points defined by the appropriate curve in Figure 2, the Generator Owner
shall arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
Draft Number of Standard
Month Year
Page 20 of 24
AAA-000-0 Supplemental Material
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facility.
Draft Number of Standard
Month Year
Page 21 of 24
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2-3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 22 of 24
AAA-000-0 Supplemental Material
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
28 – 50
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 23 of 24
AAA-000-0 Supplemental Material
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
• HVDC dynamic modeling
Draft Number of Standard
Month Year
Page 24 of 24
Implementation Plan
Regional Reliability Standard PRC-006-NPCC-2 – Automatic
Underfrequency Load Shedding
Applicable Standard(s)
•
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requested Retirement(s)
•
PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding
Applicable Entities
•
•
•
•
Generator Owners
Planning Coordinators
Distribution Providers that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Transmission Owners that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Background
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. To determine if the applicability of the standard needs to be revised in accordance with
Project 2014-01 Dispersed Generation Resources.
2. To determine if the performance requirements as contained in the criteria of NPCC
Directory#12 Sections 5.1.1 and 5.1.2 should be explicitly included in the requirements
of the Regional Standard and potential retirement of Directory 12 Automatic
Underfrequency Load Shedding Program.
3. Review Attachment C in PRC-006-NPCC-1 to address the implications of the design
assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. Review and revise Table 4 in Attachment C in accordance with the 2013 NPCC UFLS
Adequacy Assessment. Additionally, the applicability of Requirements R4 and R5 will be
reviewed to consider that Hydro Quebec is not part of the Eastern Interconnection.
Effective Date
All requirements with the exception of R3 will be enforceable on the first day of the first
calendar quarter following the applicable governmental and regulatory approvals.
R3 will be enforceable on the first day of the first calendar quarter 12 months following
the applicable governmental and regulatory approvals.
Retirement Date
The NPCC Regional Reliability Standard PRC-006-NPCC-1 shall be retired immediately
prior to the Effective Date of PRC-006-NPCC-2.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements to ensure that declining frequency is arrested and recovered in accordance
with established NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.3. Distribution Providers that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program as established by the
Planning Coordinators.
4.4. Transmission Owners that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program as established by the
Planning Coordinators.
5.
Effective Date:
Reference toSee Implementation Plan.
B. Requirements
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Note that
Figure 1 also shows the NERC criteria as defined in the NERC PRC Standard on
UFLS.
R1.
Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an
UFLS program, pertaining to islands wholly within the NPCC Region, having performance
characteristics that prevents the frequency from
remaining below 59.5 Hz for greater more than 30 seconds in accordance with Figure 1.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M1.
Each Planning Coordinator shall have evidence such as reports, system studies and/or
realtime power flow data captured from actual system events and other dated documentation
that demonstrates it meets Requirement R1.
R2.
Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and
Transmission Owners within 30 calendar days of receipt of a request. [Violation Risk Factor
1
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Lower] [Time Horizon: Long Term Planning]
M2.
Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Planning Coordinator shall, within 30 calendar days of completion of its UFLS system
studies, identify to the Regional Entity all non-BES generation facilities, within its Planning
Coordinator Area, that must not trip above the appropriate generator underfrequency trip
threshold curve in Figure 2 in order to support UFLS program performance requirements.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
M3. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
R34.
Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each island identified per the NERC continent wide
PRC-006 Standard on UFLS as follows:. [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
•
34.1.
The UFLS program shall be implemented by each Distribution Provider
and Transmission Owner according to the frequency thresholds, nominal
operating times and load shedding amounts specified in Attachment C, Tables 1
through 3; or,
•
34.2.
The program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS iIsland
identified by the Planning Coordinator per R2. These multiple Distribution
Providers or Transmission Owners, via mutual agreement, shall act as a single
entity to provide an aggregated automatic UFLS program that sheds their
coincident peak aggregated net Load according to the frequency thresholds, total
nominal operating time and load shedding amounts specified in Attachment C,
Tables 1- through 3.
M34. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the corresponding
frequency thresholds, on those circuits included in its UFLS program identified in
Requirement R34. (Attachment C Tables 1-3).
R54.
2
Each Distribution Provider or Transmission Owner that cannot meet the tolerances and/or
number of stages and frequency set points specified in the UFLS Program, shallEach
Distribution Provider or Transmission Owner in the Eastern Interconnection portion of
NPCC that does not meet the UFLS program parameters specified in Attachment C,
Table 1-3, and each Distribution Provider or Transmission Owner in the Quebec
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Interconnection that does not meet the UFLS program parameters specified by its
Planning Coordinator shall Nnotify its Planning Coordinator within 30 calendar days and
shall: notify its Planning Coordinator within the following 30 calendar days of
identification and shall: [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
• Within 30 calendar days, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates that the
deviations from the program parameters will not result in failure of UFLS performance
criteria being met for any island. The technical study must be acceptable to the Planning
Coordinator prior to implementing deviations from program parameters and shall
demonstrate coordination with UFLS programs of all entities residing within the same
island(s) identified by the Planning Coordinator in Requirement R2. The technical study
shall also demonstrate coordination with other UFLS programs of adjoining Planning
Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no alternative
load shedding solution is available that would allow the Distribution Provider or
Transmission Owner to comply with UFLS Attachment C Table 2 or Attachment C Table
3.
Notify its Planning Coordinator within 30 calendar days
Within the following 180 calendar days from notification of the Planning Coordinator,
develop a Corrective Action Plan and a schedule for implementation that is mutually
agreed upon with its Planning Coordinator; or
Within the following 180 calendar days from notification to the Planning Coordinator, provide
its Planning Coordinator with a technical study that demonstrates that the deviations from the
program parameters will not result in failure of UFLS performance criteria being met for any
island. The technical study must be acceptable to the Planning Coordinator prior to implementing
deviations from program parameters, and shall demonstrate coordination with UFLS programs of
all adjoining entities residing within the same island(s) identified by the Planning Coordinator in
R2. ,The technical study shall also demonstrate coordination and coordination with other UFLS
programs of adjoining Planning Coordinators.
of recognition
Within the following 180 calendar days of the identification, develop a Corrective Action
Plan and a schedule for implementation that is mutually agreed upon with the Planning
Coordinator, and implement the Corrective Action Plan; or.
5.1.
Within the following 90 calendar days, determine if tolerances can be met through
adjustments and notify the Planning CoordinatorWithin the following 180 calendar days of the
5.2.
3
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
identification, provide its Planning Coordinator with a technical study that demonstrates that the
deviations from the program parameters will not result in failure of UFLS performance criteria
being met for any island. This technical study shall be coordinated with UFLS programs of
adjoining entities, and shall be acceptable to the Planning Coordinator.
If adjustments are possible, make the adjustments within 180 calendar days after
determining that adjustments are possible, and notify the Planning Coordinator when complete,
or,
5.3.
5.4.
If adjustments are not possible then:
5.4.1. Each Distribution Provider or Transmission Owner subject to Attachment C, Table 1, shall
within 180 calendar days, provide its Planning Coordinator with a technical study that
demonstrates that the Distribution Provider’s or Transmission Owner’s specific deviations from
the requirements of UFLS Attachment C, Table 1 will not have a significant adverse impact on
the BES, or
5.4.2. Each Distribution Provider or Transmission Owner subject to Attachment C, Table 2 or
Table 3, or in the Quebec Interconnection, shall within 90 calendar days, provide its Planning
Coordinator with an analysis demonstrating that no alternative load shedding solution is
available that would allow the Distribution Provider or Transmission Owner to comply with the
UFLS program.
M54. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R45.
Rationale for Requirement R6: Operation of underfrequency relays results directly
in load being shed, interrupting service to customers. The security of underfrequency
relays against misoperation is therefore paramount. The 100 ms minimum time delay
specified in R6 serves to prevent premature activation of these relays during shortlived transient frequency excursions that may occur on a localized basis in the absence
of a serious system event wherein UFLS would be appropriate. This intentional delay
helps to ensure that the relays activate only for frequency excursions that are due to
actual system events that require automatic UFLS to reestablish the balance of
generation to load.
R6. Each Distribution Provider and Transmission Owner shall set each underfrequency relay
that is part of its region’s UFLS program with a 100 ms minimum time delay. [Violation
Risk Factor: Medium] [Time Horizon: Long Term Planning]
M6. Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the minimum
time delay, in accordance with Requirement R6.
Rationale for Requirement R75: An inhibit function provides supervisory control
over a UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay
4
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
operation if the sensed voltage decreases below an adjustable setting. An undervoltage
inhibit function is intended to prevent operation of a UFLS relay when the
transmission supply is lost to distribution station feeding many induction motors.
Following loss of the transmission supply, motors may support the voltage while the
motors coast down in speed. The motors coasting down (ringing down) will look like
an uUnderfrequency event to the relay. The inhibit setting is set to a voltage above
which the motor load is expected to sustain. This prevents the uUnderfrequency relay
from tripping and locking out distribution feeder breakers supplying the motor load,
between the time the transmission supply line trips and the time when the line recloses
to restore the load. Voltages sustained by motors that are coasting down (e.g. 0.70 pu)
are typically much lower than voltages at which the UFLS relays are required to
operate to meet UFLS performance criteria. However, motor loads supplied by cable
networks typically have higher ring down voltages because of cable charging.
Therefore, care must be taken so that the voltage inhibit setting is not higher than the
voltage at which UFLS relays are required to operate to meet UFLS performance
criteria.
R57.
Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least
once per five calendar years (such as but not limited to voltage, current and time) to be
utilized within its region’s UFLS program. [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
M75. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R57.
R86.
Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations
Planning]
M68. Each Planning Coordinator shall provide evidence such as letters, emails, or other dated
documentation that demonstrates that it meets Requirement R68.
R79.
Each Distribution Provider and Transmission Owner that receives a notification pursuant
to Requirement R68 shall develop and submit an implementation plan with respect to
inhibit threshold for approval by the Planning Coordinator within 90 calendar days of the
request from the Planning Coordinator. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M79. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets Requirement
R79.
5
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R810. Each Distribution Provider and Transmission Owner shall implement the inhibit
threshold
settings provided by the Planning Coordinator in accordance with Requirement R68 and
based on the Planning Coordinator approved implementation plan in accordance with
R79.
[Violation Risk Factor: High] [Time Horizon: Operations Planning]
M810.
Each Distribution Provider and Transmission Owner shall provide evidence such
as test
reports, data sheets, completed work orders, or other documentation that demonstrates
that
it meets Requirement R810.
Rationale for Requirement R911: It is recognized that, iIdeally, the amount of load
to be shed in each stage of the UFLS program for every entity should perfectly match
that prescribed in this Standard, for all phases of the load cycle, i.e., seasonal (summer
vs. winter), weekly (weekday vs. weekend vs. holidays), daily (morning, noon, and
night), etc. for all of the identified islands. Practically, however, this is obviously not
possible because the load cycles of the various areas and sub-areas within any given
island do not perfectly track the load cycle of the overall island. The UFLS program,
on the other hand, is designed based on peak conditions for the overall island. The
percentages of actual load shedding that would occur for any conditions other than
peak, therefore, can only approximate that prescribed in the Standard. This being
said, entities are required by R11 to document measured loads in the UFLS program
coincident with their own annual peak, whether or not that peak occurs at the same
time or in the same season as the peak of the identified island in which their load
resides. Using individual entity peaks vs. overall island peaks provides a consistent
approach for accounting purposes among the very entities that are responsible for
designing and maintaining their UFLS programs.
R911. Each Transmission Owner and Distribution Provider shall annually provide
documentation,
with no more than 15 calendar months between updates, to its Planning Coordinator of the
actual net Load that would have been shed by the UFLS relays at each UFLS stage. The
actual net Load shall be coincident with the entity’s integrated hourly peak net Load during
the previous year, as determined by measuring or calculating Load through the switches
that would disconnect load if triggered by the UFLS relays. If measured data is unavailable then
calculated data may be used. [Violation Risk Factor: Lower]
[Time Horizon: Long Term Planning]
M911.
6
Each Distribution Provider and Transmission Owner shall provide
evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator
that indicates the frequency set point, the net amount of load shed and the percentage of
its
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
peak load at each stage of its UFLS program to demonstrate that it meets Requirement
R911.
R102. Each Generator Owner shall set each generator underfrequency trip relay, if so equipped,
on or below the appropriate generator underfrequency trip protection settings threshold
curve in Figure 2, except as otherwise exempted in Requirements R135 and R168.
[Violation
Risk Factor: MediumHigh] [Time Horizon: Long Term Planning]
M102. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets
or
other documentation that demonstrates that it meets Requirement R102.
R113.
Each Generator Owner shall transmit the generator underfrequency
trip setting and time
delay within 45 calendar days of the Planning Coordinator’s
request.
[Violation Risk Factor: Lower] [Time Horizon: Operations Planning]
M113. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R113.
R124. Each Generator Owner with a new generating unit, or an existing generator increasing its
net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon:
Long Term Planning]
R12.1 124.1. Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate generator tripping
threshold curve in Figure 2.
.
R12.2. 124.2. Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such that they
will not trip the generating unit during underfrequency conditions above the
appropriate generator underfrequency trip protection settings threshold curve in
Figure 2.
M124. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement
R124.
R135. For existing non-nuclear units in service prior to the effective dateJuly 1, 2015 of this
standard, as
documented in accordance with Attachments A or B, that have underfrequency
protections
7
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
set to trip above the appropriate curve in Figure 2: [Violation Risk Factor: MediumHigh]
[Time
Horizon: Long Term Planning]
R135.1.
Each Generator Owner shall set the underfrequency protection to operate
at the lowest frequency allowed by the plant design and licensing limitations.
R135.2. Each Generator Owner shall transmit the existing underfrequency settings and
any changes to the underfrequency settings along with the technical basis for the
settings to the Planning Coordinator.
R135.3. Each Planning Coordinator in Ontario, Québec and the Maritime Provinces in
accordance with Attachment A and each Generator Owner in the New-England
States and in New York State in accordance with Attachment B shall arrange for
compensatory load shedding, in accordance with Attachment A and as provided by
a Distribution Provider or Transmission Owner, that is adequate to compensate for
the loss of generator(s) due to early tripping that is within the UFLS island
identified by the Planning Coordinator in Requirement R2.
R13.4. Each Generator Owner in the ISO-NE Planning Coordinator area and in NYISO
Planning Coordinator area shall arrange for compensatory load shedding, in
accordance with Attachment B and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of generator(s)
due to early tripping that is within the UFLS island identified by the Planning
Coordinator in Requirement R2.
M135. Each Generator Owner with existing non-nuclear units in service prior to the effective
date
of this StandardJuly 1, 2015 which have underfrequency tripping that is not
compliant with
Requirement R10 2shall provide evidence such as reports, spreadsheets, memorandum
or
dated documentation demonstrating that it meets Requirement R153.
R146. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the
criteria described in Attachment A to determine the compensatory load shedding that is
required in Requirement R135.3 for generating units in its respective NPCC area.
[Violation
Risk Factor: MediumHigh] [Time Horizon: Long Term Planning]
M146. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates that it
followed the methodology described in Attachment A and meets Requirement R146.
8
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R157. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning
Coordinator area of ISO-NEISO-NE Planning Coordinator area and in or the New
YorkNY ISO Planning Coordinator Area shall apply the criteria described in
Attachment B to determine the compensatory load shedding that is required in
Requirement
R135.43 for generating units in its respective NPCC area. [Violation Risk Factor:
MediumHigh]
[Time Horizon: Long Term Planning]
M157. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning
Coordinator area of ISO-NE or the New YorkNY ISO shall provide evidence such as
reports,
memorandum, or other documentation that demonstrates that it followed the
methodology
described in Attachment B and meets Requirement R157.
R168. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2, based on their licensing design basis, shall: [Violation Risk
Factor: MediumHigh] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at as a low frequency as
possible in accordance with the plant design and licensing limitations but
not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
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R16.1 Set the underfrequency protection to operate at as low a frequency as possible
in accordance with the plant design and licensing limitations but not greater than 57.8
Hz.
R16.2 Each Generator Owner of existing nuclear non-boiling water
generating plants that cannot satisfy the condition of maximum 57.8 Hz imposed by
R16.1., due to extenuating circumstances such as equipment limitations or design and
licensing limitations, shall set the underfrequency protection to operate at the lowest
frequency allowed by the existing limiting factor. Auxiliary power supplies located at
the nuclear generating plants, driven by non-nuclear prime movers, that are connected
to the grid only for the duration of testing, are considered non-nuclear units and are
subject to compliance with the obligations spelled out in requirement R13.
9
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R16.3 Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
R16.4 Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
168.1.
Set the underfrequency protection to operate at as low a frequency as
possible in accordance with the plant design and licensing limitations but not greater
than 57.8 Hz.
168.2.
Set the frequency trip setting upper tolerance to no greater than + 0.1
Hz.
168.3.
Transmit the initial frequency trip setting and any changes to the
setting and the technical basis for the settings to the Planning Coordinator.
M168. Each Generator Owner of nuclear units that have have been specifically identified by
NPCC as
having generator trip settings above the generator trip curve in Figure 2 shall provide
evidence such as letters, reports and dated documentation that demonstrates that it meets
Requirement R168.
10
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 1
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
11
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
12
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
13
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
Time (sec)
C. Compliance
1.
14
Compliance Monitoring Process
1000
55.5
55
10000
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
1.1. Compliance Enforcement Authority
Northeast Power Coordinating CouncilPCC Compliance Committee
1.2. Compliance Monitoring Period and Reset Time Frame
Not Applicable
1.3.1.2.
DataEvidence Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 24, 35, 46, 57, 810, and 911, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 3, 68, and 79, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall
keep evidence for three calendar years for Measure 17.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 118, 22, and 235.
The Generator Owner shall keep evidence for three calendar years for Measures
103, 114, 152, 136, and 169.
1.4.1.3.
Compliance Monitoring and Assessment Processes
Compliance AuditSelf -Certifications.
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
ComplaintsSpot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.
1.5. Additional Compliance Information
None.
15
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
2.
Violation Severity Levels
Requirement
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1
N/A
N/A
N/A
The Plannning
Coordinator failed to
design an UFLS program
having performance
characteristics that
prevent frequency from
remaining below 59.5 Hz
in accordance with Figure
1.
R2
The
Planning
The
Planning Coordinator
provided its UFLS
island boundaries, as
identified per the NERC
PRC Standard on UFLS
but did so more than 30
calendar days and up to
and including 40 days
following
a
request.Coordinator
provided
island
boundaries, as identified
per the NERC continent
wide PRC-006 Standard
on UFLS but did so
more than 30 calendar
days and up to and
including
40
days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC continent wide
PRC-006 Standard on
UFLS but did so more
than 40 calendar days
but less than and
including 50 days
following a request.The
Planning Coordinator
provided its UFLS
island boundaries, as
identified per the
NERC PRC Standard
on UFLS but did so
more than 40 calendar
days but less than and
including 50 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC continent wide
PRC-006 Standard on
UFLS but did so more
than 50 calendar days
but less than and
including 60 days
following a
request.The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC PRC Standard
on UFLS but did so
more than 50 calendar
days but less than and
including 60 days
following a request.
The Planning Coordinator
failed to provide its UFLS
island boundaries, as
identified per the NERC
continent wide PRC-006
Standard on UFLS. within
60 calendar days
following a request.The
Planning Coordinator
failed to provide its UFLS
island boundaries, as
identified per the NERC
PRC Standard on UFLS.
within 60 calendar days
following a request.
16
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R3
R34
R45
17
The Planning
Coordinator identified
to the Regional Entity
all non-BES generation
facilities within its
Planning Coordinator
Area that must not trip
above the appropriate
generator
underfrequency trip
threshold curve in order
to support UFLS
program performance
requirements, but did so
more than 30 calendar
daysand up to and
including 40 days after
completion of the
system studies.
The Planning
Coordinator identified
to the Regional Entity
all non-BES generation
facilities within its
Planning Coordinator
Area that must not trip
above the appropriate
generator
underfrequency trip
threshold curve in order
to support the UFLS
program performance
requirements, but did so
more than 40 days but
less than calendar days
but less than and
including 50 days after
completion of the
system studies.
The Planning
Coordinator identified
to the Regional Entity
all non-BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in
order to support the
UFLS program
performance
requirements,, but did
so more than 50
calendar days but less
than and including 60
days after completion
of the system studies.
The Planning Coordinator
identified all non-BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in order to
support the UFLS
program performance
requirements, but failed to
inform the Regional
Entity within 60 calendar
days after completion of
the system studies.
The Distribution
Provider or Transmission
Owner failed to apply
appropriate settings on
20% or less of the relays
identified as included in
the UFLS program, or
amount of load tripped is
within 10% deviation
from the required
amount of Load required
to be shed at each stage
The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
20%-40% of the relays
identified as included in
the UFLS program, or
amount of load tripped
is within 20% deviation
from the required
amount of Load
required to be shed at
each stage m
The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
40%-60% of the relays
identified as included
in the UFLS program,
or amount of load
tripped is within 30%
deviation from the
required amount of
Load required to be
shed at each stage.
The Distribution
Provider or Transmission
Owner failed to apply
appropriate settings on >
60% of the relays
identified as included in
the UFLS program, or
amount of load tripped
has a > 30% deviation
from the required
amount of Load required
to be shed at each
stageThe Distribution
Provider or Transmission
Owner failed to
implement the automatic
UFLS program on an
island basis as specified
by Requirement R4, Part
4.1 or Part 4.2.
The Distribution
Provider or Transmission
Owner that cannot meet
the tolerances and/or
The Distribution
Provider or
Transmission Owner
that cannot meet the
The Distribution
Provider or
Transmission Owner
that cannot meet the
OR
The Planning Coordinator
did not identify the BES
generation facilities
within its Planning
Coordinator Area that
must not trip above the
appropriate generator
underfrequency trip
threshold curve in order
to supportUFLS program
performance
requirements.
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The Distribution
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Owner that cannot meet
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the tolerances and/or
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations for
Requirement R5, Parts
%.1 through Part 5.4 but
exceeded the permissible
time frame for one or
more of the 4 items by a
period of up to 10
calendar days but less
than or equal to 20
calendar days.The
Distribution Provider or
Transmission Owner that
cannot meet the
tolerances and/or number
of stages and frequency
set points specified in the
UFLS Program fulfilled
its obligations ir
Requirement R5, Parts
%.1 through Part 5.4 but
exceeded the permissible
time frame for one or
more of the 4 items by a
period of up to 10
calendar days but less
than or equal to 20
calendar days.
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations for
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the 4
items within a time
greater than 20 calendar
days but less than or
equal to 30 calendar
days. The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations ir
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the 4
items within a time
greater than 20 calendar
days but less than or
equal to 30 calendar
days.
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations but
exceeded the
permissible time
frame for one or more
of the 4 items within
a time greater than 30
calendar days but less
than or equal to 60
calendar days.
R6
The Distribution
Provider or Transmission
Owner set less than
100% but more than (and
including) 95% of its
underfrequency relays
that are part of its
region’s UFLS program
with a 100 ms minimum
time delay.
The Distribution
Provider or
Transmission Owner
set less than 95% but
more than (and
including) 90% of its
underfrequency relays
that are part of its
region’s UFLS program
with a 100 ms
minimum time delay.
The Distribution
Provider or
Transmission Owner
set less than 90% but
more than (and
including) 85% of its
underfrequency relays
that are part of its
region’s UFLS
program with a 100
ms minimum time
delay.
The Distribution
Provider or Transmission
Owner set less than 85%
ot its underfrequency
relays that are part of its
region’s UFLS program
with a 100 ms minimum
time delay.
R57
The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 100%
but more than (and
The Planning
Coordinator
developed or reviewed
settings for inhibit
thresholds at least
once per five calendar
years, for less than
The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 90% but more
The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 85%
of relays within its
18
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations but
exceeded the
permissible time
frame for one or more
of the 4 items within
a time greater than 30
calendar days but less
than or equal to 60
calendar days.
number of stages and
frequency set points
specified in the UFLS
Program failed to meet
all of items in
Requirement 5 within 60
calendar days of
permissible time for each
item.
The Distribution
Provider or Transmission
Owner that cannot meet
the tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program failed to meet
all of items in
Requirement 5 within 60
calendar days of
permissible time for each
item.
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R68
R79
19
including) 95% of relays
within its region’s UFLS
program.The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 100%
but more than (and
including) 95% of relays
within its region’s UFLS
program.
95% but more than
(and including) 90%
of relays within its
region’s UFLS
program.The Planning
Coordinator
developed or reviewed
settings for inhibit
thresholds at least
once per five calendar
years, for less than
95% but more than
(and including) 90%
of relays within its
region’s UFLS
program.
than (and including)
85% of relays within
its region’s UFLS
program.The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 90% but more
than (and including)
85% of relays within
its region’s UFLS
program.
region’s UFLS
program.The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 85%
of relays within its
region’s UFLS program.
The Planning
Coordinator provided to
a Transmission Owner or
Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds more than 30
calendar days and up to
and including 40
calendar days of any
changes. The Planning
Coordinator provided to
a Transmission Owner or
Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds more than 30
calendar days and up to
and including 40
calendar days of any
changes.
The Planning
Coordinator provided to
a Transmission Owner
or Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds more than 40
calendar days but less
than and including 50
calendar days of any
changes.The Planning
Coordinator provided to
a Transmission Owner
or Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds more than 40
calendar daysbut less
than and including 50
calendar days of any
changes.
The Planning
Coordinator provided
to a Transmission
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds
more than 50 calendar
days but less than and
including 60 calendar
days of any
changes.The Planning
Coordinator provided
to a Transmission
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds
more than 50 calendar
daysbut less than and
including 60 calendar
days of any changes.
The Planning
Coordinator failed to
provide to a
Transmission Owner or
Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds within 60
calendar days after any
changes
The Distribution
Provider or Transmission
Owner developed and
submitted its
implementation plan
more than 90 calendar
days and up to and
including 100 calendar
days following the
request.The Distribution
Provider or Transmission
Owner developed and
submitted its
implementation plan
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 100 calendar
days and up to and
including 110 calendar
days following the
request.The
Distribution Provider or
Transmission Owner
developed and
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 110
calendar days and up
to and including 120
calendar days
following the
request.The
Distribution Provider
or Transmission
The Distribution
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Owner failed to develop
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and submit its
implementation plan
within 120 days
following the request.
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The Planning
Coordinator failed to
provide to a
Transmission Owner or
Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds within 60
calendar days after any
changes
The Distribution
Provider or Transmission
Owner failed to develop
and submit its
implementation plan
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
more than 90 calendar
days and up to and
including 100 calendar
days following the
request.
submitted its
implementation plan
more than 100 calendar
days and up to and
including 110 calendar
days following the
request.
Owner developed and
submitted its
implementation plan
more than 110
calendar days and up
to and including 120
calendar days
following the request.
within 120 days
following the request.
R810
Implemented the
inhibit threshold
settings provided by the
Planning Coordinator
in accordance with the
Planning Coordinator
approved
implementation plan
for less than 100% but
more than (and
including) 95% of
UFLS
relays.implemented the
inhibit threshold
settings provided by the
Planning Coordinator
in accordance with the
Planning Coordinator
approved
implementation plan
for less than 100% but
more than (and
including) 95% of
UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the inhibit
threshold settings
provided by the
Planning Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 95% but more
than (and including)
90% of UFLS
relays.The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by the
Planning Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 95% but more
than (and including)
90% of UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 90% but
more than (and
including) 85% of
UFLS relays.The
Distribution Provider
or Transmission
Owner implemented
the inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 90% but
more than (and
including) 85 % of
UFLS relays.
The Distribution
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Owner implemented the
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provided by the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 85% of UFLS
relays.The Distribution
Provider or Transmission
Owner implemented the
inhibit threshold settings
provided by the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 85 % of UFLS
relays.
R911
The Distribution
Provider or Transmission
Owner provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
more than 15 calendar
months but less than
(and including) 16
calendar months since
last update.The
The Distribution
Provider or
Transmission Owner
provided to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11 more
than 16 calendar
months but less than
(and including)17
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 17 calendar
months but less than
(and including)18
The Distribution
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Owner failed to provide
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to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
within 18 calendar
months since last
update.The Distribution
Provider or Transmission
20
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R102
Distribution Provider or
Transmission Owner
provided to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
more than 15 calendar
months but less than
(and including) 16
calendar months since
last update.
calendar months since
last update.The
Distribution Provider or
Transmission Owner
provided to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11 more
than 16 calendar
months but less than
(and including)17
calendar months since
last update.
calendar months since
last update.The
Distribution Provider
or Transmission
Owner provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 17 calendar
months but less than
(and including)18
calendar months since
last update.
Owner failed to provide
to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
within 18 calendar
months since last update.
N/A
N/A
N/A
The Generator Owner
did not set each
generator
underfrequency trip
relay, if so equipped, on
or below the appropriate
generator
underfrequency trip
protection settings
threshold curve in Figure
2, except as otherwise
exempted.
The Generator Owner
did not set each
generator
underfrequency trip
relay, if so equipped, on
or below the appropriate
generator
underfrequency trip
protection settings
threshold curve in Figure
2, except as otherwise
exempted.
R113
21
The Generator Owner
transmitted the generator
underfrequency trip
setting and time delay
more than 45calendar
days and less than (and
including) 55 calendar
days of the Planning
Coordinator’s
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 55 calendar
days and less than (and
including) 65 calendar
days of the Planning
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 65 calendar
days and less than
(and including) 75
calendar days of the
The Generator Owner
failed to transmit the
generator
underfrequency trip
setting and time delay
within 75 calendar days
of the Planning
Coordinator’s
request.The Generator
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
R124
request.The Generator
Owner transmitted the
generator
underfrequency trip
setting and time delay
more than 45calendar
days and less than (and
including) 55 calendar
days of the Planning
Coordinator’s request.
Coordinator’s
request.The Generator
Owner transmitted the
generator
underfrequency trip
setting and time delay
more than 55 calendar
days and less than (and
including) 65 calendar
days of the Planning
Coordinator’s request.
N/A
N/A
Planning
Coordinator’s
request.The Generator
Owner transmitted the
generator
underfrequency trip
setting and time delay
more than 65 calendar
days and less than
(and including) 75
calendar days of the
Planning
Coordinator’s request.
Owner failed to transmit
the generator
underfrequency trip
setting and time delay
within 75 calendar days
of the Planning
Coordinator’s request.
The Generator Owner
with a new generating
unit, or an existing
generator increasing
its net capability by
greater than 10%:
The Generator Owner
with a new generating
unit, or an existing
generator increasing its
net capability by greater
than 10%, did not fulfill
the obligations of
Requirement R12, Part
12.1 and Part 12.2.
Did not fulfill the
obligation of
Requirement R12;
Part 12.1
OR
Did not fulfill the
obligation of
Requirement R12,
Part 12.2.The
Generator Owner
with a new generating
unit, or an existing
generator increasing
its net capability by
greater than 10%:
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The Generator Owner
with a new generating
unit, or an existing
generator increasing its
net capability by greater
than 10%, did not fulfill
the obligations of
Requirement R15, Part
15.1 and Part 15.2.
Did not: fulfill the
obligation of
Requirement R14;
Part 14.1
OR
Did not fulfill the
obligation of
Requirement R14,
Part 14.2.
R135
22
N/A
The Generator Owner
failed to transmit the
existing underfrequency
settings and any
changes to the
underfrequency settings
along with the technical
basis for the settings to
The Generator Owner
failed to set the
underfrequency
protection to operate at
the lowest frequency
allowed by the plant
design and licensing
limitations a specified
The Planning
Coordinator in Ontario,
Québec and the
Maritime Provinces or
the Generator Owner
within the ISO-NE and
in NYISO Planning
Coordinator areas failed
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
the Planning
Coordinatoras specified
in Requirement R13,
Part 13.2.The
Generator Owner failed
to transmit the existing
underfrequency settings
and any changes to the
underfrequency settings
along with the technical
basis for the settings to
the Planning
Coordinator.as
specified in
Requirement R15, Part
15.2.
in Requirement 13,
Part 13.1
The Generator Owner
failed to set the
underfrequency
protection to operate at
the lowest frequency
allowed by the plant
design and licensing
limitations a specified
in Requirment 15, Part
15.1
to arrange for
compensatory load
shedding as specified in
Requirement R13, Part
13.3.The Planning
Coordinator in Ontario,
Québec and the
Maritime Provinces or
the Generator Owner in
the New-England States
and in New York State
failed to arrange for
compensatory load
shedding as specified in
Requirement R15, Part
15.3.
R146
N/A
N/A
N/A
The Planning
Coordinator did not
apply the criteria
described in Attachment
A to determine the
compensatory load
shedding that is required.
The Planning
Coordinator did not
apply the methodology
described in Attachment
A to determine the
compensatory load
shedding that is required.
R157
N/A
N/A
N/A
The Generator Owner,
Distribution Provider, or
Transmission Owner did
not apply the criteria
described in Attachment
B to determine the
compensatory load
shedding that is
required.The Generator
Owner, Distribution
Provider, or
Transmission Owner did
not apply the
methodology described
in Attachment B to
determine the
compensatory load
shedding that is required.
R168
N/A
The Generator Owner
failed to transmit the
initial frequency trip
setting and any changes
to the setting and the
technical basis for the
The Generator Owner:
The Generator Owner
did not fulfill the
obligations of
Requirement R16, Part
16.1 and Part 16.2.
23
Failed to set the
underfrequency
protection as specified
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
settings to the Planning
Coordinator as
specified in
Requirement R16, Part
16.3.The Generator
Owner failed to
transmit the initial
frequency trip setting
and any changes to the
setting and the technical
basis for the settings to
the Planning
Coordinator as
specified in
Requirement R18, Part
18.3.
in Requirement R16;
Part 16.1
OR
Failed to set the
frequency trip setting
upper tolerance as
specified in
Requirement R16, Part
16.2.The Generator
Owner:
The Generator Owner
did not fulfill the
obligations of
Requirement R18, Part
18.1 and Part 18.2.
Failed to set the
underfrequency
protection as specified
in Requirement R18;
Part 18.1
OR
Failed to set the
frequency trip setting
upper tolerance as
specified in
Requirement R18, Part
18.2.
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 2.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all UFLS islands in which the unit may operate.
24
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (April, 2017 PRC-006-NPCC-1). The list
must indicate generating units, if any, that have their underfrequency protections set to
trip above the appropriate curve in Figure 2. Generating Units not appearing on the list
as of the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate, as identified in Requirement R1
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that is
provided by the Distribution Provider or Transmission Owner shall be in addition
to the amount that the Distribution Provider or Transmission Owner is required to
shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 2 during an underfrequency event. If the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
25
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 2.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all UFLS islands in which the unit may operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units, in their Planning Coordinator area, in service prior to the
effective date of Version 1 of the regional Standard (April, 2017 PRC-006-NPCC-1).
The list must indicate generating units, if any, that have their underfrequency protections
set to trip above the appropriate curve in Figure 2. Generating Units not appearing on the
list as of the effective date of Version 1 of the regional standard, as shown above, must
have their Underfrequency protections set to trip on or below the appropriate curve in
Figure 2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS
relays within the island(s) identified by the Planning Coordinator within which
the generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that is
provided by the Distribution Provider or Transmission Owner shall be in addition
to the amount that the Distribution Provider or Transmission Owner is required to
shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 2 during an underfrequency event. If the highest
26
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
frequency at which the subject generator will trip above the appropriate curve in
Figure 2 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the electric
system for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
27
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (April, 2017 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above the
appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2. The
list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 2, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the smallest island identified by the Planning Coordinator in
Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 2, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
28
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units in service prior to the effective date of Version 1 of the regional
Standard (April, 2017 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, that have their underfrequency protections set to trip above the
appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2. The
list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 2, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
29
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
be shed within the smallest island identified by the Planning Coordinator in
Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 2, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facility.
30
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2-3
29.5 – 31.5
31
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
28 – 50
28 – 50
32
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 2
Load Shed at Stage
as % of TO or DP
Load
Cumulative Load
Shed as % of TO or
DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
33
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
27.5 – 28.5
59.5
10.0
2
29.5 – 31.5
–3
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating
Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
34
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
Guidelines and Technical Basis:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
•
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
•
Unforeseen islanding event
•
Real and reactive load distribution (including changes to location of compensatory load
shedding)
•
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
•
Load characteristics in particular frequency responsive load
•
Automatic load restoration
•
Generation geographical distribution
35
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Standard PRC-006-NPCC-2 Automatic Underfrequency Load Shedding
•
Generator trip settings
•
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
•
Generator dynamic modeling
•
Dynamic VAR device modeling
HVDC dynamic modelingRationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
• HVDC dynamic modeling
36
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
A. Introduction
2.11. Title:
Automatic Underfrequency Load Shedding
2.22. Number:
PRC-006-NPCC-21
2.33. Purpose: The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements to ensure that declining frequency is arrested and recovered in accordance
with established NPCC performance requirements stipulated in this documentTo
provide a regional reliability standard that ensures the development of an effective
automatic underfrequency load shedding (UFLS) program in order to preserve the
security and integrity of the bulk power system during declining system frequency
events in coordination with the NERC UFLS reliability standard characteristics.
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2.44. Applicability:
a.4.1. Generator Owner
b.4.2.
Planning Coordinator
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c.4.3. Distribution Providers that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program established by the Planning
CoordinatorsDistribution Provider
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d.4.4.
Transmission Owners that are responsible for the ownership, operation, or
control of UFLS equipment as required by the UFLS program established by the
Planning CoordinatorsTransmission Owner
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2.55. Effective Date:
See Implementation Plan For the Eastern Interconnection & Québec Interconnection
portions of NPCC excluding the Independent Electricity System Operator (IESO)
Planning Coordinator area of NPCC in Ontario, Canada:
The effective date for Requirements R1, R2, R3, R4, R5, R6, and R7 is the first
day of the first calendar quarter following applicable regulatory approval but no
earlier than January 1, 2016 The effective date for Requirements R8 through R23
is the first day of the first calendar quarter two years following applicable
governmental and regulatory approval.
For the Independent Electricity System Operator (IESO) Planning Coordinator’s area of
NPCC in Ontario, Canada:
All requirements are effective the first day of the first calendar quarter following
applicable governmental and regulatory approval but no earlier than April 1,
2017.
B. Requirements
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
1
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1
also shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1.
Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5 Hz
for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
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M1.
R2.
M2.
R3.
M3.
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
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Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
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Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent wide
PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the frequency
thresholds, total nominal operating time, and load shedding amounts specified
in Attachment C, Tables 1-3.
Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the corresponding
frequency thresholds, on those circuits included in its UFLS program identified in
Requirement R3. (Attachment C, Tables 1-3).
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R4.
M4.
Each Distribution Provider or Transmission Owner in the Eastern Interconnection portion
of NPCC that does not meet the UFLS program parameters specified in Attachment C,
Table 1-3, and each Distribution Provider or Transmission Owner in the Quebec
Interconnection that does not meet the UFLS program parameters specified by its
Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
• Within 30 calendar days, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates that
the deviations from the program parameters will not result in failure of UFLS
performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3
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Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
R1
Each Planning Coordinator shall establish requirements for entities
aggregating their UFLS programs for each anticipated island and requirements for
compensatory load shedding based on islanding criteria (required by the NERC PRC
Standard on UFLS). [Violation Risk Factor: Medium] [Time Horizon: Long Term
Planning]
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Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit function
is intended to prevent operation of a UFLS relay when the transmission supply is lost to
distribution station feeding many induction motors. Following loss of the transmission
supply, motors may support the voltage while the motors coast down in speed. The motors
coasting down (ringing down) will look like an underfrequency event to the relay. The
inhibit setting is set to a voltage above which the motor load is expected to sustain. This
prevents the underfrequency relay from tripping and locking out distribution feeder
breakers supplying the motor load, between the time the transmission supply line trips and
the time when the line recloses to restore the load. Voltages sustained by motors that are
3
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
coasting down (e.g. 0.70 pu) are typically much lower than voltages at which the UFLS
relays are required to operate to meet UFLS performance criteria. However, motor loads
supplied by cable networks typically have higher ring down voltages because of cable
charging. Therefore, care must be taken so that the voltage inhibit setting is not higher than
the voltage at which UFLS relays are required to operate to meet UFLS performance
criteria.
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R5.
M5.
R6.
M6.
R7.
M7.
R8.
M8.
Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and time)
to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
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Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
Each Planning Coordinator shall provide evidence such as letters, emails or other dated
documentation that demonstrates that it meets Requirement R6.
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Each Distribution Provider and Transmission Owner that receives a notification pursuant
to Requirement R6 shall develop and submit an implementation plan with respect to
inhibit thresholds for approval by the Planning Coordinator within 90 calendar days of
the request from the Planning Coordinator. [Violation Risk Factor: Lower] [Time
Horizon: Operations Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets Requirement
R7.
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Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6 and
based on the Planning Coordinator approved implementation plan in accordance with R7.
[Violation Risk Factor: High] [Time Horizon: Operation Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that demonstrates
that it meets Requirement R8.
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Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of
the UFLS program for every entity should perfectly match that prescribed in this Standard,
for all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
various areas and sub-areas within any given island do not perfectly track the load cycle of
4
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would occur
for any conditions other than peak, therefore, can only approximate that prescribed in the
Standard. To that end, Requirement R11 requires entities to document measured loads in
the UFLS program coincident with their own annual peak, whether or not that peak occurs
at the same time or in the same season as the peak of the identified island in which their
load resides. Using individual entity peaks vs. overall island peaks provides a consistent
approach for accounting purposes among the very entities that are responsible for
designing and maintaining their UFLS programs.
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Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its Planning
Coordinator of the actual net Load that would have been shed by the UFLS relays at each
UFLS stage. The actual net Load shall be coincident with the entity’s integrated hourly
peak net Load during the previous year, as determined by measuring or calculating Load
through the switches that would disconnect load if triggered by the UFLS relays. If
measured data is unavailable then calculated data may be used. [Violation Risk Factor:
Lower] [Time Horizon: Long Term Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning Coordinator
that indicates the net amount of load shed and the percentage of its peak load at each
stage of its UFLS program to demonstrate that it meets Requirement R9.
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Each Generator Owner shall set each generator underfrequency trip relay, if so equipped,
on or below the appropriate generator underfrequency trip protection setting threshold
curve in Figure 2, except as otherwise exempted in Requirements R13 and R16.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets
or other documentation that demonstrates that it meets Requirement R10.
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Each Generator Owner shall transmit the generator underfrequency trip setting and time
delay within 45 calendar days of the Planning Coordinator’s request. [Violation Risk
Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
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R12.
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R9.
M9.
R10.
R11.
Each Generator Owner with a new generating unit, or an existing generator increasing its
net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate generator
tripping threshold curve in Figure 2.
5
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency conditions
above the appropriate generator underfrequency trip protection setting
threshold curve in Figure 2.
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R2
Each Planning Coordinator shall, within 30 days of completion
of its system studies required by the NERC PRC Standard on UFLS, identify
to the Regional Entity the generation facilities within its Planning
Coordinator Area necessary to support the UFLS program performance
characteristics. [Violation Risk Factor: Medium] [Time Horizon: Long
Term Planning]
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R3
Each Planning Coordinator shall provide to the Transmission
Owner, Distribution Provider, and Generator Owner within 30 days upon
written request the requirements for entities aggregating the UFLS
programs and requirements for compensatory load shedding program
derived from each Planning Coordinator’s system studies as determined by
Requirement R1. [Violation Risk Factor: Low] [Time Horizon: Long Term
Planning]
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R4
Each Distribution Provider and Transmission Owner in the
Eastern Interconnection portion of NPCC shall implement an automatic
UFLS program reflecting normal operating conditions excluding outages for
its Facilities based on frequency thresholds, total nominal operating time and
amounts specified in Attachment C, Tables 1 through 3, or shall collectively
implement by mutual agreement with one or more Distribution Providers
and Transmission Owners within the same island identified in Requirement
R1 and acting as a single entity, provide an aggregated automatic UFLS
program that sheds their coincident peak aggregated net Load, based on
frequency thresholds, total nominal operating time and amounts specified in
Attachment C, Tables 1 through 3.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R5
Each Distribution Provider or Transmission Owner that must
arm its load to trip on underfrequency in order to meet its requirements as
specified and by doing so exceeds the tolerances and/or deviates from the
number of stages and frequency set points of the UFLS program as specified
in the tables contained in Requirement R4 above, as applicable depending on
its total peak net Load shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
5.1
Inform its Planning Coordinator of the need to exceed the
stated tolerances or the number of stages as shown in UFLS Attachment C,
Table 1 if applicable and
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5.2
Provide its Planning Coordinator with a technical study that
demonstrates that the Distribution Providers or Transmission Owners
specific deviations from the requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on the bulk power system.
5.3
Inform its Planning Coordinator of the need to exceed the
stated tolerances of UFLS Attachment C, Table 2 or Table 3, and in the case
of Attachment C, Table 2 only, the need to deviate from providing two stages
of UFLS, if applicable, and
5.4
Provide its Planning Coordinator with an analysis
demonstrating that no alternative load shedding solution is available that
would allow the Distribution Provider or Transmission Owner to comply
with UFLS Attachment C Table 2 or Attachment C Table 3.
R6 Each Distribution Provider and Transmission Owner in the
Québec Interconnection portion of NPCC shall implement an automatic
UFLS program for its Facilities based on the frequency thresholds, slopes,
total nominal operating time and amounts specified in Attachment C, Table
4 or shall collectively implement by mutual agreement with one or more
Distribution Providers and Transmission Owners within the same island,
identified in Requirement R1, an aggregated automatic UFLS program that
sheds Load based on the frequency thresholds, slopes, total nominal
operating time and amounts specified in Attachment C, Table 4. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
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R7
Each Distribution Provider and Transmission Owner shall set
each underfrequency relay that is part of its region’s UFLS program with the
following minimum time delay:
7.1
Eastern Interconnection – 100 ms
7.2
Québec Interconnection – 200 ms
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R8 Each Planning Coordinator shall develop and review once per
calendar year settings for inhibit thresholds (such as but not limited to
voltage, current and time) to be utilized within its region's UFLS program.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
7
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9
Each Planning Coordinator shall provide each Transmission
Owner and Distribution Provider within its Planning Coordinator area the
applicable inhibit thresholds within 30 days of the initial determination of
those inhibit thresholds and within 30 days of any changes to those
thresholds. [Violation Risk Factor: Medium] [Time Horizon: Operations
Planning]
R10 Each Distribution Provider and Transmission Owner shall
implement the inhibit threshold settings based on the notification provided
by the Planning Coordinator in accordance with Requirement R9. [Violation
Risk Factor: High] [Time Horizon: Operations Planning]
R11 Each Distribution Provider and Transmission Owner shall
develop and submit an implementation plan within 90 days of the request
from the Planning Coordinator for approval by the Planning Coordinator in
accordance with R9. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
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R12 Each Transmission Owner and Distribution Provider shall
annually provide documentation, with no more than 15 months between
updates, to its Planning Coordinator of the actual net Load that would have
been shed by the UFLS relays at each UFLS stage coincident with their
integrated hourly peak net Load during the previous year, as determined by
measuring actual metered Load through the switches that would be opened
by the UFLS relays. [Violation Risk Factor: Lower] [Time Horizon: Long
Term Planning]
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R13 Each Generator Owner shall set each generator
underfrequency trip relay, if so equipped, below the appropriate generator
underfrequency trip protection settings threshold curve in Figure 1, except
as otherwise exempted in Requirements R16 and R19. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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R14 Each Generator Owner shall transmit the generator
underfrequency trip setting and time delay to its Planning Coordinator
within 45 days of the Planning Coordinator’s request. [Violation Risk
Factor: High] [Time Horizon: Operations Planning]
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Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R15 Each Generator Owner with a new generating unit, scheduled
to be in service on or after the effective date of this Standard, or an existing
generator increasing its net capability by greater than 10% shall: [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
15.1 Design measures to prevent the generating unit from tripping
directly or indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 1.
15.2 Design auxiliary system(s) or devices used for the control and
protection of auxiliary system(s), necessary for the generating unit operation
such that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip protection
settings threshold curve in Figure 1.
R16 Each Generator Owner of existing non-nuclear units in service
prior to the effective date of this standard that have underfrequency
protections set to trip above the appropriate curve in Figure 1 shall:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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16.1 Set the underfrequency protection to operate at the lowest
frequency allowed by the plant design and licensing limitations.
16.2 Transmit the existing underfrequency settings and any changes
to the underfrequency settings along with the technical basis for the settings
to the Planning Coordinator.
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16.3 Have compensatory load shedding, as provided by a
Distribution Provider or Transmission Owner that is adequate to
compensate for the loss of their generator due to early tripping.
R17 Each Planning Coordinator in Ontario, Quebec and the
Maritime provinces shall apply the criteria described in Attachment A to
determine the compensatory load shedding that is required in Requirement
R16.3 for generating units in its respective NPCC area. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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R18
Each Generator Owner, Distribution Provider or Transmission
Owner within the Planning Coordinator area of ISO-NE or the New York
ISO shall apply the criteria described in Attachment B to determine the
compensatory load shedding that is required in Requirement R16.3 for
9
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
generating units in its respective NPCC area. [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
R19 Each Generator Owner of existing nuclear generating plants with units
that have underfrequency relay threshold settings above the Eastern
Interconnection generator tripping curve in Figure 1, based on their
licensing design basis, shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
19.1
Set the underfrequency protection to operate at as low a
frequency as possible in accordance with the plant design and licensing
limitations but not greater than 57.8Hz.
19.2
0.1 Hz.
Set the frequency trip setting upper tolerance to no greater than +
19.3
Transmit the initial frequency trip setting and any changes to the
setting and the technical basis for the settings to the Planning Coordinator.
R20
The Planning Coordinator shall update its UFLS program
database as specified by the NERC PRC Standard on UFLS. This database
shall include the following information: [Violation Risk Factor: Lower]
[Time Horizon: Operations Planning]
20.1
For each UFLS relay, including those used for compensatory load
shedding, the amount and location of load shed at peak, the corresponding
frequency threshold and time delay settings.
20.2
The buses at which the Load is modeled in the NPCC library
power flow case.
20.3
A list of all generating units that may be tripped for
underfrequency conditions above the appropriate generator underfrequency
trip protection settings threshold curve in Figure 1, including the frequency
trip threshold and time delay for each protection system.
20.4
The location and amount of additional elements to be switched for
voltage control that are coordinated with UFLS program tripping.
20.5 A list of all UFLS relay inhibit functions along with the corresponding
settings and locations of these relays.
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R21
Each Planning Coordinator shall notify each Distribution
Provider, Transmission Owner, and Generator Owner within its Planning
Coordinator area of changes to load distribution needed to satisfy UFLS
program performance characteristics as specified by the NERC PRC
Standard on UFLS.[Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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R22
Each Distribution Provider, Transmission Owner and Generator
Owner shall implement the load distribution changes based on the
notification provided by the Planning Coordinator in accordance with
Requirement R21. [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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R23
Each Distribution Provider, Transmission Owner and Generator
Owner shall develop and submit an implementation plan within 90 days of
the request from the Planning Coordinator for approval by the Planning
Coordinator in accordance with Requirement R21. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
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M12. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement R12.
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R13.
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For existing non-nuclear units in service prior to July 1, 2015, that have underfrequency
protections set to trip above the appropriate curve in Figure 2: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to operate
at the lowest frequency allowed by the plant design and licensing
limitations.
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
13.2
Each Generator Owner shall transmit the existing underfrequency settings
and any changes to the underfrequency settings along with the technical
basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is within
the UFLS island identified by the Planning Coordinator in Requirement
R2.
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the same style
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated documentation
demonstrating that it meets Requirement R13.
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R14.
Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding that
is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates that it
followed the methodology described in Attachment A and meets Requirement R14.
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R15.
Each Generator Owner, Distribution Provider or Transmission Owner within the ISO-NE
Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that is
required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed the
methodology described in Attachment B and meets Requirement R15.
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R16.
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Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
12
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
16.1
Set the underfrequency protection to operate at as a low frequency as possible in
accordance with the plant design and licensing limitations but not greater than
57.8 Hz.
16.2 Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3 Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and dated
documentation that demonstrates that it meets Requirement R16.
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Figure 1
Frequency (Hz)
Thresholds for Setting Underfrequency Trip Protection for Generators
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
Figure 1
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
13
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Formatted: List Number
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
14
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
Formatted: List Number
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Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
C. Measures
M1
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
M3 Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
M4 Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped, and the corresponding frequency thresholds,
on those circuits included in its UFLS program to achieve the individual and
cumulative percentages identified in Requirement R4. (Attachment C Tables 1-3).
M5 Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
M6 Each Distribution Provider and Transmission Owner in the Québec Interconnection
shall have evidence such as documentation or reports containing the location and
amount of load to be tripped and the corresponding frequency thresholds on those
circuits included in its UFLS program to achieve the load values identified in Table 4
of Requirement R6. (Attachment C Table 4).
M7 Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the
minimum time delay, in accordance with Requirement R7.
M8 Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R8.
M9 Each Planning Coordinator shall provide evidence such as letters, emails, or other
dated documentation that demonstrates that it meets Requirement R9.
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M10 Each Distribution Provider and Transmission Owner shall provide evidence such as
test reports, data sheets or other documentation that demonstrates that it meets
Requirement R10.
M11 Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails or other dated documentation that demonstrates that it meets
Requirement R11.
M12 Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the frequency set point, the net amount of load shed and the
percentage of its peak load at each stage of its UFLS program coincident with the
integrated hourly peak of the previous year that demonstrates that it meets Requirement
R12.
M13 Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement R13.
M14 Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R14.
M15 Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R15.
M16 Each Generator Owner with existing non-nuclear units in service prior to the effective
date of this Standard which have underfrequency tripping that is not compliant with
Requirement R13 shall provide evidence such as reports, spreadsheets, memorandum
or dated documentation demonstrating that it meets Requirement R16.
M17 Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall
provide evidence such as emails, memorandum or other documentation that
demonstrates that it followed the methodology described in Attachment A and meets
Requirement R17.
M18 Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the New York ISO shall provide evidence
such as emails, memorandum, or other documentation that demonstrates that it
followed the methodology described in Attachment B and meets Requirement R18.
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Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M19 Each Generator Owner of nuclear units that have been specifically identified by NPCC
as having generator trip settings above the generator trip curve in Figure 1 shall
provide evidence such as letters, reports and dated documentation that demonstrates
that it meets Requirement R19.
M20 Each Planning Coordinator shall provide evidence such as spreadsheets, system
studies, or other documentation that demonstrates that it meets the requirements of
Requirement R20.
M21 Each Planning Coordinator shall provide evidence such as emails, memorandum or
other dated documentation that it meets Requirement R21.
M22 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as reports, spreadsheets or other documentation that demonstrates that it
meets Requirement R22.
M23 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as letters, emails or other dated documentation that demonstrates it
meets Requirement 23.
Compliance
D.C.
1.11. Compliance Monitoring Process
a.1.1.
Compliance Enforcement Authority
Northeast Power Coordinating CouncilPCC Compliance Committee
a.
Compliance Monitoring Period and Reset Time Frame
Not Applicable
b.1.2.
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DataEvidence Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 24, 35, 46, 57, 810, and 119, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 3, 86, and 79, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall keep evidence
for three calendar years for Measure 17.
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 185, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
103, 114, 125, 136, and 169.
c.1.3. Compliance Monitoring and Assessment Processes
ComSelf -Certifications.
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Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.pliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
d.
Additional Compliance Information
None.
19
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
1.21. Violation Severity Levels
Requirement
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1
N/A
N/A
N/A
The Planning Coordinator
failed to design an UFLS
program having
performance
characteristics that
prevent frequency from
remaining below 59.5 Hz
in accordance with Figure
1.
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R2
The
Planning
Coordinator provided
its
UFLS
island
boundaries,
as
identified per the
NERC continent wide
PRC-006 Standard on
UFLS but did so
more than 30 calendar
days and up to and
including 40 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC continent wide
PRC-006 Standard on
UFLS but did so more
than 40 calendar days
but less than and
including 50 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC continent wide
PRC-006 Standard on
UFLS but did so more
than 50 calendar days
but less than and
including 60 days
following a request.
The Planning Coordinator
failed to provide its UFLS
island boundaries, as
identified per the NERC
continent wide PRC-006
Standard on UFLS. within
60 calendar days
following a request.
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The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
20% or less of the
relays identified as
included in the UFLS
program, or amount of
load tripped is within
10% deviation from
the required amount of
The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
20%-40% of the relays
identified as included in
the UFLS program, or
amount of load tripped
is within 20% deviation
from the required
amount of Load
The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
40%-60% of the relays
identified as included
in the UFLS program,
or amount of load
tripped is within 30%
deviation from the
required amount of
The Distribution
Provider or Transmission
Owner failed to apply
appropriate settings on >
60% of the relays
identified as included in
the UFLS program, or
amount of load tripped
has a > 30% deviation
from the required
amount of Load required
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R3
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R4
R5
R6
Load required to be
shed at each stage
required to be shed at
each stage m
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations for
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the
4 items by a period of
up to 10 calendar days
but less than or equal
to 20 calendar days.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations for
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the 4
items within a time
greater than 20 calendar
days but less than or
equal to 30 calendar
days.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations but
exceeded the
permissible time
frame for one or more
of the 4 items within
a time greater than 30
calendar days but less
than or equal to 60
calendar days.
The Distribution
Provider or Transmission
Owner that cannot meet
the tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program failed to meet
all of items in
Requirement 5 within 60
calendar days of
permissible time for each
item.
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The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 100% but more
than (and including)
95% of relays within
its region’s UFLS
program.
The Planning
Coordinator
developed or reviewed
settings for inhibit
thresholds at least
once per five calendar
years, for less than
95% but more than
(and including) 90%
of relays within its
region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 90% but more
than (and including)
85% of relays within
its region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 85%
of relays within its
region’s UFLS program.
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The Planning
Coordinator provided
to a Transmission
The Planning
Coordinator provided to
a Transmission Owner
The Planning
Coordinator provided
to a Transmission
The Planning
Coordinator failed to
provide to a
21
Adopted by Board of Trustees: February 9, 2012
Load required to be
shed at each stage.
to be shed at each stage
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R7
R8
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds more
than 30 calendar days
and up to and
including 40 calendar
days of any changes.
or Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds more than 40
calendar days but less
than and including 50
calendar days of any
changes.
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds
more than 50 calendar
days but less than and
including 60 calendar
days of any changes.
Transmission Owner or
Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds within 60
calendar days after any
changes
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 90 calendar
days and up to and
including 100 calendar
days following the
request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 100 calendar
days and up to and
including 110 calendar
days following the
request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 110
calendar days and up
to and including 120
calendar days
following the request.
The Distribution
Provider or Transmission
Owner failed to develop
and submit its
implementation plan
within 120 days
following the request.
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Implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 100%
but more than (and
including) 95% of
UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the inhibit
threshold settings
provided by the
Planning Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 95% but more
than (and including)
90% of UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 90% but
more than (and
including) 85% of
UFLS relays.
The Distribution
Provider or Transmission
Owner implemented the
inhibit threshold settings
provided by the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 85% of UFLS
relays.
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9
R10
R11
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 15 calendar
months but less than
(and including) 16
calendar months since
last update.
The Distribution
Provider or
Transmission Owner
provided to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11 more
than 16 calendar
months but less than
(and including)17
calendar months since
last update.
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 17 calendar
months but less than
(and including)18
calendar months since
last update.
The Distribution
Provider or Transmission
Owner failed to provide
to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
within 18 calendar
months since last update.
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N/A
N/A
N/A
The Generator Owner
did not set each
generator
underfrequency trip
relay, if so equipped, on
or below the appropriate
generator
underfrequency trip
protection settings
threshold curve in Figure
2, except as otherwise
exempted.
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The Generator Owner
failed to transmit the
generator
underfrequency trip
setting and time delay
within 75 calendar days
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The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 45calendar
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 55 calendar
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Adopted by Board of Trustees: February 9, 2012
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 65 calendar
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R12
days and less than (and
including) 55 calendar
days of the Planning
Coordinator’s request.
days and less than (and
including) 65 calendar
days of the Planning
Coordinator’s request.
N/A
N/A
days and less than
(and including) 75
calendar days of the
Planning
Coordinator’s request.
The Generator Owner
with a new generating
unit, or an existing
generator increasing
its net capability by
greater than 10%:
Did not fulfill the
obligation of
Requirement R12;
Part 12.1
of the Planning
Coordinator’s request.
The Generator Owner
with a new generating
unit, or an existing
generator increasing its
net capability by greater
than 10%, did not fulfill
the obligations of
Requirement R12, Part
12.1 and Part 12.2.
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The Planning
Coordinator in Ontario,
Québec and the
Maritime Provinces or
the Generator Owner
within the ISO-NE and
in NYISO Planning
Coordinator areas failed
to arrange for
compensatory load
shedding as specified in
Requirement R13, Part
13.3.
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OR
Did not fulfill the
obligation of
Requirement R12,
Part 12.2.
R13
R14
N/A
N/A
The Generator Owner
failed to transmit the
existing underfrequency
settings and any
changes to the
underfrequency settings
along with the technical
basis for the settings to
the Planning
Coordinatoras specified
in Requirement R13,
Part 13.2.
The Generator Owner
failed to set the
underfrequency
protection to operate at
the lowest frequency
allowed by the plant
design and licensing
limitations a specified
in Requirement 13,
Part 13.1
N/A
N/A
The Planning
Coordinator did not
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Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
apply the criteria
described in Attachment
A to determine the
compensatory load
shedding that is required.
R15
R16
N/A
N/A
N/A
The Generator Owner
failed to transmit the
initial frequency trip
setting and any changes
to the setting and the
technical basis for the
settings to the Planning
Coordinator as
specified in
Requirement R16, Part
16.3.
25
Adopted by Board of Trustees: February 9, 2012
N/A
The Generator Owner:
Failed to set the
underfrequency
protection as specified
in Requirement R16;
Part 16.1
OR
Failed to set the
frequency trip setting
upper tolerance as
specified in
Requirement R16, Part
16.2.
The Generator Owner,
Distribution Provider, or
Transmission Owner did
not apply the criteria
described in Attachment
B to determine the
compensatory load
shedding that is required.
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The Generator Owner
did not fulfill the
obligations of
Requirement R16, Part
16.1 and Part 16.2.
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
PRC-006-NPCC-1 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 2.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all UFLS islands in which the unit may operateThe
Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 1.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all islands identified in Requirement R1 in which the
unit may operate.
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The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (April, 2017 PRC-006-NPCC-1). The list
must indicate generating units, if any, that have their underfrequency protections set to
trip above the appropriate curve in Figure 2. Generating Units not appearing on the list
as of the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information for each unitThe Planning Coordinator
shall identify, compile and maintain an updated list of all existing non-nuclear generating
units in service prior to the effective date of this standard that have underfrequency
protections set to trip above the appropriate curve in Figure 1. The list shall include the
following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate, as identified in Requirement R1
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
26
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load sheddingArrange for a
Distribution Provider or Transmission Owner that owns UFLS relays within the
island(s) identified by the Planning Coordinator in Requirement R1 within which
the generator may operate to provide compensatory load shedding.
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2.2 In Ontario and in the Maritime provinces, Tthe compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4..
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2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 2 during an underfrequency event. If the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 2The
compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 1 during an underfrequency event. If the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 1 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 1.
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2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
systemThe amount of compensatory load shedding shall be equivalent (±5%) to
the average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
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In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
27
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facilityIn the specific instance of a
generating unit that has been interconnected to the electric system for less than
two calendar years, the amount of compensatory load shedding shall be equivalent
(±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon
loss of the facility.
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
28
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirementsThe Generator Owner in the New England states or New York State are
responsible for establishing a compensatory load shedding program for all existing non-nuclear
units with underfrequency protection set to trip above the appropriate curve in Figure 1 of this
standard. The Generator Owner shall follow the methodology below to determine compensatory
load shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (April, 2017 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above the
appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2. The
list shall include the following information associated with each unitThe Generator
Owner shall identify and compile a list of all existing non-nuclear generating units in
service prior to the effective date of this standard that has underfrequency protection set
to trip above the appropriate curve in Figure 1. The list shall include the following
information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 2, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the smallest island identified by the Planning Coordinator in
Requirement R1 of this standardIn cases where a Distribution Provider or
Transmission Owner has coordinated protection settings with the Generator
Owner to cause the generator to trip above the appropriate curve in Figure 1, the
Distribution Provider or Transmission Owner is responsible to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.74" +
Indent at: 0.99"
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.75" +
Indent at: 1"
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2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 2, the Generator Owner shall
29
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.75" +
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standardIn cases
where a Generator Owner has a generator that cannot physically meet the set
points defined by the appropriate curve in Figure 1, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the smallest island
identified by the Planning Coordinator in Requirement R1 of this standard.
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4The compensatory load shedding that is provided by the Distribution Provider
or Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
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2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip The compensatory load shedding shall be
provided at the UFLS program stage with the frequency threshold setting at or
closest to but above the frequency at which the subject generator will trip.
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2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.75" +
Indent at: 1"
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.75" +
Indent at: 1"
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
systemThe amount of compensatory load shedding shall be equivalent (±5%) to
the average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facilityIn the specific instance of a
generating unit that has been interconnected to the electric system for less than
two calendar years, the amount of compensatory load shedding shall be equivalent
(±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon
loss of the facility.
30
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
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PRC-006-NPCC-1 Attachment C
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31
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW or more of peak net Load shall
implement a UFLS program with the following attributes:
Frequency
Threshold
(Hz)
Total Nominal
Operating
Time (s) 1
Load Shed at Stage as
% of TO or DP
Load
Cumulative Load Shed as % of
TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
27.5 – 28.5
59.5
10.0
2–3
– 31.5
Formatted Table
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW or more and less than 100 MW
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1. The total nominal operating time includes the underfrequency relay
operating time plus any interposing auxiliary relay operating times, communication times, and the rated
breaker interrupting time. The underfrequency relay operating time is measured from the time when
frequency passes through the frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per
second. If the relay operating time is dependent on the rate of frequency decay, the underfrequency relay
operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear frequency
decay of 0.2 Hz per second.
32
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.19" +
Indent at: 0.44"
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW or more and less than 50 MW of
peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1. The total nominal operating time includes the underfrequency relay
operating time plus any interposing auxiliary relay operating times, communication times, and the rated
breaker interrupting time. The underfrequency relay operating time is measured from the time when
frequency passes through the frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per
second. If the relay operating time is dependent on the rate of frequency decay, the underfrequency relay
operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear frequency
decay of 0.2 Hz per second.
33
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 4: Quebec Interconnection
MW
at peak
Mvar
at peak
Total
Nominal
Operating
Time (s) 2
Rate
Frequency
(Hz)
(*Load must
be fixed at all
times when
above 60% of
peak load..)
Threshold Stage 1
–––
58.5
1000*
1000
0.30
Threshold Stage 2
–––
58.0
800*
800
0.30
Threshold Stage 3
–––
57.5
800
800
0.30
Threshold Stage 4
–––
57.0
800
800
0.30
–––
59.0
500
500
20.0
Slope Stage 1
-0.3 Hz/s
58.5
400
400
0.30
Slope Stage 2
-0.4 Hz/s
59.8
800*
800
0.30
Slope Stage 3
-0.6 Hz/s
59.8
800*
800
0.30
Slope Stage 4
-0.9 Hz/s
59.8
800
800
0.30
Threshold Stage 5
(anti-stall)
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
2. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communications time, and the rated breaker interrupting time. The
underfrequency relay operating time shall be measured from the time when the frequency passes through the
frequency threshold set point.
34
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
1
2
3
4
5
(Hz)
Delay (s)
59.5
59.3
59.1
58.9
59.5
0.10
0.10
0.10
0.10
0.10
Operating
Time (s) 2
0.30
0.30
0.30
0.30
10.0
TO or DP
Load
6.5 – 7.5
6.5 – 7.5
6.5 – 7.5
6.5 – 7.5
2-3
% of TO or
DP Load
6.5 – 7.5
13.5 – 14.5
20.5 – 21.5
27.5 – 28.5
29.5 – 31.5
Formatted: Font: (Default) Times New Roman
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
Formatted: Font: (Default) Times New Roman
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
35
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
Formatted: Numbered + Level: 1 + Numbering Style: 1, 2,
3, … + Start at: 1 + Alignment: Left + Aligned at: 0.19" +
Indent at: 0.44"
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
1
59.5
0.10
0.30
28 – 50
28 – 50
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
2.
36
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Formatted: Font: Times New Roman
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
•
•
•
•
•
•
•
•
•
•
•
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
Generator dynamic modeling
Dynamic VAR device modeling
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Indent at: 0.5"
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between paragraphs of the same style, Numbered + Level: 1
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37
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes
No
Comments: Additional modifications are needed. The requirement states that that an entity
that does not meet the UFLS program parameters to develop a mutually agreeable CAP with the
Planning Coordinator within 30 days but does not identify from what start date the 30 days kicks
off from. There are no other requirements that either specify a requirement for notification or a
due date.
If the drafting team is going to resolve the issue that an entity cannot meet the plan due to too
narrow of range, then there must be a timeframe for identifying when a validation has to occur.
There either needs to be a requirement that specifies a date when they want UFLS plan
validations or they need to give a date when the UFLS entities need to re-evaluate.
In addition, 30 day turn is also narrow and we prefer 90 days.
Drafting Team Responses:
The SDT accepted the comments and made the necessary modification to the requirement.
The NERC defined glossary term for Corrective Action Plan includes a timeline for corrective
actions.
Requirement 9 requires TO and DP annual provide documentation with no more than 15
calendar month between updates to its Planning Coordinator.
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes X
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes X
No
Comments:
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes X
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes X
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments:
Drafting Team Responses:
Thank you for your support and comments.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes
No
Comments: We believe that the language could be enhanced by adding some wording as
follows to clarify that a determination has been made:
Each Distribution Provider or Transmission Owner in the Eastern Interconnection portion of
NPCC that determines that it does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec…
Within 30 calendar days of determining that it does not meet the specified parameters, notify its
Planning Coordinator that it does not meet the UFLS program parameters; and
Drafting Team Responses:
The SDT accepted the comments and made the necessary modification to the requirement.
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: We suggest providing the curve definitions for Figure 1 (these are included in
the continent wide version and should make it easier for entities to determine if they are meeting
the curves). We also suggest deleting the red line showing the NERC underfrequency
requirements (continent wide standard on UFLS) since entities within NPCC must meet the
NPCC performance.
There is a typographical error in Attachment B, PRC-006-NPCC-1 was effective July 1,
2015. Revise to:
The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (April, 2017 July 1, 2015 PRC-006-NPCC-1).
For Attachment B, 2.1 and 2.2, compensatory load shedding must be in both the same and
smallest island as the generator (for example, there may be a unit that’s in the NE and CT
islands. We would need to make sure that the compensatory load shedding was in the CT
island., revise as follows:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated protection
settings with the Generator Owner to cause the generator to trip above the appropriate curve in
Figure 2, the Distribution Provider or Transmission Owner is responsible to provide the
appropriate amount of compensatory load to be shed within the smallest island as identified by
the Planning Coordinator in Requirement R1 of this standard that contains the generator.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the set points
defined by the appropriate curve in Figure 2, the Generator Owner shall arrange for a
Distribution Provider or Transmission Owner to provide the appropriate amount of
compensatory load to be shed within the smallest island as identified by the Planning
Coordinator in Requirement R1 of this standard that contains the generator.
Drafting Team Responses:
The SDT accepted the comments and made the necessary modification to Figure 1.
The SDT accepted the comments and made the necessary date change to the Attachment A and
B.
The SDT accepted the comments and made the necessary modifications to the Attachment B.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes
No
Comments: We believe that the language could be enhanced by adding some wording as
follows to clarify that a determination has been made:
Each Distribution Provider or Transmission Owner in the Eastern Interconnection portion of
NPCC that determines that it does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec…
Within 30 calendar days of determining that it does not meet the specified parameters, notify its
Planning Coordinator that it does not meet the UFLS program parameters; and
Drafting Team Responses:
The SDT accepted the comments and made the necessary modification to the requirement.
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes
No
Comments:
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments:
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: We suggest providing the curve definitions for Figure 1 (these are included in
the continent wide version and should make it easier for entities to determine if they are meeting
the curves). We also suggest deleting the red line showing the NERC underfrequency
requirements (continent wide standard on UFLS) since entities within NPCC must meet the
NPCC performance.
There is a typographical error in Attachment B, PRC-006-NPCC-1 was effective July 1,
2015. Revise to:
The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (April, 2017 July 1, 2015 PRC-006-NPCC-1).
For Attachment B, 2.1 and 2.2, compensatory load shedding must be in both the same and
smallest island as the generator (for example, there may be a unit that’s in the NE and CT
islands. We would need to make sure that the compensatory load shedding was in the CT
island., revise as follows:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated protection
settings with the Generator Owner to cause the generator to trip above the appropriate curve in
Figure 2, the Distribution Provider or Transmission Owner is responsible to provide the
appropriate amount of compensatory load to be shed within the smallest island as identified by
the Planning Coordinator in Requirement R1 of this standard that contains the generator.
2.2 In cases where a Generator Owner has a generator that cannot physically meet the set points
defined by the appropriate curve in Figure 2, the Generator Owner shall arrange for a
Distribution Provider or Transmission Owner to provide the appropriate amount of
compensatory load to be shed within the smallest island as identified by the Planning
Coordinator in Requirement R1 of this standard that contains the generator.
Drafting Team Responses:
The SDT accepted the comments and made the necessary modification to Figure 1.
The SDT accepted the comments and made the necessary date change to the Attachment A and
B.
The SDT accepted the comments and made the necessary modifications to the Attachment B.
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
Comment Form
Background Information
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. PRC-006-NPCC-1 is to be reviewed to determine if the applicability of the standard
needs to be revised in accordance with Project 2014-01 Dispersed Generation Resources.
2. PRC-006-NPCC-1 is to be reviewed in order to determine if the performance
requirements as contained in the criteria of NPCC Directory#12 Sections 5.1.1 and 5.1.2
should be explicitly included in the requirements of the Regional Standard and potential
retirement of Directory 12 Automatic Underfrequency Load Shedding Program.
3. Attachment C in PRC-006-NPCC-1 is to be reviewed to address the implications of the
design assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. PRC-006-NPCC-1 is to be reviewed in order to update Table 4 in Attachment C in
accordance with the 2013 NPCC UFLS Adequacy Assessment. Additionally, the
applicability of Requirements R4 and R5 will be reviewed to consider that Hydro Quebec
is not part of the Eastern Interconnection.
The comment period is open from August 10, 2018 through September 25, 2018.
Please submit your comments using this form and upload it to the NPCC website or provide your
responses directly:
PRC-006-NPCC-02 Automatic Underfrequency Load Shedding
1. Do you agree with the proposed revisions to the PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding? If not, please explain why and include any suggestions.
Yes
No
Comments:
2. Do you agree with the proposed revisions to Requirement 4? If not, please explain why
and include any suggestions.
Yes
No
Comments:
3. Do you agree with the proposed revisions to Requirement 16? If not, please explain why
and include any suggestions.
Yes
No
Comments: For the sake of clarity consider the following language, which spells out what
we want: “Set the underfrequency protection to operate at a frequency setting that is as low as
possible in accordance with the plant design”
Drafting Team Response:
The SDT accepted the comments and made the necessary modification to the requirement.
4. Do you agree with the drafting team proposal to retire Directory 12 Automatic
Underfrequency Load Shedding Program? If not, please explain why and include any
suggestions.
Yes
No
Comments:
5. Are each of the draft requirements, as written, cost effective or is there a more costeffective alternative to meeting the reliability objective. If so, please provide alternative
language for the particular requirement(s), along with any technical supporting
information demonstrating that the reliability objective would still be met.
Comments: The requirements are cost-effective as written
Drafting Team Response:
Thank you for your comment.
6. Provide any additional comments for the drafting team to consider, if desired.
Comments: The purpose paragraph notes that the standard establishes more stringent
program requirements. It is unclear what we are comparing against. Are we comparing this
standard against Directory 12, the NERC PRC-006-3 standard, the previous NPCC PRC-006NPCC-01? Consider clarifying the purpose with something like:
“The NPCC Automatic Underfrequency Load Shedding (UFLS) regional Reliability Standard
establishes specific NPCC UFLS program requirements that are more stringent than those of
prior NPCC standards to ensure that declining frequency is arrested and recovered in
accordance with established NPCC performance requirements stipulated in this document.”
Drafting Team Responses:
The SDT accepted the comments and made the necessary modification to the purpose statement.
Mapping Document
Draft NPCC Regional Automatic Underfrequency Load Shedding Standard
PRC-006-NPCC-2
NPCC’s regional standard PRC-006-NPCC-2 “Automatic Underfrequency Load Shedding” (UFLS) was effective in the US in July 2015. The
standard is currently under revision to align with the continent-wide PRC-006-2 UFLS standard which became effective on October 2015. The
draft of PRC-006-NPCC-2 removes duplicity with the continent wide standard and adds specificity to allow retirement of the NPCC UFLS
Directory #12 containing more stringent UFLS performance criteria and harmonizes the requirements and criteria of all these documents.
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
PRC-006-NPCC-1
Translation to New Standard or Other
Action
Description and Change Justification
PRC-006-NPCC-2
R1 Each Planning Coordinator shall establish
R2. Each Planning Coordinator shall provide
requirements for entities aggregating their
UFLS island boundaries, as identified per
UFLS programs for each anticipated island and
the NERC continent wide PRC-006
requirements for compensatory load
Standard on UFLS, to Distribution
shedding based on islanding criteria (required
Providers, Generator Owners, and
by the NERC PRC Standard on UFLS).
Transmission Owners within 30 calendar
[Violation Risk Factor: Medium] [Time
days of receipt of a request. [Violation
Horizon: Long Term Planning]
Risk Factor: Lower] [Time Horizon: Long
Term Planning]
R3. Each Distribution Provider and
Transmission Owner in the Eastern
The purpose of R1 in PRC-006-NPCC-1 was
to ensure entities that aggregate their load
understand what the UFLS island
boundaries are and establish criteria for
compensatory load shedding. The revised
R2, R3, and R13 clearly address this in the
proposed PRC-006-NPCC-2.
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
Interconnection portion of NPCC shall
implement an automatic UFLS program,
reflecting normal operating conditions,
excluding outages. The automatic UFLS
program shall be implemented on an
island basis for each identified island per
the NERC continent wide PRC-006
Standard on UFLS as follows: [Violation
Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be
implemented by each
Distribution Provider and
Transmission Owner according
to the frequency thresholds,
nominal operating times, and
load shedding amounts
specified in Attachment C,
Tables 1-3; or
• The UFLS program shall be
implemented collectively by
multiple Distribution Providers
or Transmission Owners, as long
as they reside in the same UFLS
island identified by the Planning
Mapping Document
Project Number and Name | Month Year
2
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
Coordinator per Requirement
R2. These multiple Distribution
Providers or Transmission
Owners, via mutual agreement,
shall act as a single entity to
provide an aggregated
automatic UFLS program that
sheds their coincident peak
aggregated net Load according
to the frequency thresholds,
total nominal operating time,
and load shedding amounts
specified in Attachment C,
Tables 1-3.
R13. For existing non-nuclear units in
service prior to July 1, 2015, that have
underfrequency protections set to trip
above the appropriate curve in Figure
2: [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
13.1. Each Generator Owner shall
set the underfrequency
protection to operate at the
lowest frequency allowed by
Mapping Document
Project Number and Name | Month Year
3
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
the plant design and licensing
limitations.
13.2. Each Generator Owner shall
transmit the existing
underfrequency settings and
any changes to the
underfrequency settings along
with the technical basis for the
settings to the Planning
Coordinator.
13.3. Each Planning Coordinator in
Ontario, Québec and the
Maritime Provinces shall
arrange for compensatory load
shedding, in accordance with
Attachment A and as provided
by a Distribution Provider or
Transmission Owner, that is
adequate to compensate for
the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
Mapping Document
Project Number and Name | Month Year
4
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
13.4. Each Generator Owner in the
ISO-NE Planning Coordinator
area and in NYISO Planning
Coordinator area shall arrange
for compensatory load
shedding, in accordance with
Attachment B and as provided
by a Distribution Provider or
Transmission Owner, that is
adequate to compensate for
the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
PRC-006-NPCC-1
PRC-006-NPCC-2
R2 Each Planning Coordinator shall, within 30
days of completion of its system studies
required by the NERC PRC Standard on UFLS,
identify to the Regional Entity the generation
facilities within its Planning Coordinator Area
R1. Each Planning Coordinator in the
Eastern Interconnection portion of NPCC
shall design an UFLS program, pertaining
to islands wholly within the NPCC
Region, having performance
Mapping Document
Project Number and Name | Month Year
The original R2 is redundant and it is being
covered by the new R1, R2 and R3.
5
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
necessary to support the UFLS program
performance characteristics. [Violation Risk
Factor: Medium] [Time Horizon: Long Term
Planning]
Translation to New Standard or Other
Action
Description and Change Justification
characteristics that prevents the
frequency from remaining below 59.5
Hz for more than 30 seconds in
accordance with Figure 1 [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
R2. Each Planning Coordinator shall provide
UFLS island boundaries, as identified per
the NERC continent wide PRC-006
Standard on UFLS, to Distribution
Providers, Generator Owners, and
Transmission Owners within 30 calendar
days of receipt of a request. [Violation
Risk Factor: Lower] [Time Horizon: Long
Term Planning]
R3. Each Distribution Provider and
Transmission Owner in the Eastern
Interconnection portion of NPCC shall
implement an automatic UFLS program,
reflecting normal operating conditions,
excluding outages. The automatic UFLS
program shall be implemented on an
island basis for each identified island per
Mapping Document
Project Number and Name | Month Year
6
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
the NERC continent wide PRC-006
Standard on UFLS as follows: [Violation
Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be
implemented by each
Distribution Provider and
Transmission Owner according
to the frequency thresholds,
nominal operating times, and
load shedding amounts
specified in Attachment C,
Tables 1-3; or
•
Mapping Document
Project Number and Name | Month Year
The UFLS program shall be
implemented collectively by
multiple Distribution Providers
or Transmission Owners, as long
as they reside in the same UFLS
island identified by the Planning
Coordinator per Requirement
R2. These multiple Distribution
Providers or Transmission
Owners, via mutual agreement,
shall act as a single entity to
provide an aggregated
7
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
automatic UFLS program that
sheds their coincident peak
aggregated net Load according
to the frequency thresholds,
total nominal operating time,
and load shedding amounts
specified in Attachment C,
Tables 1-3
PRC-006-NPCC-1
PRC-006-NPCC-2
R3 Each Planning Coordinator shall provide to R2. Each Planning Coordinator shall provide
the Transmission Owner, Distribution
UFLS island boundaries, as identified per
Provider, and Generator Owner within 30
the NERC continent wide PRC-006
days upon written request the requirements
Standard on UFLS, to Distribution
for entities aggregating the UFLS programs
Providers, Generator Owners, and
and requirements for compensatory load
Transmission Owners within 30 calendar
shedding program derived from each Planning
days of receipt of a request. [Violation
Coordinator’s system studies as determined
Risk Factor: Lower] [Time Horizon: Long
by Requirement R1. [Violation Risk Factor:
Term Planning]
Low] [Time Horizon: Long Term Planning]
R13. For existing non-nuclear units in
service prior to July 1, 2015, that have
underfrequency protections set to trip
above the appropriate curve in Figure
Mapping Document
Project Number and Name | Month Year
The reliability intent of Version 1 R3 was to
ensure that the entities aggregating load
were aware of the island boundaries. This is
covered in draft R2 of the proposed revision
to the standard. Requirements regarding
compensatory load shedding have been
clarified and are covered through draft R13.
8
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
2: [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
13.1. Each Generator Owner shall
set the underfrequency
protection to operate at the
lowest frequency allowed by
the plant design and licensing
limitations.
13.2. Each Generator Owner shall
transmit the existing
underfrequency settings and
any changes to the
underfrequency settings along
with the technical basis for the
settings to the Planning
Coordinator.
13.3. Each Planning Coordinator in
Ontario, Québec and the
Maritime Provinces shall
arrange for compensatory load
shedding, in accordance with
Attachment A and as provided
by a Distribution Provider or
Transmission Owner, that is
Mapping Document
Project Number and Name | Month Year
9
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
adequate to compensate for
the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
13.4. Each Generator Owner in the
ISO-NE Planning Coordinator
area and in NYISO Planning
Coordinator area shall arrange
for compensatory load shedding,
in accordance with Attachment B
and as provided by a Distribution
Provider or Transmission Owner,
that is adequate to compensate
for the loss of generator(s) due
to early tripping that is within
the UFLS island identified by the
Planning Coordinator in
Requirement R2.
PRC-006-NPCC-1
PRC-006-NPCC-2
R4 Each Distribution Provider and
Transmission Owner in the Eastern
R4. Each Distribution Provider or
Transmission Owner in the Eastern
Mapping Document
Project Number and Name | Month Year
Added clarity and combined with the
original R4 and R5 into one requirement.
10
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Interconnection portion of NPCC shall
implement an automatic UFLS program
reflecting normal operating conditions
excluding outages for its Facilities based on
frequency thresholds, total nominal operating
time and amounts specified in Attachment C,
Tables 1 through 3, or shall collectively
implement by mutual agreement with one or
more Distribution Providers and Transmission
Owners within the same island identified in
Requirement R1 and acting as a single entity,
provide an aggregated automatic UFLS
program that sheds their coincident peak
aggregated net Load, based on frequency
thresholds, total nominal operating time and
amounts specified in Attachment C, Tables 1
through 3. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning
Mapping Document
Project Number and Name | Month Year
Translation to New Standard or Other
Action
Description and Change Justification
Interconnection portion of NPCC that does
not meet the UFLS program parameters
specified in Attachment C, Table 1-3, and
each Distribution Provider or Transmission
Owner in the Quebec Interconnection that
does not meet the UFLS program
parameters specified by its Planning
Coordinator shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
• Within 30 calendar days of
determining that it does not meet the
specified parameters, notify its Planning
Coordinator that it does not meet the
UFLS program parameters; and
• Within the following 180 calendar
days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and
a schedule for implementation
that is mutually agreed upon with
its Planning Coordinator or
(2) provide its Planning Coordinator with
a technical study that
demonstrates that the deviations
from the program parameters will
11
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
not result in failure of UFLS
performance criteria being met for
any island. The technical study
must be acceptable to the
Planning Coordinator prior to
implementing deviations from
program parameters and shall
demonstrate coordination with
UFLS programs of all entities
residing within the same island(s)
identified by the Planning
Coordinator in Requirement R2.
The technical study shall also
demonstrate coordination with
other UFLS programs of adjoining
Planning Coordinators, or
(3) provide its Planning Coordinator with
an analysis demonstrating that no
alternative load shedding solution
is available that would allow the
Distribution Provider or
Transmission Owner to comply
with UFLS Attachment C Table 2 or
Attachment C Table 3
Mapping Document
Project Number and Name | Month Year
12
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
PRC-006-NPCC-1
PRC-006-NPCC-2
R5 Each Distribution Provider or Transmission
Owner that must arm its load to trip on
underfrequency in order to meet its
requirements as specified and by doing so
exceeds the tolerances and/or deviates from
the number of stages and frequency set
points of the UFLS program as specified in the
tables contained in Requirement R4 above, as
applicable depending on its total peak net
Load shall: [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
R4. Each Distribution Provider or
Transmission Owner in the Eastern
Interconnection portion of NPCC that does
not meet the UFLS program parameters
specified in Attachment C, Table 1-3, and
each Distribution Provider or Transmission
Owner in the Quebec Interconnection that
does not meet the UFLS program
parameters specified by its Planning
Coordinator shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
• Within 30 calendar days of
determining that it does not meet the
specified parameters, notify its Planning
Coordinator that it does not meet the
UFLS program parameters; and
• Within the following 180 calendar
days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and
a schedule for implementation
that is mutually agreed upon with
its Planning Coordinator or
5.1 Inform its Planning Coordinator of the
need to exceed the stated tolerances or the
number of stages as shown in UFLS
Attachment C, Table 1 if applicable and
5.2 Provide its Planning Coordinator with a
technical study that demonstrates that the
Distribution Providers or Transmission
Owners specific deviations from the
requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on
the bulk power system.
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Added clarity and combined with the
original R4 and R5 into one requirement.
13
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
5.3 Inform its Planning Coordinator of the
need to exceed the stated tolerances of UFLS
Attachment C, Table 2 or Table 3, and in the
case of Attachment C, Table 2 only, the need
to deviate from providing two stages of UFLS,
if applicable, and
5.4 Provide its Planning Coordinator with an
analysis demonstrating that no alternative
load shedding solution is available that would
allow the Distribution Provider or
Transmission Owner to comply with UFLS
Attachment C Table 2 or Attachment C Table
3.
Mapping Document
Project Number and Name | Month Year
Translation to New Standard or Other
Action
Description and Change Justification
(2) provide its Planning Coordinator with
a technical study that
demonstrates that the deviations
from the program parameters will
not result in failure of UFLS
performance criteria being met for
any island. The technical study
must be acceptable to the
Planning Coordinator prior to
implementing deviations from
program parameters and shall
demonstrate coordination with
UFLS programs of all entities
residing within the same island(s)
identified by the Planning
Coordinator in Requirement R2.
The technical study shall also
demonstrate coordination with
other UFLS programs of adjoining
Planning Coordinators, or
(3) provide its Planning Coordinator with
an analysis demonstrating that no
alternative load shedding solution
is available that would allow the
Distribution Provider or
14
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
Transmission Owner to comply
with UFLS Attachment C Table 2 or
Attachment C Table 3
PRC-006-NPCC-1
R6 Each Distribution Provider and
Transmission Owner in the Québec
Interconnection portion of NPCC shall
implement an automatic UFLS program for its
Facilities based on the frequency thresholds,
slopes, total nominal operating time and
amounts specified in Attachment C, Table 4
or shall collectively implement by mutual
agreement with one or more Distribution
Providers and Transmission Owners within
the same island, identified in Requirement R1,
an aggregated automatic UFLS program that
sheds Load based on the frequency
thresholds, slopes, total nominal operating
time and amounts specified in Attachment C,
Table 4. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
Mapping Document
Project Number and Name | Month Year
The drafting team agreed to retire the
requirement because it is redundant to the
Quebec Variance section of the PRC-006-3
NERC standard.
15
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
PRC-006-NPCC-1
Translation to New Standard or Other
Action
PRC-006-NPCC-2
The drafting team agreed to retire the
requirement because the time delay is
added into Attachment C tables.
PRC-006-NPCC-2
Periodicty of develop and review settings
has been increased from once per calendar
year to once per five calendar years. This
coincides with the the periodicity of UFLS
studies. Having a yearly “develop and
review” without taking any further action is
strictly administrative and does nothing for
reliability (P-81 type of issue).
R7 Each Distribution Provider and
Transmission Owner shall set each
underfrequency relay that is part of its
region’s UFLS program with the following
minimum time delay: 7.1 Eastern
Interconnection – 100 ms 7.2 Québec
Interconnection – 200 ms [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
PRC-006-NPCC-1
R8 Each Planning Coordinator shall develop
R5. Each Planning Coordinator shall
and review once per calendar year settings for
develop and review settings for inhibit
inhibit thresholds (such as but not limited to
thresholds at least once per five
voltage, current and time) to be utilized
calendar years (such as, but not limited
within its region's UFLS program. [Violation
to, voltage, current and time) to be
Risk Factor: Medium] [Time Horizon: Long
utilized within its region’s UFLS
Term Planning]
program. [Violation Risk Factor:
Medium] [Time Horizon: Long Term
Planning]
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
16
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
NPCC-006-NPCC-1
NPCC-006-NPCC-2
R9 Each Planning Coordinator shall provide
each Transmission Owner and Distribution
Provider within its Planning Coordinator area
the applicable inhibit thresholds within 30
days of the initial determination of those
inhibit thresholds and within 30 days of any
changes to those thresholds. [Violation Risk
Factor: Medium] [Time Horizon: Operations
Planning]
R6. Each Planning Coordinator shall provide Clarified the language.
each Transmission Owner and
Distribution Provider within its Planning
Coordinator area the applicable inhibit
thresholds within 30 calendar days of
any changes. [Violation Risk Factor:
Lower] [Time Horizon: Operations
Planning]
NPCC-006-NPCC-1
NPCC-006-NPCC-2
R10 Each Distribution Provider and
Transmission Owner shall implement the
inhibit threshold settings based on the
notification provided by the Planning
Coordinator in accordance with Requirement
R9. [Violation Risk Factor: High] [Time
Horizon: Operations Planning]
R8. Each Distribution Provider and
Transmission Owner shall implement
the inhibit thresholds provided by the
Planning Coordinator in accordance
with Requirement R6 and based on the
Planning Coordinator approved
implementation plan in accordance
with R7. [Violation Risk Factor: High]
[Time Horizon: Operations Planning]
Mapping Document
Project Number and Name | Month Year
Only made changes to requirement
numbers referenced only.
Added clarification for Planning Coordinator
developes implementation plan.
17
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
NPCC-006-NPCC-1
PRC-006-NPCC-2
R11 Each Distribution Provider and
Transmission Owner shall develop and submit
an implementation plan within 90 days of the
request from the Planning Coordinator for
approval by the Planning Coordinator in
accordance with R9. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
R7. Each Distribution Provider and
Transmission Owner that receives a
notification pursuant to Requirement R6
shall develop and submit an
implementation plan with respect to inhibit
thresholds for approval by the Planning
Coordinator within 90 calendar days of the
request from the Planning Coordinator.
[Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R12 Each Transmission Owner and
Distribution Provider shall annually provide
documentation, with no more than 15
months between updates, to its Planning
Coordinator of the actual net Load that would
have been shed by the UFLS relays at each
UFLS stage coincident with their integrated
hourly peak net Load during the previous
year, as determined by measuring actual
metered Load through the switches that
would be opened by the UFLS relays.
R9. Each Transmission Owner and
Distribution Provider shall annually
provide documentation, with no more
than 15 calendar months between
updates, to its Planning Coordinator of
the actual net Load that would have
been shed by the UFLS relays at each
UFLS stage. The actual net Load shall be
coincident with the entity’s integrated
hourly peak net Load during the
previous year, as determined by
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Language clarifications and changes to
requirement numbers referenced.
Added language that allows calculation of
load from nearest available metering rather
than actual metering. The requirement as it
exists is placing undo burden to install
metering when it can be accurately
calculated as a cost effective alternative.
18
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
[Violation Risk Factor: Lower] [Time Horizon:
Long Term Planning]
Translation to New Standard or Other
Action
measuring or calculating Load through
the switches that would disconnect
load if triggered by the UFLS relays. If
measured data is unavailable then
calculated data may be used. [Violation
Risk Factor: Lower] [Time Horizon: Long
Term Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R13 Each Generator Owner shall set each
generator underfrequency trip relay, if so
equipped, below the appropriate generator
underfrequency trip protection settings
threshold curve in Figure 1, except as
otherwise exempted in Requirements R16
and R19. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
R10. Each Generator Owner shall set each
generator underfrequency trip relay, if
so equipped, on or below the
appropriate generator underfrequency
trip protection setting threshold curve
in Figure 2, except as otherwise
exempted in Requirements R13 and
R16. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
NPCC-006-NPCC-1
PRC-006-NPCC-2
R14 Each Generator Owner shall transmit the R11. Each Generator Owner shall transmit
generator underfrequency trip setting and
the generator underfrequency trip
time delay to its Planning Coordinator within
setting and time delay within 45
45 days of the Planning Coordinator’s request.
calendar days of the Planning
Coordinator’s request. [Violation Risk
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Clarification was made that the
Underfrequency trip relay must to be set to
operate “on or below” the appropriate
curve. In Version 1 it currently states below
and questions arose whether settings on
the curve were considered in compliance.
No Change from Version 1 only requirement
numbering
19
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
[Violation Risk Factor: High] [Time Horizon:
Operations Planning]
Translation to New Standard or Other
Action
Factor: Lower] [Time Horizon:
Operations Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R15 Each Generator Owner with a new
generating unit, scheduled to be in service on
or after the effective date of this Standard, or
an existing generator increasing its net
capability by greater than 10% shall:
[Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
R12. Each Generator Owner with a new
generating unit, or an existing
generator increasing its net capability
by greater than 10% shall: [Violation
Risk Factor: Medium] [Time Horizon:
Long Term Planning]
12.1. Design measures to prevent
the generating unit from
tripping directly or indirectly
for underfrequency conditions
above the appropriate
generator tripping threshold
curve in Figure 2.
15.1 Design measures to prevent the
generating unit from tripping directly or
indirectly for underfrequency conditions
above the appropriate generator tripping
threshold curve in Figure 1.
15.2 Design auxiliary system(s) or devices
used for the control and protection of
auxiliary system(s), necessary for the
generating unit operation such that they will
not trip the generating unit during
underfrequency conditions above the
appropriate generator underfrequency trip
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Removed language pertaining to the
Version 1 of the standard regarding on or
after the effective date. Version 1 has been
in place and transition/implementation
concerns need not be addressed in this
requirement.
12.2. Design auxiliary system(s) or
devices used for the control
and protection of auxiliary
system(s), necessary for the
generating unit operation such
that they will not trip the
20
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
protection settings threshold curve in Figure
1.
Translation to New Standard or Other
Action
generating unit during
underfrequency conditions
above the appropriate
generator underfrequency trip
protection setting threshold
curve in Figure 2.
PRC-006-NPCC-1
PRC-006-NPCC-2
R16 Each Generator Owner of existing nonnuclear units in service prior to the effective
date of this standard that have
underfrequency protections set to trip above
the appropriate curve in Figure 1 shall:
[Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
R13. For existing non-nuclear units in
service prior to July 1, 2015, that have
underfrequency protections set to trip
above the appropriate curve in Figure
2: [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
13.1. Each Generator Owner shall set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations.
16.1 Set the underfrequency protection to
operate at the lowest frequency allowed by
the plant design and licensing limitations.
16.2 Transmit the existing underfrequency
settings and any changes to the
underfrequency settings along with the
technical basis for the settings to the Planning
Coordinator.
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Addition made to R13.3 and R13.4 which is
the approved requirement R16 to clarify
that any compensatory load shedding must
be in the island the generating unit resides
in.
13.2. Each Generator Owner shall
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
21
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
16.3 Have compensatory load shedding, as
provided by a Distribution Provider or
Transmission Owner that is adequate to
compensate for the loss of their generator
due to early tripping.
Translation to New Standard or Other
Action
Description and Change Justification
basis for the settings to the
Planning Coordinator.
13.3. Each Planning Coordinator in
Ontario, Québec and the Maritime
Provinces shall arrange for
compensatory load shedding, in
accordance with Attachment A
and as provided by a Distribution
Provider or Transmission Owner,
that is adequate to compensate
for the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
13.4. Each Generator Owner in the ISONE Planning Coordinator area and
in NYISO Planning Coordinator
area shall arrange for
compensatory load shedding, in
accordance with Attachment B
and as provided by a Distribution
Provider or Transmission Owner,
that is adequate to compensate
Mapping Document
Project Number and Name | Month Year
22
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
for the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
PRC-006-NPCC-1
PRC-006-NPCC-2
R17 Each Planning Coordinator in Ontario,
Quebec and the Maritime provinces shall
apply the criteria described in Attachment A
to determine the compensatory load
shedding that is required in Requirement
R16.3 for generating units in its respective
NPCC area. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
R14. Each Planning Coordinator in Ontario,
Quebec and the Maritime provinces
shall apply the criteria described in
Attachment A to determine the
compensatory load shedding that is
required in Requirement R13.3 for
generating units in its respective NPCC
area. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R18 Each Generator Owner, Distribution
Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the
New York ISO shall apply the criteria
described in Attachment B to determine the
compensatory load shedding that is required
in Requirement R16.3 for generating units in
R15. Each Generator Owner, Distribution
Provider or Transmission Owner within
the ISO-NE Planning Coordinator area
and in NYISO Planning Coordinator
Area shall apply the criteria described
in Attachment B to determine the
compensatory load shedding that is
Mapping Document
Project Number and Name | Month Year
Only made changes to the requirement
number.
Only made changes to the requirement
number.
23
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
its respective NPCC area. [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
Translation to New Standard or Other
Action
required in Requirement R13.4 for
generating units in its respective NPCC
area. [Violation Risk Factor: High][Time
Horizon: Long Term Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R19 Each Generator Owner of existing
nuclear generating plants with units that have
underfrequency relay threshold settings
above the Eastern Interconnection generator
tripping curve in Figure 1, based on their
licensing design basis, shall: [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
R16. Each Generator Owner of existing
nuclear generating plants with units
that have underfrequency relay
threshold settings above the Eastern
Interconnection generator tripping
curve in Figure 2 based on their
licensing design shall: [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
16.1. Set the underfrequency
protection to operate at a
frequency as low as possible
in accordance with the plant
design and licensing
limitations but not greater
than 57.8 Hz.
19.1 Set the underfrequency protection to
operate at as low a frequency as possible in
accordance with the plant design and
licensing limitations but not greater than
57.8Hz.
19.2 Set the frequency trip setting upper
tolerance to no greater than + 0.1 Hz.
19.3 Transmit the initial frequency trip
setting and any changes to the setting and the
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Only made changes to the requirement
number and Figure reference update.
16.2. Set the frequency trip setting
upper tolerance to no greater
than + 0.1 Hz.
24
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
technical basis for the settings to the Planning
Coordinator.
PRC-006-NPCC-1
R20 The Planning Coordinator shall update its
UFLS program database as specified by the
NERC PRC Standard on UFLS. This database
shall include the following information:
[Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
20.1 For each UFLS relay, including those
used for compensatory load shedding, the
amount and location of load shed at peak, the
corresponding frequency threshold and time
delay settings.
Translation to New Standard or Other
Action
Description and Change Justification
16.3. Transmit the initial frequency
trip setting and any changes
to the setting and the
technical basis for the
settings to the Planning
Coordinator.
PRC-006-2 (Existing in force continent-wide
standard)
The drafting team decided to remove
requirement 19 and 20 because they are
covered by the continent-wide PRC-006-2
requirement 6.
R6. Each Planning Coordinator shall
The requirement 19 and 20 language will be
maintain a UFLS database containing data
necessary to model its UFLS program for use transferred over to new guideline
document.
in event analyses and assessment of the
UFLS program at least once each calendar
year, with no more than 15 months
between maintenance activities. [VRF:
Lower][Time Horizon: Long-term Planning]
20.2 The buses at which the Load is modeled
in the NPCC library power flow case.
20.3 A list of all generating units that may be
tripped for underfrequency conditions above
the appropriate generator underfrequency
Mapping Document
Project Number and Name | Month Year
25
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
trip protection settings threshold curve in
Figure 1, including the frequency trip
threshold and time delay for each protection
system.
20.4 The location and amount of additional
elements to be switched for voltage control
that are coordinated with UFLS program
tripping.
20.5 A list of all UFLS relay inhibit functions
along with the corresponding settings and
locations of these relays.
PRC-006-NPCC-1
R21 Each Planning Coordinator shall notify
each Distribution Provider, Transmission
Owner, and Generator Owner within its
Planning Coordinator area of changes to load
distribution needed to satisfy UFLS program
performance characteristics as specified by
the NERC PRC Standard on UFLS.[Violation
Risk Factor: High] [Time Horizon: Long Term
Planning]
Mapping Document
Project Number and Name | Month Year
PRC-006-2 (Existing in force continent-wide
standard)
R3. Each Planning Coordinator shall
develop a UFLS program,
including notification of and a
schedule for implementation by
UFLS entities within its area, that
meets the following performance
characteristics in simulations of
underfrequency conditions
resulting from an imbalance
scenario, where an imbalance =
PRC-006-NPCC-1 R21 is now redundant with
the NERC continent wide standard R3. This
requirement, R21 is proposed for
retirement under the P-81 criteria.
26
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
[(load — actual generation
output) / (load)], of up to 25
percent within the identified
island(s). [VRF: High][Time
Horizon: Long-term Planning]
3.1. Frequency shall remain above
the Underfrequency Performance
Characteristic curve in PRC-006-2
- Attachment 1, either for 60
seconds or until a steady-state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.2. Frequency shall remain below
the Overfrequency Performance
Characteristic curve in PRC-006-2
- Attachment 1, either for 60
seconds or until a steady-state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.3. Volts per Hz (V/Hz) shall not
exceed 1.18 per unit for longer
than two seconds cumulatively
per simulated event, and shall not
exceed 1.10 per unit for longer
Mapping Document
Project Number and Name | Month Year
27
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
than 45 seconds cumulatively per
simulated event at each
generator bus and generator
step-up transformer high-side bus
associated with each of the
following:
•
•
•
PRC-006-NPCC-1
R22 Each Distribution Provider, Transmission
Owner and Generator Owner shall implement
the load distribution changes based on the
Mapping Document
Project Number and Name | Month Year
Individual generating units
greater than 20 MVA (gross
nameplate rating) directly
connected to the BES
Generating plants/facilities
greater than 75 MVA (gross
aggregate nameplate rating)
directly connected to the BES
Facilities consisting of one or
more units connected to the
BES at a common bus with
total generation above 75
MVA gross nameplate rating.
PRC-006-2 (Existing in force continent-wide
standard)
PRC-006-NPCC-1 R22 is now redundant with
the NERC continent wide standard R9 and
R9. Each UFLS entity shall provide automatic this requirement, R22 is proposed for
retirement under the P-81 criteria.
tripping of Load in accordance with the
28
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
notification provided by the Planning
Coordinator in accordance with Requirement
R21. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
UFLS program design and schedule for
implementation, including any Corrective
Action Plan, as determined by its Planning
Coordinator(s) in each Planning Coordinator
area in which it owns assets. [VRF:
High][Time Horizon: Long-term Planning]
PRC-006-NPCC-1
PRC-006-2 (Existing in force continent-wide
standard)
R23 Each Distribution Provider, Transmission
Owner and Generator Owner shall develop
and submit an implementation plan within 90
days of the request from the Planning
Coordinator for approval by the Planning
Coordinator in accordance with Requirement
R21. [Violation Risk Factor: Lower] [Time
Horizon: Operations Planning]
Mapping Document
Project Number and Name | Month Year
R3. Each Planning Coordinator shall
develop a UFLS program,
including notification of and a
schedule for implementation by
UFLS entities within its area, that
meets the following performance
characteristics in simulations of
underfrequency conditions
resulting from an imbalance
scenario, where an imbalance =
[(load — actual generation
output) / (load)], of up to 25
percent within the identified
island(s). [VRF: High][Time
Horizon: Long-term Planning]
Description and Change Justification
PRC-006-NPCC-1 states an implemention
plan for changes needs to be submitted to
the PC for their approval within 90 days of
the request. However in R22 of the regional
standard it states that the changes shall be
implemented based on the PC’s notification.
We believe this is fully covered in R3 and an
additional implementation plan beyond the
PC’s plan, which includes the notification
and schedule for the UFLS entities to follow
is now unnecessary in the regional standard.
We are recommending that R23 in the
regional standard be retired.
29
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
3.1. Frequency shall remain above
the Underfrequency Performance
Characteristic curve in PRC-006-2
- Attachment 1, either for 60
seconds or until a steady-state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.2. Frequency shall remain below
the Overfrequency Performance
Characteristic curve in PRC-006-2
- Attachment 1, either for 60
seconds or until a steady-state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.3. Volts per Hz (V/Hz) shall not
exceed 1.18 per unit for longer
than two seconds cumulatively
per simulated event, and shall not
exceed 1.10 per unit for longer
than 45 seconds cumulatively per
simulated event at each
generator bus and generator
step-up transformer high-side bus
Mapping Document
Project Number and Name | Month Year
30
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
associated with each of the
following:
•
•
Individual generating units
greater than 20 MVA (gross
nameplate rating) directly
connected to the BES
Generating plants/facilities
greater than 75 MVA (gross
aggregate nameplate rating)
directly connected to the BES
Facilities consisting of one or more units
connected to the BES at a common bus with
total generation above 75 MVA gross
nameplate rating.
Mapping Document
Project Number and Name | Month Year
31
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Formatted
A. Introduction
2.11. Title:
Automatic Underfrequency Load Shedding
2.22. Number:
PRC-006-NPCC-21
2.33. Purpose: The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this documentTo provide a
regional reliability standard that ensures the development of an effective automatic
underfrequency load shedding (UFLS) program in order to preserve the security and
integrity of the bulk power system during declining system frequency events in
coordination with the NERC UFLS reliability standard characteristics.
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Style: 1, 2, 3, … + Start at: 1 + Alignment: Left + Aligned at:
0.25" + Tab after: 0.65" + Indent at: 0.65"
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2.44. Applicability:
a.4.1. Generator Owner
b.4.2.
Planning Coordinator
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Style: 1, 2, 3, … + Start at: 1 + Alignment: Left + Aligned at:
0.56" + Tab after: 0.91" + Indent at: 0.91"
c.4.3. Distribution Providers that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program established by the Planning
CoordinatorsDistribution Provider
Formatted: Font: (Default) Times New Roman
d.4.4.
Transmission Owners that are responsible for the ownership, operation, or
control of UFLS equipment as required by the UFLS program established by the
Planning CoordinatorsTransmission Owner
Formatted: Font: (Default) Times New Roman
2.55. Effective Date:
See Implementation Plan For the Eastern Interconnection & Québec Interconnection
portions of NPCC excluding the Independent Electricity System Operator (IESO)
Planning Coordinator area of NPCC in Ontario, Canada:
The effective date for Requirements R1, R2, R3, R4, R5, R6, and R7 is the first
day of the first calendar quarter following applicable regulatory approval but no
earlier than January 1, 2016 The effective date for Requirements R8 through R23
is the first day of the first calendar quarter two years following applicable
governmental and regulatory approval.
For the Independent Electricity System Operator (IESO) Planning Coordinator’s area of
NPCC in Ontario, Canada:
All requirements are effective the first day of the first calendar quarter following
applicable governmental and regulatory approval but no earlier than April 1,
2017.
B. Requirements
1
Adopted by Board of Trustees: February 9, 2012
Formatted: Outline numbered + Level: 1 + Numbering
Style: 1, 2, 3, … + Start at: 1 + Alignment: Left + Aligned at:
0.25" + Tab after: 0.65" + Indent at: 0.65"
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1
also shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1.
Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5 Hz
for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
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M1.
R2.
M2.
R3.
M3.
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
Formatted: Font: Bold
Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
Formatted: Font: Bold
Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent wide
PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the frequency
thresholds, total nominal operating time, and load shedding amounts specified
in Attachment C, Tables 1-3.
Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the corresponding
frequency thresholds, on those circuits included in its UFLS program identified in
Requirement R3. (Attachment C, Tables 1-3).
Formatted: Font: Bold
2
Adopted by Board of Trustees: February 9, 2012
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Indent at: 1.13"
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R4.
M4.
Each Distribution Provider or Transmission Owner in the Eastern Interconnection portion
of NPCC that does not meet the UFLS program parameters specified in Attachment C,
Table 1-3, and each Distribution Provider or Transmission Owner in the Quebec
Interconnection that does not meet the UFLS program parameters specified by its
Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
• Within 30 calendar days of determining that it does not meet the specified
parameters, notify its Planning Coordinator that it does not meet the UFLS
program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates that
the deviations from the program parameters will not result in failure of UFLS
performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3
Formatted: Font: Times New Roman, Bold
Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
R1
Each Planning Coordinator shall establish requirements for entities
aggregating their UFLS programs for each anticipated island and requirements for
compensatory load shedding based on islanding criteria (required by the NERC PRC
Standard on UFLS). [Violation Risk Factor: Medium] [Time Horizon: Long Term
Planning]
Formatted: Font: Times New Roman, Bold
Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit function
is intended to prevent operation of a UFLS relay when the transmission supply is lost to
distribution station feeding many induction motors. Following loss of the transmission
supply, motors may support the voltage while the motors coast down in speed. The motors
coasting down (ringing down) will look like an underfrequency event to the relay. The
inhibit setting is set to a voltage above which the motor load is expected to sustain. This
prevents the underfrequency relay from tripping and locking out distribution feeder
breakers supplying the motor load, between the time the transmission supply line trips and
3
Adopted by Board of Trustees: February 9, 2012
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Add space between paragraphs of the same style
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
the time when the line recloses to restore the load. Voltages sustained by motors that are
coasting down (e.g. 0.70 pu) are typically much lower than voltages at which the UFLS
relays are required to operate to meet UFLS performance criteria. However, motor loads
supplied by cable networks typically have higher ring down voltages because of cable
charging. Therefore, care must be taken so that the voltage inhibit setting is not higher than
the voltage at which UFLS relays are required to operate to meet UFLS performance
criteria.
Formatted: Font: Times New Roman
R5.
M5.
R6.
M6.
R7.
M7.
R8.
M8.
Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and time)
to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
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Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
Each Planning Coordinator shall provide evidence such as letters, emails or other dated
documentation that demonstrates that it meets Requirement R6.
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Each Distribution Provider and Transmission Owner that receives a notification pursuant
to Requirement R6 shall develop and submit an implementation plan with respect to
inhibit thresholds for approval by the Planning Coordinator within 90 calendar days of
the request from the Planning Coordinator. [Violation Risk Factor: Lower] [Time
Horizon: Operations Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets Requirement
R7.
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Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6 and
based on the Planning Coordinator approved implementation plan in accordance with R7.
[Violation Risk Factor: High] [Time Horizon: Operation Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that demonstrates
that it meets Requirement R8.
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Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of
the UFLS program for every entity should perfectly match that prescribed in this Standard,
for all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
4
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
various areas and sub-areas within any given island do not perfectly track the load cycle of
the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would occur
for any conditions other than peak, therefore, can only approximate that prescribed in the
Standard. To that end, Requirement R11 requires entities to document measured loads in
the UFLS program coincident with their own annual peak, whether or not that peak occurs
at the same time or in the same season as the peak of the identified island in which their
load resides. Using individual entity peaks vs. overall island peaks provides a consistent
approach for accounting purposes among the very entities that are responsible for
designing and maintaining their UFLS programs.
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Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its Planning
Coordinator of the actual net Load that would have been shed by the UFLS relays at each
UFLS stage. The actual net Load shall be coincident with the entity’s integrated hourly
peak net Load during the previous year, as determined by measuring or calculating Load
through the switches that would disconnect load if triggered by the UFLS relays. If
measured data is unavailable then calculated data may be used. [Violation Risk Factor:
Lower] [Time Horizon: Long Term Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning Coordinator
that indicates the net amount of load shed and the percentage of its peak load at each
stage of its UFLS program to demonstrate that it meets Requirement R9.
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Each Generator Owner shall set each generator underfrequency trip relay, if so equipped,
on or below the appropriate generator underfrequency trip protection setting threshold
curve in Figure 2, except as otherwise exempted in Requirements R13 and R16.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets
or other documentation that demonstrates that it meets Requirement R10.
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R11.
Each Generator Owner shall transmit the generator underfrequency trip setting and time
delay within 45 calendar days of the Planning Coordinator’s request. [Violation Risk
Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
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R12.
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R9.
M9.
R10.
Each Generator Owner with a new generating unit, or an existing generator increasing its
net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate generator
tripping threshold curve in Figure 2.
5
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency conditions
above the appropriate generator underfrequency trip protection setting
threshold curve in Figure 2.
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R2
Each Planning Coordinator shall, within 30 days of completion
of its system studies required by the NERC PRC Standard on UFLS, identify
to the Regional Entity the generation facilities within its Planning
Coordinator Area necessary to support the UFLS program performance
characteristics. [Violation Risk Factor: Medium] [Time Horizon: Long
Term Planning]
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R3
Each Planning Coordinator shall provide to the Transmission
Owner, Distribution Provider, and Generator Owner within 30 days upon
written request the requirements for entities aggregating the UFLS
programs and requirements for compensatory load shedding program
derived from each Planning Coordinator’s system studies as determined by
Requirement R1. [Violation Risk Factor: Low] [Time Horizon: Long Term
Planning]
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R4
Each Distribution Provider and Transmission Owner in the
Eastern Interconnection portion of NPCC shall implement an automatic
UFLS program reflecting normal operating conditions excluding outages for
its Facilities based on frequency thresholds, total nominal operating time and
amounts specified in Attachment C, Tables 1 through 3, or shall collectively
implement by mutual agreement with one or more Distribution Providers
and Transmission Owners within the same island identified in Requirement
R1 and acting as a single entity, provide an aggregated automatic UFLS
program that sheds their coincident peak aggregated net Load, based on
frequency thresholds, total nominal operating time and amounts specified in
Attachment C, Tables 1 through 3.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R5
Each Distribution Provider or Transmission Owner that must
arm its load to trip on underfrequency in order to meet its requirements as
specified and by doing so exceeds the tolerances and/or deviates from the
number of stages and frequency set points of the UFLS program as specified
in the tables contained in Requirement R4 above, as applicable depending on
its total peak net Load shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
5.1
Inform its Planning Coordinator of the need to exceed the
stated tolerances or the number of stages as shown in UFLS Attachment C,
Table 1 if applicable and
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5.2
Provide its Planning Coordinator with a technical study that
demonstrates that the Distribution Providers or Transmission Owners
specific deviations from the requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on the bulk power system.
5.3
Inform its Planning Coordinator of the need to exceed the
stated tolerances of UFLS Attachment C, Table 2 or Table 3, and in the case
of Attachment C, Table 2 only, the need to deviate from providing two stages
of UFLS, if applicable, and
5.4
Provide its Planning Coordinator with an analysis
demonstrating that no alternative load shedding solution is available that
would allow the Distribution Provider or Transmission Owner to comply
with UFLS Attachment C Table 2 or Attachment C Table 3.
R6 Each Distribution Provider and Transmission Owner in the
Québec Interconnection portion of NPCC shall implement an automatic
UFLS program for its Facilities based on the frequency thresholds, slopes,
total nominal operating time and amounts specified in Attachment C, Table
4 or shall collectively implement by mutual agreement with one or more
Distribution Providers and Transmission Owners within the same island,
identified in Requirement R1, an aggregated automatic UFLS program that
sheds Load based on the frequency thresholds, slopes, total nominal
operating time and amounts specified in Attachment C, Table 4. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
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R7
Each Distribution Provider and Transmission Owner shall set
each underfrequency relay that is part of its region’s UFLS program with the
following minimum time delay:
7.1
Eastern Interconnection – 100 ms
7.2
Québec Interconnection – 200 ms
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R8 Each Planning Coordinator shall develop and review once per
calendar year settings for inhibit thresholds (such as but not limited to
voltage, current and time) to be utilized within its region's UFLS program.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
7
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9
Each Planning Coordinator shall provide each Transmission
Owner and Distribution Provider within its Planning Coordinator area the
applicable inhibit thresholds within 30 days of the initial determination of
those inhibit thresholds and within 30 days of any changes to those
thresholds. [Violation Risk Factor: Medium] [Time Horizon: Operations
Planning]
R10 Each Distribution Provider and Transmission Owner shall
implement the inhibit threshold settings based on the notification provided
by the Planning Coordinator in accordance with Requirement R9. [Violation
Risk Factor: High] [Time Horizon: Operations Planning]
R11 Each Distribution Provider and Transmission Owner shall
develop and submit an implementation plan within 90 days of the request
from the Planning Coordinator for approval by the Planning Coordinator in
accordance with R9. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
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R12 Each Transmission Owner and Distribution Provider shall
annually provide documentation, with no more than 15 months between
updates, to its Planning Coordinator of the actual net Load that would have
been shed by the UFLS relays at each UFLS stage coincident with their
integrated hourly peak net Load during the previous year, as determined by
measuring actual metered Load through the switches that would be opened
by the UFLS relays. [Violation Risk Factor: Lower] [Time Horizon: Long
Term Planning]
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R13 Each Generator Owner shall set each generator
underfrequency trip relay, if so equipped, below the appropriate generator
underfrequency trip protection settings threshold curve in Figure 1, except
as otherwise exempted in Requirements R16 and R19. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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R14 Each Generator Owner shall transmit the generator
underfrequency trip setting and time delay to its Planning Coordinator
within 45 days of the Planning Coordinator’s request. [Violation Risk
Factor: High] [Time Horizon: Operations Planning]
8
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R15 Each Generator Owner with a new generating unit, scheduled
to be in service on or after the effective date of this Standard, or an existing
generator increasing its net capability by greater than 10% shall: [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
15.1 Design measures to prevent the generating unit from tripping
directly or indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 1.
15.2 Design auxiliary system(s) or devices used for the control and
protection of auxiliary system(s), necessary for the generating unit operation
such that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip protection
settings threshold curve in Figure 1.
R16 Each Generator Owner of existing non-nuclear units in service
prior to the effective date of this standard that have underfrequency
protections set to trip above the appropriate curve in Figure 1 shall:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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16.1 Set the underfrequency protection to operate at the lowest
frequency allowed by the plant design and licensing limitations.
16.2 Transmit the existing underfrequency settings and any changes
to the underfrequency settings along with the technical basis for the settings
to the Planning Coordinator.
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16.3 Have compensatory load shedding, as provided by a
Distribution Provider or Transmission Owner that is adequate to
compensate for the loss of their generator due to early tripping.
R17 Each Planning Coordinator in Ontario, Quebec and the
Maritime provinces shall apply the criteria described in Attachment A to
determine the compensatory load shedding that is required in Requirement
R16.3 for generating units in its respective NPCC area. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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R18
Each Generator Owner, Distribution Provider or Transmission
Owner within the Planning Coordinator area of ISO-NE or the New York
ISO shall apply the criteria described in Attachment B to determine the
compensatory load shedding that is required in Requirement R16.3 for
9
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
generating units in its respective NPCC area. [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
R19 Each Generator Owner of existing nuclear generating plants with units
that have underfrequency relay threshold settings above the Eastern
Interconnection generator tripping curve in Figure 1, based on their
licensing design basis, shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
19.1
Set the underfrequency protection to operate at as low a
frequency as possible in accordance with the plant design and licensing
limitations but not greater than 57.8Hz.
19.2
0.1 Hz.
Set the frequency trip setting upper tolerance to no greater than +
19.3
Transmit the initial frequency trip setting and any changes to the
setting and the technical basis for the settings to the Planning Coordinator.
R20
The Planning Coordinator shall update its UFLS program
database as specified by the NERC PRC Standard on UFLS. This database
shall include the following information: [Violation Risk Factor: Lower]
[Time Horizon: Operations Planning]
20.1
For each UFLS relay, including those used for compensatory load
shedding, the amount and location of load shed at peak, the corresponding
frequency threshold and time delay settings.
20.2
The buses at which the Load is modeled in the NPCC library
power flow case.
20.3
A list of all generating units that may be tripped for
underfrequency conditions above the appropriate generator underfrequency
trip protection settings threshold curve in Figure 1, including the frequency
trip threshold and time delay for each protection system.
20.4
The location and amount of additional elements to be switched for
voltage control that are coordinated with UFLS program tripping.
20.5 A list of all UFLS relay inhibit functions along with the corresponding
settings and locations of these relays.
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R21
Each Planning Coordinator shall notify each Distribution
Provider, Transmission Owner, and Generator Owner within its Planning
Coordinator area of changes to load distribution needed to satisfy UFLS
program performance characteristics as specified by the NERC PRC
Standard on UFLS.[Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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R22
Each Distribution Provider, Transmission Owner and Generator
Owner shall implement the load distribution changes based on the
notification provided by the Planning Coordinator in accordance with
Requirement R21. [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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R23
Each Distribution Provider, Transmission Owner and Generator
Owner shall develop and submit an implementation plan within 90 days of
the request from the Planning Coordinator for approval by the Planning
Coordinator in accordance with Requirement R21. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
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M12. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement R12.
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R13.
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For existing non-nuclear units in service prior to July 1, 2015, that have underfrequency
protections set to trip above the appropriate curve in Figure 2: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to operate
at the lowest frequency allowed by the plant design and licensing
limitations.
11
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
13.2
Each Generator Owner shall transmit the existing underfrequency settings
and any changes to the underfrequency settings along with the technical
basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is within
the UFLS island identified by the Planning Coordinator in Requirement
R2.
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M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated documentation
demonstrating that it meets Requirement R13.
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R14.
Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding that
is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates that it
followed the methodology described in Attachment A and meets Requirement R14.
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R15.
Each Generator Owner, Distribution Provider or Transmission Owner within the ISO-NE
Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that is
required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed the
methodology described in Attachment B and meets Requirement R15.
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R16.
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Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
12
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
16.1
Set the underfrequency protection to operate at a frequency setting that is as low
as possible in accordance with the plant design and licensing limitations but not
greater than 57.8 Hz.
16.2 Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3 Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and dated
documentation that demonstrates that it meets Requirement R16.
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Figure 1
Frequency (Hz)
Thresholds for Setting Underfrequency Trip Protection for Generators
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
Figure 1
13
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
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Curve Data:
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Overfrequency Requirements
Source
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t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
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t > 30 s
f = 60.7 Hz
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NERC PRC-006 (Continent-Wide Standard on UFLS)
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Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
Source
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NERC PRC-006 (Continent-Wide Standard on UFLS)
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NERC PRC-006-NPCC (Regional Standard on UFLS)
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
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Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
15
Adopted by Board of Trustees: February 9, 2012
Frequency (Hz)
60
59.5
59
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
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C. Measures
16
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M1
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
M3 Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
M4 Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped, and the corresponding frequency thresholds,
on those circuits included in its UFLS program to achieve the individual and
cumulative percentages identified in Requirement R4. (Attachment C Tables 1-3).
M5 Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
M6 Each Distribution Provider and Transmission Owner in the Québec Interconnection
shall have evidence such as documentation or reports containing the location and
amount of load to be tripped and the corresponding frequency thresholds on those
circuits included in its UFLS program to achieve the load values identified in Table 4
of Requirement R6. (Attachment C Table 4).
M7 Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the
minimum time delay, in accordance with Requirement R7.
M8 Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R8.
M9 Each Planning Coordinator shall provide evidence such as letters, emails, or other
dated documentation that demonstrates that it meets Requirement R9.
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M10 Each Distribution Provider and Transmission Owner shall provide evidence such as
test reports, data sheets or other documentation that demonstrates that it meets
Requirement R10.
M11 Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails or other dated documentation that demonstrates that it meets
Requirement R11.
M12 Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the frequency set point, the net amount of load shed and the
percentage of its peak load at each stage of its UFLS program coincident with the
integrated hourly peak of the previous year that demonstrates that it meets Requirement
R12.
M13 Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement R13.
M14 Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R14.
M15 Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R15.
M16 Each Generator Owner with existing non-nuclear units in service prior to the effective
date of this Standard which have underfrequency tripping that is not compliant with
Requirement R13 shall provide evidence such as reports, spreadsheets, memorandum
or dated documentation demonstrating that it meets Requirement R16.
M17 Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall
provide evidence such as emails, memorandum or other documentation that
demonstrates that it followed the methodology described in Attachment A and meets
Requirement R17.
M18 Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the New York ISO shall provide evidence
such as emails, memorandum, or other documentation that demonstrates that it
followed the methodology described in Attachment B and meets Requirement R18.
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Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M19 Each Generator Owner of nuclear units that have been specifically identified by NPCC
as having generator trip settings above the generator trip curve in Figure 1 shall
provide evidence such as letters, reports and dated documentation that demonstrates
that it meets Requirement R19.
M20 Each Planning Coordinator shall provide evidence such as spreadsheets, system
studies, or other documentation that demonstrates that it meets the requirements of
Requirement R20.
M21 Each Planning Coordinator shall provide evidence such as emails, memorandum or
other dated documentation that it meets Requirement R21.
M22 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as reports, spreadsheets or other documentation that demonstrates that it
meets Requirement R22.
M23 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as letters, emails or other dated documentation that demonstrates it
meets Requirement 23.
Compliance
D.C.
1.11. Compliance Monitoring Process
a.1.1.
Compliance Enforcement Authority
Northeast Power Coordinating CouncilPCC Compliance Committee
a.
Compliance Monitoring Period and Reset Time Frame
Not Applicable
b.1.2.
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DataEvidence Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 24, 35, 46, 57, 810, and 119, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 3, 86, and 79, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall keep evidence
for three calendar years for Measure 17.
19
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 185, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
103, 114, 125, 136, and 169.
c.1.3. Compliance Monitoring and Assessment Processes
ComSelf -Certifications.
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Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.pliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
d.
Additional Compliance Information
None.
20
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Formatted
1.21. Violation Severity Levels
Requirement
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1
N/A
N/A
N/A
The Planning Coordinator
failed to design an UFLS
program having
performance
characteristics that
prevent frequency from
remaining below 59.5 Hz
in accordance with Figure
1.
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R2
The
Planning
Coordinator provided
its
UFLS
island
boundaries,
as
identified per the
NERC continent-wide
PRC-006 Standard on
UFLS but did so
more than 30 calendar
days and up to and
including 40 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC continent-wide
PRC-006 Standard on
UFLS but did so more
than 40 calendar days
but less than and
including 50 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC continent-wide
PRC-006 Standard on
UFLS but did so more
than 50 calendar days
but less than and
including 60 days
following a request.
The Planning Coordinator
failed to provide its UFLS
island boundaries, as
identified per the NERC
continent-wide PRC-006
Standard on UFLS. within
60 calendar days
following a request.
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The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
20% or less of the
relays identified as
included in the UFLS
program, or amount of
load tripped is within
10% deviation from
the required amount of
The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
20%-40% of the relays
identified as included in
the UFLS program, or
amount of load tripped
is within 20% deviation
from the required
amount of Load
The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
40%-60% of the relays
identified as included
in the UFLS program,
or amount of load
tripped is within 30%
deviation from the
required amount of
The Distribution
Provider or Transmission
Owner failed to apply
appropriate settings on >
60% of the relays
identified as included in
the UFLS program, or
amount of load tripped
has a > 30% deviation
from the required
amount of Load required
R3
21
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R4
R5
R6
Load required to be
shed at each stage
required to be shed at
each stage m
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations for
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the
4 items by a period of
up to 10 calendar days
but less than or equal
to 20 calendar days.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations for
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the 4
items within a time
greater than 20 calendar
days but less than or
equal to 30 calendar
days.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations but
exceeded the
permissible time
frame for one or more
of the 4 items within
a time greater than 30
calendar days but less
than or equal to 60
calendar days.
The Distribution
Provider or Transmission
Owner that cannot meet
the tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program failed to meet
all of items in
Requirement 5 within 60
calendar days of
permissible time for each
item.
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The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 100% but more
than (and including)
95% of relays within
its region’s UFLS
program.
The Planning
Coordinator
developed or reviewed
settings for inhibit
thresholds at least
once per five calendar
years, for less than
95% but more than
(and including) 90%
of relays within its
region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 90% but more
than (and including)
85% of relays within
its region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 85%
of relays within its
region’s UFLS program.
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The Planning
Coordinator provided
to a Transmission
The Planning
Coordinator provided to
a Transmission Owner
The Planning
Coordinator provided
to a Transmission
The Planning
Coordinator failed to
provide to a
22
Adopted by Board of Trustees: February 9, 2012
Load required to be
shed at each stage.
to be shed at each stage
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R7
R8
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds more
than 30 calendar days
and up to and
including 40 calendar
days of any changes.
or Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds more than 40
calendar days but less
than and including 50
calendar days of any
changes.
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds
more than 50 calendar
days but less than and
including 60 calendar
days of any changes.
Transmission Owner or
Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds within 60
calendar days after any
changes
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 90 calendar
days and up to and
including 100 calendar
days following the
request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 100 calendar
days and up to and
including 110 calendar
days following the
request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 110
calendar days and up
to and including 120
calendar days
following the request.
The Distribution
Provider or Transmission
Owner failed to develop
and submit its
implementation plan
within 120 days
following the request.
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Implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 100%
but more than (and
including) 95% of
UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the inhibit
threshold settings
provided by the
Planning Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 95% but more
than (and including)
90% of UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 90% but
more than (and
including) 85% of
UFLS relays.
The Distribution
Provider or Transmission
Owner implemented the
inhibit threshold settings
provided by the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 85% of UFLS
relays.
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23
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9
R10
R11
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 15 calendar
months but less than
(and including) 16
calendar months since
last update.
The Distribution
Provider or
Transmission Owner
provided to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11 more
than 16 calendar
months but less than
(and including)17
calendar months since
last update.
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 17 calendar
months but less than
(and including)18
calendar months since
last update.
The Distribution
Provider or Transmission
Owner failed to provide
to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
within 18 calendar
months since last update.
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N/A
N/A
N/A
The Generator Owner
did not set each
generator
underfrequency trip
relay, if so equipped, on
or below the appropriate
generator
underfrequency trip
protection settings
threshold curve in Figure
2, except as otherwise
exempted.
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The Generator Owner
failed to transmit the
generator
underfrequency trip
setting and time delay
within 75 calendar days
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The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 45calendar
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 55 calendar
24
Adopted by Board of Trustees: February 9, 2012
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 65 calendar
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R12
days and less than (and
including) 55 calendar
days of the Planning
Coordinator’s request.
days and less than (and
including) 65 calendar
days of the Planning
Coordinator’s request.
N/A
N/A
days and less than
(and including) 75
calendar days of the
Planning
Coordinator’s request.
The Generator Owner
with a new generating
unit, or an existing
generator increasing
its net capability by
greater than 10%:
Did not fulfill the
obligation of
Requirement R12;
Part 12.1
of the Planning
Coordinator’s request.
The Generator Owner
with a new generating
unit, or an existing
generator increasing its
net capability by greater
than 10%, did not fulfill
the obligations of
Requirement R12, Part
12.1 and Part 12.2.
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The Planning
Coordinator in Ontario,
Québec and the
Maritime Provinces or
the Generator Owner
within the ISO-NE and
in NYISO Planning
Coordinator areas failed
to arrange for
compensatory load
shedding as specified in
Requirement R13, Part
13.3.
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OR
Did not fulfill the
obligation of
Requirement R12,
Part 12.2.
R13
R14
N/A
N/A
The Generator Owner
failed to transmit the
existing underfrequency
settings and any
changes to the
underfrequency settings
along with the technical
basis for the settings to
the Planning
Coordinatoras specified
in Requirement R13,
Part 13.2.
The Generator Owner
failed to set the
underfrequency
protection to operate at
the lowest frequency
allowed by the plant
design and licensing
limitations a specified
in Requirement 13,
Part 13.1
N/A
N/A
The Planning
Coordinator did not
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25
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
apply the criteria
described in Attachment
A to determine the
compensatory load
shedding that is required.
R15
R16
N/A
N/A
N/A
The Generator Owner
failed to transmit the
initial frequency trip
setting and any changes
to the setting and the
technical basis for the
settings to the Planning
Coordinator as
specified in
Requirement R16, Part
16.3.
26
Adopted by Board of Trustees: February 9, 2012
N/A
The Generator Owner:
Failed to set the
underfrequency
protection as specified
in Requirement R16;
Part 16.1
OR
Failed to set the
frequency trip setting
upper tolerance as
specified in
Requirement R16, Part
16.2.
The Generator Owner,
Distribution Provider, or
Transmission Owner did
not apply the criteria
described in Attachment
B to determine the
compensatory load
shedding that is required.
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The Generator Owner
did not fulfill the
obligations of
Requirement R16, Part
16.1 and Part 16.2.
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Formatted
PRC-006-NPCC-1 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 2.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all UFLS islands in which the unit may operateThe
Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 1.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all islands identified in Requirement R1 in which the
unit may operate.
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The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (July 1, 2015 PRC-006-NPCC-1). The list
must indicate generating units, if any, that have their underfrequency protections set to
trip above the appropriate curve in Figure 2. Generating Units not appearing on the list
as of the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information for each unitThe Planning Coordinator
shall identify, compile and maintain an updated list of all existing non-nuclear generating
units in service prior to the effective date of this standard that have underfrequency
protections set to trip above the appropriate curve in Figure 1. The list shall include the
following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate, as identified in Requirement R1
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
27
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load sheddingArrange for a
Distribution Provider or Transmission Owner that owns UFLS relays within the
island(s) identified by the Planning Coordinator in Requirement R1 within which
the generator may operate to provide compensatory load shedding.
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2.2 In Ontario and in the Maritime provinces, Tthe compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4..
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2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 2 during an underfrequency event. If the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 2The
compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 1 during an underfrequency event. If the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 1 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 1.
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2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
systemThe amount of compensatory load shedding shall be equivalent (±5%) to
the average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
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In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
28
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facilityIn the specific instance of a
generating unit that has been interconnected to the electric system for less than
two calendar years, the amount of compensatory load shedding shall be equivalent
(±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon
loss of the facility.
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
29
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirementsThe Generator Owner in the New England states or New York State are
responsible for establishing a compensatory load shedding program for all existing non-nuclear
units with underfrequency protection set to trip above the appropriate curve in Figure 1 of this
standard. The Generator Owner shall follow the methodology below to determine compensatory
load shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (July 1, 2015 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above the
appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2. The
list shall include the following information associated with each unitThe Generator
Owner shall identify and compile a list of all existing non-nuclear generating units in
service prior to the effective date of this standard that has underfrequency protection set
to trip above the appropriate curve in Figure 1. The list shall include the following
information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 2, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the same and smallest island identified by the Planning
Coordinator in Requirement R1 of this standardIn cases where a Distribution
Provider or Transmission Owner has coordinated protection settings with the
Generator Owner to cause the generator to trip above the appropriate curve in
Figure 1, the Distribution Provider or Transmission Owner is responsible to
provide the appropriate amount of compensatory load to be shed within the
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
30
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 2, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and smallest
island identified by the Planning Coordinator in Requirement R1 of this
standardIn cases where a Generator Owner has a generator that cannot physically
meet the set points defined by the appropriate curve in Figure 1, the Generator
Owner shall arrange for a Distribution Provider or Transmission Owner to
provide the appropriate amount of compensatory load to be shed within the
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
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2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4The compensatory load shedding that is provided by the Distribution Provider
or Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
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2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip The compensatory load shedding shall be
provided at the UFLS program stage with the frequency threshold setting at or
closest to but above the frequency at which the subject generator will trip.
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2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
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average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
systemThe amount of compensatory load shedding shall be equivalent (±5%) to
the average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facilityIn the specific instance of a
generating unit that has been interconnected to the electric system for less than
two calendar years, the amount of compensatory load shedding shall be equivalent
(±5%) to the maximum claimed seasonal capability of the generator over two
31
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
calendar years, plus expected station loads to be transferred to the system upon
loss of the facility.
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PRC-006-NPCC-1 Attachment C
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32
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW or more of peak net Load shall
implement a UFLS program with the following attributes:
Frequency
Threshold
(Hz)
Total Nominal
Operating
Time (s) 1
Load Shed at Stage as
% of TO or DP
Load
Cumulative Load Shed as % of
TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
27.5 – 28.5
59.5
10.0
2–3
– 31.5
Formatted Table
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW or more and less than 100 MW
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1. The total nominal operating time includes the underfrequency relay
operating time plus any interposing auxiliary relay operating times, communication times, and the rated
breaker interrupting time. The underfrequency relay operating time is measured from the time when
frequency passes through the frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per
second. If the relay operating time is dependent on the rate of frequency decay, the underfrequency relay
operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear frequency
decay of 0.2 Hz per second.
33
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW or more and less than 50 MW of
peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1. The total nominal operating time includes the underfrequency relay
operating time plus any interposing auxiliary relay operating times, communication times, and the rated
breaker interrupting time. The underfrequency relay operating time is measured from the time when
frequency passes through the frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per
second. If the relay operating time is dependent on the rate of frequency decay, the underfrequency relay
operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear frequency
decay of 0.2 Hz per second.
34
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 4: Quebec Interconnection
MW
at peak
Mvar
at peak
Total
Nominal
Operating
Time (s) 2
Rate
Frequency
(Hz)
(*Load must
be fixed at all
times when
above 60% of
peak load..)
Threshold Stage 1
–––
58.5
1000*
1000
0.30
Threshold Stage 2
–––
58.0
800*
800
0.30
Threshold Stage 3
–––
57.5
800
800
0.30
Threshold Stage 4
–––
57.0
800
800
0.30
–––
59.0
500
500
20.0
Slope Stage 1
-0.3 Hz/s
58.5
400
400
0.30
Slope Stage 2
-0.4 Hz/s
59.8
800*
800
0.30
Slope Stage 3
-0.6 Hz/s
59.8
800*
800
0.30
Slope Stage 4
-0.9 Hz/s
59.8
800
800
0.30
Threshold Stage 5
(anti-stall)
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
2. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communications time, and the rated breaker interrupting time. The
underfrequency relay operating time shall be measured from the time when the frequency passes through the
frequency threshold set point.
35
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
1
2
3
4
5
(Hz)
Delay (s)
59.5
59.3
59.1
58.9
59.5
0.10
0.10
0.10
0.10
0.10
Operating
Time (s) 2
0.30
0.30
0.30
0.30
10.0
TO or DP
Load
6.5 – 7.5
6.5 – 7.5
6.5 – 7.5
6.5 – 7.5
2-3
% of TO or
DP Load
6.5 – 7.5
13.5 – 14.5
20.5 – 21.5
27.5 – 28.5
29.5 – 31.5
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UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
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UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
36
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
1
59.5
0.10
0.30
28 – 50
28 – 50
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
2.
37
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
•
•
•
•
•
•
•
•
•
•
•
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
Generator dynamic modeling
Dynamic VAR device modeling
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38
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Standard Development Timeline
This section is maintained by the drafting team during the development of the standard and will
be removed when the standard is adopted by the NERC Board of Trustees (Board).
Description of Current Draft
Completed Actions
Regional Standards Committee approved Regional Standard
Authorization Request (RSAR) for posting
Anticipated Actions
Date
June 23, 2015
Date
1st 45-day Formal Comment Period
September 1, 2017 October 18, 2017
2nd 45-day Formal Comment Period
April 16, 2018 –
June 1, 2018
30-day Pre-ballot Period
10-day ballot Period
Board adoption
PRC-006-NPCC-2
Page 1 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Upon Board adoption, the rationale boxes will be moved to the Supplemental Material Section.
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Functional Entities:
4.1.1. Generator Owner
4.1.2. Planning Coordinator
4.1.3. Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
4.1.4. Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
5.
Effective Date: See Implementation Plan.
B. Requirements and Measures
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1 also
shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5
Hz for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
PRC-006-NPCC-2
Page 2 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent-wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent-wide
PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1-3.
M3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1-3).
R4. Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified
by its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• Within 30 calendar days of determining that it does not meet the
specified parameters, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
PRC-006-NPCC-2
Page 3 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3.
M4. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit
function is intended to prevent operation of a UFLS relay when the transmission supply is
lost to distribution station feeding many induction motors. Following loss of the
transmission supply, motors may support the voltage while the motors coast down in
speed. The motors coasting down (ringing down) will look like an underfrequency event
to the relay. The inhibit setting is set to a voltage above which the motor load is expected
to sustain. This prevents the underfrequency relay from tripping and locking out
distribution feeder breakers supplying the motor load, between the time the transmission
supply line trips and the time when the line recloses to restore the load. Voltages
sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower than
voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring
down voltages because of cable charging. Therefore, care must be taken so that the
voltage inhibit setting is not higher than the voltage at which UFLS relays are required to
operate to meet UFLS performance criteria.
R5. Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and
time) to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M5. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
PRC-006-NPCC-2
Page 4 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R6. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within
30 calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M6. Each Planning Coordinator shall provide evidence such as letters, emails or other
dated documentation that demonstrates that it meets Requirement R6.
R7. Each Distribution Provider and Transmission Owner that receives a notification
pursuant to Requirement R6 shall develop and submit an implementation plan with
respect to inhibit thresholds for approval by the Planning Coordinator within 90
calendar days of the request from the Planning Coordinator. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
M7. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
R8.
Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
M8. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the
UFLS program for every entity should perfectly match that prescribed in this Standard, for
all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
various areas and sub-areas within any given island do not perfectly track the load cycle
of the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would
occur for any conditions other than peak, therefore, can only approximate that
prescribed in the Standard. To that end, Requirement R11 requires entities to document
measured loads in the UFLS program coincident with their own annual peak, whether or
not that peak occurs at the same time or in the same season as the peak of the identified
island in which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
PRC-006-NPCC-2
Page 5 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R9.
Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by
measuring or calculating Load through the switches that would disconnect load if
triggered by the UFLS relays. If measured data is unavailable then calculated data may
be used. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
R10. Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements
R13 and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
R11. Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
R12. Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
PRC-006-NPCC-2
Page 6 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R13. For existing non-nuclear units in service prior to July 1, 2015, that have
underfrequency protections set to trip above the appropriate curve in Figure 2:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R13.
R14. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
R15. Each Generator Owner, Distribution Provider or Transmission Owner within the ISONE Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that
PRC-006-NPCC-2
Page 7 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
is required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed
the methodology described in Attachment B and meets Requirement R15.
R16. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at a frequency setting that
is as low as possible in accordance with the plant design and licensing
limitations but not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and
dated documentation that demonstrates that it meets Requirement R16.
PRC-006-NPCC-2
Page 8 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 1
Curve Data:
Overfrequency Requirements
t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
t > 30 s
f = 60.7 Hz
Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
PRC-006-NPCC-2
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
NERC PRC-006-NPCC (Regional Standard on UFLS)
Page 9 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
PRC-006-NPCC-2
Page 10 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority:
Northeast Power Coordinating Council
1.2. Evidence Retention:
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 2, 3, 4, 5, 8, and 9.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 6, and 7.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 15.
The Generator Owner shall keep evidence for three calendar years for Measures
10, 11, 12, 13, and 16.
1.3. Compliance Monitoring and Enforcement Program:
Compliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
PRC-006-NPCC-2
Page 11 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Violation Severity Levels
Violation Severity Levels
R#
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator failed to
design an UFLS program having
performance characteristics that
prevent frequency from remaining
below 59.5 Hz in accordance with
Figure 1.
R2.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 30 calendar
days and up to and including 40
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 40 calendar
days but less than and including 50
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 50 calendar
days but less than and including 60
days following a request.
The Planning Coordinator failed to
provide its UFLS island boundaries,
as identified per the NERC
continent-wide PRC-006 Standard
on UFLS. within 60 calendar days
following a request.
R3.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%
or less of the relays identified as
included in the UFLS program, or
amount of load tripped is within
10% deviation from the required
amount of Load required to be
shed at each stage
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%40% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
20% deviation from the required
amount of Load required to be
shed at each stage m
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 40%60% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
30% deviation from the required
amount of Load required to be
shed at each stage.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on >
60% of the relays identified as
included in the UFLS program, or
amount of load tripped has a >
30% deviation from the required
amount of Load required to be
shed at each stage
R4.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
but exceeded the permissible
PRC-006-NPCC-1
July 2018
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program failed to meet all of items
in Requirement 5 within 60
Page 12 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items within a time
greater than 20 calendar days but
less than or equal to 30 calendar
days.
time frame for one or more of the
4 items within a time greater than
30 calendar days but less than or
equal to 60 calendar days.
calendar days of permissible time
for each item.
R5.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
100% but more than (and
including) 95% of relays within its
region’s UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
95% but more than (and including)
90% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and including)
85% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
85% of relays within its region’s
UFLS program.
R6.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 30 calendar days and up to
and including 40 calendar days of
any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 40 calendar days but less
than and including 50 calendar
days of any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar days but less
than and including 60 calendar
days of any changes.
R7.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 100 calendar days
and up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
R8.
Implemented the inhibit threshold
settings provided by the Planning
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
PRC-006-NPCC-1
July 2018
The Planning Coordinator failed to
provide to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds
within 60 calendar days after any
changes
The Distribution Provider or
Transmission Owner failed to
develop and submit its
implementation plan within 120
days following the request.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
Page 13 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
less than 100% but more than (and
including) 95% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 95% but more than (and
including) 90% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 90% but more than (and
including) 85% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 85% of UFLS relays.
R9.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 16 calendar
months but less than (and
including)17 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar
months but less than (and
including)18 calendar months
since last update.
The Distribution Provider or
Transmission Owner failed to
provide to its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 within 18 calendar months
since last update.
R10.
N/A
N/A
N/A
R11.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
45calendar days and less than (and
including) 55 calendar days of the
Planning Coordinator’s request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
55 calendar days and less than
(and including) 65 calendar days of
the Planning Coordinator’s
request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
65 calendar days and less than
(and including) 75 calendar days of
the Planning Coordinator’s
request.
The Generator Owner failed to
transmit the generator
underfrequency trip setting and
time delay within 75 calendar days
of the Planning Coordinator’s
request.
R12.
N/A
N/A
The Generator Owner with a new
generating unit, or an existing
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
PRC-006-NPCC-1
July 2018
The Generator Owner did not set
each generator underfrequency
trip relay, if so equipped, on or
below the appropriate generator
underfrequency trip protection
settings threshold curve in Figure
2, except as otherwise exempted.
Page 14 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
generator increasing its net
capability by greater than 10%:
Did not fulfill the obligation of
Requirement R12; Part 12.1
capability by greater than 10%, did
not fulfill the obligations of
Requirement R12, Part 12.1 and
Part 12.2.
OR
Did not fulfill the obligation of
Requirement R12, Part 12.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirement 13, Part 13.1
R13.
N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinatoras specified
in Requirement R13, Part 13.2.
R14.
N/A
N/A
N/A
The Planning Coordinator did not
apply the criteria described in
Attachment A to determine the
compensatory load shedding that
is required.
R15.
N/A
N/A
N/A
The Generator Owner, Distribution
Provider, or Transmission Owner
did not apply the criteria described
in Attachment B to determine the
compensatory load shedding that
is required.
R16.
N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis for
the settings to the Planning
The Generator Owner:
The Generator Owner did not
fulfill the obligations of
Requirement R16, Part 16.1 and
Part 16.2.
PRC-006-NPCC-1
July 2018
Failed to set the underfrequency
protection as specified in
Requirement R16; Part 16.1
The Planning Coordinator in
Ontario, Québec and the Maritime
Provinces or the Generator Owner
within the ISO-NE and in NYISO
Planning Coordinator areas failed
to arrange for compensatory load
shedding as specified in
Requirement R13, Part 13.3.
OR
Page 15 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Coordinator as specified in
Requirement R16, Part 16.3.
Failed to set the frequency trip
setting upper tolerance as
specified in Requirement R16, Part
16.2.
D. Regional Variances
None.
E. Associated Documents
Technical Rationale
PRC-006-NPCC-1
July 2018
Page 16 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Version History
Version
Date
Action
1
2-9-2012
Adopted by Board of Trustees
2
6-23-2015
RSAR Submitted
PRC-006-NPCC-1
July 2018
Change
Tracking
Page 17 of 24
AAA-000-0 Supplemental Material
Standard Attachments
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (July 1, 2015 PRC-006-NPCC-1). The list must
indicate generating units, if any, that have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
Draft Number of Standard
Month Year
Page 18 of 24
AAA-000-0 Supplemental Material
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage
(or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the electric system
for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
Draft Number of Standard
Month Year
Page 19 of 24
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (July 1, 2015 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above
the appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip
above the appropriate curve in Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the same and smallest island identified by
the Planning Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet
the set points defined by the appropriate curve in Figure 2, the Generator Owner
shall arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
Draft Number of Standard
Month Year
Page 20 of 24
AAA-000-0 Supplemental Material
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facility.
Draft Number of Standard
Month Year
Page 21 of 24
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2-3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 22 of 24
AAA-000-0 Supplemental Material
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
28 – 50
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 23 of 24
AAA-000-0 Supplemental Material
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
• HVDC dynamic modeling
Draft Number of Standard
Month Year
Page 24 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Standard Development Timeline
This section is maintained by the drafting team during the development of the standard and will
be removed when the standard is adopted by the NERC Board of Trustees (Board).
Description of Current Draft
Completed Actions
Regional Standards Committee approved Regional Standard
Authorization Request (RSAR) for posting
Anticipated Actions
Date
June 23, 2015
Date
1st 45-day Formal Comment Period
September 1, 2017 October 18, 2017
2nd 45-day Formal Comment Period
April 16, 2018 –
June 1, 2018
30-day Pre-ballot Period
10-day ballot Period
Board adoption
PRC-006-NPCC-2
Page 1 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Upon Board adoption, the rationale boxes will be moved to the Supplemental Material Section.
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Functional Entities:
4.1.1. Generator Owner
4.1.2. Planning Coordinator
4.1.3. Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
4.1.4. Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
5.
Effective Date: See Implementation Plan.
B. Requirements and Measures
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1 also
shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5
Hz for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
PRC-006-NPCC-2
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PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent- wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continentwide PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1-3.
M3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1-3).
R4. Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified
by its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• Within 30 calendar days of determining that it does not meet the
specified parameters, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
PRC-006-NPCC-2
Page 3 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3.
M4. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit
function is intended to prevent operation of a UFLS relay when the transmission supply is
lost to distribution station feeding many induction motors. Following loss of the
transmission supply, motors may support the voltage while the motors coast down in
speed. The motors coasting down (ringing down) will look like an underfrequency event
to the relay. The inhibit setting is set to a voltage above which the motor load is expected
to sustain. This prevents the underfrequency relay from tripping and locking out
distribution feeder breakers supplying the motor load, between the time the transmission
supply line trips and the time when the line recloses to restore the load. Voltages
sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower than
voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring
down voltages because of cable charging. Therefore, care must be taken so that the
voltage inhibit setting is not higher than the voltage at which UFLS relays are required to
operate to meet UFLS performance criteria.
R5. Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and
time) to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M5. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
PRC-006-NPCC-2
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PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R6. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within
30 calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M6. Each Planning Coordinator shall provide evidence such as letters, emails or other
dated documentation that demonstrates that it meets Requirement R6.
R7. Each Distribution Provider and Transmission Owner that receives a notification
pursuant to Requirement R6 shall develop and submit an implementation plan with
respect to inhibit thresholds for approval by the Planning Coordinator within 90
calendar days of the request from the Planning Coordinator. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
M7. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
R8.
Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
M8. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the
UFLS program for every entity should perfectly match that prescribed in this Standard, for
all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
various areas and sub-areas within any given island do not perfectly track the load cycle
of the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would
occur for any conditions other than peak, therefore, can only approximate that
prescribed in the Standard. To that end, Requirement R11 requires entities to document
measured loads in the UFLS program coincident with their own annual peak, whether or
not that peak occurs at the same time or in the same season as the peak of the identified
island in which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
PRC-006-NPCC-2
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PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R9.
Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by
measuring or calculating Load through the switches that would disconnect load if
triggered by the UFLS relays. If measured data is unavailable then calculated data may
be used. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
R10. Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements
R13 and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
R11. Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
R12. Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
PRC-006-NPCC-2
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PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R13. For existing non-nuclear units in service prior to July 1, 2015, that have
underfrequency protections set to trip above the appropriate curve in Figure 2:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R13.
R14. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
R15. Each Generator Owner, Distribution Provider or Transmission Owner within the ISONE Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that
PRC-006-NPCC-2
Page 7 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
is required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed
the methodology described in Attachment B and meets Requirement R15.
R16. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at as a low frequency
setting that is as low as possible in accordance with the plant design and
licensing limitations but not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and
dated documentation that demonstrates that it meets Requirement R16.
PRC-006-NPCC-2
Page 8 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 1
Formatted: Left
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
PRC-006-NPCC-2
Page 9 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 10 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 11 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 12 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 13 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 14 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Formatted: Indent: Left: 0.65", No bullets or numbering
Curve Data:
Overfrequency Requirements
t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
t > 30 s
f = 60.7 Hz
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
Formatted: Indent: Left: 0.65", No bullets or numbering
Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
PRC-006-NPCC-2
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
NERC PRC-006-NPCC (Regional Standard on UFLS)
Page 15 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
PRC-006-NPCC-2
Page 16 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority:
Northeast Power Coordinating Council
1.2. Evidence Retention:
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 2, 3, 4, 5, 8, and 9.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 6, and 7.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 15.
The Generator Owner shall keep evidence for three calendar years for Measures
10, 11, 12, 13, and 16.
1.3. Compliance Monitoring and Enforcement Program:
Compliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
PRC-006-NPCC-2
Page 17 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Violation Severity Levels
Violation Severity Levels
R#
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator failed to
design an UFLS program having
performance characteristics that
prevent frequency from remaining
below 59.5 Hz in accordance with
Figure 1.
R2.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 30 calendar days and up to
and including 40 days following a
request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 40 calendar days but less
than and including 50 days
following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 50 calendar days but less
than and including 60 days
following a request.
The Planning Coordinator failed to
provide its UFLS island boundaries,
as identified per the NERC
continent widecontinent-wide
PRC-006 Standard on UFLS. within
60 calendar days following a
request.
R3.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%
or less of the relays identified as
included in the UFLS program, or
amount of load tripped is within
10% deviation from the required
amount of Load required to be
shed at each stage
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%40% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
20% deviation from the required
amount of Load required to be
shed at each stage m
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 40%60% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
30% deviation from the required
amount of Load required to be
shed at each stage.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on >
60% of the relays identified as
included in the UFLS program, or
amount of load tripped has a >
30% deviation from the required
amount of Load required to be
shed at each stage
R4.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
PRC-006-NPCC-1
July 2018
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program failed to meet all of items
Page 18 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Program fulfilled its obligations for
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
Program fulfilled its obligations for
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items within a time
greater than 20 calendar days but
less than or equal to 30 calendar
days.
but exceeded the permissible
time frame for one or more of the
4 items within a time greater than
30 calendar days but less than or
equal to 60 calendar days.
in Requirement 5 within 60
calendar days of permissible time
for each item.
R5.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
100% but more than (and
including) 95% of relays within its
region’s UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
95% but more than (and including)
90% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and including)
85% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
85% of relays within its region’s
UFLS program.
R6.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 30 calendar days and up to
and including 40 calendar days of
any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 40 calendar days but less
than and including 50 calendar
days of any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar days but less
than and including 60 calendar
days of any changes.
R7.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 100 calendar days
and up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
R8.
Implemented the inhibit threshold
settings provided by the Planning
Coordinator in accordance with
the Planning Coordinator
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
PRC-006-NPCC-1
July 2018
The Planning Coordinator failed to
provide to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds
within 60 calendar days after any
changes
The Distribution Provider or
Transmission Owner failed to
develop and submit its
implementation plan within 120
days following the request.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Page 19 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
approved implementation plan for
less than 100% but more than (and
including) 95% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 95% but more than (and
including) 90% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 90% but more than (and
including) 85% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 85% of UFLS relays.
R9.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 16 calendar
months but less than (and
including)17 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar
months but less than (and
including)18 calendar months
since last update.
The Distribution Provider or
Transmission Owner failed to
provide to its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 within 18 calendar months
since last update.
R10.
N/A
N/A
N/A
R11.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
45calendar days and less than (and
including) 55 calendar days of the
Planning Coordinator’s request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
55 calendar days and less than
(and including) 65 calendar days of
the Planning Coordinator’s
request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
65 calendar days and less than
(and including) 75 calendar days of
the Planning Coordinator’s
request.
PRC-006-NPCC-1
July 2018
The Generator Owner did not set
each generator underfrequency
trip relay, if so equipped, on or
below the appropriate generator
underfrequency trip protection
settings threshold curve in Figure
2, except as otherwise exempted.
The Generator Owner failed to
transmit the generator
underfrequency trip setting and
time delay within 75 calendar days
of the Planning Coordinator’s
request.
Page 20 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R12.
N/A
N/A
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
capability by greater than 10%:
Did not fulfill the obligation of
Requirement R12; Part 12.1
OR
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
capability by greater than 10%, did
not fulfill the obligations of
Requirement R12, Part 12.1 and
Part 12.2.
Did not fulfill the obligation of
Requirement R12, Part 12.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirement 13, Part 13.1
R13.
N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinatoras specified
in Requirement R13, Part 13.2.
R14.
N/A
N/A
N/A
The Planning Coordinator did not
apply the criteria described in
Attachment A to determine the
compensatory load shedding that
is required.
R15.
N/A
N/A
N/A
The Generator Owner, Distribution
Provider, or Transmission Owner
did not apply the criteria described
in Attachment B to determine the
compensatory load shedding that
is required.
R16.
N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis for
The Generator Owner:
The Generator Owner did not
fulfill the obligations of
Requirement R16, Part 16.1 and
Part 16.2.
PRC-006-NPCC-1
July 2018
Failed to set the underfrequency
protection as specified in
Requirement R16; Part 16.1
The Planning Coordinator in
Ontario, Québec and the Maritime
Provinces or the Generator Owner
within the ISO-NE and in NYISO
Planning Coordinator areas failed
to arrange for compensatory load
shedding as specified in
Requirement R13, Part 13.3.
Page 21 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
the settings to the Planning
Coordinator as specified in
Requirement R16, Part 16.3.
OR
Failed to set the frequency trip
setting upper tolerance as
specified in Requirement R16, Part
16.2.
D. Regional Variances
None.
E. Associated Documents
Technical Rationale
PRC-006-NPCC-1
July 2018
Page 22 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Version History
Version
Date
Action
1
2-9-2012
Adopted by Board of Trustees
2
6-23-2015
RSAR Submitted
PRC-006-NPCC-1
July 2018
Change
Tracking
Page 23 of 30
AAA-000-0 Supplemental Material
Standard Attachments
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (AprilJuly 1, 20157 PRC-006-NPCC-1). The list
must indicate generating units, if any, that have their underfrequency protections set to
trip above the appropriate curve in Figure 2. Generating Units not appearing on the list
as of the effective date of Version 1 of the regional standard, as shown above, must
have their Underfrequency protections set to trip on or below the appropriate curve in
Figure 2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
Draft Number of Standard
Month Year
Page 24 of 30
AAA-000-0 Supplemental Material
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage
(or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the electric system
for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
Draft Number of Standard
Month Year
Page 25 of 30
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (AprilJuly 1, 20157 PRC-006-NPCC-1). The list must indicate the Generator
Owner’s generating units, if any, which have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip
above the appropriate curve in Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the same and smallest island identified by
the Planning Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet
the set points defined by the appropriate curve in Figure 2, the Generator Owner
shall arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
Draft Number of Standard
Month Year
Page 26 of 30
AAA-000-0 Supplemental Material
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facility.
Draft Number of Standard
Month Year
Page 27 of 30
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2-3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 28 of 30
AAA-000-0 Supplemental Material
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
28 – 50
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 29 of 30
AAA-000-0 Supplemental Material
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
• HVDC dynamic modeling
Draft Number of Standard
Month Year
Page 30 of 30
Implementation Plan
Regional Reliability Standard PRC-006-NPCC-2 – Automatic
Underfrequency Load Shedding
Applicable Standard(s)
•
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requested Retirement(s)
•
PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding
Applicable Entities
•
•
•
•
Generator Owners
Planning Coordinators
Distribution Providers that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Transmission Owners that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Background
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. To determine if the applicability of the standard needs to be revised in accordance with
Project 2014-01 Dispersed Generation Resources.
2. To determine if the performance requirements as contained in the criteria of NPCC
Directory#12 Sections 5.1.1 and 5.1.2 should be explicitly included in the requirements
of the Regional Standard and potential retirement of Directory 12 Automatic
Underfrequency Load Shedding Program.
3. Review Attachment C in PRC-006-NPCC-1 to address the implications of the design
assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. Review and revise Table 4 in Attachment C in accordance with the 2013 NPCC UFLS
Adequacy Assessment. Additionally, the applicability of Requirements R4 and R5 will be
reviewed to consider that Hydro Quebec is not part of the Eastern Interconnection.
Effective Date
All requirements with the exception of R3 will be enforceable on the first day of the first
calendar quarter following the applicable governmental and regulatory approvals.
R3 will be enforceable on the first day of the first calendar quarter 12 months following
the applicable governmental and regulatory approvals.
Retirement Date
The NPCC Regional Reliability Standard PRC-006-NPCC-1 shall be retired immediately
prior to the Effective Date of PRC-006-NPCC-2.
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Standard Development Timeline
This section is maintained by the drafting team during the development of the standard and will
be removed when the standard is adopted by the NERC Board of Trustees (Board).
Description of Current Draft
Completed Actions
Regional Standards Committee approved Regional Standard
Authorization Request (RSAR) for posting
Anticipated Actions
Date
June 23, 2015
Date
1st 45-day Formal Comment Period
September 1, 2017 October 18, 2017
2nd 45-day Formal Comment Period
April 16, 2018 –
June 1, 2018
30-day Pre-ballot Period
10-day ballot Period
Board adoption
PRC-006-NPCC-2
Page 1 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Upon Board adoption, the rationale boxes will be moved to the Supplemental Material Section.
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Functional Entities:
4.1.1. Generator Owner
4.1.2. Planning Coordinator
4.1.3. Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
4.1.4. Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
5.
Effective Date: See Implementation Plan.
B. Requirements and Measures
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1 also
shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5
Hz for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
PRC-006-NPCC-2
Page 2 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent- wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continentwide PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1-3.
M3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1-3).
R4. Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified
by its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• Within 30 calendar days of determining that it does not meet the
specified parameters, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
PRC-006-NPCC-2
Page 3 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3.
M4. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit
function is intended to prevent operation of a UFLS relay when the transmission supply is
lost to distribution station feeding many induction motors. Following loss of the
transmission supply, motors may support the voltage while the motors coast down in
speed. The motors coasting down (ringing down) will look like an underfrequency event
to the relay. The inhibit setting is set to a voltage above which the motor load is expected
to sustain. This prevents the underfrequency relay from tripping and locking out
distribution feeder breakers supplying the motor load, between the time the transmission
supply line trips and the time when the line recloses to restore the load. Voltages
sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower than
voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring
down voltages because of cable charging. Therefore, care must be taken so that the
voltage inhibit setting is not higher than the voltage at which UFLS relays are required to
operate to meet UFLS performance criteria.
R5. Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and
time) to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M5. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
PRC-006-NPCC-2
Page 4 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R6. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within
30 calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M6. Each Planning Coordinator shall provide evidence such as letters, emails or other
dated documentation that demonstrates that it meets Requirement R6.
R7. Each Distribution Provider and Transmission Owner that receives a notification
pursuant to Requirement R6 shall develop and submit an implementation plan with
respect to inhibit thresholds for approval by the Planning Coordinator within 90
calendar days of the request from the Planning Coordinator. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
M7. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
R8.
Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
M8. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the
UFLS program for every entity should perfectly match that prescribed in this Standard, for
all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
various areas and sub-areas within any given island do not perfectly track the load cycle
of the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would
occur for any conditions other than peak, therefore, can only approximate that
prescribed in the Standard. To that end, Requirement R11 requires entities to document
measured loads in the UFLS program coincident with their own annual peak, whether or
not that peak occurs at the same time or in the same season as the peak of the identified
island in which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
PRC-006-NPCC-2
Page 5 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R9.
Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by
measuring or calculating Load through the switches that would disconnect load if
triggered by the UFLS relays. If measured data is unavailable then calculated data may
be used. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
R10. Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements
R13 and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
R11. Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
R12. Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
PRC-006-NPCC-2
Page 6 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R13. For existing non-nuclear units in service prior to July 1, 2015, that have
underfrequency protections set to trip above the appropriate curve in Figure 2:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R13.
R14. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
R15. Each Generator Owner, Distribution Provider or Transmission Owner within the ISONE Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that
PRC-006-NPCC-2
Page 7 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
is required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed
the methodology described in Attachment B and meets Requirement R15.
R16. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at as a low frequency
setting that is as low as possible in accordance with the plant design and
licensing limitations but not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and
dated documentation that demonstrates that it meets Requirement R16.
PRC-006-NPCC-2
Page 8 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 1
Formatted: Left
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
PRC-006-NPCC-2
Page 9 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 10 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 11 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 12 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 13 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 14 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Formatted: Indent: Left: 0.65", No bullets or numbering
Curve Data:
Overfrequency Requirements
t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
t > 30 s
f = 60.7 Hz
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
Formatted: Indent: Left: 0.65", No bullets or numbering
Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
PRC-006-NPCC-2
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
NERC PRC-006-NPCC (Regional Standard on UFLS)
Page 15 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
PRC-006-NPCC-2
Page 16 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority:
Northeast Power Coordinating Council
1.2. Evidence Retention:
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 2, 3, 4, 5, 8, and 9.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 6, and 7.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 15.
The Generator Owner shall keep evidence for three calendar years for Measures
10, 11, 12, 13, and 16.
1.3. Compliance Monitoring and Enforcement Program:
Compliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
PRC-006-NPCC-2
Page 17 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Violation Severity Levels
Violation Severity Levels
R#
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator failed to
design an UFLS program having
performance characteristics that
prevent frequency from remaining
below 59.5 Hz in accordance with
Figure 1.
R2.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 30 calendar days and up to
and including 40 days following a
request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 40 calendar days but less
than and including 50 days
following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 50 calendar days but less
than and including 60 days
following a request.
The Planning Coordinator failed to
provide its UFLS island boundaries,
as identified per the NERC
continent widecontinent-wide
PRC-006 Standard on UFLS. within
60 calendar days following a
request.
R3.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%
or less of the relays identified as
included in the UFLS program, or
amount of load tripped is within
10% deviation from the required
amount of Load required to be
shed at each stage
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%40% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
20% deviation from the required
amount of Load required to be
shed at each stage m
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 40%60% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
30% deviation from the required
amount of Load required to be
shed at each stage.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on >
60% of the relays identified as
included in the UFLS program, or
amount of load tripped has a >
30% deviation from the required
amount of Load required to be
shed at each stage
R4.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
PRC-006-NPCC-1
July 2018
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program failed to meet all of items
Page 18 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Program fulfilled its obligations for
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
Program fulfilled its obligations for
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items within a time
greater than 20 calendar days but
less than or equal to 30 calendar
days.
but exceeded the permissible
time frame for one or more of the
4 items within a time greater than
30 calendar days but less than or
equal to 60 calendar days.
in Requirement 5 within 60
calendar days of permissible time
for each item.
R5.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
100% but more than (and
including) 95% of relays within its
region’s UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
95% but more than (and including)
90% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and including)
85% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
85% of relays within its region’s
UFLS program.
R6.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 30 calendar days and up to
and including 40 calendar days of
any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 40 calendar days but less
than and including 50 calendar
days of any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar days but less
than and including 60 calendar
days of any changes.
R7.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 100 calendar days
and up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
R8.
Implemented the inhibit threshold
settings provided by the Planning
Coordinator in accordance with
the Planning Coordinator
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
PRC-006-NPCC-1
July 2018
The Planning Coordinator failed to
provide to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds
within 60 calendar days after any
changes
The Distribution Provider or
Transmission Owner failed to
develop and submit its
implementation plan within 120
days following the request.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Page 19 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
approved implementation plan for
less than 100% but more than (and
including) 95% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 95% but more than (and
including) 90% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 90% but more than (and
including) 85% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 85% of UFLS relays.
R9.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 16 calendar
months but less than (and
including)17 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar
months but less than (and
including)18 calendar months
since last update.
The Distribution Provider or
Transmission Owner failed to
provide to its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 within 18 calendar months
since last update.
R10.
N/A
N/A
N/A
R11.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
45calendar days and less than (and
including) 55 calendar days of the
Planning Coordinator’s request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
55 calendar days and less than
(and including) 65 calendar days of
the Planning Coordinator’s
request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
65 calendar days and less than
(and including) 75 calendar days of
the Planning Coordinator’s
request.
PRC-006-NPCC-1
July 2018
The Generator Owner did not set
each generator underfrequency
trip relay, if so equipped, on or
below the appropriate generator
underfrequency trip protection
settings threshold curve in Figure
2, except as otherwise exempted.
The Generator Owner failed to
transmit the generator
underfrequency trip setting and
time delay within 75 calendar days
of the Planning Coordinator’s
request.
Page 20 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R12.
N/A
N/A
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
capability by greater than 10%:
Did not fulfill the obligation of
Requirement R12; Part 12.1
OR
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
capability by greater than 10%, did
not fulfill the obligations of
Requirement R12, Part 12.1 and
Part 12.2.
Did not fulfill the obligation of
Requirement R12, Part 12.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirement 13, Part 13.1
R13.
N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinatoras specified
in Requirement R13, Part 13.2.
R14.
N/A
N/A
N/A
The Planning Coordinator did not
apply the criteria described in
Attachment A to determine the
compensatory load shedding that
is required.
R15.
N/A
N/A
N/A
The Generator Owner, Distribution
Provider, or Transmission Owner
did not apply the criteria described
in Attachment B to determine the
compensatory load shedding that
is required.
R16.
N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis for
The Generator Owner:
The Generator Owner did not
fulfill the obligations of
Requirement R16, Part 16.1 and
Part 16.2.
PRC-006-NPCC-1
July 2018
Failed to set the underfrequency
protection as specified in
Requirement R16; Part 16.1
The Planning Coordinator in
Ontario, Québec and the Maritime
Provinces or the Generator Owner
within the ISO-NE and in NYISO
Planning Coordinator areas failed
to arrange for compensatory load
shedding as specified in
Requirement R13, Part 13.3.
Page 21 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
the settings to the Planning
Coordinator as specified in
Requirement R16, Part 16.3.
OR
Failed to set the frequency trip
setting upper tolerance as
specified in Requirement R16, Part
16.2.
D. Regional Variances
None.
E. Associated Documents
Technical Rationale
PRC-006-NPCC-1
July 2018
Page 22 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Version History
Version
Date
Action
1
2-9-2012
Adopted by Board of Trustees
2
6-23-2015
RSAR Submitted
PRC-006-NPCC-1
July 2018
Change
Tracking
Page 23 of 30
AAA-000-0 Supplemental Material
Standard Attachments
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (AprilJuly 1, 20157 PRC-006-NPCC-1). The list
must indicate generating units, if any, that have their underfrequency protections set to
trip above the appropriate curve in Figure 2. Generating Units not appearing on the list
as of the effective date of Version 1 of the regional standard, as shown above, must
have their Underfrequency protections set to trip on or below the appropriate curve in
Figure 2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
Draft Number of Standard
Month Year
Page 24 of 30
AAA-000-0 Supplemental Material
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage
(or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the electric system
for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
Draft Number of Standard
Month Year
Page 25 of 30
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (AprilJuly 1, 20157 PRC-006-NPCC-1). The list must indicate the Generator
Owner’s generating units, if any, which have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip
above the appropriate curve in Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the same and smallest island identified by
the Planning Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet
the set points defined by the appropriate curve in Figure 2, the Generator Owner
shall arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
Draft Number of Standard
Month Year
Page 26 of 30
AAA-000-0 Supplemental Material
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facility.
Draft Number of Standard
Month Year
Page 27 of 30
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2-3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 28 of 30
AAA-000-0 Supplemental Material
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
28 – 50
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 29 of 30
AAA-000-0 Supplemental Material
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
• HVDC dynamic modeling
Draft Number of Standard
Month Year
Page 30 of 30
Consolidated Edison Company
of New York, Inc.
4 Irving Place
New York NY 10003-0987
November 2, 2018
VIA EMAIL
Regional Standards Committee (RSC)
NPCC
[email protected]
Subject: PRC-006-NPCC-02 Automatic Underfrequency Load Shedding – Approval
to Post for Pre-Ballot and Ballot Period
Dear RSC Members:
The PRC-006-NPCC-2 Automatic Underfrequency Load Shedding Regional Standard
has been posted for three 45-day comment periods. The drafting team has responded to
every comment from all three periods. NPCC’s Manager of Reliability Standards has
posted all comment responses onto the NPCC website. The next step, in accordance with
the NPCC Regional Standard Processes Manual, is to obtain the RSC’s approval to post
for a 30-day pre-ballot review period and a subsequent 10-day ballot period. If you have
not already done so, please email your approval to Mr. Ruida Shu so he can post the
documents for pre-ballot and ballot period.
I’d like to take this opportunity to commend all the members of the Standard Drafting
Team, and those who supported them, for their perseverance through the arduous task of
re-writing this Regional Standard over the course of the past two years and five months.
Their dedication was essential to accomplish the team’s mission.
If you have any questions, please don’t hesitate to contact me.
Regards
Dan Taft
Chief Engineer – Control Systems Engineering Department
Chair – NPCC PRC-006-NPCC-2 Standard Drafting Team
(212) 460 – 4536
[email protected]
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Formatted
A. Introduction
2.11. Title:
Automatic Underfrequency Load Shedding
2.22. Number:
PRC-006-NPCC-21
2.33. Purpose: The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this documentTo provide a
regional reliability standard that ensures the development of an effective automatic
underfrequency load shedding (UFLS) program in order to preserve the security and
integrity of the bulk power system during declining system frequency events in
coordination with the NERC UFLS reliability standard characteristics.
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2.44. Applicability:
a.4.1. Generator Owner
b.4.2.
Planning Coordinator
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c.4.3. Distribution Providers that are responsible for the ownership, operation, or control
of UFLS equipment as required by the UFLS program established by the Planning
CoordinatorsDistribution Provider
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d.4.4.
Transmission Owners that are responsible for the ownership, operation, or
control of UFLS equipment as required by the UFLS program established by the
Planning CoordinatorsTransmission Owner
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2.55. Effective Date:
See Implementation Plan For the Eastern Interconnection & Québec Interconnection
portions of NPCC excluding the Independent Electricity System Operator (IESO)
Planning Coordinator area of NPCC in Ontario, Canada:
The effective date for Requirements R1, R2, R3, R4, R5, R6, and R7 is the first
day of the first calendar quarter following applicable regulatory approval but no
earlier than January 1, 2016 The effective date for Requirements R8 through R23
is the first day of the first calendar quarter two years following applicable
governmental and regulatory approval.
For the Independent Electricity System Operator (IESO) Planning Coordinator’s area of
NPCC in Ontario, Canada:
All requirements are effective the first day of the first calendar quarter following
applicable governmental and regulatory approval but no earlier than April 1,
2017.
B. Requirements
1
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1
also shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1.
Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5 Hz
for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
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M1.
R2.
M2.
R3.
M3.
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
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Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
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Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent wide
PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the frequency
thresholds, total nominal operating time, and load shedding amounts specified
in Attachment C, Tables 1-3.
Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the corresponding
frequency thresholds, on those circuits included in its UFLS program identified in
Requirement R3. (Attachment C, Tables 1-3).
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2
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R4.
M4.
Each Distribution Provider or Transmission Owner in the Eastern Interconnection portion
of NPCC that does not meet the UFLS program parameters specified in Attachment C,
Table 1-3, and each Distribution Provider or Transmission Owner in the Quebec
Interconnection that does not meet the UFLS program parameters specified by its
Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
• Within 30 calendar days of determining that it does not meet the specified
parameters, notify its Planning Coordinator that it does not meet the UFLS
program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates that
the deviations from the program parameters will not result in failure of UFLS
performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3
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Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
R1
Each Planning Coordinator shall establish requirements for entities
aggregating their UFLS programs for each anticipated island and requirements for
compensatory load shedding based on islanding criteria (required by the NERC PRC
Standard on UFLS). [Violation Risk Factor: Medium] [Time Horizon: Long Term
Planning]
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Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit function
is intended to prevent operation of a UFLS relay when the transmission supply is lost to
distribution station feeding many induction motors. Following loss of the transmission
supply, motors may support the voltage while the motors coast down in speed. The motors
coasting down (ringing down) will look like an underfrequency event to the relay. The
inhibit setting is set to a voltage above which the motor load is expected to sustain. This
prevents the underfrequency relay from tripping and locking out distribution feeder
breakers supplying the motor load, between the time the transmission supply line trips and
3
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
the time when the line recloses to restore the load. Voltages sustained by motors that are
coasting down (e.g. 0.70 pu) are typically much lower than voltages at which the UFLS
relays are required to operate to meet UFLS performance criteria. However, motor loads
supplied by cable networks typically have higher ring down voltages because of cable
charging. Therefore, care must be taken so that the voltage inhibit setting is not higher than
the voltage at which UFLS relays are required to operate to meet UFLS performance
criteria.
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R5.
M5.
R6.
M6.
R7.
M7.
R8.
M8.
Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and time)
to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
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Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within 30
calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
Each Planning Coordinator shall provide evidence such as letters, emails or other dated
documentation that demonstrates that it meets Requirement R6.
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Each Distribution Provider and Transmission Owner that receives a notification pursuant
to Requirement R6 shall develop and submit an implementation plan with respect to
inhibit thresholds for approval by the Planning Coordinator within 90 calendar days of
the request from the Planning Coordinator. [Violation Risk Factor: Lower] [Time
Horizon: Operations Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets Requirement
R7.
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Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6 and
based on the Planning Coordinator approved implementation plan in accordance with R7.
[Violation Risk Factor: High] [Time Horizon: Operation Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that demonstrates
that it meets Requirement R8.
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Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of
the UFLS program for every entity should perfectly match that prescribed in this Standard,
for all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
4
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
various areas and sub-areas within any given island do not perfectly track the load cycle of
the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would occur
for any conditions other than peak, therefore, can only approximate that prescribed in the
Standard. To that end, Requirement R11 requires entities to document measured loads in
the UFLS program coincident with their own annual peak, whether or not that peak occurs
at the same time or in the same season as the peak of the identified island in which their
load resides. Using individual entity peaks vs. overall island peaks provides a consistent
approach for accounting purposes among the very entities that are responsible for
designing and maintaining their UFLS programs.
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Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its Planning
Coordinator of the actual net Load that would have been shed by the UFLS relays at each
UFLS stage. The actual net Load shall be coincident with the entity’s integrated hourly
peak net Load during the previous year, as determined by measuring or calculating Load
through the switches that would disconnect load if triggered by the UFLS relays. If
measured data is unavailable then calculated data may be used. [Violation Risk Factor:
Lower] [Time Horizon: Long Term Planning]
Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning Coordinator
that indicates the net amount of load shed and the percentage of its peak load at each
stage of its UFLS program to demonstrate that it meets Requirement R9.
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Each Generator Owner shall set each generator underfrequency trip relay, if so equipped,
on or below the appropriate generator underfrequency trip protection setting threshold
curve in Figure 2, except as otherwise exempted in Requirements R13 and R16.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets, spreadsheets
or other documentation that demonstrates that it meets Requirement R10.
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R11.
Each Generator Owner shall transmit the generator underfrequency trip setting and time
delay within 45 calendar days of the Planning Coordinator’s request. [Violation Risk
Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
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R12.
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R9.
M9.
R10.
Each Generator Owner with a new generating unit, or an existing generator increasing its
net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate generator
tripping threshold curve in Figure 2.
5
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency conditions
above the appropriate generator underfrequency trip protection setting
threshold curve in Figure 2.
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R2
Each Planning Coordinator shall, within 30 days of completion
of its system studies required by the NERC PRC Standard on UFLS, identify
to the Regional Entity the generation facilities within its Planning
Coordinator Area necessary to support the UFLS program performance
characteristics. [Violation Risk Factor: Medium] [Time Horizon: Long
Term Planning]
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R3
Each Planning Coordinator shall provide to the Transmission
Owner, Distribution Provider, and Generator Owner within 30 days upon
written request the requirements for entities aggregating the UFLS
programs and requirements for compensatory load shedding program
derived from each Planning Coordinator’s system studies as determined by
Requirement R1. [Violation Risk Factor: Low] [Time Horizon: Long Term
Planning]
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R4
Each Distribution Provider and Transmission Owner in the
Eastern Interconnection portion of NPCC shall implement an automatic
UFLS program reflecting normal operating conditions excluding outages for
its Facilities based on frequency thresholds, total nominal operating time and
amounts specified in Attachment C, Tables 1 through 3, or shall collectively
implement by mutual agreement with one or more Distribution Providers
and Transmission Owners within the same island identified in Requirement
R1 and acting as a single entity, provide an aggregated automatic UFLS
program that sheds their coincident peak aggregated net Load, based on
frequency thresholds, total nominal operating time and amounts specified in
Attachment C, Tables 1 through 3.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R5
Each Distribution Provider or Transmission Owner that must
arm its load to trip on underfrequency in order to meet its requirements as
specified and by doing so exceeds the tolerances and/or deviates from the
number of stages and frequency set points of the UFLS program as specified
in the tables contained in Requirement R4 above, as applicable depending on
its total peak net Load shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
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6
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
5.1
Inform its Planning Coordinator of the need to exceed the
stated tolerances or the number of stages as shown in UFLS Attachment C,
Table 1 if applicable and
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5.2
Provide its Planning Coordinator with a technical study that
demonstrates that the Distribution Providers or Transmission Owners
specific deviations from the requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on the bulk power system.
5.3
Inform its Planning Coordinator of the need to exceed the
stated tolerances of UFLS Attachment C, Table 2 or Table 3, and in the case
of Attachment C, Table 2 only, the need to deviate from providing two stages
of UFLS, if applicable, and
5.4
Provide its Planning Coordinator with an analysis
demonstrating that no alternative load shedding solution is available that
would allow the Distribution Provider or Transmission Owner to comply
with UFLS Attachment C Table 2 or Attachment C Table 3.
R6 Each Distribution Provider and Transmission Owner in the
Québec Interconnection portion of NPCC shall implement an automatic
UFLS program for its Facilities based on the frequency thresholds, slopes,
total nominal operating time and amounts specified in Attachment C, Table
4 or shall collectively implement by mutual agreement with one or more
Distribution Providers and Transmission Owners within the same island,
identified in Requirement R1, an aggregated automatic UFLS program that
sheds Load based on the frequency thresholds, slopes, total nominal
operating time and amounts specified in Attachment C, Table 4. [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
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R7
Each Distribution Provider and Transmission Owner shall set
each underfrequency relay that is part of its region’s UFLS program with the
following minimum time delay:
7.1
Eastern Interconnection – 100 ms
7.2
Québec Interconnection – 200 ms
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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R8 Each Planning Coordinator shall develop and review once per
calendar year settings for inhibit thresholds (such as but not limited to
voltage, current and time) to be utilized within its region's UFLS program.
[Violation Risk Factor: Medium] [Time Horizon: Long Term Planning]
7
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9
Each Planning Coordinator shall provide each Transmission
Owner and Distribution Provider within its Planning Coordinator area the
applicable inhibit thresholds within 30 days of the initial determination of
those inhibit thresholds and within 30 days of any changes to those
thresholds. [Violation Risk Factor: Medium] [Time Horizon: Operations
Planning]
R10 Each Distribution Provider and Transmission Owner shall
implement the inhibit threshold settings based on the notification provided
by the Planning Coordinator in accordance with Requirement R9. [Violation
Risk Factor: High] [Time Horizon: Operations Planning]
R11 Each Distribution Provider and Transmission Owner shall
develop and submit an implementation plan within 90 days of the request
from the Planning Coordinator for approval by the Planning Coordinator in
accordance with R9. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
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R12 Each Transmission Owner and Distribution Provider shall
annually provide documentation, with no more than 15 months between
updates, to its Planning Coordinator of the actual net Load that would have
been shed by the UFLS relays at each UFLS stage coincident with their
integrated hourly peak net Load during the previous year, as determined by
measuring actual metered Load through the switches that would be opened
by the UFLS relays. [Violation Risk Factor: Lower] [Time Horizon: Long
Term Planning]
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R13 Each Generator Owner shall set each generator
underfrequency trip relay, if so equipped, below the appropriate generator
underfrequency trip protection settings threshold curve in Figure 1, except
as otherwise exempted in Requirements R16 and R19. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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R14 Each Generator Owner shall transmit the generator
underfrequency trip setting and time delay to its Planning Coordinator
within 45 days of the Planning Coordinator’s request. [Violation Risk
Factor: High] [Time Horizon: Operations Planning]
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Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R15 Each Generator Owner with a new generating unit, scheduled
to be in service on or after the effective date of this Standard, or an existing
generator increasing its net capability by greater than 10% shall: [Violation
Risk Factor: High] [Time Horizon: Long Term Planning]
15.1 Design measures to prevent the generating unit from tripping
directly or indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 1.
15.2 Design auxiliary system(s) or devices used for the control and
protection of auxiliary system(s), necessary for the generating unit operation
such that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip protection
settings threshold curve in Figure 1.
R16 Each Generator Owner of existing non-nuclear units in service
prior to the effective date of this standard that have underfrequency
protections set to trip above the appropriate curve in Figure 1 shall:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
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16.1 Set the underfrequency protection to operate at the lowest
frequency allowed by the plant design and licensing limitations.
16.2 Transmit the existing underfrequency settings and any changes
to the underfrequency settings along with the technical basis for the settings
to the Planning Coordinator.
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16.3 Have compensatory load shedding, as provided by a
Distribution Provider or Transmission Owner that is adequate to
compensate for the loss of their generator due to early tripping.
R17 Each Planning Coordinator in Ontario, Quebec and the
Maritime provinces shall apply the criteria described in Attachment A to
determine the compensatory load shedding that is required in Requirement
R16.3 for generating units in its respective NPCC area. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]
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R18
Each Generator Owner, Distribution Provider or Transmission
Owner within the Planning Coordinator area of ISO-NE or the New York
ISO shall apply the criteria described in Attachment B to determine the
compensatory load shedding that is required in Requirement R16.3 for
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
generating units in its respective NPCC area. [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
R19 Each Generator Owner of existing nuclear generating plants with units
that have underfrequency relay threshold settings above the Eastern
Interconnection generator tripping curve in Figure 1, based on their
licensing design basis, shall: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
19.1
Set the underfrequency protection to operate at as low a
frequency as possible in accordance with the plant design and licensing
limitations but not greater than 57.8Hz.
19.2
0.1 Hz.
Set the frequency trip setting upper tolerance to no greater than +
19.3
Transmit the initial frequency trip setting and any changes to the
setting and the technical basis for the settings to the Planning Coordinator.
R20
The Planning Coordinator shall update its UFLS program
database as specified by the NERC PRC Standard on UFLS. This database
shall include the following information: [Violation Risk Factor: Lower]
[Time Horizon: Operations Planning]
20.1
For each UFLS relay, including those used for compensatory load
shedding, the amount and location of load shed at peak, the corresponding
frequency threshold and time delay settings.
20.2
The buses at which the Load is modeled in the NPCC library
power flow case.
20.3
A list of all generating units that may be tripped for
underfrequency conditions above the appropriate generator underfrequency
trip protection settings threshold curve in Figure 1, including the frequency
trip threshold and time delay for each protection system.
20.4
The location and amount of additional elements to be switched for
voltage control that are coordinated with UFLS program tripping.
20.5 A list of all UFLS relay inhibit functions along with the corresponding
settings and locations of these relays.
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R21
Each Planning Coordinator shall notify each Distribution
Provider, Transmission Owner, and Generator Owner within its Planning
Coordinator area of changes to load distribution needed to satisfy UFLS
program performance characteristics as specified by the NERC PRC
Standard on UFLS.[Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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R22
Each Distribution Provider, Transmission Owner and Generator
Owner shall implement the load distribution changes based on the
notification provided by the Planning Coordinator in accordance with
Requirement R21. [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
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R23
Each Distribution Provider, Transmission Owner and Generator
Owner shall develop and submit an implementation plan within 90 days of
the request from the Planning Coordinator for approval by the Planning
Coordinator in accordance with Requirement R21. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
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M12. Each Generator Owner shall provide evidence such as reports, data sheets, specifications,
memorandum or other documentation that demonstrates that it meets Requirement R12.
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R13.
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For existing non-nuclear units in service prior to July 1, 2015, that have underfrequency
protections set to trip above the appropriate curve in Figure 2: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to operate
at the lowest frequency allowed by the plant design and licensing
limitations.
11
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
13.2
Each Generator Owner shall transmit the existing underfrequency settings
and any changes to the underfrequency settings along with the technical
basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is within
the UFLS island identified by the Planning Coordinator in Requirement
R2.
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M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated documentation
demonstrating that it meets Requirement R13.
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R14.
Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding that
is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates that it
followed the methodology described in Attachment A and meets Requirement R14.
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R15.
Each Generator Owner, Distribution Provider or Transmission Owner within the ISO-NE
Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that is
required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed the
methodology described in Attachment B and meets Requirement R15.
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R16.
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Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
12
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
16.1
Set the underfrequency protection to operate at a frequency setting that is as low
as possible in accordance with the plant design and licensing limitations but not
greater than 57.8 Hz.
16.2 Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3 Transmit the initial frequency trip setting and any changes to the setting and the
technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and dated
documentation that demonstrates that it meets Requirement R16.
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Figure 1
Frequency (Hz)
Thresholds for Setting Underfrequency Trip Protection for Generators
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
Figure 1
13
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
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Curve Data:
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Overfrequency Requirements
Source
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Formatted Table
t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
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t > 30 s
f = 60.7 Hz
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NERC PRC-006 (Continent-Wide Standard on UFLS)
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Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
Source
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NERC PRC-006 (Continent-Wide Standard on UFLS)
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NERC PRC-006-NPCC (Regional Standard on UFLS)
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Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
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Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
15
Adopted by Board of Trustees: February 9, 2012
Frequency (Hz)
60
59.5
59
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
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C. Measures
16
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M1
Each Planning Coordinator shall have evidence such as reports, system studies and/or
real time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
M3 Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets Requirement R3.
M4 Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped, and the corresponding frequency thresholds,
on those circuits included in its UFLS program to achieve the individual and
cumulative percentages identified in Requirement R4. (Attachment C Tables 1-3).
M5 Each Distribution Provider or Transmission Owner shall have evidence such as reports,
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R5.
M6 Each Distribution Provider and Transmission Owner in the Québec Interconnection
shall have evidence such as documentation or reports containing the location and
amount of load to be tripped and the corresponding frequency thresholds on those
circuits included in its UFLS program to achieve the load values identified in Table 4
of Requirement R6. (Attachment C Table 4).
M7 Each Distribution Provider and Transmission Owner shall have evidence such as
documentation or reports that their underfrequency relays have been set with the
minimum time delay, in accordance with Requirement R7.
M8 Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R8.
M9 Each Planning Coordinator shall provide evidence such as letters, emails, or other
dated documentation that demonstrates that it meets Requirement R9.
17
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M10 Each Distribution Provider and Transmission Owner shall provide evidence such as
test reports, data sheets or other documentation that demonstrates that it meets
Requirement R10.
M11 Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails or other dated documentation that demonstrates that it meets
Requirement R11.
M12 Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the frequency set point, the net amount of load shed and the
percentage of its peak load at each stage of its UFLS program coincident with the
integrated hourly peak of the previous year that demonstrates that it meets Requirement
R12.
M13 Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement R13.
M14 Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R14.
M15 Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R15.
M16 Each Generator Owner with existing non-nuclear units in service prior to the effective
date of this Standard which have underfrequency tripping that is not compliant with
Requirement R13 shall provide evidence such as reports, spreadsheets, memorandum
or dated documentation demonstrating that it meets Requirement R16.
M17 Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall
provide evidence such as emails, memorandum or other documentation that
demonstrates that it followed the methodology described in Attachment A and meets
Requirement R17.
M18 Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the New York ISO shall provide evidence
such as emails, memorandum, or other documentation that demonstrates that it
followed the methodology described in Attachment B and meets Requirement R18.
18
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
M19 Each Generator Owner of nuclear units that have been specifically identified by NPCC
as having generator trip settings above the generator trip curve in Figure 1 shall
provide evidence such as letters, reports and dated documentation that demonstrates
that it meets Requirement R19.
M20 Each Planning Coordinator shall provide evidence such as spreadsheets, system
studies, or other documentation that demonstrates that it meets the requirements of
Requirement R20.
M21 Each Planning Coordinator shall provide evidence such as emails, memorandum or
other dated documentation that it meets Requirement R21.
M22 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as reports, spreadsheets or other documentation that demonstrates that it
meets Requirement R22.
M23 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as letters, emails or other dated documentation that demonstrates it
meets Requirement 23.
Compliance
D.C.
1.11. Compliance Monitoring Process
a.1.1.
Compliance Enforcement Authority
Northeast Power Coordinating CouncilPCC Compliance Committee
a.
Compliance Monitoring Period and Reset Time Frame
Not Applicable
b.1.2.
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DataEvidence Retention
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 24, 35, 46, 57, 810, and 119, and 12.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 3, 86, and 79, 20, and 21.
The Planning Coordinator in Ontario, Quebec, and the Maritime Provinces shall keep evidence
for three calendar years for Measure 17.
19
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 185, 22, and 23.
The Generator Owner shall keep evidence for three calendar years for Measures
103, 114, 125, 136, and 169.
c.1.3. Compliance Monitoring and Assessment Processes
ComSelf -Certifications.
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Spot Checking.
Compliance Audits.
Self- Reporting.
Compliance Violation Investigations.
Complaints.pliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
d.
Additional Compliance Information
None.
20
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
Formatted
1.21. Violation Severity Levels
Requirement
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1
N/A
N/A
N/A
The Planning Coordinator
failed to design an UFLS
program having
performance
characteristics that
prevent frequency from
remaining below 59.5 Hz
in accordance with Figure
1.
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R2
The
Planning
Coordinator provided
its
UFLS
island
boundaries,
as
identified per the
NERC continent-wide
PRC-006 Standard on
UFLS but did so
more than 30 calendar
days and up to and
including 40 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC continent-wide
PRC-006 Standard on
UFLS but did so more
than 40 calendar days
but less than and
including 50 days
following a request.
The Planning
Coordinator provided
its UFLS island
boundaries, as
identified per the
NERC continent-wide
PRC-006 Standard on
UFLS but did so more
than 50 calendar days
but less than and
including 60 days
following a request.
The Planning Coordinator
failed to provide its UFLS
island boundaries, as
identified per the NERC
continent-wide PRC-006
Standard on UFLS. within
60 calendar days
following a request.
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The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
20% or less of the
relays identified as
included in the UFLS
program, or amount of
load tripped is within
10% deviation from
the required amount of
The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
20%-40% of the relays
identified as included in
the UFLS program, or
amount of load tripped
is within 20% deviation
from the required
amount of Load
The Distribution
Provider or
Transmission Owner
failed to apply
appropriate settings on
40%-60% of the relays
identified as included
in the UFLS program,
or amount of load
tripped is within 30%
deviation from the
required amount of
The Distribution
Provider or Transmission
Owner failed to apply
appropriate settings on >
60% of the relays
identified as included in
the UFLS program, or
amount of load tripped
has a > 30% deviation
from the required
amount of Load required
R3
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Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R4
R5
R6
Load required to be
shed at each stage
required to be shed at
each stage m
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations for
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the
4 items by a period of
up to 10 calendar days
but less than or equal
to 20 calendar days.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations for
Requirement R5, Parts
%.1 through Part 5.4
but exceeded the
permissible time frame
for one or more of the 4
items within a time
greater than 20 calendar
days but less than or
equal to 30 calendar
days.
The Distribution
Provider or
Transmission Owner
that cannot meet the
tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program fulfilled its
obligations but
exceeded the
permissible time
frame for one or more
of the 4 items within
a time greater than 30
calendar days but less
than or equal to 60
calendar days.
The Distribution
Provider or Transmission
Owner that cannot meet
the tolerances and/or
number of stages and
frequency set points
specified in the UFLS
Program failed to meet
all of items in
Requirement 5 within 60
calendar days of
permissible time for each
item.
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The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 100% but more
than (and including)
95% of relays within
its region’s UFLS
program.
The Planning
Coordinator
developed or reviewed
settings for inhibit
thresholds at least
once per five calendar
years, for less than
95% but more than
(and including) 90%
of relays within its
region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings
for inhibit thresholds
at least once per five
calendar years, for less
than 90% but more
than (and including)
85% of relays within
its region’s UFLS
program.
The Planning
Coordinator developed
or reviewed settings for
inhibit thresholds at least
once per five calendar
years, for less than 85%
of relays within its
region’s UFLS program.
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The Planning
Coordinator provided
to a Transmission
The Planning
Coordinator provided to
a Transmission Owner
The Planning
Coordinator provided
to a Transmission
The Planning
Coordinator failed to
provide to a
22
Adopted by Board of Trustees: February 9, 2012
Load required to be
shed at each stage.
to be shed at each stage
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R7
R8
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds more
than 30 calendar days
and up to and
including 40 calendar
days of any changes.
or Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds more than 40
calendar days but less
than and including 50
calendar days of any
changes.
Owner or Distribution
Provider within its
Planning Coordinator
area the applicable
inhibit thresholds
more than 50 calendar
days but less than and
including 60 calendar
days of any changes.
Transmission Owner or
Distribution Provider
within its Planning
Coordinator area the
applicable inhibit
thresholds within 60
calendar days after any
changes
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 90 calendar
days and up to and
including 100 calendar
days following the
request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 100 calendar
days and up to and
including 110 calendar
days following the
request.
The Distribution
Provider or
Transmission Owner
developed and
submitted its
implementation plan
more than 110
calendar days and up
to and including 120
calendar days
following the request.
The Distribution
Provider or Transmission
Owner failed to develop
and submit its
implementation plan
within 120 days
following the request.
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Implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 100%
but more than (and
including) 95% of
UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the inhibit
threshold settings
provided by the
Planning Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 95% but more
than (and including)
90% of UFLS relays.
The Distribution
Provider or
Transmission Owner
implemented the
inhibit threshold
settings provided by
the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan
for less than 90% but
more than (and
including) 85% of
UFLS relays.
The Distribution
Provider or Transmission
Owner implemented the
inhibit threshold settings
provided by the Planning
Coordinator in
accordance with the
Planning Coordinator
approved
implementation plan for
less than 85% of UFLS
relays.
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23
Adopted by Board of Trustees: February 9, 2012
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R9
R10
R11
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 15 calendar
months but less than
(and including) 16
calendar months since
last update.
The Distribution
Provider or
Transmission Owner
provided to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11 more
than 16 calendar
months but less than
(and including)17
calendar months since
last update.
The Distribution
Provider or
Transmission Owner
provided to its
Planning Coordinator
documentation of the
actual net Load that
would have been shed
by the UFLS relays at
each UFLS stage as
described in
Requirement R11
more than 17 calendar
months but less than
(and including)18
calendar months since
last update.
The Distribution
Provider or Transmission
Owner failed to provide
to its Planning
Coordinator
documentation of the
actual net Load that
would have been shed by
the UFLS relays at each
UFLS stage as described
in Requirement R11
within 18 calendar
months since last update.
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N/A
N/A
N/A
The Generator Owner
did not set each
generator
underfrequency trip
relay, if so equipped, on
or below the appropriate
generator
underfrequency trip
protection settings
threshold curve in Figure
2, except as otherwise
exempted.
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The Generator Owner
failed to transmit the
generator
underfrequency trip
setting and time delay
within 75 calendar days
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The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 45calendar
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 55 calendar
24
Adopted by Board of Trustees: February 9, 2012
The Generator Owner
transmitted the
generator
underfrequency trip
setting and time delay
more than 65 calendar
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Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
R12
days and less than (and
including) 55 calendar
days of the Planning
Coordinator’s request.
days and less than (and
including) 65 calendar
days of the Planning
Coordinator’s request.
N/A
N/A
days and less than
(and including) 75
calendar days of the
Planning
Coordinator’s request.
The Generator Owner
with a new generating
unit, or an existing
generator increasing
its net capability by
greater than 10%:
Did not fulfill the
obligation of
Requirement R12;
Part 12.1
of the Planning
Coordinator’s request.
The Generator Owner
with a new generating
unit, or an existing
generator increasing its
net capability by greater
than 10%, did not fulfill
the obligations of
Requirement R12, Part
12.1 and Part 12.2.
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The Planning
Coordinator in Ontario,
Québec and the
Maritime Provinces or
the Generator Owner
within the ISO-NE and
in NYISO Planning
Coordinator areas failed
to arrange for
compensatory load
shedding as specified in
Requirement R13, Part
13.3.
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OR
Did not fulfill the
obligation of
Requirement R12,
Part 12.2.
R13
R14
N/A
N/A
The Generator Owner
failed to transmit the
existing underfrequency
settings and any
changes to the
underfrequency settings
along with the technical
basis for the settings to
the Planning
Coordinatoras specified
in Requirement R13,
Part 13.2.
The Generator Owner
failed to set the
underfrequency
protection to operate at
the lowest frequency
allowed by the plant
design and licensing
limitations a specified
in Requirement 13,
Part 13.1
N/A
N/A
The Planning
Coordinator did not
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25
Adopted by Board of Trustees: February 9, 2012
Standard PRC-006-NPCC-21 Automatic Underfrequency Load Shedding
apply the criteria
described in Attachment
A to determine the
compensatory load
shedding that is required.
R15
R16
N/A
N/A
N/A
The Generator Owner
failed to transmit the
initial frequency trip
setting and any changes
to the setting and the
technical basis for the
settings to the Planning
Coordinator as
specified in
Requirement R16, Part
16.3.
26
Adopted by Board of Trustees: February 9, 2012
N/A
The Generator Owner:
Failed to set the
underfrequency
protection as specified
in Requirement R16;
Part 16.1
OR
Failed to set the
frequency trip setting
upper tolerance as
specified in
Requirement R16, Part
16.2.
The Generator Owner,
Distribution Provider, or
Transmission Owner did
not apply the criteria
described in Attachment
B to determine the
compensatory load
shedding that is required.
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The Generator Owner
did not fulfill the
obligations of
Requirement R16, Part
16.1 and Part 16.2.
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Formatted
PRC-006-NPCC-1 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 2.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all UFLS islands in which the unit may operateThe
Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in its
NPCC area with underfrequency protections set to trip above the appropriate curve in Figure 1.
In addition, it is the Planning Coordinator’s responsibility to communicate these requirements to
the appropriate Distribution Provider or Transmission Owner and to ensure that adequate
compensatory load shedding is provided in all islands identified in Requirement R1 in which the
unit may operate.
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The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based on
the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (July 1, 2015 PRC-006-NPCC-1). The list
must indicate generating units, if any, that have their underfrequency protections set to
trip above the appropriate curve in Figure 2. Generating Units not appearing on the list
as of the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information for each unitThe Planning Coordinator
shall identify, compile and maintain an updated list of all existing non-nuclear generating
units in service prior to the effective date of this standard that have underfrequency
protections set to trip above the appropriate curve in Figure 1. The list shall include the
following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate, as identified in Requirement R1
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
27
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load sheddingArrange for a
Distribution Provider or Transmission Owner that owns UFLS relays within the
island(s) identified by the Planning Coordinator in Requirement R1 within which
the generator may operate to provide compensatory load shedding.
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.75" +
Indent at: 1"
2.2 In Ontario and in the Maritime provinces, Tthe compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4..
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2.3 The compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 2 during an underfrequency event. If the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 2The
compensatory load shedding shall be provided at the UFLS program stage (or
threshold stage for Quebec) with a frequency threshold setting that corresponds to
the highest frequency at which the subject generator will trip above the
appropriate curve in Figure 1 during an underfrequency event. If the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 1 does not correspond to a specific UFLS program stage threshold setting,
the compensatory load shedding shall be provided at the UFLS program stage
with a frequency threshold setting that is higher than the highest frequency at
which the subject generator will trip above the appropriate curve in Figure 1.
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2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
systemThe amount of compensatory load shedding shall be equivalent (±5%) to
the average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
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In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
28
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Style: 1, 2, 3, … + Start at: 4 + Alignment: Left + Aligned at:
0.75" + Tab after: 1" + Indent at: 1"
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facilityIn the specific instance of a
generating unit that has been interconnected to the electric system for less than
two calendar years, the amount of compensatory load shedding shall be equivalent
(±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon
loss of the facility.
PRC-006-NPCC-1 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
29
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirementsThe Generator Owner in the New England states or New York State are
responsible for establishing a compensatory load shedding program for all existing non-nuclear
units with underfrequency protection set to trip above the appropriate curve in Figure 1 of this
standard. The Generator Owner shall follow the methodology below to determine compensatory
load shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (July 1, 2015 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above the
appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2. The
list shall include the following information associated with each unitThe Generator
Owner shall identify and compile a list of all existing non-nuclear generating units in
service prior to the effective date of this standard that has underfrequency protection set
to trip above the appropriate curve in Figure 1. The list shall include the following
information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip above
the appropriate curve in Figure 2, the Distribution Provider or Transmission
Owner is responsible to provide the appropriate amount of compensatory load to
be shed within the same and smallest island identified by the Planning
Coordinator in Requirement R1 of this standardIn cases where a Distribution
Provider or Transmission Owner has coordinated protection settings with the
Generator Owner to cause the generator to trip above the appropriate curve in
Figure 1, the Distribution Provider or Transmission Owner is responsible to
provide the appropriate amount of compensatory load to be shed within the
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
30
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2.2 In cases where a Generator Owner has a generator that cannot physically meet the
set points defined by the appropriate curve in Figure 2, the Generator Owner shall
arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and smallest
island identified by the Planning Coordinator in Requirement R1 of this
standardIn cases where a Generator Owner has a generator that cannot physically
meet the set points defined by the appropriate curve in Figure 1, the Generator
Owner shall arrange for a Distribution Provider or Transmission Owner to
provide the appropriate amount of compensatory load to be shed within the
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
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2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4The compensatory load shedding that is provided by the Distribution Provider
or Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
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2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip The compensatory load shedding shall be
provided at the UFLS program stage with the frequency threshold setting at or
closest to but above the frequency at which the subject generator will trip.
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2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.75" +
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.75" +
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.75" +
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average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
systemThe amount of compensatory load shedding shall be equivalent (±5%) to
the average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the electric
system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory load
shedding shall be equivalent (±5%) to the maximum claimed seasonal capability
of the generator over two calendar years, plus expected station loads to be
transferred to the system upon loss of the facilityIn the specific instance of a
generating unit that has been interconnected to the electric system for less than
two calendar years, the amount of compensatory load shedding shall be equivalent
(±5%) to the maximum claimed seasonal capability of the generator over two
31
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
calendar years, plus expected station loads to be transferred to the system upon
loss of the facility.
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PRC-006-NPCC-1 Attachment C
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32
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW or more of peak net Load shall
implement a UFLS program with the following attributes:
Frequency
Threshold
(Hz)
Total Nominal
Operating
Time (s) 1
Load Shed at Stage as
% of TO or DP
Load
Cumulative Load Shed as % of
TO or DP Load
59.5
0.30
6.5 – 7.5
6.5 – 7.5
59.3
0.30
6.5 – 7.5
13.5 – 14.5
59.1
0.30
6.5 – 7.5
20.5 – 21.5
58.9
0.30
6.5 – 7.5
27.5 – 28.5
59.5
10.0
2–3
– 31.5
Formatted Table
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW or more and less than 100 MW
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time(s)1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
14-25
14-25
2
59.1
0.30
14-25
28-50
1. The total nominal operating time includes the underfrequency relay
operating time plus any interposing auxiliary relay operating times, communication times, and the rated
breaker interrupting time. The underfrequency relay operating time is measured from the time when
frequency passes through the frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per
second. If the relay operating time is dependent on the rate of frequency decay, the underfrequency relay
operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear frequency
decay of 0.2 Hz per second.
33
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.19" +
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW or more and less than 50 MW of
peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Threshold (Hz)
Total Nominal
Operating Time
(s) 1
Load Shed at
Stage as % of TO
or DP Load
Cumulative Load
Shed as % of TO
or DP Load
1
59.5
0.30
28-50
28-50
1. The total nominal operating time includes the underfrequency relay
operating time plus any interposing auxiliary relay operating times, communication times, and the rated
breaker interrupting time. The underfrequency relay operating time is measured from the time when
frequency passes through the frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per
second. If the relay operating time is dependent on the rate of frequency decay, the underfrequency relay
operating time and any subsequent testing of the UFLS relays shall utilize a test rate of linear frequency
decay of 0.2 Hz per second.
34
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS Table 4: Quebec Interconnection
MW
at peak
Mvar
at peak
Total
Nominal
Operating
Time (s) 2
Rate
Frequency
(Hz)
(*Load must
be fixed at all
times when
above 60% of
peak load..)
Threshold Stage 1
–––
58.5
1000*
1000
0.30
Threshold Stage 2
–––
58.0
800*
800
0.30
Threshold Stage 3
–––
57.5
800
800
0.30
Threshold Stage 4
–––
57.0
800
800
0.30
–––
59.0
500
500
20.0
Slope Stage 1
-0.3 Hz/s
58.5
400
400
0.30
Slope Stage 2
-0.4 Hz/s
59.8
800*
800
0.30
Slope Stage 3
-0.6 Hz/s
59.8
800*
800
0.30
Slope Stage 4
-0.9 Hz/s
59.8
800
800
0.30
Threshold Stage 5
(anti-stall)
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
2. The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communications time, and the rated breaker interrupting time. The
underfrequency relay operating time shall be measured from the time when the frequency passes through the
frequency threshold set point.
35
Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
1
2
3
4
5
(Hz)
Delay (s)
59.5
59.3
59.1
58.9
59.5
0.10
0.10
0.10
0.10
0.10
Operating
Time (s) 2
0.30
0.30
0.30
0.30
10.0
TO or DP
Load
6.5 – 7.5
6.5 – 7.5
6.5 – 7.5
6.5 – 7.5
2-3
% of TO or
DP Load
6.5 – 7.5
13.5 – 14.5
20.5 – 21.5
27.5 – 28.5
29.5 – 31.5
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UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
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UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
36
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
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3, … + Start at: 1 + Alignment: Left + Aligned at: 0.19" +
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
1
59.5
0.10
0.30
28 – 50
28 – 50
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
2.
37
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
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Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
•
•
•
•
•
•
•
•
•
•
•
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
Generator dynamic modeling
Dynamic VAR device modeling
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38
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Standard Development Timeline
This section is maintained by the drafting team during the development of the standard and will
be removed when the standard is adopted by the NERC Board of Trustees (Board).
Description of Current Draft
Completed Actions
Regional Standards Committee approved Regional Standard
Authorization Request (RSAR) for posting
Anticipated Actions
Date
June 23, 2015
Date
1st 45-day Formal Comment Period
September 1, 2017 October 18, 2017
2nd 45-day Formal Comment Period
April 16, 2018 –
June 1, 2018
30-day Pre-ballot Period
10-day ballot Period
Board adoption
PRC-006-NPCC-2
Page 1 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Upon Board adoption, the rationale boxes will be moved to the Supplemental Material Section.
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Functional Entities:
4.1.1. Generator Owner
4.1.2. Planning Coordinator
4.1.3. Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
4.1.4. Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
5.
Effective Date: See Implementation Plan.
B. Requirements and Measures
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1 also
shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5
Hz for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
PRC-006-NPCC-2
Page 2 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent-wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent-wide
PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1-3.
M3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1-3).
R4. Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified
by its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• Within 30 calendar days of determining that it does not meet the
specified parameters, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
PRC-006-NPCC-2
Page 3 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3.
M4. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit
function is intended to prevent operation of a UFLS relay when the transmission supply is
lost to distribution station feeding many induction motors. Following loss of the
transmission supply, motors may support the voltage while the motors coast down in
speed. The motors coasting down (ringing down) will look like an underfrequency event
to the relay. The inhibit setting is set to a voltage above which the motor load is expected
to sustain. This prevents the underfrequency relay from tripping and locking out
distribution feeder breakers supplying the motor load, between the time the transmission
supply line trips and the time when the line recloses to restore the load. Voltages
sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower than
voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring
down voltages because of cable charging. Therefore, care must be taken so that the
voltage inhibit setting is not higher than the voltage at which UFLS relays are required to
operate to meet UFLS performance criteria.
R5. Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and
time) to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M5. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
PRC-006-NPCC-2
Page 4 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R6. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within
30 calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M6. Each Planning Coordinator shall provide evidence such as letters, emails or other
dated documentation that demonstrates that it meets Requirement R6.
R7. Each Distribution Provider and Transmission Owner that receives a notification
pursuant to Requirement R6 shall develop and submit an implementation plan with
respect to inhibit thresholds for approval by the Planning Coordinator within 90
calendar days of the request from the Planning Coordinator. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
M7. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
R8.
Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
M8. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the
UFLS program for every entity should perfectly match that prescribed in this Standard, for
all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
various areas and sub-areas within any given island do not perfectly track the load cycle
of the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would
occur for any conditions other than peak, therefore, can only approximate that
prescribed in the Standard. To that end, Requirement R11 requires entities to document
measured loads in the UFLS program coincident with their own annual peak, whether or
not that peak occurs at the same time or in the same season as the peak of the identified
island in which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
PRC-006-NPCC-2
Page 5 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R9.
Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by
measuring or calculating Load through the switches that would disconnect load if
triggered by the UFLS relays. If measured data is unavailable then calculated data may
be used. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
R10. Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements
R13 and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
R11. Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
R12. Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
PRC-006-NPCC-2
Page 6 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R13. For existing non-nuclear units in service prior to July 1, 2015, that have
underfrequency protections set to trip above the appropriate curve in Figure 2:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R13.
R14. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
R15. Each Generator Owner, Distribution Provider or Transmission Owner within the ISONE Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that
PRC-006-NPCC-2
Page 7 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
is required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed
the methodology described in Attachment B and meets Requirement R15.
R16. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at a frequency setting that
is as low as possible in accordance with the plant design and licensing
limitations but not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and
dated documentation that demonstrates that it meets Requirement R16.
PRC-006-NPCC-2
Page 8 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 1
Curve Data:
Overfrequency Requirements
t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
t > 30 s
f = 60.7 Hz
Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
PRC-006-NPCC-2
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
NERC PRC-006-NPCC (Regional Standard on UFLS)
Page 9 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
PRC-006-NPCC-2
Page 10 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority:
Northeast Power Coordinating Council
1.2. Evidence Retention:
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 2, 3, 4, 5, 8, and 9.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 6, and 7.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 15.
The Generator Owner shall keep evidence for three calendar years for Measures
10, 11, 12, 13, and 16.
1.3. Compliance Monitoring and Enforcement Program:
Compliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
PRC-006-NPCC-2
Page 11 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Violation Severity Levels
Violation Severity Levels
R#
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator failed to
design an UFLS program having
performance characteristics that
prevent frequency from remaining
below 59.5 Hz in accordance with
Figure 1.
R2.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 30 calendar
days and up to and including 40
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 40 calendar
days but less than and including 50
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continentwide PRC-006 Standard on UFLS
but did so more than 50 calendar
days but less than and including 60
days following a request.
The Planning Coordinator failed to
provide its UFLS island boundaries,
as identified per the NERC
continent-wide PRC-006 Standard
on UFLS. within 60 calendar days
following a request.
R3.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%
or less of the relays identified as
included in the UFLS program, or
amount of load tripped is within
10% deviation from the required
amount of Load required to be
shed at each stage
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%40% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
20% deviation from the required
amount of Load required to be
shed at each stage m
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 40%60% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
30% deviation from the required
amount of Load required to be
shed at each stage.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on >
60% of the relays identified as
included in the UFLS program, or
amount of load tripped has a >
30% deviation from the required
amount of Load required to be
shed at each stage
R4.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
but exceeded the permissible
PRC-006-NPCC-1
July 2018
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program failed to meet all of items
in Requirement 5 within 60
Page 12 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items within a time
greater than 20 calendar days but
less than or equal to 30 calendar
days.
time frame for one or more of the
4 items within a time greater than
30 calendar days but less than or
equal to 60 calendar days.
calendar days of permissible time
for each item.
R5.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
100% but more than (and
including) 95% of relays within its
region’s UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
95% but more than (and including)
90% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and including)
85% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
85% of relays within its region’s
UFLS program.
R6.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 30 calendar days and up to
and including 40 calendar days of
any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 40 calendar days but less
than and including 50 calendar
days of any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar days but less
than and including 60 calendar
days of any changes.
R7.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 100 calendar days
and up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
R8.
Implemented the inhibit threshold
settings provided by the Planning
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
PRC-006-NPCC-1
July 2018
The Planning Coordinator failed to
provide to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds
within 60 calendar days after any
changes
The Distribution Provider or
Transmission Owner failed to
develop and submit its
implementation plan within 120
days following the request.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
Page 13 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
less than 100% but more than (and
including) 95% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 95% but more than (and
including) 90% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 90% but more than (and
including) 85% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 85% of UFLS relays.
R9.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 16 calendar
months but less than (and
including)17 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar
months but less than (and
including)18 calendar months
since last update.
The Distribution Provider or
Transmission Owner failed to
provide to its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 within 18 calendar months
since last update.
R10.
N/A
N/A
N/A
R11.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
45calendar days and less than (and
including) 55 calendar days of the
Planning Coordinator’s request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
55 calendar days and less than
(and including) 65 calendar days of
the Planning Coordinator’s
request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
65 calendar days and less than
(and including) 75 calendar days of
the Planning Coordinator’s
request.
The Generator Owner failed to
transmit the generator
underfrequency trip setting and
time delay within 75 calendar days
of the Planning Coordinator’s
request.
R12.
N/A
N/A
The Generator Owner with a new
generating unit, or an existing
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
PRC-006-NPCC-1
July 2018
The Generator Owner did not set
each generator underfrequency
trip relay, if so equipped, on or
below the appropriate generator
underfrequency trip protection
settings threshold curve in Figure
2, except as otherwise exempted.
Page 14 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
generator increasing its net
capability by greater than 10%:
Did not fulfill the obligation of
Requirement R12; Part 12.1
capability by greater than 10%, did
not fulfill the obligations of
Requirement R12, Part 12.1 and
Part 12.2.
OR
Did not fulfill the obligation of
Requirement R12, Part 12.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirement 13, Part 13.1
R13.
N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinatoras specified
in Requirement R13, Part 13.2.
R14.
N/A
N/A
N/A
The Planning Coordinator did not
apply the criteria described in
Attachment A to determine the
compensatory load shedding that
is required.
R15.
N/A
N/A
N/A
The Generator Owner, Distribution
Provider, or Transmission Owner
did not apply the criteria described
in Attachment B to determine the
compensatory load shedding that
is required.
R16.
N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis for
the settings to the Planning
The Generator Owner:
The Generator Owner did not
fulfill the obligations of
Requirement R16, Part 16.1 and
Part 16.2.
PRC-006-NPCC-1
July 2018
Failed to set the underfrequency
protection as specified in
Requirement R16; Part 16.1
The Planning Coordinator in
Ontario, Québec and the Maritime
Provinces or the Generator Owner
within the ISO-NE and in NYISO
Planning Coordinator areas failed
to arrange for compensatory load
shedding as specified in
Requirement R13, Part 13.3.
OR
Page 15 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Coordinator as specified in
Requirement R16, Part 16.3.
Failed to set the frequency trip
setting upper tolerance as
specified in Requirement R16, Part
16.2.
D. Regional Variances
None.
E. Associated Documents
Technical Rationale
PRC-006-NPCC-1
July 2018
Page 16 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Version History
Version
Date
Action
1
2-9-2012
Adopted by Board of Trustees
2
6-23-2015
RSAR Submitted
PRC-006-NPCC-1
July 2018
Change
Tracking
Page 17 of 24
AAA-000-0 Supplemental Material
Standard Attachments
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (July 1, 2015 PRC-006-NPCC-1). The list must
indicate generating units, if any, that have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
Draft Number of Standard
Month Year
Page 18 of 24
AAA-000-0 Supplemental Material
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage
(or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the electric system
for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
Draft Number of Standard
Month Year
Page 19 of 24
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (July 1, 2015 PRC-006-NPCC-1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above
the appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip
above the appropriate curve in Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the same and smallest island identified by
the Planning Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet
the set points defined by the appropriate curve in Figure 2, the Generator Owner
shall arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
Draft Number of Standard
Month Year
Page 20 of 24
AAA-000-0 Supplemental Material
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facility.
Draft Number of Standard
Month Year
Page 21 of 24
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2-3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 22 of 24
AAA-000-0 Supplemental Material
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
28 – 50
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 23 of 24
AAA-000-0 Supplemental Material
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
• HVDC dynamic modeling
Draft Number of Standard
Month Year
Page 24 of 24
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Standard Development Timeline
This section is maintained by the drafting team during the development of the standard and will
be removed when the standard is adopted by the NERC Board of Trustees (Board).
Description of Current Draft
Completed Actions
Regional Standards Committee approved Regional Standard
Authorization Request (RSAR) for posting
Anticipated Actions
Date
June 23, 2015
Date
1st 45-day Formal Comment Period
September 1, 2017 October 18, 2017
2nd 45-day Formal Comment Period
April 16, 2018 –
June 1, 2018
30-day Pre-ballot Period
10-day ballot Period
Board adoption
PRC-006-NPCC-2
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PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Upon Board adoption, the rationale boxes will be moved to the Supplemental Material Section.
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC-006-NPCC-2
3.
Purpose:
The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent-wide PRC-006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Functional Entities:
4.1.1. Generator Owner
4.1.2. Planning Coordinator
4.1.3. Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
4.1.4. Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
5.
Effective Date: See Implementation Plan.
B. Requirements and Measures
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1 also
shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5
Hz for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or
real-time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
PRC-006-NPCC-2
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PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent- wide PRC-006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continentwide PRC-006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
• The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1-3; or
• The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1-3.
M3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1-3).
R4. Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1-3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified
by its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
• Within 30 calendar days of determining that it does not meet the
specified parameters, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
• Within the following 180 calendar days from notification of the Planning
Coordinator,
PRC-006-NPCC-2
Page 3 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3.
M4. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit
function is intended to prevent operation of a UFLS relay when the transmission supply is
lost to distribution station feeding many induction motors. Following loss of the
transmission supply, motors may support the voltage while the motors coast down in
speed. The motors coasting down (ringing down) will look like an underfrequency event
to the relay. The inhibit setting is set to a voltage above which the motor load is expected
to sustain. This prevents the underfrequency relay from tripping and locking out
distribution feeder breakers supplying the motor load, between the time the transmission
supply line trips and the time when the line recloses to restore the load. Voltages
sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower than
voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring
down voltages because of cable charging. Therefore, care must be taken so that the
voltage inhibit setting is not higher than the voltage at which UFLS relays are required to
operate to meet UFLS performance criteria.
R5. Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and
time) to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M5. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
PRC-006-NPCC-2
Page 4 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R6. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within
30 calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M6. Each Planning Coordinator shall provide evidence such as letters, emails or other
dated documentation that demonstrates that it meets Requirement R6.
R7. Each Distribution Provider and Transmission Owner that receives a notification
pursuant to Requirement R6 shall develop and submit an implementation plan with
respect to inhibit thresholds for approval by the Planning Coordinator within 90
calendar days of the request from the Planning Coordinator. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
M7. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
R8.
Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
M8. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the
UFLS program for every entity should perfectly match that prescribed in this Standard, for
all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
various areas and sub-areas within any given island do not perfectly track the load cycle
of the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would
occur for any conditions other than peak, therefore, can only approximate that
prescribed in the Standard. To that end, Requirement R11 requires entities to document
measured loads in the UFLS program coincident with their own annual peak, whether or
not that peak occurs at the same time or in the same season as the peak of the identified
island in which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
PRC-006-NPCC-2
Page 5 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R9.
Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by
measuring or calculating Load through the switches that would disconnect load if
triggered by the UFLS relays. If measured data is unavailable then calculated data may
be used. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
R10. Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements
R13 and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
R11. Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
R12. Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
PRC-006-NPCC-2
Page 6 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R13. For existing non-nuclear units in service prior to July 1, 2015, that have
underfrequency protections set to trip above the appropriate curve in Figure 2:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO-NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M13. Each Generator Owner with existing non-nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R13.
R14. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
R15. Each Generator Owner, Distribution Provider or Transmission Owner within the ISONE Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that
PRC-006-NPCC-2
Page 7 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
is required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed
the methodology described in Attachment B and meets Requirement R15.
R16. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at as a low frequency
setting that is as low as possible in accordance with the plant design and
licensing limitations but not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and
dated documentation that demonstrates that it meets Requirement R16.
PRC-006-NPCC-2
Page 8 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 1
Formatted: Left
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Eastern Interconnection Frequency Hz
Design Performance Requirements
PRC-006-NPCC-2
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PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 10 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 11 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 12 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 13 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
PRC-006-NPCC-2
Page 14 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Formatted: Indent: Left: 0.65", No bullets or numbering
Curve Data:
Overfrequency Requirements
t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
t > 30 s
f = 60.7 Hz
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
Formatted: Indent: Left: 0.65", No bullets or numbering
Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
PRC-006-NPCC-2
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
NERC PRC-006-NPCC (Regional Standard on UFLS)
Page 15 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Figure 2
PRC-006-NPCC-2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
1
10
100
1000
55.5
55
10000
Time (sec)
PRC-006-NPCC-2
Page 16 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority:
Northeast Power Coordinating Council
1.2. Evidence Retention:
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 2, 3, 4, 5, 8, and 9.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 6, and 7.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 15.
The Generator Owner shall keep evidence for three calendar years for Measures
10, 11, 12, 13, and 16.
1.3. Compliance Monitoring and Enforcement Program:
Compliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
PRC-006-NPCC-2
Page 17 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Violation Severity Levels
Violation Severity Levels
R#
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator failed to
design an UFLS program having
performance characteristics that
prevent frequency from remaining
below 59.5 Hz in accordance with
Figure 1.
R2.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 30 calendar days and up to
and including 40 days following a
request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 40 calendar days but less
than and including 50 days
following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent
widecontinent-wide PRC-006
Standard on UFLS but did so more
than 50 calendar days but less
than and including 60 days
following a request.
The Planning Coordinator failed to
provide its UFLS island boundaries,
as identified per the NERC
continent widecontinent-wide
PRC-006 Standard on UFLS. within
60 calendar days following a
request.
R3.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%
or less of the relays identified as
included in the UFLS program, or
amount of load tripped is within
10% deviation from the required
amount of Load required to be
shed at each stage
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%40% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
20% deviation from the required
amount of Load required to be
shed at each stage m
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 40%60% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
30% deviation from the required
amount of Load required to be
shed at each stage.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on >
60% of the relays identified as
included in the UFLS program, or
amount of load tripped has a >
30% deviation from the required
amount of Load required to be
shed at each stage
R4.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
PRC-006-NPCC-1
July 2018
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program failed to meet all of items
Page 18 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Program fulfilled its obligations for
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
Program fulfilled its obligations for
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items within a time
greater than 20 calendar days but
less than or equal to 30 calendar
days.
but exceeded the permissible
time frame for one or more of the
4 items within a time greater than
30 calendar days but less than or
equal to 60 calendar days.
in Requirement 5 within 60
calendar days of permissible time
for each item.
R5.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
100% but more than (and
including) 95% of relays within its
region’s UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
95% but more than (and including)
90% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and including)
85% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
85% of relays within its region’s
UFLS program.
R6.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 30 calendar days and up to
and including 40 calendar days of
any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 40 calendar days but less
than and including 50 calendar
days of any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar days but less
than and including 60 calendar
days of any changes.
R7.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 100 calendar days
and up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
R8.
Implemented the inhibit threshold
settings provided by the Planning
Coordinator in accordance with
the Planning Coordinator
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
PRC-006-NPCC-1
July 2018
The Planning Coordinator failed to
provide to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds
within 60 calendar days after any
changes
The Distribution Provider or
Transmission Owner failed to
develop and submit its
implementation plan within 120
days following the request.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Page 19 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
approved implementation plan for
less than 100% but more than (and
including) 95% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 95% but more than (and
including) 90% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 90% but more than (and
including) 85% of UFLS relays.
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
less than 85% of UFLS relays.
R9.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 16 calendar
months but less than (and
including)17 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar
months but less than (and
including)18 calendar months
since last update.
The Distribution Provider or
Transmission Owner failed to
provide to its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 within 18 calendar months
since last update.
R10.
N/A
N/A
N/A
R11.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
45calendar days and less than (and
including) 55 calendar days of the
Planning Coordinator’s request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
55 calendar days and less than
(and including) 65 calendar days of
the Planning Coordinator’s
request.
The Generator Owner transmitted
the generator underfrequency trip
setting and time delay more than
65 calendar days and less than
(and including) 75 calendar days of
the Planning Coordinator’s
request.
PRC-006-NPCC-1
July 2018
The Generator Owner did not set
each generator underfrequency
trip relay, if so equipped, on or
below the appropriate generator
underfrequency trip protection
settings threshold curve in Figure
2, except as otherwise exempted.
The Generator Owner failed to
transmit the generator
underfrequency trip setting and
time delay within 75 calendar days
of the Planning Coordinator’s
request.
Page 20 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
R12.
N/A
N/A
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
capability by greater than 10%:
Did not fulfill the obligation of
Requirement R12; Part 12.1
OR
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
capability by greater than 10%, did
not fulfill the obligations of
Requirement R12, Part 12.1 and
Part 12.2.
Did not fulfill the obligation of
Requirement R12, Part 12.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirement 13, Part 13.1
R13.
N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinatoras specified
in Requirement R13, Part 13.2.
R14.
N/A
N/A
N/A
The Planning Coordinator did not
apply the criteria described in
Attachment A to determine the
compensatory load shedding that
is required.
R15.
N/A
N/A
N/A
The Generator Owner, Distribution
Provider, or Transmission Owner
did not apply the criteria described
in Attachment B to determine the
compensatory load shedding that
is required.
R16.
N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis for
The Generator Owner:
The Generator Owner did not
fulfill the obligations of
Requirement R16, Part 16.1 and
Part 16.2.
PRC-006-NPCC-1
July 2018
Failed to set the underfrequency
protection as specified in
Requirement R16; Part 16.1
The Planning Coordinator in
Ontario, Québec and the Maritime
Provinces or the Generator Owner
within the ISO-NE and in NYISO
Planning Coordinator areas failed
to arrange for compensatory load
shedding as specified in
Requirement R13, Part 13.3.
Page 21 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
the settings to the Planning
Coordinator as specified in
Requirement R16, Part 16.3.
OR
Failed to set the frequency trip
setting upper tolerance as
specified in Requirement R16, Part
16.2.
D. Regional Variances
None.
E. Associated Documents
Technical Rationale
PRC-006-NPCC-1
July 2018
Page 22 of 30
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Version History
Version
Date
Action
1
2-9-2012
Adopted by Board of Trustees
2
6-23-2015
RSAR Submitted
PRC-006-NPCC-1
July 2018
Change
Tracking
Page 23 of 30
AAA-000-0 Supplemental Material
Standard Attachments
PRC-006-NPCC-2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non-nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing nonnuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (AprilJuly 1, 20157 PRC-006-NPCC-1). The list
must indicate generating units, if any, that have their underfrequency protections set to
trip above the appropriate curve in Figure 2. Generating Units not appearing on the list
as of the effective date of Version 1 of the regional standard, as shown above, must
have their Underfrequency protections set to trip on or below the appropriate curve in
Figure 2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
Draft Number of Standard
Month Year
Page 24 of 30
AAA-000-0 Supplemental Material
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage
(or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the electric system
for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
Draft Number of Standard
Month Year
Page 25 of 30
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment B
Compensatory Load Shedding Criteria for ISO-NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non-nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing nonnuclear generating units that were in service prior to the effective date of the regional
Standard (AprilJuly 1, 20157 PRC-006-NPCC-1). The list must indicate the Generator
Owner’s generating units, if any, which have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip
above the appropriate curve in Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the same and smallest island identified by
the Planning Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet
the set points defined by the appropriate curve in Figure 2, the Generator Owner
shall arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
Draft Number of Standard
Month Year
Page 26 of 30
AAA-000-0 Supplemental Material
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facility.
Draft Number of Standard
Month Year
Page 27 of 30
AAA-000-0 Supplemental Material
PRC-006-NPCC-2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2-3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 28 of 30
AAA-000-0 Supplemental Material
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
Time (s) 1
Load
DP Load
1
59.5
0.10
0.30
28 – 50
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
Draft Number of Standard
Month Year
Page 29 of 30
AAA-000-0 Supplemental Material
Rationale Box:
Standard PRC-006-3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time-frame.
PRC-006-NPCC-01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
• Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
• Unforeseen islanding event
• Real and reactive load distribution (including changes to location of compensatory load
shedding)
• Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
• Load characteristics in particular frequency responsive load
• Automatic load restoration
• Generation geographical distribution
• Generator trip settings
• Generation mix in particular non-BES generation that may not be subject to frequency
ride-through criteria
• Generator dynamic modeling
• Dynamic VAR device modeling
• HVDC dynamic modeling
Draft Number of Standard
Month Year
Page 30 of 30
Implementation Plan
Regional Reliability Standard PRC-006-NPCC-2 – Automatic
Underfrequency Load Shedding
Applicable Standard(s)
•
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requested Retirement(s)
•
PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding
Applicable Entities
•
•
•
•
Generator Owners
Planning Coordinators
Distribution Providers that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Transmission Owners that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Background
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. To determine if the applicability of the standard needs to be revised in accordance with
Project 2014-01 Dispersed Generation Resources.
2. To determine if the performance requirements as contained in the criteria of NPCC
Directory#12 Sections 5.1.1 and 5.1.2 should be explicitly included in the requirements
of the Regional Standard and potential retirement of Directory 12 Automatic
Underfrequency Load Shedding Program.
3. Review Attachment C in PRC-006-NPCC-1 to address the implications of the design
assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. Review and revise Table 4 in Attachment C in accordance with the 2013 NPCC UFLS
Adequacy Assessment. Additionally, the applicability of Requirements R4 and R5 will be
reviewed to consider that Hydro Quebec is not part of the Eastern Interconnection.
Effective Date
All requirements with the exception of R3 will be enforceable on the first day of the first
calendar quarter following the applicable governmental and regulatory approvals.
R3 will be enforceable on the first day of the first calendar quarter 12 months following
the applicable governmental and regulatory approvals.
Retirement Date
The NPCC Regional Reliability Standard PRC-006-NPCC-1 shall be retired immediately
prior to the Effective Date of PRC-006-NPCC-2.
Mapping Document
Draft NPCC Regional Automatic Underfrequency Load Shedding Standard
PRC-006-NPCC-2
NPCC’s regional standard PRC-006-NPCC-2 “Automatic Underfrequency Load Shedding” (UFLS) was effective in the US in July 2015. The
standard is currently under revision to align with the continent-wide PRC-006-2 UFLS standard which became effective on October 2015. The
draft of PRC-006-NPCC-2 removes duplicity with the continent wide standard and adds specificity to allow retirement of the NPCC UFLS
Directory #12 containing more stringent UFLS performance criteria and harmonizes the requirements and criteria of all these documents.
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
PRC-006-NPCC-1
Translation to New Standard or Other
Action
Description and Change Justification
PRC-006-NPCC-2
R1 Each Planning Coordinator shall establish
R2. Each Planning Coordinator shall provide
requirements for entities aggregating their
UFLS island boundaries, as identified per
UFLS programs for each anticipated island and
the NERC continent wide PRC-006
requirements for compensatory load
Standard on UFLS, to Distribution
shedding based on islanding criteria (required
Providers, Generator Owners, and
by the NERC PRC Standard on UFLS).
Transmission Owners within 30 calendar
[Violation Risk Factor: Medium] [Time
days of receipt of a request. [Violation
Horizon: Long Term Planning]
Risk Factor: Lower] [Time Horizon: Long
Term Planning]
R3. Each Distribution Provider and
Transmission Owner in the Eastern
The purpose of R1 in PRC-006-NPCC-1 was
to ensure entities that aggregate their load
understand what the UFLS island
boundaries are and establish criteria for
compensatory load shedding. The revised
R2, R3, and R13 clearly address this in the
proposed PRC-006-NPCC-2.
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
Interconnection portion of NPCC shall
implement an automatic UFLS program,
reflecting normal operating conditions,
excluding outages. The automatic UFLS
program shall be implemented on an
island basis for each identified island per
the NERC continent wide PRC-006
Standard on UFLS as follows: [Violation
Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be
implemented by each
Distribution Provider and
Transmission Owner according
to the frequency thresholds,
nominal operating times, and
load shedding amounts
specified in Attachment C,
Tables 1-3; or
• The UFLS program shall be
implemented collectively by
multiple Distribution Providers
or Transmission Owners, as long
as they reside in the same UFLS
island identified by the Planning
Mapping Document
Project Number and Name | Month Year
2
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
Coordinator per Requirement
R2. These multiple Distribution
Providers or Transmission
Owners, via mutual agreement,
shall act as a single entity to
provide an aggregated
automatic UFLS program that
sheds their coincident peak
aggregated net Load according
to the frequency thresholds,
total nominal operating time,
and load shedding amounts
specified in Attachment C,
Tables 1-3.
R13. For existing non-nuclear units in
service prior to July 1, 2015, that have
underfrequency protections set to trip
above the appropriate curve in Figure
2: [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
13.1. Each Generator Owner shall
set the underfrequency
protection to operate at the
lowest frequency allowed by
Mapping Document
Project Number and Name | Month Year
3
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
the plant design and licensing
limitations.
13.2. Each Generator Owner shall
transmit the existing
underfrequency settings and
any changes to the
underfrequency settings along
with the technical basis for the
settings to the Planning
Coordinator.
13.3. Each Planning Coordinator in
Ontario, Québec and the
Maritime Provinces shall
arrange for compensatory load
shedding, in accordance with
Attachment A and as provided
by a Distribution Provider or
Transmission Owner, that is
adequate to compensate for
the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
Mapping Document
Project Number and Name | Month Year
4
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
13.4. Each Generator Owner in the
ISO-NE Planning Coordinator
area and in NYISO Planning
Coordinator area shall arrange
for compensatory load
shedding, in accordance with
Attachment B and as provided
by a Distribution Provider or
Transmission Owner, that is
adequate to compensate for
the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
PRC-006-NPCC-1
PRC-006-NPCC-2
R2 Each Planning Coordinator shall, within 30
days of completion of its system studies
required by the NERC PRC Standard on UFLS,
identify to the Regional Entity the generation
facilities within its Planning Coordinator Area
R1. Each Planning Coordinator in the
Eastern Interconnection portion of NPCC
shall design an UFLS program, pertaining
to islands wholly within the NPCC
Region, having performance
Mapping Document
Project Number and Name | Month Year
The original R2 is redundant and it is being
covered by the new R1, R2 and R3.
5
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
necessary to support the UFLS program
performance characteristics. [Violation Risk
Factor: Medium] [Time Horizon: Long Term
Planning]
Translation to New Standard or Other
Action
Description and Change Justification
characteristics that prevents the
frequency from remaining below 59.5
Hz for more than 30 seconds in
accordance with Figure 1 [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
R2. Each Planning Coordinator shall provide
UFLS island boundaries, as identified per
the NERC continent wide PRC-006
Standard on UFLS, to Distribution
Providers, Generator Owners, and
Transmission Owners within 30 calendar
days of receipt of a request. [Violation
Risk Factor: Lower] [Time Horizon: Long
Term Planning]
R3. Each Distribution Provider and
Transmission Owner in the Eastern
Interconnection portion of NPCC shall
implement an automatic UFLS program,
reflecting normal operating conditions,
excluding outages. The automatic UFLS
program shall be implemented on an
island basis for each identified island per
Mapping Document
Project Number and Name | Month Year
6
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
the NERC continent wide PRC-006
Standard on UFLS as follows: [Violation
Risk Factor: High] [Time Horizon: Long
Term Planning]
• The UFLS program shall be
implemented by each
Distribution Provider and
Transmission Owner according
to the frequency thresholds,
nominal operating times, and
load shedding amounts
specified in Attachment C,
Tables 1-3; or
•
Mapping Document
Project Number and Name | Month Year
The UFLS program shall be
implemented collectively by
multiple Distribution Providers
or Transmission Owners, as long
as they reside in the same UFLS
island identified by the Planning
Coordinator per Requirement
R2. These multiple Distribution
Providers or Transmission
Owners, via mutual agreement,
shall act as a single entity to
provide an aggregated
7
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
automatic UFLS program that
sheds their coincident peak
aggregated net Load according
to the frequency thresholds,
total nominal operating time,
and load shedding amounts
specified in Attachment C,
Tables 1-3
PRC-006-NPCC-1
PRC-006-NPCC-2
R3 Each Planning Coordinator shall provide to R2. Each Planning Coordinator shall provide
the Transmission Owner, Distribution
UFLS island boundaries, as identified per
Provider, and Generator Owner within 30
the NERC continent wide PRC-006
days upon written request the requirements
Standard on UFLS, to Distribution
for entities aggregating the UFLS programs
Providers, Generator Owners, and
and requirements for compensatory load
Transmission Owners within 30 calendar
shedding program derived from each Planning
days of receipt of a request. [Violation
Coordinator’s system studies as determined
Risk Factor: Lower] [Time Horizon: Long
by Requirement R1. [Violation Risk Factor:
Term Planning]
Low] [Time Horizon: Long Term Planning]
R13. For existing non-nuclear units in
service prior to July 1, 2015, that have
underfrequency protections set to trip
above the appropriate curve in Figure
Mapping Document
Project Number and Name | Month Year
The reliability intent of Version 1 R3 was to
ensure that the entities aggregating load
were aware of the island boundaries. This is
covered in draft R2 of the proposed revision
to the standard. Requirements regarding
compensatory load shedding have been
clarified and are covered through draft R13.
8
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
2: [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
13.1. Each Generator Owner shall
set the underfrequency
protection to operate at the
lowest frequency allowed by
the plant design and licensing
limitations.
13.2. Each Generator Owner shall
transmit the existing
underfrequency settings and
any changes to the
underfrequency settings along
with the technical basis for the
settings to the Planning
Coordinator.
13.3. Each Planning Coordinator in
Ontario, Québec and the
Maritime Provinces shall
arrange for compensatory load
shedding, in accordance with
Attachment A and as provided
by a Distribution Provider or
Transmission Owner, that is
Mapping Document
Project Number and Name | Month Year
9
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
adequate to compensate for
the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
13.4. Each Generator Owner in the
ISO-NE Planning Coordinator
area and in NYISO Planning
Coordinator area shall arrange
for compensatory load shedding,
in accordance with Attachment B
and as provided by a Distribution
Provider or Transmission Owner,
that is adequate to compensate
for the loss of generator(s) due
to early tripping that is within
the UFLS island identified by the
Planning Coordinator in
Requirement R2.
PRC-006-NPCC-1
PRC-006-NPCC-2
R4 Each Distribution Provider and
Transmission Owner in the Eastern
R4. Each Distribution Provider or
Transmission Owner in the Eastern
Mapping Document
Project Number and Name | Month Year
Added clarity and combined with the
original R4 and R5 into one requirement.
10
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Interconnection portion of NPCC shall
implement an automatic UFLS program
reflecting normal operating conditions
excluding outages for its Facilities based on
frequency thresholds, total nominal operating
time and amounts specified in Attachment C,
Tables 1 through 3, or shall collectively
implement by mutual agreement with one or
more Distribution Providers and Transmission
Owners within the same island identified in
Requirement R1 and acting as a single entity,
provide an aggregated automatic UFLS
program that sheds their coincident peak
aggregated net Load, based on frequency
thresholds, total nominal operating time and
amounts specified in Attachment C, Tables 1
through 3. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning
Mapping Document
Project Number and Name | Month Year
Translation to New Standard or Other
Action
Description and Change Justification
Interconnection portion of NPCC that does
not meet the UFLS program parameters
specified in Attachment C, Table 1-3, and
each Distribution Provider or Transmission
Owner in the Quebec Interconnection that
does not meet the UFLS program
parameters specified by its Planning
Coordinator shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
• Within 30 calendar days of
determining that it does not meet the
specified parameters, notify its Planning
Coordinator that it does not meet the
UFLS program parameters; and
• Within the following 180 calendar
days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and
a schedule for implementation
that is mutually agreed upon with
its Planning Coordinator or
(2) provide its Planning Coordinator with
a technical study that
demonstrates that the deviations
from the program parameters will
11
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
not result in failure of UFLS
performance criteria being met for
any island. The technical study
must be acceptable to the
Planning Coordinator prior to
implementing deviations from
program parameters and shall
demonstrate coordination with
UFLS programs of all entities
residing within the same island(s)
identified by the Planning
Coordinator in Requirement R2.
The technical study shall also
demonstrate coordination with
other UFLS programs of adjoining
Planning Coordinators, or
(3) provide its Planning Coordinator with
an analysis demonstrating that no
alternative load shedding solution
is available that would allow the
Distribution Provider or
Transmission Owner to comply
with UFLS Attachment C Table 2 or
Attachment C Table 3
Mapping Document
Project Number and Name | Month Year
12
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
PRC-006-NPCC-1
PRC-006-NPCC-2
R5 Each Distribution Provider or Transmission
Owner that must arm its load to trip on
underfrequency in order to meet its
requirements as specified and by doing so
exceeds the tolerances and/or deviates from
the number of stages and frequency set
points of the UFLS program as specified in the
tables contained in Requirement R4 above, as
applicable depending on its total peak net
Load shall: [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
R4. Each Distribution Provider or
Transmission Owner in the Eastern
Interconnection portion of NPCC that does
not meet the UFLS program parameters
specified in Attachment C, Table 1-3, and
each Distribution Provider or Transmission
Owner in the Quebec Interconnection that
does not meet the UFLS program
parameters specified by its Planning
Coordinator shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
• Within 30 calendar days of
determining that it does not meet the
specified parameters, notify its Planning
Coordinator that it does not meet the
UFLS program parameters; and
• Within the following 180 calendar
days from notification of the Planning
Coordinator,
(1) develop a Corrective Action Plan and
a schedule for implementation
that is mutually agreed upon with
its Planning Coordinator or
5.1 Inform its Planning Coordinator of the
need to exceed the stated tolerances or the
number of stages as shown in UFLS
Attachment C, Table 1 if applicable and
5.2 Provide its Planning Coordinator with a
technical study that demonstrates that the
Distribution Providers or Transmission
Owners specific deviations from the
requirements of UFLS Attachment C, Table 1
will not have a significant adverse impact on
the bulk power system.
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Added clarity and combined with the
original R4 and R5 into one requirement.
13
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
5.3 Inform its Planning Coordinator of the
need to exceed the stated tolerances of UFLS
Attachment C, Table 2 or Table 3, and in the
case of Attachment C, Table 2 only, the need
to deviate from providing two stages of UFLS,
if applicable, and
5.4 Provide its Planning Coordinator with an
analysis demonstrating that no alternative
load shedding solution is available that would
allow the Distribution Provider or
Transmission Owner to comply with UFLS
Attachment C Table 2 or Attachment C Table
3.
Mapping Document
Project Number and Name | Month Year
Translation to New Standard or Other
Action
Description and Change Justification
(2) provide its Planning Coordinator with
a technical study that
demonstrates that the deviations
from the program parameters will
not result in failure of UFLS
performance criteria being met for
any island. The technical study
must be acceptable to the
Planning Coordinator prior to
implementing deviations from
program parameters and shall
demonstrate coordination with
UFLS programs of all entities
residing within the same island(s)
identified by the Planning
Coordinator in Requirement R2.
The technical study shall also
demonstrate coordination with
other UFLS programs of adjoining
Planning Coordinators, or
(3) provide its Planning Coordinator with
an analysis demonstrating that no
alternative load shedding solution
is available that would allow the
Distribution Provider or
14
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
Transmission Owner to comply
with UFLS Attachment C Table 2 or
Attachment C Table 3
PRC-006-NPCC-1
R6 Each Distribution Provider and
Transmission Owner in the Québec
Interconnection portion of NPCC shall
implement an automatic UFLS program for its
Facilities based on the frequency thresholds,
slopes, total nominal operating time and
amounts specified in Attachment C, Table 4
or shall collectively implement by mutual
agreement with one or more Distribution
Providers and Transmission Owners within
the same island, identified in Requirement R1,
an aggregated automatic UFLS program that
sheds Load based on the frequency
thresholds, slopes, total nominal operating
time and amounts specified in Attachment C,
Table 4. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
Mapping Document
Project Number and Name | Month Year
The drafting team agreed to retire the
requirement because it is redundant to the
Quebec Variance section of the PRC-006-3
NERC standard.
15
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
PRC-006-NPCC-1
Translation to New Standard or Other
Action
PRC-006-NPCC-2
The drafting team agreed to retire the
requirement because the time delay is
added into Attachment C tables.
PRC-006-NPCC-2
Periodicty of develop and review settings
has been increased from once per calendar
year to once per five calendar years. This
coincides with the the periodicity of UFLS
studies. Having a yearly “develop and
review” without taking any further action is
strictly administrative and does nothing for
reliability (P-81 type of issue).
R7 Each Distribution Provider and
Transmission Owner shall set each
underfrequency relay that is part of its
region’s UFLS program with the following
minimum time delay: 7.1 Eastern
Interconnection – 100 ms 7.2 Québec
Interconnection – 200 ms [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
PRC-006-NPCC-1
R8 Each Planning Coordinator shall develop
R5. Each Planning Coordinator shall
and review once per calendar year settings for
develop and review settings for inhibit
inhibit thresholds (such as but not limited to
thresholds at least once per five
voltage, current and time) to be utilized
calendar years (such as, but not limited
within its region's UFLS program. [Violation
to, voltage, current and time) to be
Risk Factor: Medium] [Time Horizon: Long
utilized within its region’s UFLS
Term Planning]
program. [Violation Risk Factor:
Medium] [Time Horizon: Long Term
Planning]
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
16
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
NPCC-006-NPCC-1
NPCC-006-NPCC-2
R9 Each Planning Coordinator shall provide
each Transmission Owner and Distribution
Provider within its Planning Coordinator area
the applicable inhibit thresholds within 30
days of the initial determination of those
inhibit thresholds and within 30 days of any
changes to those thresholds. [Violation Risk
Factor: Medium] [Time Horizon: Operations
Planning]
R6. Each Planning Coordinator shall provide Clarified the language.
each Transmission Owner and
Distribution Provider within its Planning
Coordinator area the applicable inhibit
thresholds within 30 calendar days of
any changes. [Violation Risk Factor:
Lower] [Time Horizon: Operations
Planning]
NPCC-006-NPCC-1
NPCC-006-NPCC-2
R10 Each Distribution Provider and
Transmission Owner shall implement the
inhibit threshold settings based on the
notification provided by the Planning
Coordinator in accordance with Requirement
R9. [Violation Risk Factor: High] [Time
Horizon: Operations Planning]
R8. Each Distribution Provider and
Transmission Owner shall implement
the inhibit thresholds provided by the
Planning Coordinator in accordance
with Requirement R6 and based on the
Planning Coordinator approved
implementation plan in accordance
with R7. [Violation Risk Factor: High]
[Time Horizon: Operations Planning]
Mapping Document
Project Number and Name | Month Year
Only made changes to requirement
numbers referenced only.
Added clarification for Planning Coordinator
developes implementation plan.
17
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
NPCC-006-NPCC-1
PRC-006-NPCC-2
R11 Each Distribution Provider and
Transmission Owner shall develop and submit
an implementation plan within 90 days of the
request from the Planning Coordinator for
approval by the Planning Coordinator in
accordance with R9. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
R7. Each Distribution Provider and
Transmission Owner that receives a
notification pursuant to Requirement R6
shall develop and submit an
implementation plan with respect to inhibit
thresholds for approval by the Planning
Coordinator within 90 calendar days of the
request from the Planning Coordinator.
[Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R12 Each Transmission Owner and
Distribution Provider shall annually provide
documentation, with no more than 15
months between updates, to its Planning
Coordinator of the actual net Load that would
have been shed by the UFLS relays at each
UFLS stage coincident with their integrated
hourly peak net Load during the previous
year, as determined by measuring actual
metered Load through the switches that
would be opened by the UFLS relays.
R9. Each Transmission Owner and
Distribution Provider shall annually
provide documentation, with no more
than 15 calendar months between
updates, to its Planning Coordinator of
the actual net Load that would have
been shed by the UFLS relays at each
UFLS stage. The actual net Load shall be
coincident with the entity’s integrated
hourly peak net Load during the
previous year, as determined by
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Language clarifications and changes to
requirement numbers referenced.
Added language that allows calculation of
load from nearest available metering rather
than actual metering. The requirement as it
exists is placing undo burden to install
metering when it can be accurately
calculated as a cost effective alternative.
18
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
[Violation Risk Factor: Lower] [Time Horizon:
Long Term Planning]
Translation to New Standard or Other
Action
measuring or calculating Load through
the switches that would disconnect
load if triggered by the UFLS relays. If
measured data is unavailable then
calculated data may be used. [Violation
Risk Factor: Lower] [Time Horizon: Long
Term Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R13 Each Generator Owner shall set each
generator underfrequency trip relay, if so
equipped, below the appropriate generator
underfrequency trip protection settings
threshold curve in Figure 1, except as
otherwise exempted in Requirements R16
and R19. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
R10. Each Generator Owner shall set each
generator underfrequency trip relay, if
so equipped, on or below the
appropriate generator underfrequency
trip protection setting threshold curve
in Figure 2, except as otherwise
exempted in Requirements R13 and
R16. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
NPCC-006-NPCC-1
PRC-006-NPCC-2
R14 Each Generator Owner shall transmit the R11. Each Generator Owner shall transmit
generator underfrequency trip setting and
the generator underfrequency trip
time delay to its Planning Coordinator within
setting and time delay within 45
45 days of the Planning Coordinator’s request.
calendar days of the Planning
Coordinator’s request. [Violation Risk
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Clarification was made that the
Underfrequency trip relay must to be set to
operate “on or below” the appropriate
curve. In Version 1 it currently states below
and questions arose whether settings on
the curve were considered in compliance.
No Change from Version 1 only requirement
numbering
19
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
[Violation Risk Factor: High] [Time Horizon:
Operations Planning]
Translation to New Standard or Other
Action
Factor: Lower] [Time Horizon:
Operations Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R15 Each Generator Owner with a new
generating unit, scheduled to be in service on
or after the effective date of this Standard, or
an existing generator increasing its net
capability by greater than 10% shall:
[Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
R12. Each Generator Owner with a new
generating unit, or an existing
generator increasing its net capability
by greater than 10% shall: [Violation
Risk Factor: Medium] [Time Horizon:
Long Term Planning]
12.1. Design measures to prevent
the generating unit from
tripping directly or indirectly
for underfrequency conditions
above the appropriate
generator tripping threshold
curve in Figure 2.
15.1 Design measures to prevent the
generating unit from tripping directly or
indirectly for underfrequency conditions
above the appropriate generator tripping
threshold curve in Figure 1.
15.2 Design auxiliary system(s) or devices
used for the control and protection of
auxiliary system(s), necessary for the
generating unit operation such that they will
not trip the generating unit during
underfrequency conditions above the
appropriate generator underfrequency trip
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Removed language pertaining to the
Version 1 of the standard regarding on or
after the effective date. Version 1 has been
in place and transition/implementation
concerns need not be addressed in this
requirement.
12.2. Design auxiliary system(s) or
devices used for the control
and protection of auxiliary
system(s), necessary for the
generating unit operation such
that they will not trip the
20
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
protection settings threshold curve in Figure
1.
Translation to New Standard or Other
Action
generating unit during
underfrequency conditions
above the appropriate
generator underfrequency trip
protection setting threshold
curve in Figure 2.
PRC-006-NPCC-1
PRC-006-NPCC-2
R16 Each Generator Owner of existing nonnuclear units in service prior to the effective
date of this standard that have
underfrequency protections set to trip above
the appropriate curve in Figure 1 shall:
[Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
R13. For existing non-nuclear units in
service prior to July 1, 2015, that have
underfrequency protections set to trip
above the appropriate curve in Figure
2: [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
13.1. Each Generator Owner shall set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations.
16.1 Set the underfrequency protection to
operate at the lowest frequency allowed by
the plant design and licensing limitations.
16.2 Transmit the existing underfrequency
settings and any changes to the
underfrequency settings along with the
technical basis for the settings to the Planning
Coordinator.
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Addition made to R13.3 and R13.4 which is
the approved requirement R16 to clarify
that any compensatory load shedding must
be in the island the generating unit resides
in.
13.2. Each Generator Owner shall
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
21
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
16.3 Have compensatory load shedding, as
provided by a Distribution Provider or
Transmission Owner that is adequate to
compensate for the loss of their generator
due to early tripping.
Translation to New Standard or Other
Action
Description and Change Justification
basis for the settings to the
Planning Coordinator.
13.3. Each Planning Coordinator in
Ontario, Québec and the Maritime
Provinces shall arrange for
compensatory load shedding, in
accordance with Attachment A
and as provided by a Distribution
Provider or Transmission Owner,
that is adequate to compensate
for the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
13.4. Each Generator Owner in the ISONE Planning Coordinator area and
in NYISO Planning Coordinator
area shall arrange for
compensatory load shedding, in
accordance with Attachment B
and as provided by a Distribution
Provider or Transmission Owner,
that is adequate to compensate
Mapping Document
Project Number and Name | Month Year
22
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
for the loss of generator(s) due to
early tripping that is within the
UFLS island identified by the
Planning Coordinator in
Requirement R2.
PRC-006-NPCC-1
PRC-006-NPCC-2
R17 Each Planning Coordinator in Ontario,
Quebec and the Maritime provinces shall
apply the criteria described in Attachment A
to determine the compensatory load
shedding that is required in Requirement
R16.3 for generating units in its respective
NPCC area. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
R14. Each Planning Coordinator in Ontario,
Quebec and the Maritime provinces
shall apply the criteria described in
Attachment A to determine the
compensatory load shedding that is
required in Requirement R13.3 for
generating units in its respective NPCC
area. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R18 Each Generator Owner, Distribution
Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the
New York ISO shall apply the criteria
described in Attachment B to determine the
compensatory load shedding that is required
in Requirement R16.3 for generating units in
R15. Each Generator Owner, Distribution
Provider or Transmission Owner within
the ISO-NE Planning Coordinator area
and in NYISO Planning Coordinator
Area shall apply the criteria described
in Attachment B to determine the
compensatory load shedding that is
Mapping Document
Project Number and Name | Month Year
Only made changes to the requirement
number.
Only made changes to the requirement
number.
23
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
its respective NPCC area. [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
Translation to New Standard or Other
Action
required in Requirement R13.4 for
generating units in its respective NPCC
area. [Violation Risk Factor: High][Time
Horizon: Long Term Planning]
PRC-006-NPCC-1
PRC-006-NPCC-2
R19 Each Generator Owner of existing
nuclear generating plants with units that have
underfrequency relay threshold settings
above the Eastern Interconnection generator
tripping curve in Figure 1, based on their
licensing design basis, shall: [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
R16. Each Generator Owner of existing
nuclear generating plants with units
that have underfrequency relay
threshold settings above the Eastern
Interconnection generator tripping
curve in Figure 2 based on their
licensing design shall: [Violation Risk
Factor: High] [Time Horizon: Long Term
Planning]
16.1. Set the underfrequency
protection to operate at a
frequency as low as possible
in accordance with the plant
design and licensing
limitations but not greater
than 57.8 Hz.
19.1 Set the underfrequency protection to
operate at as low a frequency as possible in
accordance with the plant design and
licensing limitations but not greater than
57.8Hz.
19.2 Set the frequency trip setting upper
tolerance to no greater than + 0.1 Hz.
19.3 Transmit the initial frequency trip
setting and any changes to the setting and the
Mapping Document
Project Number and Name | Month Year
Description and Change Justification
Only made changes to the requirement
number and Figure reference update.
16.2. Set the frequency trip setting
upper tolerance to no greater
than + 0.1 Hz.
24
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
technical basis for the settings to the Planning
Coordinator.
PRC-006-NPCC-1
R20 The Planning Coordinator shall update its
UFLS program database as specified by the
NERC PRC Standard on UFLS. This database
shall include the following information:
[Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
20.1 For each UFLS relay, including those
used for compensatory load shedding, the
amount and location of load shed at peak, the
corresponding frequency threshold and time
delay settings.
Translation to New Standard or Other
Action
Description and Change Justification
16.3. Transmit the initial frequency
trip setting and any changes
to the setting and the
technical basis for the
settings to the Planning
Coordinator.
PRC-006-2 (Existing in force continent-wide
standard)
The drafting team decided to remove
requirement 19 and 20 because they are
covered by the continent-wide PRC-006-2
requirement 6.
R6. Each Planning Coordinator shall
The requirement 19 and 20 language will be
maintain a UFLS database containing data
necessary to model its UFLS program for use transferred over to new guideline
document.
in event analyses and assessment of the
UFLS program at least once each calendar
year, with no more than 15 months
between maintenance activities. [VRF:
Lower][Time Horizon: Long-term Planning]
20.2 The buses at which the Load is modeled
in the NPCC library power flow case.
20.3 A list of all generating units that may be
tripped for underfrequency conditions above
the appropriate generator underfrequency
Mapping Document
Project Number and Name | Month Year
25
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
trip protection settings threshold curve in
Figure 1, including the frequency trip
threshold and time delay for each protection
system.
20.4 The location and amount of additional
elements to be switched for voltage control
that are coordinated with UFLS program
tripping.
20.5 A list of all UFLS relay inhibit functions
along with the corresponding settings and
locations of these relays.
PRC-006-NPCC-1
R21 Each Planning Coordinator shall notify
each Distribution Provider, Transmission
Owner, and Generator Owner within its
Planning Coordinator area of changes to load
distribution needed to satisfy UFLS program
performance characteristics as specified by
the NERC PRC Standard on UFLS.[Violation
Risk Factor: High] [Time Horizon: Long Term
Planning]
Mapping Document
Project Number and Name | Month Year
PRC-006-2 (Existing in force continent-wide
standard)
R3. Each Planning Coordinator shall
develop a UFLS program,
including notification of and a
schedule for implementation by
UFLS entities within its area, that
meets the following performance
characteristics in simulations of
underfrequency conditions
resulting from an imbalance
scenario, where an imbalance =
PRC-006-NPCC-1 R21 is now redundant with
the NERC continent wide standard R3. This
requirement, R21 is proposed for
retirement under the P-81 criteria.
26
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
[(load — actual generation
output) / (load)], of up to 25
percent within the identified
island(s). [VRF: High][Time
Horizon: Long-term Planning]
3.1. Frequency shall remain above
the Underfrequency Performance
Characteristic curve in PRC-006-2
- Attachment 1, either for 60
seconds or until a steady-state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.2. Frequency shall remain below
the Overfrequency Performance
Characteristic curve in PRC-006-2
- Attachment 1, either for 60
seconds or until a steady-state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.3. Volts per Hz (V/Hz) shall not
exceed 1.18 per unit for longer
than two seconds cumulatively
per simulated event, and shall not
exceed 1.10 per unit for longer
Mapping Document
Project Number and Name | Month Year
27
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
than 45 seconds cumulatively per
simulated event at each
generator bus and generator
step-up transformer high-side bus
associated with each of the
following:
•
•
•
PRC-006-NPCC-1
R22 Each Distribution Provider, Transmission
Owner and Generator Owner shall implement
the load distribution changes based on the
Mapping Document
Project Number and Name | Month Year
Individual generating units
greater than 20 MVA (gross
nameplate rating) directly
connected to the BES
Generating plants/facilities
greater than 75 MVA (gross
aggregate nameplate rating)
directly connected to the BES
Facilities consisting of one or
more units connected to the
BES at a common bus with
total generation above 75
MVA gross nameplate rating.
PRC-006-2 (Existing in force continent-wide
standard)
PRC-006-NPCC-1 R22 is now redundant with
the NERC continent wide standard R9 and
R9. Each UFLS entity shall provide automatic this requirement, R22 is proposed for
retirement under the P-81 criteria.
tripping of Load in accordance with the
28
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
notification provided by the Planning
Coordinator in accordance with Requirement
R21. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning]
UFLS program design and schedule for
implementation, including any Corrective
Action Plan, as determined by its Planning
Coordinator(s) in each Planning Coordinator
area in which it owns assets. [VRF:
High][Time Horizon: Long-term Planning]
PRC-006-NPCC-1
PRC-006-2 (Existing in force continent-wide
standard)
R23 Each Distribution Provider, Transmission
Owner and Generator Owner shall develop
and submit an implementation plan within 90
days of the request from the Planning
Coordinator for approval by the Planning
Coordinator in accordance with Requirement
R21. [Violation Risk Factor: Lower] [Time
Horizon: Operations Planning]
Mapping Document
Project Number and Name | Month Year
R3. Each Planning Coordinator shall
develop a UFLS program,
including notification of and a
schedule for implementation by
UFLS entities within its area, that
meets the following performance
characteristics in simulations of
underfrequency conditions
resulting from an imbalance
scenario, where an imbalance =
[(load — actual generation
output) / (load)], of up to 25
percent within the identified
island(s). [VRF: High][Time
Horizon: Long-term Planning]
Description and Change Justification
PRC-006-NPCC-1 states an implemention
plan for changes needs to be submitted to
the PC for their approval within 90 days of
the request. However in R22 of the regional
standard it states that the changes shall be
implemented based on the PC’s notification.
We believe this is fully covered in R3 and an
additional implementation plan beyond the
PC’s plan, which includes the notification
and schedule for the UFLS entities to follow
is now unnecessary in the regional standard.
We are recommending that R23 in the
regional standard be retired.
29
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
3.1. Frequency shall remain above
the Underfrequency Performance
Characteristic curve in PRC-006-2
- Attachment 1, either for 60
seconds or until a steady-state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.2. Frequency shall remain below
the Overfrequency Performance
Characteristic curve in PRC-006-2
- Attachment 1, either for 60
seconds or until a steady-state
condition between 59.3 Hz and
60.7 Hz is reached, and
3.3. Volts per Hz (V/Hz) shall not
exceed 1.18 per unit for longer
than two seconds cumulatively
per simulated event, and shall not
exceed 1.10 per unit for longer
than 45 seconds cumulatively per
simulated event at each
generator bus and generator
step-up transformer high-side bus
Mapping Document
Project Number and Name | Month Year
30
Standard: PRC-006-NPCC-2
Requirement in Approved Standard
Translation to New Standard or Other
Action
Description and Change Justification
associated with each of the
following:
•
•
Individual generating units
greater than 20 MVA (gross
nameplate rating) directly
connected to the BES
Generating plants/facilities
greater than 75 MVA (gross
aggregate nameplate rating)
directly connected to the BES
Facilities consisting of one or more units
connected to the BES at a common bus with
total generation above 75 MVA gross
nameplate rating.
Mapping Document
Project Number and Name | Month Year
31
Consolidated Edison Company
of New York, Inc.
4 Irving Place
New York NY 10003-0987
November 2, 2018
VIA EMAIL
Regional Standards Committee (RSC)
NPCC
[email protected]
Subject: PRC-006-NPCC-02 Automatic Underfrequency Load Shedding – Approval
to Post for Pre-Ballot and Ballot Period
Dear RSC Members:
The PRC-006-NPCC-2 Automatic Underfrequency Load Shedding Regional Standard
has been posted for three 45-day comment periods. The drafting team has responded to
every comment from all three periods. NPCC’s Manager of Reliability Standards has
posted all comment responses onto the NPCC website. The next step, in accordance with
the NPCC Regional Standard Processes Manual, is to obtain the RSC’s approval to post
for a 30-day pre-ballot review period and a subsequent 10-day ballot period. If you have
not already done so, please email your approval to Mr. Ruida Shu so he can post the
documents for pre-ballot and ballot period.
I’d like to take this opportunity to commend all the members of the Standard Drafting
Team, and those who supported them, for their perseverance through the arduous task of
re-writing this Regional Standard over the course of the past two years and five months.
Their dedication was essential to accomplish the team’s mission.
If you have any questions, please don’t hesitate to contact me.
Regards
Dan Taft
Chief Engineer – Control Systems Engineering Department
Chair – NPCC PRC-006-NPCC-2 Standard Drafting Team
(212) 460 – 4536
[email protected]
Consolidated Edison Company
of New York, Inc.
4 Irving Place
New York NY 10003-0987
October 30, 2018
VIA EMAIL
Guy V. Zito
Assistant Vice-President Standards
NPCC
[email protected]
Subject: PRC-006-NPCC-02 Automatic Underfrequency Load Shedding – CEAP
Dear Mr. Zito,
Following the review and revision of draft PRC-006-NPCC-02 Automatic
Underfrequency Load Shedding Regional Standard, in accordance with the NPCC
Regional Standard Processes Manual, the next step in the process towards adoption
would normally be to determine if it is necessary to implement the Cost-Effective
Analysis Process (CEAP). Considering the drafting team only clarified the requirement
language within the standard, removed redundant requirements with the Continent-wide
UFLS Standard, and did not make any revisions that could potentially incur additional
costs, I propose to waive the formal CEAP on behalf of the PRC-006-NPCC-02
Automatic Underfrequency Load Shedding Standard drafting team. Additionally, the
Standard drafting team did post a cost effectiveness question to allow the industry to
propose any cost-effective alternatives during the third posting for comment period. The
industry did not provide any alternatives. If you have any questions, please contact me.
Regards
Dan Taft
Chief Engineer – Control Systems Engineering Department
Chair – NPCC PRC-006-NPCC-2 Standard Drafting Team
(212) 460 – 4536
[email protected]
1. Determine Quorum
NPCC Registered Members
Sector 1, Transmission Owners
Central Hudson Gas and Electric Corporation
Central Maine Power Company
Consolidated Edison Company of New York, Inc.
Emera Maine
Eversource Energy
Hydro One Inc
Hydro-Quebec TransEnergie
Long Island Power Authority
National Grid
New Hampshire Transmission, LLC
New York Power Authority
New York State Electric & Gas Corporation
Nova Scotia Power Inc.
Orange and Rockland Utilities Inc
Rochester Gas & Electric Corporation
The United Illuminating Company
Vermont Transco
17
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
In Attendance
By Proxy
(denote w/ 1) (denote w/ 1)
17
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2. Vote/Ballot Recording
Affirmative
Negative
Abstain
(denote w/ 1) (denote w/ 1) (denote w/ 1)
17
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1. Determine Quorum
NPCC Registered Members
Sector 2, Reliability Coordinators
Hydro-Quebec TransEnergie
Independent Electricity System Operator
ISO-New England, Inc.
New Brunswick Power Corporation
New York Independent System Operator
5
1
1
1
1
1
In Attendance
By Proxy
(denote w/ 1) (denote w/ 1)
5
0
1
1
1
1
1
2. Vote/Ballot Recording
Affirmative
Negative
Abstain
(denote w/ 1) (denote w/ 1) (denote w/ 1)
5
0
0
1
1
1
1
1
1. Determine Quorum
NPCC Registered Members
Sector 3, TDUs, Dist. And LSE
Braintree Electric Light Department
Consolidated Edison Company of New York, Inc.
Eversource Energy
Groton Electric Light
Hingham Municipal Lighting Plant
Hydro One Inc
Hydro Quebec Distribution
Ipswich Municipal Light Department
Long Island Power Authority
Marblehead Municipal Light Department
National Grid USA
New Brunswick Power Corporation
New York Power Authority
Orange and Rockland Utilities, Inc
Princeton Municipal Light Department
Shrewsbury Electric & Cable Operations
Sterling Municipal Light Department
Toronto Hydro Electric System Ltd.
Vermont Electric Cooperative, Inc.
Wakefield Municipal Gas and Light Department
Westfield Gas & Electric
21
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
In Attendance
By Proxy
(denote w/ 1) (denote w/ 1)
17
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2. Vote/Ballot Recording
Affirmative
Negative
Abstain
(denote w/ 1) (denote w/ 1) (denote w/ 1)
19
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
NPCC Registered Members
Sector 4, Generator Owners
Bruce Power L.P.
Consolidated Edison Company of New York, Inc.
Covanta Energy
Dominion Resources, Inc.
Eastern Generation LLC
Entergy Nuclear Northeast, Inc
Exelon Generation Company, LLC
First Wind Operations & Maintenance
Long Island Power Authority
Massachusetts Municipal Wholesale Electric Company
New York Power Authority
NextEra Energy Resources, LLC
NRG Energy Inc.
Nova Scotia Power Inc.
Ontario Power Generation Inc.
PSEG Fossil LLC
Talen Energy Supply, LLC
TransCanada
Vistra Energy Corp
Wheelabrator Westchester LP
1. Determine Quorum
2. Vote/Ballot Recording
In Attendance
By Proxy
(denote w/ 1) (denote w/ 1)
20
16
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Affirmative
Negative
Abstain
(denote w/ 1) (denote w/ 1) (denote w/ 1)
2
10
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
NPCC Registered Members
Sector 5, Marketers, Brokers, Aggragators
Brookfield Power Corporation
Consolidated Edison Company of New York, Inc.
Consolidated Edison Energy/Development
HQ Energy Marketing Inc.
H.Q. Energy Services (U.S.) Inc.
Long Island Power Authority
Massachusetts Municipal Wholesale Electric Company
Nalcor Energy
New York Power Authority
Nexus Energy Inc.
Shell Energy North America
Utility Services Inc.
1. Determine Quorum
2. Vote/Ballot Recording
In Attendance
By Proxy
(denote w/ 1) (denote w/ 1)
12
9
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Affirmative
Negative
Abstain
(denote w/ 1) (denote w/ 1) (denote w/ 1)
8
0
1
1
1
1
1
1
1
1
1
1
1. Determine Quorum
NPCC Registered Members
In Attendance
By Proxy
(denote w/ 1) (denote w/ 1)
Sector 6, State and Provincial Reg. and Govt. Aut 5
3
0
Long Island Power Authority
1
1
Maine Public Utilities Commission
1
1
New Hampshire Public Utilities Commission
1
New York Power Authority
1
1
New York State Department of Public Service
1
2. Vote/Ballot Recording
Affirmative
Negative
Abstain
(denote w/ 1) (denote w/ 1) (denote w/ 1)
3
0
0
1
1
1
NPCC Registered Members
Sector 7, Sub Regional Rel. Councils, REs and Others
4g Technologies, LP
Abloy Security, Inc.
AESI Acumen Engineered Solutions Internaiontal Inc.
Ascendant Energy Solutions, Inc.
Casimir Systemics LLC
Ciufo & Cooperberg Consulting Inc.
DataCapable, Inc.
David Kiguel
ERLPhase Power Technologies
GDS Associateds, Inc.
Genieall
International Business Machines Corporation
Ironhouse Inc.
McCoy Power Consultants, Inc.
Network & Security Technologies, Inc.
New Power Technologies, Inc
New York State Reliability Council, LLC
Oxbow-Sherman Energy, LLC
PLM, Inc.
Preti, Flaherty, Beliveau, and Pachios, LLP.
Proven Compliance Solutions, Inc.
SGC Engineering, LLC
Sund Technologies, LLC
TRC Solutions
VIASYN, Inc.
1. Determine Quorum
2. Vote/Ballot Recording
In Attendance
By Proxy
(denote w/ 1) (denote w/ 1)
25
16
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Affirmative
Negative
Abstain
(denote w/ 1) (denote w/ 1) (denote w/ 1)
14
0
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Determine Electronic Quorum
Sector
1
2
3
4
5
6
7
Sector Name
Transmission Owners
Reliability Coordinators
TDUs, Dist. And LSE
Generator Owners
Marketers, Brokers, Aggragators
Customers- large and small
State and Provincial Reg. and Govt. Authorities
Total
In
Registered Attendance
17
17
5
5
21
17
20
16
12
9
5
3
25
16
105
83
Electronic Vote Quorum= at least 2/3 of the Total Registered
Quorum Present?
YES
By
Proxy
0
0
2
0
0
0
0
2
Total
Represented
17
5
19
16
9
3
16
85
Sector %
Attending
1.00
1.00
0.90
0.80
0.75
0.60
0.64
Determine if Motion or Item Passes
Sector
1
2
3
4
5
6
7
Sector Name
Transmission Owners
Reliability Coordinators
TDUs, Dist. And LSE
Generator Owners
Marketers, Brokers, Aggragators
Customers- large and small
State and Provincial Reg. and Govt. Authorities
Totals
Total
Sector %
Affirmative
Negative
Abstain
Votes Cast
Sector has
Registered Attending # of Votes Fraction # of Votes Fraction # of Votes Total (-Abstentions) Voted(1-Y, 0-N)
17
1.00
17 1.000
0 0.000
0
17
1
5
1.00
5 1.000
0 0.000
0
5
1
21
0.90
19 1.000
0 0.000
0
19
1
20
0.80
10 0.714
4 0.286
2
14
1
12
0.75
8 1.000
0 0.000
1
8
1
5
0.60
3 1.000
0 0.000
0
3
1
25
0.64
14 1.000
0 0.000
2
14
1
105
76
Sum of Affirmative/Number of Sectors that Voted
MUST BE AT LEAST 2/3 to pass
0.959
Did MOTION PASS?
PASS
6.714
4
0.286
5
80
7
Comment Report
Project Name:
Regional Reliability Standard (NPCC) | PRC-006-NPCC-2
Comment Period Start Date:
5/8/2019
Comment Period End Date:
6/21/2019
Associated Ballots:
There were 1 sets of responses, including comments from approximately 1 different people from approximately 1 companies
representing 1 of the Industry Segments as shown in the table on the following pages.
Questions
1. Do you agree the development of PRC-006-NPCC-2 met the “Open” criteria as outlined above? If “No”, please explain in the comment area
below:
2. Do you agree the development of PRC-006-NPCC-2 met the “Inclusive” criteria as outlined above? If “No”, please explain in the comment
area below:
3. Do you agree the development of PRC-006-NPCC-2 met the “Balanced” criteria as outlined above? If “No”, please explain in the comment
area below:
4. Do you agree the development of PRC-006-NPCC-2 met the “Due Process” criteria as outlined above? If “No”, please explain in the
comment area below:
5. Do you agree the development of PRC-006-NPCC-2 met the “Transparent” criteria as outlined above? If “No”, please explain in the
comment area below:
Organization
Name
Name
Segment(s)
Region
Group Name
Group Member
Name
Group
Member
Organization
Group
Member
Segment(s)
Group Member
Region
1. Do you agree the development of PRC-006-NPCC-2 met the “Open” criteria as outlined above? If “No”, please explain in the comment area
below:
Leonard Kula - Independent Electricity System Operator - 2
Answer
Yes
Document Name
Comment
N/A
Likes
0
Dislikes
Response
0
2. Do you agree the development of PRC-006-NPCC-2 met the “Inclusive” criteria as outlined above? If “No”, please explain in the comment
area below:
Leonard Kula - Independent Electricity System Operator - 2
Answer
Yes
Document Name
Comment
N/A
Likes
0
Dislikes
Response
0
3. Do you agree the development of PRC-006-NPCC-2 met the “Balanced” criteria as outlined above? If “No”, please explain in the comment
area below:
Leonard Kula - Independent Electricity System Operator - 2
Answer
Yes
Document Name
Comment
N/A
Likes
0
Dislikes
Response
0
4. Do you agree the development of PRC-006-NPCC-2 met the “Due Process” criteria as outlined above? If “No”, please explain in the
comment area below:
Leonard Kula - Independent Electricity System Operator - 2
Answer
Yes
Document Name
Comment
N/A
Likes
0
Dislikes
Response
0
5. Do you agree the development of PRC-006-NPCC-2 met the “Transparent” criteria as outlined above? If “No”, please explain in the
comment area below:
Leonard Kula - Independent Electricity System Operator - 2
Answer
Yes
Document Name
Comment
N/A
Likes
0
Dislikes
Response
0
Unofficial Comment Form
Regional Reliability Standard | PRC-006-NPCC-2
DO NOT use this form for submitting comments. Use the electronic form to submit comments on Regional
Reliability Standard PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding. The form must be
submitted by 8 p.m. Eastern, Friday, June 21, 2019.
Documents and information about this project are available on the NPCC’s Standards In Development
page. If you have questions, contact Senior Reliability Standards Analyst, Nasheema Santos (via email) or
at (404) 446-2564.
Background Information
The NPCC drafting team reviewed Regional Reliability Standard PRC-006-NPCC-1 and made the following
changes:
1. Remove redundancies with the most recent of the Continent-wide NERC Standard, PRC006-3. Some of the redundancies removed from the Regional Standard PRC-006-NPCC-2 are
those related to:
• The Québec Interconnection portion of NPCC shall implement an automatic UFLS program
in accordance with Attachment C Table 4;
• Requirements for a UFLS Database;
• Notification of changes to load distribution needed to satisfy UFLS program performance
characteristics; and
• Development of an implementation plan when changes to load distribution are needed.
2. Ensure that UFLS island boundaries, once identified, are provided upon request, to affected
entities.
3. Minimum time UFLS relay time delay added to Attachment C tables and removed as a separate
requirement.
4. Added the ability for a TO or DP to calculate net load shed for UFLS if direct metering is not
available.
5. A number of minor clarifications were made to the standard such as requiring the
Underfrequency trip relay must to be set to operate “on or below” the appropriate curve. In
Version 1 it currently states below and questions arose whether settings on the curve were
considered in compliance.
6. Clarification that any compensatory load shedding for non-conformance with the
Underfrequency trip specification for generation (in service prior to July 1, 2015) must be
within the same island as the generator resides.
NERC Criteria for Developing or Modifying a Regional Reliability Standard
Regional Reliability Standard shall be: (1) a regional reliability standard that is more stringent than the
continent-wide reliability standard, including a regional standard that addresses matters that the
continent-wide reliability standard does not; or (2) a regional reliability standard that is necessitated by a
physical difference in the bulk power system. Regional reliability standards shall provide for as much
uniformity as possible with reliability standards across the interconnected bulk power system of the North
American continent. Regional reliability standards, when approved by FERC and applicable authorities in
Mexico and Canada, shall be made part of the body of NERC reliability standards and shall be enforced
upon all applicable bulk power system owners, operators, and users within the applicable area, regardless
of membership in the region.
The approval process for a regional reliability standard requires NERC to publicly notice and request
comment on the proposed standard. Comments shall be permitted only on the following criteria
(technical aspects of the standard are vetted through the regional standards development process):
Open — Regional reliability standards shall provide that any person or entity that is directly and
materially affected by the reliability of the bulk power system within the regional entity shall be
able to participate in the development and approval of reliability standards. There shall be no
undue financial barriers to participation. Participation shall not be conditional upon membership
in the regional entity, a regional entity or any organization, and shall not be unreasonably
restricted on the basis of technical qualifications or other such requirements.
Inclusive — Regional reliability standards shall provide that any person with a direct and material
interest has a right to participate by expressing an opinion and its basis, having that position
considered, and appealing through an established appeals process, if adversely affected.
Balanced — Regional reliability standards shall have a balance of interests and shall not be
dominated by any two-interest categories and no single-interest category shall be able to defeat a
matter.
Due Process — Regional reliability standards shall provide for reasonable notice and opportunity
for public comment. At a minimum, the standard shall include public notice of the intent to
develop a standard, a public comment period on the proposed standard, due consideration of
those public comments, and a ballot of interested stakeholders.
Transparent — All actions material to the development of regional reliability standards shall be
transparent. All standards development meetings shall be open and publicly noticed on the
regional entity’s Web site.
Unofficial Comment Form
Regional Reliability Standard PRC-006-NPCC-2 | May 2019
2
Review the revised Regional Reliability Standard and answer the following questions.
1. Do you agree the development of PRC-006-NPCC-2 met the “Open” criteria as outlined above? If
“No”, please explain in the comment area below:
Yes
No
Comments:
2. Do you agree the development of PRC-006-NPCC-2 met the “Inclusive” criteria as outlined above?
If “No”, please explain in the comment area below:
Yes
No
Comments:
3. Do you agree the development of PRC-006-NPCC-2 met the “Balanced” criteria as outlined above?
If “No”, please explain in the comment area below:
Yes
No
Comments:
4. Do you agree the development of PRC-006-NPCC-2 met the “Due Process” criteria as outlined
above? If “No”, please explain in the comment area below:
Yes
No
Comments:
5. Do you agree the development of PRC-006-NPCC-2 met the “Transparent” criteria as outlined
above? If “No”, please explain in the comment area below:
Yes
No
Comments:
Unofficial Comment Form
Regional Reliability Standard PRC-006-NPCC-2 | May 2019
3
Implementation Plan
Regional Reliability Standard PRC-006-NPCC-2 – Automatic
Underfrequency Load Shedding
Applicable Standard(s)
•
PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding
Requested Retirement(s)
•
PRC-006-NPCC-1 – Automatic Underfrequency Load Shedding
Applicable Entities
•
•
•
•
Generator Owners
Planning Coordinators
Distribution Providers that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Transmission Owners that are responsible for the ownership, operation, or control of
UFLS equipment as required by the UFLS program.
Background
The revisions to the PRC-006-NPCC-1 Automatic Underfrequency Load Shedding have been
developed to address the following concerns.
1. To determine if the applicability of the standard needs to be revised in accordance with
Project 2014-01 Dispersed Generation Resources.
2. To determine if the performance requirements as contained in the criteria of NPCC
Directory#12 Sections 5.1.1 and 5.1.2 should be explicitly included in the requirements
of the Regional Standard and potential retirement of Directory 12 Automatic
Underfrequency Load Shedding Program.
3. Review Attachment C in PRC-006-NPCC-1 to address the implications of the design
assessment, in accordance with Requirement R4 of PRC-006-1/PRC-006-2, of not
meeting the program performance characteristics as identified in Requirement R3 of
PRC-006-1/PRC-006-2.
4. Review and revise Table 4 in Attachment C in accordance with the 2013 NPCC UFLS
Adequacy Assessment. Additionally, the applicability of Requirements R4 and R5 will be
reviewed to consider that Hydro Quebec is not part of the Eastern Interconnection.
Effective Date
All requirements with the exception of R3 will be enforceable on the first day of the first
calendar quarter following the applicable governmental and regulatory approvals.
R3 will be enforceable on the first day of the first calendar quarter 12 months following
the applicable governmental and regulatory approvals.
Retirement Date
The NPCC Regional Reliability Standard PRC-006-NPCC-1 shall be retired immediately
prior to the Effective Date of PRC-006-NPCC-2.
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Standard Development Timeline
This section is maintained by the drafting team during the development of the standard and will
be removed when the standard is adopted by the NERC Board of Trustees (Board).
Description of Current Draft
Completed Actions
Regional Standards Committee approved Regional Standard
Authorization Request (RSAR) for posting
Date
June 23, 2015
Anticipated Actions
Date
1st 45‐day Formal Comment Period
September 1, 2017 ‐
October 18, 2017
2nd 45‐day Formal Comment Period
April 16, 2018 –
June 1, 2018
3rd 45‐day Formal Comment Period
August 10, 2018‐
September 24, 2018
30‐day Pre‐ballot Period
November 12, 2018‐
December 12, 2018
10‐day ballot Period (Extended to achieve quorum)
December 12, 2018‐
February 10, 2019
NPCC Board of Directors Approval
May 1, 2019
NERC Board adoption
PRC‐006‐NPCC‐2
Page 1 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Upon Board adoption, the rationale boxes will be moved to the Supplemental Material Section.
A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.
Number:
PRC‐006‐NPCC‐2
3.
Purpose: The NPCC Automatic Underfrequency Load Shedding (UFLS) regional
Reliability Standard establishes more stringent and specific NPCC UFLS program
requirements than the NERC continent‐wide PRC‐006 standard. The program is
designed such that declining frequency is arrested and recovered in accordance with
established NPCC performance requirements stipulated in this document.
4.
Applicability:
4.1. Functional Entities:
4.1.1. Generator Owner
4.1.2. Planning Coordinator
4.1.3. Distribution Providers that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
4.1.4. Transmission Owners that are responsible for the ownership, operation,
or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators
5.
Effective Date: See Implementation Plan.
B. Requirements and Measures
Rationale for Requirement R1: Figure 1 of this document shows the NPCC
underfrequency criteria for the Eastern Interconnection portion of NPCC. Figure 1 also
shows the NERC criteria as defined in the NERC PRC Standard on UFLS.
R1. Each Planning Coordinator in the Eastern Interconnection portion of NPCC shall design
an UFLS program, pertaining to islands wholly within the NPCC Region, having
performance characteristics that prevents the frequency from remaining below 59.5
Hz for more than 30 seconds in accordance with Figure 1 [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]
M1. Each Planning Coordinator shall have evidence such as reports, system studies and/or
real‐time power flow data captured from actual system events and other dated
documentation that demonstrates it meets Requirement R1.
PRC‐006‐NPCC‐2
Page 2 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
R2. Each Planning Coordinator shall provide UFLS island boundaries, as identified per the
NERC continent‐wide PRC‐006 Standard on UFLS, to Distribution Providers, Generator
Owners, and Transmission Owners within 30 calendar days of receipt of a request.
[Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M2. Each Planning Coordinator shall have evidence such as dated documentation that
demonstrates that it meets requirement R2.
R3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall implement an automatic UFLS program, reflecting normal
operating conditions, excluding outages. The automatic UFLS program shall be
implemented on an island basis for each identified island per the NERC continent‐wide
PRC‐006 Standard on UFLS as follows: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
The UFLS program shall be implemented by each Distribution Provider and
Transmission Owner according to the frequency thresholds, nominal operating
times, and load shedding amounts specified in Attachment C, Tables 1‐3; or
The UFLS program shall be implemented collectively by multiple Distribution
Providers or Transmission Owners, as long as they reside in the same UFLS
island identified by the Planning Coordinator per Requirement R2. These
multiple Distribution Providers or Transmission Owners, via mutual agreement,
shall act as a single entity to provide an aggregated automatic UFLS program
that sheds their coincident peak aggregated net Load according to the
frequency thresholds, total nominal operating time, and load shedding
amounts specified in Attachment C, Tables 1‐3.
M3. Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC shall have evidence such as documentation or reports containing the
location and amount of load to be tripped in their respective areas, and the
corresponding frequency thresholds, on those circuits included in its UFLS program
identified in Requirement R3. (Attachment C, Tables 1‐3).
R4. Each Distribution Provider or Transmission Owner in the Eastern Interconnection
portion of NPCC that does not meet the UFLS program parameters specified in
Attachment C, Table 1‐3, and each Distribution Provider or Transmission Owner in the
Quebec Interconnection that does not meet the UFLS program parameters specified
by its Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long
Term Planning]
Within 30 calendar days of determining that it does not meet the
specified parameters, notify its Planning Coordinator that it does not
meet the UFLS program parameters; and
Within the following 180 calendar days from notification of the Planning
Coordinator,
PRC‐006‐NPCC‐2
Page 3 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
(1) develop a Corrective Action Plan and a schedule for implementation that is
mutually agreed upon with its Planning Coordinator or
(2) provide its Planning Coordinator with a technical study that demonstrates
that the deviations from the program parameters will not result in failure of
UFLS performance criteria being met for any island. The technical study must be
acceptable to the Planning Coordinator prior to implementing deviations from
program parameters and shall demonstrate coordination with UFLS programs of
all entities residing within the same island(s) identified by the Planning
Coordinator in Requirement R2. The technical study shall also demonstrate
coordination with other UFLS programs of adjoining Planning Coordinators, or
(3) provide its Planning Coordinator with an analysis demonstrating that no
alternative load shedding solution is available that would allow the Distribution
Provider or Transmission Owner to comply with UFLS Attachment C Table 2 or
Attachment C Table 3.
M4. Each Distribution Provider or Transmission Owner shall have evidence such as reports
analysis, system studies and dated documentation that demonstrates that it meets
Requirement R4.
Rationale for Requirement R5: An inhibit function provides supervisory control over a
UFLS relay. For example, an undervoltage inhibit feature prevents UFLS relay operation if
the sensed voltage decreases below an adjustable setting. An undervoltage inhibit
function is intended to prevent operation of a UFLS relay when the transmission supply is
lost to distribution station feeding many induction motors. Following loss of the
transmission supply, motors may support the voltage while the motors coast down in
speed. The motors coasting down (ringing down) will look like an underfrequency event
to the relay. The inhibit setting is set to a voltage above which the motor load is expected
to sustain. This prevents the underfrequency relay from tripping and locking out
distribution feeder breakers supplying the motor load, between the time the transmission
supply line trips and the time when the line recloses to restore the load. Voltages
sustained by motors that are coasting down (e.g. 0.70 pu) are typically much lower than
voltages at which the UFLS relays are required to operate to meet UFLS performance
criteria. However, motor loads supplied by cable networks typically have higher ring
down voltages because of cable charging. Therefore, care must be taken so that the
voltage inhibit setting is not higher than the voltage at which UFLS relays are required to
operate to meet UFLS performance criteria.
R5. Each Planning Coordinator shall develop and review settings for inhibit thresholds at
least once per five calendar years (such as, but not limited to, voltage, current and
time) to be utilized within its region’s UFLS program. [Violation Risk Factor: Medium]
[Time Horizon: Long Term Planning]
M5. Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R5.
PRC‐006‐NPCC‐2
Page 4 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
R6. Each Planning Coordinator shall provide each Transmission Owner and Distribution
Provider within its Planning Coordinator area the applicable inhibit thresholds within
30 calendar days of any changes. [Violation Risk Factor: Lower] [Time Horizon:
Operations Planning]
M6. Each Planning Coordinator shall provide evidence such as letters, emails or other
dated documentation that demonstrates that it meets Requirement R6.
R7. Each Distribution Provider and Transmission Owner that receives a notification
pursuant to Requirement R6 shall develop and submit an implementation plan with
respect to inhibit thresholds for approval by the Planning Coordinator within 90
calendar days of the request from the Planning Coordinator. [Violation Risk Factor:
Lower] [Time Horizon: Operations Planning]
M7. Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails, or other dated documentation that demonstrates that it meets
Requirement R7.
R8. Each Distribution Provider and Transmission Owner shall implement the inhibit
thresholds provided by the Planning Coordinator in accordance with Requirement R6
and based on the Planning Coordinator approved implementation plan in accordance
with R7. [Violation Risk Factor: High] [Time Horizon: Operation Planning]
M8. Each Distribution Provider and Transmission Owner shall provide evidence such as test
reports, data sheets, completed work orders, or other documentation that
demonstrates that it meets Requirement R8.
Rationale for Requirement R9: Ideally, the amount of load to be shed in each stage of the
UFLS program for every entity should perfectly match that prescribed in this Standard, for
all phases of the load cycle, i.e., seasonal (summer vs. winter), weekly (weekday vs.
weekend vs. holidays), daily (morning, noon, and night), etc. for all of the identified
islands. Practically, however, this is obviously not possible because the load cycles of the
various areas and sub‐areas within any given island do not perfectly track the load cycle
of the overall island. The UFLS program, on the other hand, is designed based on peak
conditions for the overall island. The percentages of actual load shedding that would
occur for any conditions other than peak, therefore, can only approximate that
prescribed in the Standard. To that end, Requirement R11 requires entities to document
measured loads in the UFLS program coincident with their own annual peak, whether or
not that peak occurs at the same time or in the same season as the peak of the identified
island in which their load resides. Using individual entity peaks vs. overall island peaks
provides a consistent approach for accounting purposes among the very entities that are
responsible for designing and maintaining their UFLS programs.
PRC‐006‐NPCC‐2
Page 5 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
R9. Each Transmission Owner and Distribution Provider shall annually provide
documentation, with no more than 15 calendar months between updates, to its
Planning Coordinator of the actual net Load that would have been shed by the UFLS
relays at each UFLS stage. The actual net Load shall be coincident with the entity’s
integrated hourly peak net Load during the previous year, as determined by
measuring or calculating Load through the switches that would disconnect load if
triggered by the UFLS relays. If measured data is unavailable then calculated data may
be used. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]
M9. Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets or other dated documentation submitted to its Planning
Coordinator that indicates the net amount of load shed and the percentage of its peak
load at each stage of its UFLS program to demonstrate that it meets Requirement R9.
R10. Each Generator Owner shall set each generator underfrequency trip relay, if so
equipped, on or below the appropriate generator underfrequency trip protection
setting threshold curve in Figure 2, except as otherwise exempted in Requirements
R13 and R16. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M10. Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement
R10.
R11. Each Generator Owner shall transmit the generator underfrequency trip setting and
time delay within 45 calendar days of the Planning Coordinator’s request. [Violation
Risk Factor: Lower] [Time Horizon: Operations Planning]
M11. Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R11.
R12. Each Generator Owner with a new generating unit, or an existing generator increasing
its net capability by greater than 10% shall: [Violation Risk Factor: Medium] [Time
Horizon: Long Term Planning]
12.1
Design measures to prevent the generating unit from tripping directly or
indirectly for underfrequency conditions above the appropriate
generator tripping threshold curve in Figure 2.
12.2
Design auxiliary system(s) or devices used for the control and protection
of auxiliary system(s), necessary for the generating unit operation such
that they will not trip the generating unit during underfrequency
conditions above the appropriate generator underfrequency trip
protection setting threshold curve in Figure 2.
M12. Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R12.
PRC‐006‐NPCC‐2
Page 6 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
R13. For existing non‐nuclear units in service prior to July 1, 2015, that have
underfrequency protections set to trip above the appropriate curve in Figure 2:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
13.1
Each Generator Owner shall set the underfrequency protection to
operate at the lowest frequency allowed by the plant design and licensing
limitations.
13.2
Each Generator Owner shall transmit the existing underfrequency
settings and any changes to the underfrequency settings along with the
technical basis for the settings to the Planning Coordinator.
13.3
Each Planning Coordinator in Ontario, Québec and the Maritime
Provinces shall arrange for compensatory load shedding, in accordance
with Attachment A and as provided by a Distribution Provider or
Transmission Owner, that is adequate to compensate for the loss of
generator(s) due to early tripping that is within the UFLS island identified
by the Planning Coordinator in Requirement R2.
13.4
Each Generator Owner in the ISO‐NE Planning Coordinator area and in
NYISO Planning Coordinator area shall arrange for compensatory load
shedding, in accordance with Attachment B and as provided by a
Distribution Provider or Transmission Owner, that is adequate to
compensate for the loss of generator(s) due to early tripping that is
within the UFLS island identified by the Planning Coordinator in
Requirement R2.
M13. Each Generator Owner with existing non‐nuclear units in service prior to July 1, 2015
which have underfrequency tripping that is not compliant with Requirement R10 shall
provide evidence such as reports, spreadsheets, memorandum or dated
documentation demonstrating that it meets Requirement R13.
R14. Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the criteria described in Attachment A to determine the compensatory load shedding
that is required in Requirement R13.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M14. Each Planning Coordinator in Ontario, Quebec and Maritime provinces shall provide
evidence such as reports, memorandum or other documentation that demonstrates
that it followed the methodology described in Attachment A and meets Requirement
R14.
R15. Each Generator Owner, Distribution Provider or Transmission Owner within the ISO‐
NE Planning Coordinator area and in NYISO Planning Coordinator Area shall apply the
criteria described in Attachment B to determine the compensatory load shedding that
PRC‐006‐NPCC‐2
Page 7 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
is required in Requirement R13.4 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
M15. Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO‐NE or the NYISO shall provide evidence such as
reports, memorandum, or other documentation that demonstrates that it followed
the methodology described in Attachment B and meets Requirement R15.
R16. Each Generator Owner of existing nuclear generating plants with units that have
underfrequency relay threshold settings above the Eastern Interconnection generator
tripping curve in Figure 2 based on their licensing design shall: [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
16.1
Set the underfrequency protection to operate at a frequency setting that
is as low as possible in accordance with the plant design and licensing
limitations but not greater than 57.8 Hz.
16.2
Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.
16.3
Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.
M16. Each Generator Owner of nuclear units that have generator trip settings above the
generator trip curve in Figure 2 shall provide evidence such as letters, reports and
dated documentation that demonstrates that it meets Requirement R16.
PRC‐006‐NPCC‐2
Page 8 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Figure 1
Curve Data:
Overfrequency Requirements
t≤4s
f = 61.8 Hz
4 s < t ≤ 30 s
f = -0.686log(t) + 62.21 Hz
t > 30 s
f = 60.7 Hz
Underfrequency Requirements
t≤2s
f = 58.0 Hz
2 s < t ≤ 30 s
f = 0.575log(t) + 57.83 Hz
t > 30 s
f = 59.5 Hz
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
Source
NERC PRC-006 (Continent-Wide Standard on UFLS)
NERC PRC-006-NPCC (Regional Standard on UFLS)
PRC‐006‐NPCC‐2
Page 9 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Figure 2
PRC‐006‐NPCC‐2
Underfrequency Load Shedding Program – Thresholds for Setting Underfrequency
Trip Protection for Generators
Figure 2
Thresholds for Setting Underfrequency Trip Protection for Generators
Frequency (Hz)
60
59.5
59
58.5
58
57.5
57
56.5
56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping
0.1
PRC‐006‐NPCC‐2
1
10
100
1000
55.5
55
10000
Time (sec)
Page 10 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
C. Compliance
1.
Compliance Monitoring Process
1.1. Compliance Enforcement Authority:
Northeast Power Coordinating Council
1.2. Evidence Retention:
The Distribution Provider and Transmission Owner shall keep evidences for three
calendar years for Measures 2, 3, 4, 5, 8, and 9.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 5, 6, and 7.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measures 15.
The Generator Owner shall keep evidence for three calendar years for Measures
10, 11, 12, 13, and 16.
1.3. Compliance Monitoring and Enforcement Program:
Compliance Audit
Self‐Certification
Spot Checking
Compliance Violation Investigation
Self‐Reporting
Complaints
PRC‐006‐NPCC‐2
Page 11 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Violation Severity Levels
Violation Severity Levels
R#
Lower VSL
Moderate VSL
High VSL
Severe VSL
R1.
N/A
N/A
N/A
The Planning Coordinator failed to
design an UFLS program having
performance characteristics that
prevent frequency from remaining
below 59.5 Hz in accordance with
Figure 1.
R2.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent‐
wide PRC‐006 Standard on UFLS
but did so more than 30 calendar
days and up to and including 40
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent‐
wide PRC‐006 Standard on UFLS
but did so more than 40 calendar
days but less than and including 50
days following a request.
The Planning Coordinator provided
its UFLS island boundaries, as
identified per the NERC continent‐
wide PRC‐006 Standard on UFLS
but did so more than 50 calendar
days but less than and including 60
days following a request.
The Planning Coordinator failed to
provide its UFLS island boundaries,
as identified per the NERC
continent‐wide PRC‐006 Standard
on UFLS. within 60 calendar days
following a request.
R3.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%
or less of the relays identified as
included in the UFLS program, or
amount of load tripped is within
10% deviation from the required
amount of Load required to be
shed at each stage
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 20%‐
40% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
20% deviation from the required
amount of Load required to be
shed at each stage m
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on 40%‐
60% of the relays identified as
included in the UFLS program, or
amount of load tripped is within
30% deviation from the required
amount of Load required to be
shed at each stage.
The Distribution Provider or
Transmission Owner failed to
apply appropriate settings on >
60% of the relays identified as
included in the UFLS program, or
amount of load tripped has a >
30% deviation from the required
amount of Load required to be
shed at each stage
R4.
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations for
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program fulfilled its obligations
but exceeded the permissible
PRC‐006‐NPCC‐1
October 2018
The Distribution Provider or
Transmission Owner that cannot
meet the tolerances and/or
number of stages and frequency
set points specified in the UFLS
Program failed to meet all of items
in Requirement 5 within 60
Page 12 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items by a period of
up to 10 calendar days but less
than or equal to 20 calendar days.
Requirement R5, Parts %.1
through Part 5.4 but exceeded the
permissible time frame for one or
more of the 4 items within a time
greater than 20 calendar days but
less than or equal to 30 calendar
days.
R5.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
100% but more than (and
including) 95% of relays within its
region’s UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
95% but more than (and including)
90% of relays within its region’s
UFLS program.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
90% but more than (and including)
85% of relays within its region’s
UFLS program.
R6.
The Planning Coordinator
provided to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 30 calendar days and up to
and including 40 calendar days of
any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 40 calendar days but less
than and including 50 calendar
days of any changes.
The Planning Coordinator provided
to a Transmission Owner or
Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds more
than 50 calendar days but less
than and including 60 calendar
days of any changes.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 calendar days
and up to and including 100
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 100 calendar days
and up to and including 110
calendar days following the
request.
The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 calendar days
and up to and including 120
calendar days following the
request.
Implemented the inhibit threshold
settings provided by the Planning
Coordinator in accordance with
the Planning Coordinator
approved implementation plan for
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
R7.
R8.
PRC‐006‐NPCC‐1
October 2018
time frame for one or more of the calendar days of permissible time
4 items within a time greater than for each item.
30 calendar days but less than or
equal to 60 calendar days.
The Planning Coordinator
developed or reviewed settings for
inhibit thresholds at least once per
five calendar years, for less than
85% of relays within its region’s
UFLS program.
The Planning Coordinator failed to
provide to a Transmission Owner
or Distribution Provider within its
Planning Coordinator area the
applicable inhibit thresholds
within 60 calendar days after any
changes
The Distribution Provider or
Transmission Owner failed to
develop and submit its
implementation plan within 120
days following the request.
The Distribution Provider or
Transmission Owner implemented
the inhibit threshold settings
provided by the Planning
Coordinator in accordance with
Page 13 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
R9.
less than 100% but more than (and the Planning Coordinator
including) 95% of UFLS relays.
approved implementation plan for
less than 95% but more than (and
including) 90% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 90% but more than (and
including) 85% of UFLS relays.
the Planning Coordinator
approved implementation plan for
less than 85% of UFLS relays.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 15 calendar
months but less than (and
including) 16 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 16 calendar
months but less than (and
including)17 calendar months
since last update.
The Distribution Provider or
Transmission Owner provided to
its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 more than 17 calendar
months but less than (and
including)18 calendar months
since last update.
The Distribution Provider or
Transmission Owner failed to
provide to its Planning Coordinator
documentation of the actual net
Load that would have been shed
by the UFLS relays at each UFLS
stage as described in Requirement
R11 within 18 calendar months
since last update.
N/A
N/A
R10. N/A
The Generator Owner did not set
each generator underfrequency
trip relay, if so equipped, on or
below the appropriate generator
underfrequency trip protection
settings threshold curve in Figure
2, except as otherwise exempted.
R11. The Generator Owner transmitted The Generator Owner transmitted The Generator Owner transmitted The Generator Owner failed to
the generator underfrequency trip
setting and time delay more than
45calendar days and less than (and
including) 55 calendar days of the
Planning Coordinator’s request.
R12. N/A
PRC‐006‐NPCC‐1
October 2018
the generator underfrequency trip
setting and time delay more than
55 calendar days and less than
(and including) 65 calendar days of
the Planning Coordinator’s
request.
N/A
the generator underfrequency trip
setting and time delay more than
65 calendar days and less than
(and including) 75 calendar days of
the Planning Coordinator’s
request.
transmit the generator
underfrequency trip setting and
time delay within 75 calendar days
of the Planning Coordinator’s
request.
The Generator Owner with a new
generating unit, or an existing
The Generator Owner with a new
generating unit, or an existing
generator increasing its net
Page 14 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
generator increasing its net
capability by greater than 10%:
Did not fulfill the obligation of
Requirement R12; Part 12.1
OR
capability by greater than 10%, did
not fulfill the obligations of
Requirement R12, Part 12.1 and
Part 12.2.
Did not fulfill the obligation of
Requirement R12, Part 12.2.
R13. N/A
The Generator Owner failed to
transmit the existing
underfrequency settings and any
changes to the underfrequency
settings along with the technical
basis for the settings to the
Planning Coordinatoras specified
in Requirement R13, Part 13.2.
The Generator Owner failed to set
the underfrequency protection to
operate at the lowest frequency
allowed by the plant design and
licensing limitations a specified in
Requirement 13, Part 13.1
The Planning Coordinator in
Ontario, Québec and the Maritime
Provinces or the Generator Owner
within the ISO‐NE and in NYISO
Planning Coordinator areas failed
to arrange for compensatory load
shedding as specified in
Requirement R13, Part 13.3.
R14. N/A
N/A
N/A
The Planning Coordinator did not
apply the criteria described in
Attachment A to determine the
compensatory load shedding that
is required.
R15. N/A
N/A
N/A
The Generator Owner, Distribution
Provider, or Transmission Owner
did not apply the criteria described
in Attachment B to determine the
compensatory load shedding that
is required.
R16. N/A
The Generator Owner failed to
transmit the initial frequency trip
setting and any changes to the
setting and the technical basis for
the settings to the Planning
The Generator Owner:
The Generator Owner did not
fulfill the obligations of
Requirement R16, Part 16.1 and
Part 16.2.
PRC‐006‐NPCC‐1
October 2018
Failed to set the underfrequency
protection as specified in
Requirement R16; Part 16.1
OR
Page 15 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Coordinator as specified in
Requirement R16, Part 16.3.
Failed to set the frequency trip
setting upper tolerance as
specified in Requirement R16, Part
16.2.
D. Regional Variances
None.
E. Associated Documents
Technical Rationale
PRC‐006‐NPCC‐1
October 2018
Page 16 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Version History
Version
Date
Action
Change
Tracking
1
2‐9‐2012
Adopted by Board of Trustees
2
6‐23‐2015
RSAR Submitted
PRC‐006‐NPCC‐1
October 2018
Page 17 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Standard Attachments
PRC‐006‐NPCC‐2 Attachment A
Compensatory Load Shedding Criteria for Ontario, Quebec, and the Maritime Provinces:
The Planning Coordinator in Ontario, Quebec and the Maritime provinces is responsible for
establishing the compensatory load shedding requirements for all existing non‐nuclear units in
its NPCC area with underfrequency protections set to trip above the appropriate curve in Figure
2. In addition, it is the Planning Coordinator’s responsibility to communicate these
requirements to the appropriate Distribution Provider or Transmission Owner and to ensure
that adequate compensatory load shedding is provided in all UFLS islands in which the unit may
operate.
The methodology below provides a set of criteria for the Planning Coordinator to follow for
determining compensatory load shedding requirements as part of its UFLS Assessment based
on the NERC PRC Standard on UFLS:
1. The Planning Coordinator shall identify, compile and maintain a list of all existing non‐
nuclear generating units in their Planning Coordinator area that were in service prior to
the effective date of the regional Standard (July 1, 2015 PRC‐006‐NPCC‐1). The list must
indicate generating units, if any, that have their underfrequency protections set to trip
above the appropriate curve in Figure 2. Generating Units not appearing on the list as of
the effective date of Version 1 of the regional standard, as shown above, must have
their Underfrequency protections set to trip on or below the appropriate curve in Figure
2. The list shall include the following information for each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 All islands within which the unit may operate
2. For each generating unit identified in (1) above, the Planning Coordinator shall establish
the requirements for compensatory load shedding based on criteria outlined below:
2.1 Arrange for a Distribution Provider or Transmission Owner that owns UFLS relays
within the island(s) identified by the Planning Coordinator within which the
generator may operate to provide compensatory load shedding.
2.2 In Ontario and in the Maritime provinces, the compensatory load shedding that
is provided by the Distribution Provider or Transmission Owner shall be in
PRC‐006‐NPCC‐1
October 2018
Page 18 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
addition to the amount that the Distribution Provider or Transmission Owner is
required to shed as specified in Requirement R4.
2.3 The compensatory load shedding shall be provided at the UFLS program stage
(or threshold stage for Quebec) with a frequency threshold setting that
corresponds to the highest frequency at which the subject generator will trip
above the appropriate curve in Figure 2 during an underfrequency event. If the
highest frequency at which the subject generator will trip above the appropriate
curve in Figure 2 does not correspond to a specific UFLS program stage threshold
setting, the compensatory load shedding shall be provided at the UFLS program
stage with a frequency threshold setting that is higher than the highest
frequency at which the subject generator will trip above the appropriate curve in
Figure 2.
2.4 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the electric system
for less than two calendar years, the amount of compensatory load shedding shall be
equivalent (±5%) to the maximum claimed seasonal capability of the generator over two
calendar years, plus expected station loads to be transferred to the system upon loss of the
facility.
PRC‐006‐NPCC‐1
October 2018
Page 19 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
PRC‐006‐NPCC‐2 Attachment B
Compensatory Load Shedding Criteria for ISO‐NE and NYISO:
The Generator Owner in the New England states or New York State are responsible for
establishing a compensatory load shedding program for all existing non‐nuclear units with
underfrequency protection set to trip above the appropriate curve in Figure 2 of this standard.
The Generator Owner shall follow the methodology below to determine compensatory load
shedding requirements:
1. The Generator Owner shall identify, compile, and maintain a list of all of its existing non‐
nuclear generating units that were in service prior to the effective date of the regional
Standard (July 1, 2015 PRC‐006‐NPCC‐1). The list must indicate the Generator Owner’s
generating units, if any, which have their underfrequency protections set to trip above
the appropriate curve in Figure 2. Generating Units not appearing on the list as of the
effective date of Version 1 of the regional standard, as shown above, must have their
Underfrequency protections set to trip on or below the appropriate curve in Figure 2.
The list shall include the following information associated with each unit:
1.1 Generator name and generating capacity
1.2 Underfrequency protection trip settings, including frequency trip set points and
time delays
1.3 Physical and electrical location of the unit
1.4 Smallest island within which the unit may operate as identified by the Planning
Coordinator in Requirement R1 of this Standard.
2. For each generating unit identified in (1) above, the Generator Owner shall establish the
requirements for compensatory load shedding based on criteria outlined below:
2.1 In cases where a Distribution Provider or Transmission Owner has coordinated
protection settings with the Generator Owner to cause the generator to trip
above the appropriate curve in Figure 2, the Distribution Provider or
Transmission Owner is responsible to provide the appropriate amount of
compensatory load to be shed within the same and smallest island identified by
the Planning Coordinator in Requirement R1 of this standard.
2.2 In cases where a Generator Owner has a generator that cannot physically meet
the set points defined by the appropriate curve in Figure 2, the Generator Owner
shall arrange for a Distribution Provider or Transmission Owner to provide the
appropriate amount of compensatory load to be shed within the same and
smallest island identified by the Planning Coordinator in Requirement R1 of this
standard.
PRC‐006‐NPCC‐1
October 2018
Page 20 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
2.3 The compensatory load shedding that is provided by the Distribution Provider or
Transmission Owner shall be in addition to the amount that the Distribution
Provider or Transmission Owner is required to shed as specified in Requirement
R4.
2.4 The compensatory load shedding shall be provided at the UFLS program stage
with the frequency threshold setting at or closest to but above the frequency at
which the subject generator will trip.
2.5 The amount of compensatory load shedding shall be equivalent (±5%) to the
average net generator megawatt output for the prior two calendar years, as
specified by the Planning Coordinator, plus expected station loads to be
transferred to the system upon loss of the facility. The net generation output
should only include those hours when the unit was a net generator to the
electric system.
In the specific instance of a generating unit that has been interconnected to the
electric system for less than two calendar years, the amount of compensatory
load shedding shall be equivalent (±5%) to the maximum claimed seasonal
capability of the generator over two calendar years, plus expected station loads
to be transferred to the system upon loss of the facility.
PRC‐006‐NPCC‐1
October 2018
Page 21 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
PRC‐006‐NPCC‐2 Attachment C
UFLS Table 1: Eastern Interconnection
Distribution Providers and Transmission Owners with 100 MW2 or more of peak net Load
shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
6.5 – 7.5
6.5 – 7.5
2
59.3
0.10
0.30
6.5 – 7.5
13.5 – 14.5
3
59.1
0.10
0.30
6.5 – 7.5
20.5 – 21.5
4
58.9
0.10
0.30
6.5 – 7.5
27.5 – 28.5
5
59.5
0.10
10.0
2 ‐ 3
29.5 – 31.5
UFLS Table 2: Eastern Interconnection
Distribution Providers and Transmission Owners with 50 MW2 or more and less than 100
MW2 of peak net Load shall implement a UFLS program with the following attributes:
UFLS Stage
Frequency
Minimum
Total
Load Shed at Cumulative
Threshold
Relay Time
Nominal
Stage as % of Load Shed as
(Hz)
Delay (s)
Operating
TO or DP
% of TO or
1
Time (s)
Load
DP Load
1
59.5
0.10
0.30
14 – 25
14 – 25
2
59.1
0.10
0.30
14 – 25
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
PRC‐006‐NPCC‐1
October 2018
Page 22 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
UFLS Table 3: Eastern Interconnection
Distribution Providers and Transmission Owners with 25 MW2 or more and less than 50 MW2
of peak net Load shall implement a UFLS program with the following attributes:
Load Shed at Cumulative
UFLS Stage
Frequency
Minimum
Total
Stage as % of Load Shed as
Threshold
Relay Time
Nominal
TO or DP
% of TO or
(Hz)
Delay (s)
Operating
1
Load
DP Load
Time (s)
1
59.5
0.10
0.30
28 – 50
28 – 50
1.
The total nominal operating time includes the underfrequency relay operating time plus any interposing
auxiliary relay operating times, communication times, and the rated breaker interrupting time. The
underfrequency relay operating time is measured from the time when frequency passes through the
frequency threshold setpoint, using a test rate of frequency decay of 0.2 Hz per second. If the relay operating
time is dependent on the rate of frequency decay, the underfrequency relay operating time and any
subsequent testing of the UFLS relays shall utilize a test rate of linear frequency decay of 0.2 Hz per second.
2.
Peak net load shall be calculated as an average of the peak net load from the previous 3 years, excluding the
current year.
PRC‐006‐NPCC‐1
October 2018
Page 23 of 24
PRC‐006‐NPCC‐2 – Automatic Underfrequency Load Shedding
Rationale Box:
Standard PRC‐006‐3, R4 requires the Planning Coordinator to conduct a UFLS assessment at
least once every five years. However, aside from a UFLS islanding event, it does not prescribe
other factors or events which could warrant a new UFLS assessment in less than the five years
time‐frame.
PRC‐006‐NPCC‐01 contained requirements if changes to load distribution impacted UFLS
program performance (R21) but did not consider many other factors. The drafting team
recommends retiring these requirements (R21, R22, R23) and replacing them with the following
guidance.
Significant variations in the following factors could require a Planning Coordinator to conduct a
new assessment:
Changes to the BES that could modify the creation of islands or the severity of events
such as new transmission topologies, revised protection schemes or new or revised RAS.
Unforeseen islanding event
Real and reactive load distribution (including changes to location of compensatory load
shedding)
Transmission Owner or Distribution Provider’s inability to implement the UFLS program
within the stated tolerances
Load characteristics in particular frequency responsive load
Automatic load restoration
Generation geographical distribution
Generator trip settings
Generation mix in particular non‐BES generation that may not be subject to frequency
ride‐through criteria
Generator dynamic modeling
Dynamic VAR device modeling
HVDC dynamic modeling
PRC‐006‐NPCC‐1
October 2018
Page 24 of 24
Date:
May 2, 2019
To:
Mr. Howard Gugel
Vice President of Engineering and Standards
From:
Mr. Guy V. Zito
Assistant Vice President – Standards
Chair, Regional Standards Committee
Subject:
NPCC Regional Standard, PRC-006-NPCC-02 “Automatic
Underfrequency Load Shedding” for NERC BOT Consideration
and Adoption
In this transmittal, please find a clean version of the subject Regional Standard and the proposed
Implementation Plan. This represents a revision to the existing FERC approved PRC-006NPCC-1 Regional Standard and was completed in accordance with the FERC approved NPCC
Regional Standard Processes Manual by a drafting team of NPCC subject matter experts who
perform, or are involved with analysis of, the UFLS studies in the Region.
The Standard was posted for three industry comment periods and a pre-ballot review. A ballot
was then conducted which closed at 23:59 PM on February 10th, 2019 achieving a 96% approval
with 81% quorum.
On May 1, 2019 the NPCC Board of Directors approved, PRC-006-NPCC-02. A full
developmental record for the standard, including a mapping document detailing changes from
the existing FERC approved version of the standard requirements to this revised version, may be
found at:
NPCC Automatic Underfrequency Load Shedding Regional Standard Development Page
A summary of the revisions to the previous version of the standard is as follows:
1) Remove redundancies with the most recent of the Continent-wide NERC Standard, PRC006-3. Some of the redundancies removed from the Regional Standard PRC-006-NPCC2 are those related to:
The Québec Interconnection portion of NPCC shall implement an automatic UFLS
program in accordance with Attachment C Table 4
Requirements for a UFLS Database
Notification of changes to load distribution needed to satisfy UFLS program
performance characteristics
Development of an implementation plan when changes to load distribution are needed
2) Ensure that UFLS island boundaries, once identified, are provided upon request, to
affected entities.
3) Minimum time UFLS relay time delay added to Attachment C tables and removed as a
separate requirement
4) Added the ability for a TO or DP to calculate net load shed for UFLS if direct metering is
not available
5) A number of minor clarifications were made to the standard such as requiring the
Underfrequency trip relay must to be set to operate “on or below” the appropriate curve.
In Version 1 it currently states below and questions arose whether settings on the curve
were considered in compliance.
6) Clarification that any compensatory load shedding for non-conformance with the
Underfrequency trip specification for generation (in service prior to July 1, 2015) must be
within the same island as the generator resides.
NPCC hereby requests that the NPCC Regional Standard PRC-006-NPCC-02, “Automatic
Underfrequency Load Shedding the PRC-006-NPCC-2 be submitted to the NERC Board of
Trustees for their consideration and adoption at their August 15, 2019 meeting.
Please contact me if you have further questions or need additional information.
Updated
Regional Reliability Standards
Announcement
Northeast Power Coordinating Council
PRC-006-NPCC-2
Comment Period Open through June 21, 2019
Now Available
The Northeast Power Coordinating Council, Inc. (NPCC) requested that NERC post Regional Reliability
Standard PRC-006-NPCC-2 – Automatic Underfrequency Load Shedding for industry review and
comment in accordance with the NERC Rules of Procedure.
Background
The NPCC drafting team reviewed Regional Reliability Standard PRC-006-NPCC-1. The revisions made
to PRC-006-NPCC-1 can be found in the Summary of Changes.
Commenting
Use the Standards Balloting and Commenting System (SBS) to submit comments. If you experience any
difficulties using the electronic form, contact Nasheema Santos. The form must be submitted by 8 p.m.
Eastern, Friday, June 21, 2019. An unofficial Word version of the comment form is posted on the
Regional Reliability Standards Under Development page.
Regional Reliability Standards Development Process
Section 300 of NERC’s Rules of Procedures of the Electric Reliability Organization governs the regional
reliability standards development process. Although the technical aspects of this Regional Reliability
Standard have been vetted through NPCC’s Regional Standards development process, the final
approval process for a Regional Reliability Standard requires NERC publicly to notice and request
comment on the criteria outlined in the unofficial comment form.
Documents and information about this project are available on the NPCC’s Standards In Development
page.
For more information or assistance, contact Senior Reliability Standards Analyst, Nasheema Santos (via
email) or at (404) 446-2564.
North American Electric Reliability Corporation
3353 Peachtree Rd, NE
Suite 600, North Tower
Atlanta, GA 30326
404-446-2560 | www.nerc.com
Exhibit E
Standard Drafting Team Roster
1
DRAFTING TEAM--RSAR PRC-006-NPCC-02
1
2
3
4
5
6
7
8
9
9/28/15
Self-Nominations
Dan Taft
Jonathan Appelbaum (Resigned
from United Illuminating)
Tim Kucey (Resigned from
drafting team)
Vincent Morissette
Dean Latulipe
Brian Robinson--RSAR Requester
Hamid Hamadani
Daniel Kidney
Ruida Shu
Consolidated Edison Company of New York
The United Illuminating Company
PSEG Fossil LLC
Hydro-Québec TransÉnergie
National Grid
Utility Services, Inc.
Hydro One Networks, Inc.
NPCC Compliance Staff
NPCC Standards Staff
Exhibit F
Violation Risk Factor and Violation Severity Level Justification
Exhibit F
Violation Risk Factor and Violation Severity Level Justification
The modifications in proposed Regional Reliability Standard PRC-006-NPCC-2 are
extensive and best understood by reviewing the Summary of Changes and the NPCC mapping
document, both in Exhibit D. These modifications have resulted in some changes to the
Violation Risk Factors (VRFs) and Violation Severity Levels (VSLs) as compared to the current
version of the Regional Reliability Standard PRC-006-NPCC-1. The Standard Drafting Team
(SDT) considered the NERC Criteria for VRFs and the FERC Guidelines for VRFs and the
NERC Criteria for VSLs and the FERC Order of VSLs when developing the VRFs and VSLs for
the proposed Regional Reliability Standard.
1. PRC-006-NPCC-2 Requirement R1. Proposed Requirement R1 replaces in part
currently effective PRC-006-NPCC-1 Requirement R2, the substance of which is now
addressed by proposed Requirements R1, R2, and R3.
VRF Justification: The justification for the VRF is provided in the table below.
VRF Justifications for PRC-006-NPCC-2 Requirement R1
Proposed VRF
High
VRF Discussion
A VRF of “High” is being proposed for
this Requirement.
A VRF of “High” is appropriate because
the proposed Requirement is associated
with the design of an UFLS program
pertaining to islands within the NPCC
region, having performance characteristics
that prevents the frequency from
remaining below 59.5 Hz for more than
30 seconds. If violated, this Requirement
in the planning timeframe could, under
emergency, abnormal, or restorative
conditions anticipated by the preparations,
1
VRF Justifications for PRC-006-NPCC-2 Requirement R1
directly cause or contribute to Bulk
Electric System instability, separation, or
a cascading sequence of failures, place the
Bulk Electric System at an unacceptable
risk of instability, separation, or cascading
failures, or could hinder restoration to a
normal condition.
FERC VRF Guideline 1
Consistency with Blackout Report
Emergency operations, protection systems
and their coordination, system modeling
and data exchange, and clearer criteria for
operationally critical facilities
FERC VRF Guideline 2
Consistency within a Reliability Standard
Not applicable. There are no subRequirement VRFs in the Regional
Reliability Standard.
FERC VRF Guideline 3
Consistency among Reliability Standards
The proposed VRF is consistent with
other FERC-approved VRFs in different
Reliability Standards that address similar
reliability goals. Specifically, the
proposed VRF of “High” is consistent
with the VRF of “High” in PRC-006-3
Requirement R3, which requires the
development of a UFLS program.
FERC VRF Guideline 4
Consistency with NERC Definition of
VRFs
FERC VRF Guideline 5
Treatment of Requirements that comingle
more than one obligation
The team relied on NERC’s definition of a
high risk requirement.
Not applicable. The Requirement does
not comingle a higher risk reliability
objective with a lower risk reliability
objective.
VSL Justification: The justification for the VSL is provided in the table below.
VSL Justifications for PRC-006-NPCC-2 Requirement R1
FERC VSL Guideline 1
Violation Severity Level assignments
should not have the unintended
consequence of lowering the current level
of compliance
2
The proposed Requirement is new and has
a single VSL of “Severe.” Therefore, the
proposed VSLs do not have the
unintended consequence of lowering the
level of compliance.
VSL Justifications for PRC-006-NPCC-2 Requirement R1
FERC VSL Guideline 2
Violation Severity Level assignments
should ensure uniformity and consistency
in the determination of penalties
Guideline 2a: A violation of a “binary”
type requirement must be a “Severe” VSL
Guideline 2b: Do not use ambiguous
terms to describe noncompliant
performance
FERC VSL Guideline 3
Violation Severity Level assignment
should be consistent with the
corresponding Requirement
The proposed VSL is “Severe” as required
for a “binary” type requirement and does
not use any ambiguous terminology,
thereby supporting uniformity and
consistency in the determination of similar
penalties for similar violations.
FERC VSL Guideline 4
Violation Severity Level assignment
should be based on a single violation, not
a cumulative number of violations
Each VSL is based on a single violation
and not cumulative violations.
The proposed VSLs use the same
terminology as used in the associated
Requirement and are, therefore, consistent
with the Requirement.
2. PRC-006-NPCC-2 Requirement R2. Proposed Requirement R2 carries forward
currently effective PRC-006-NPCC-1 Requirement R3 largely unchanged, keeping the
requirement to provide information about UFLS island boundaries to affected entities
while moving the requirements regarding compensator load shedding to proposed
Requirement R13. Aspects of currently effective PRC-006-NPCC-1 Requirements R1
and R2 were incorporated into proposed Requirement R2 as well.
VRF Justification: The justification for the VRF is in the table below.
VRF Justifications for PRC-006-NPCC-2 Requirement R2
Proposed VRF
Lower
VRF Discussion
A VRF of “Lower” is being proposed for
this Requirement.
A VRF of “Lower” is appropriate because
the proposed Requirement is
administrative in nature and is associated
with providing UFLS island boundaries to
relevant entities within 30 calendar days
3
VRF Justifications for PRC-006-NPCC-2 Requirement R2
of receipt of a request. If violated, this
Requirement in the planning timeframe
would not, under the emergency,
abnormal, or restorative conditions
anticipated by the preparations, be
expected to adversely affect the electrical
state or capability of the Bulk Electric
System, or the ability to effectively
monitor, control, or restore the Bulk
Electric System.
FERC VRF Guideline 1
Consistency with Blackout Report
Emergency operations, protection systems
and their coordination, system modeling
and data exchange, and clearer criteria for
operationally critical facilities
FERC VRF Guideline 2
Consistency within a Reliability Standard
Not applicable. There are no subRequirement VRFs in the Regional
Reliability Standard.
FERC VRF Guideline 3
Consistency among Reliability Standards
The proposed VRF is consistent with
other FERC-approved VRFs in different
Reliability Standards that address similar
reliability goals. Specifically, the
proposed VRF of “Lower” is consistent
with the VRF of “Lower” in PRC-006-3
Requirement R7, which requires relevant
entities to provide information to other
entities within 30 calendar days of a
request.
FERC VRF Guideline 4
Consistency with NERC Definition of
VRFs
FERC VRF Guideline 5
Treatment of Requirements that comingle
more than one obligation
The team relied on NERC’s definition of a
lower risk requirement.
Not applicable. The Requirement does
not comingle a higher risk reliability
objective with a lower risk reliability
objective.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
4
3. PRC-006-NPCC-2 Requirement R3. Proposed Requirement R3 replaces in part
currently effective PRC-006-NPCC-1 Requirement R1, the substance of which is now
addressed by the proposed Requirements R2, R3, and R13, and also replaces in part the
currently effective PRC-006-NPCC-1 Requirement R2, the substance of which is now
addressed by the proposed Requirements R1, R2, and R3.
VRF Justification: The justification for the VRF is in the table below.
VRF Justifications for PRC-006-NPCC-2 Requirement R3
Proposed VRF
High
VRF Discussion
A VRF of “High” is being proposed for
this Requirement.
A VRF of “High” is appropriate because
the proposed Requirement is associated
with implementation of an automatic
UFLS program on an island basis. If
violated, this Requirement in the planning
timeframe could, under emergency,
abnormal, or restorative conditions
anticipated by the preparations, directly
cause or contribute to Bulk Electric
System instability, separation, or a
cascading sequence of failures, place the
Bulk Electric System at an unacceptable
risk of instability, separation, or cascading
failures, or could hinder restoration to a
normal condition.
FERC VRF Guideline 1
Consistency with Blackout Report
Emergency operations, protection systems
and their coordination, system modeling
and data exchange, and clearer criteria for
operationally critical facilities
FERC VRF Guideline 2
Consistency within a Reliability Standard
Not applicable. There are no subRequirement VRFs in the Regional
Reliability Standard.
FERC VRF Guideline 3
Consistency among Reliability Standards
The proposed VRF is consistent with
other FERC-approved VRFs in different
Reliability Standards that address similar
reliability goals. Specifically, the
proposed VRF of “High” is consistent
5
VRF Justifications for PRC-006-NPCC-2 Requirement R3
with the VRF of “High” in PRC-006-3
Requirement R9, which requires
automatic tripping of Load in accordance
with the UFLS program design and
schedule for implementation.
FERC VRF Guideline 4
Consistency with NERC Definition of
VRFs
FERC VRF Guideline 5
Treatment of Requirements that comingle
more than one obligation
The team relied on NERC’s definition of a
high risk requirement.
Not applicable. The Requirement does
not comingle a higher risk reliability
objective with a lower risk reliability
objective.
VSL Justification: The justification for the VSL is provided in the table below.
VSL Justifications for PRC-006-NPCC-2 Requirement R3
FERC VSL Guideline 1
Violation Severity Level assignments
should not have the unintended
consequence of lowering the current level
of compliance
The proposed Requirement is a reworking
of several requirements from the currently
effective Regional Reliability Standard,
with the VSLs based on the percentage of
relays in the UFLS program that entities
failed to apply appropriate settings or the
percentage deviation from the required
amount of Load to be shed at each stage
that was actually tripped. Therefore, the
proposed VSLs do not have the
unintended consequence of lowering the
level of noncompliance.
FERC VSL Guideline 2
Violation Severity Level assignments
should ensure uniformity and consistency
in the determination of penalties
Guideline 2a: A violation of a “binary”
type requirement must be a “Severe” VSL
Guideline 2b: Do not use ambiguous
terms to describe noncompliant
performance
FERC VSL Guideline 3
Violation Severity Level assignment
should be consistent with the
corresponding Requirement
The proposed VSLs are not binary and do
not use any ambiguous terminology,
thereby supporting uniformity and
consistency in the determination of similar
penalties for similar violations.
6
The proposed VSLs use the same
terminology as used in the associated
Requirement and are, therefore, consistent
with the Requirement.
VSL Justifications for PRC-006-NPCC-2 Requirement R3
FERC VSL Guideline 4
Violation Severity Level assignment
should be based on a single violation, not
a cumulative number of violations
Each VSL is based on a single violation
and not cumulative violations.
4. PRC-006-NPCC-2 Requirement R4. Proposed Requirement R4 combines currently
effective PRC-006-NPCC-1 Requirements R4 and R5 into a single new requirement and
clarifies what registered entities must do in the event they are unable to meet the UFLS
program parameters specified in the Tables of Attachment C or by its Planning
Coordinator, and in what timeframe the registered entities must take the defined actions.
VRF Justification: The VRF of “High” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
VSL Justification: The justification for the VSL is provided in the table below.
VSL Justifications for PRC-006-NPCC-2 Requirement R4
FERC VSL Guideline 1
Violation Severity Level assignments
should not have the unintended
consequence of lowering the current level
of compliance
The proposed Requirement is a
combination of two Requirements from
the currently effective Regional
Reliability Standard. Therefore, the
proposed VSLs do not have the
unintended consequence of lowering the
level of noncompliance.
FERC VSL Guideline 2
Violation Severity Level assignments
should ensure uniformity and consistency
in the determination of penalties
Guideline 2a: A violation of a “binary”
type requirement must be a “Severe” VSL
Guideline 2b: Do not use ambiguous
terms to describe noncompliant
performance
FERC VSL Guideline 3
Violation Severity Level assignment
should be consistent with the
corresponding Requirement
The proposed VSLs are not binary and do
not use any ambiguous terminology,
thereby supporting uniformity and
consistency in the determination of similar
penalties for similar violations.
7
The proposed VSLs use the same
terminology as used in the associated
Requirement and are, therefore, consistent
with the Requirement.
VSL Justifications for PRC-006-NPCC-2 Requirement R4
FERC VSL Guideline 4
Violation Severity Level assignment
should be based on a single violation, not
a cumulative number of violations
Each VSL is based on a single violation
and not cumulative violations.
5. PRC-006-NPCC-2 Requirement R5. Proposed Requirement R5 carries forward
currently effective PRC-006-NPCC-1 Requirement R8 largely unchanged, but
lengthens the periodicity of developing and reviewing settings for inhibit thresholds
from once per calendar year to once per five calendar years.
VRF Justification: The VRF of “Medium” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
VSL Justification: The justification for the VSL is provided in the table below.
VSL Justifications for PRC-006-NPCC-2 Requirement R5
FERC VSL Guideline 1
Violation Severity Level assignments
should not have the unintended
consequence of lowering the current level
of compliance
The proposed Requirement lengthens the
periodicity of reviewing inhibit
thresholds, while the proposed VSLs are
based on the percentage of relays that
were not included in the development or
review of inhibit threshold settings during
the longer period. Therefore, the
proposed VSLs do not have the
unintended consequence of lowering the
level of noncompliance.
FERC VSL Guideline 2
Violation Severity Level assignments
should ensure uniformity and consistency
in the determination of penalties
Guideline 2a: A violation of a “binary”
type requirement must be a “Severe” VSL
Guideline 2b: Do not use ambiguous
terms to describe noncompliant
performance
FERC VSL Guideline 3
The proposed VSLs are not binary and do
not use any ambiguous terminology,
thereby supporting uniformity and
consistency in the determination of similar
penalties for similar violations.
8
The proposed VSLs use the same
terminology as used in the associated
VSL Justifications for PRC-006-NPCC-2 Requirement R5
Violation Severity Level assignment
should be consistent with the
corresponding Requirement
FERC VSL Guideline 4
Violation Severity Level assignment
should be based on a single violation, not
a cumulative number of violations
Requirement and are, therefore, consistent
with the Requirement.
Each VSL is based on a single violation
and not cumulative violations.
6. PRC-006-NPCC-2 Requirement R6. Proposed Requirement R6 carries forward
currently effective PRC-006-NPCC-1 Requirement R9 substantively unchanged,
clarifying matters by removing language about initial determination of inhibit thresholds
that is no longer needed.
VRF Justification: The justification for the VRF is in the table below.
VRF Justifications for PRC-006-NPCC-2 Requirement R6
Proposed VRF
Lower
VRF Discussion
A VRF of “Lower” is being proposed for
this Requirement.
A VRF of “Lower” is appropriate because
the proposed Requirement is
administrative in nature and is associated
with providing relevant entities with
applicable inhibit thresholds within 30
calendar days of a change. If violated,
this Requirement in the planning
timeframe would not, under the
emergency, abnormal, or restorative
conditions anticipated by the preparations,
be expected to adversely affect the
electrical state or capability of the Bulk
Electric System, or the ability to
effectively monitor, control, or restore the
Bulk Electric System.
Emergency operations, protection systems
and their coordination, system modeling
and data exchange, and clearer criteria for
operationally critical facilities
FERC VRF Guideline 1
Consistency with Blackout Report
9
VRF Justifications for PRC-006-NPCC-2 Requirement R6
FERC VRF Guideline 2
Consistency within a Reliability Standard
Not applicable. There are no subRequirement VRFs in the Regional
Reliability Standard.
FERC VRF Guideline 3
Consistency among Reliability Standards
The proposed VRF is consistent with
other FERC-approved VRFs in different
Reliability Standards that address similar
reliability goals. Specifically, the
proposed VRF of “Lower” is consistent
with the VRF of “Lower” in PRC-006-3
Requirement R14, which requires
Planning Coordinators to respond to
comments provided by UFLS entities and
Transmission Owners in its Planning
Coordinator area and indicate whether the
changes will be made or why changes will
not be made to the UFLS program.
FERC VRF Guideline 4
Consistency with NERC Definition of
VRFs
FERC VRF Guideline 5
Treatment of Requirements that comingle
more than one obligation
The team relied on NERC’s definition of a
lower risk requirement.
Not applicable. The Requirement does
not comingle a higher risk reliability
objective with a lower risk reliability
objective.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
7. PRC-006-NPCC-2 Requirement R7. Proposed Requirement R7 carries forward
currently effective PRC-006-NPCC-1 Requirement R11 substantively unchanged,
clarifying that the trigger for action is receipt of a notification pursuant to proposed
Requirement R6, and changing the requirement numbers that are referenced.
VRF Justification: The VRF of “Lower” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
10
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
8. PRC-006-NPCC-2 Requirement R8. Proposed Requirement R8 carries forward
currently effective Requirement R10 substantively unchanged, updating the requirement
numbers referenced and adding clarification that the Planning Coordinator provides the
inhibit thresholds and approves the implementation plan.
VRF Justification: The VRF of “High” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
VSL Justification: The justification for the VSL is provided in the table below.
VSL Justifications for PRC-006-NPCC-2 Requirement R8
FERC VSL Guideline 1
Violation Severity Level assignments
should not have the unintended
consequence of lowering the current level
of compliance
The proposed Requirement carries
forward a currently effective Requirement
substantively unchanged, while the
proposed VSLs are based on the
percentage of UFLS relays for which the
entity implemented the inhibit threshold
settings that were provided. Therefore,
the proposed VSLs do not have the
unintended consequence of lowering the
level of noncompliance.
FERC VSL Guideline 2
Violation Severity Level assignments
should ensure uniformity and consistency
in the determination of penalties
Guideline 2a: A violation of a “binary”
type requirement must be a “Severe” VSL
Guideline 2b: Do not use ambiguous
terms to describe noncompliant
performance
FERC VSL Guideline 3
Violation Severity Level assignment
should be consistent with the
corresponding Requirement
The proposed VSLs are not binary and do
not use any ambiguous terminology,
thereby supporting uniformity and
consistency in the determination of similar
penalties for similar violations.
11
The proposed VSLs use the same
terminology as used in the associated
Requirement and are, therefore, consistent
with the Requirement.
VSL Justifications for PRC-006-NPCC-2 Requirement R8
FERC VSL Guideline 4
Violation Severity Level assignment
should be based on a single violation, not
a cumulative number of violations
Each VSL is based on a single violation
and not cumulative violations.
9. PRC-006-NPCC-2 Requirement R9. Proposed Requirement R9 revises currently
effective PRC-006-NPCC-1 Requirement R12 by adding language that allows the
calculation of load from the nearest available metering rather than actual metering.
VRF Justification: The VRF of “Lower” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
VSL Justification: The justification for the VSL is provided in the table below.
VSL Justifications for PRC-006-NPCC-2 Requirement R9
FERC VSL Guideline 1
Violation Severity Level assignments
should not have the unintended
consequence of lowering the current level
of compliance
The proposed Requirement carries
forward a Requirement from the currently
effective Regional Reliability Standard
substantively unchanged, with the VSLs
based on how late the entity was in
providing the required documentation.
Therefore, the proposed VSLs do not have
the unintended consequence of lowering
the level of noncompliance.
FERC VSL Guideline 2
Violation Severity Level assignments
should ensure uniformity and consistency
in the determination of penalties
Guideline 2a: A violation of a “binary”
type requirement must be a “Severe” VSL
Guideline 2b: Do not use ambiguous
terms to describe noncompliant
performance
FERC VSL Guideline 3
Violation Severity Level assignment
should be consistent with the
corresponding Requirement
The proposed VSLs are not binary and do
not use any ambiguous terminology,
thereby supporting uniformity and
consistency in the determination of similar
penalties for similar violations.
FERC VSL Guideline 4
Each VSL is based on a single violation
and not cumulative violations.
12
The proposed VSLs use the same
terminology as used in the associated
Requirement and are, therefore, consistent
with the Requirement.
VSL Justifications for PRC-006-NPCC-2 Requirement R9
Violation Severity Level assignment
should be based on a single violation, not
a cumulative number of violations
10. PRC-006-NPCC-2 Requirement R10. Proposed Requirement R10 carries forward
currently effective PRC-006-NPCC-1 Requirement R13 substantively unchanged, but
clarifies that the Underfrequency trip relay must be set to operate “on or below” the
appropriate curve instead of “below” the appropriate curve in order to clarify what
settings are considered compliant under the proposed Regional Reliability Standard.
VRF Justification: The VRF of “High” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
11. PRC-006-NPCC-2 Requirement R11. Proposed Requirement R11 carries forward
currently effective PRC-006-NPCC-1 Requirement R14 substantively unchanged,
updating only the numbering of the requirement.
VRF Justification: The justification for the VRF is in the table below.
VRF Justifications for PRC-006-NPCC-2 Requirement R11
Proposed VRF
Lower
VRF Discussion
A VRF of “Lower” is being proposed for
this Requirement.
A VRF of “Lower” is appropriate because
the proposed Requirement is
administrative in nature and is associated
with transmitting the generator
underfrequency trip setting and time delay
within 45 calendar days of a request. If
13
VRF Justifications for PRC-006-NPCC-2 Requirement R11
violated, this Requirement in the planning
timeframe would not, under the
emergency, abnormal, or restorative
conditions anticipated by the preparations,
be expected to adversely affect the
electrical state or capability of the Bulk
Electric System, or the ability to
effectively monitor, control, or restore the
Bulk Electric System.
FERC VRF Guideline 1
Consistency with Blackout Report
Emergency operations, protection systems
and their coordination, system modeling
and data exchange, and clearer criteria for
operationally critical facilities
FERC VRF Guideline 2
Consistency within a Reliability Standard
Not applicable. There are no subRequirement VRFs in the Regional
Reliability Standard.
FERC VRF Guideline 3
Consistency among Reliability Standards
The proposed VRF is consistent with
other FERC-approved VRFs in different
Reliability Standards that address similar
reliability goals. Specifically, the
proposed VRF of “Lower” is consistent
with the VRF of “Lower” in PRC-006-3
Requirement R8, which requires entities
to provide the Planning Coordinator with
requested information within a specified
timeframe.
FERC VRF Guideline 4
Consistency with NERC Definition of
VRFs
FERC VRF Guideline 5
Treatment of Requirements that comingle
more than one obligation
The team relied on NERC’s definition of a
lower risk requirement.
Not applicable. The Requirement does
not comingle a higher risk reliability
objective with a lower risk reliability
objective.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
14
12. PRC-006-NPCC-2 Requirement R12. Proposed Requirement R12 carries forward
currently effective PRC-006-NPCC-1 Requirement R15 substantively unchanged,
removing “on or after the effective date” language from the currently effective
Requirement because Version 1 of the Regional Reliability Standard has been in place
and transition and implementation concerns no longer need to be addressed in the
proposed Requirement, and also changes the numbers of Figures referenced in the
currently effective Requirement.
VRF Justification: The justification for the VRF is in the table below.
VRF Justifications for PRC-006-NPCC-2 Requirement R12
Proposed VRF
Medium
VRF Discussion
A VRF of “Medium” is being proposed
for this Requirement.
A VRF of “Medium” is appropriate
because the proposed Requirement is
associated with, for new generating units
or an existing generator unit increasing its
net capability by greater than 10%,
designing measures or auxiliary systems
or devices used for the control and
protection of auxiliary systems to prevent
the generating unit from tripping during
underfrequency conditions. If violated,
this Requirement in the planning
timeframe, would be unlikely, under
emergency, abnormal, or restoration
conditions anticipated by the preparations,
to lead to Bulk Electric System instability,
separation, or cascading failures, nor to
hinder restoration to a normal condition.
Emergency operations, protection systems
and their coordination, system modeling
and data exchange, and clearer criteria for
operationally critical facilities
FERC VRF Guideline 1
Consistency with Blackout Report
15
VRF Justifications for PRC-006-NPCC-2 Requirement R12
FERC VRF Guideline 2
Consistency within a Reliability Standard
Not applicable. There are no subRequirement VRFs in the Regional
Reliability Standard.
FERC VRF Guideline 3
Consistency among Reliability Standards
The proposed VRF is consistent with
other FERC-approved VRFs in different
Reliability Standards that address similar
reliability goals. Specifically, the
proposed VRF of “Medium” is consistent
with the VRF of “Medium” in PRC-006-3
Requirement R12, which requires entities
to conduct and document a design
assessment to address identified UFLS
program deficiencies.
FERC VRF Guideline 4
Consistency with NERC Definition of
VRFs
FERC VRF Guideline 5
Treatment of Requirements that comingle
more than one obligation
The team relied on NERC’s definition of a
medium risk requirement.
Not applicable. The Requirement does
not comingle a higher risk reliability
objective with a lower risk reliability
objective.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
13. PRC-006-NPCC-2 Requirement R13. Proposed Requirement R13 carries forward
currently effective PRC-006-NPCC-1 Requirement R16 substantively unchanged, adding
language to clarify that any compensatory load shedding must be within the same island
as the generating unit resides.
VRF Justification: The justification for the VRF is in the table below.
VRF Justifications for PRC-006-NPCC-2 Requirement R13
Proposed VRF
High
VRF Discussion
A VRF of “High” is being proposed for
this Requirement.
16
VRF Justifications for PRC-006-NPCC-2 Requirement R13
A VRF of “High” is appropriate because
the proposed Requirement is associated
with setting underfrequency protection to
operate at the lowest frequency allowed
by the plant design and licensing
limitations and arranging for
compensatory load shedding that is
adequate to compensate for the loss of
generator(s) due to early tripping that is
within the identified UFLS island. If
violated, this Requirement in the planning
timeframe could, under emergency,
abnormal, or restorative conditions
anticipated by the preparations, directly
cause or contribute to Bulk Electric
System instability, separation, or a
cascading sequence of failures, place the
Bulk Electric System at an unacceptable
risk of instability, separation, or cascading
failures, or could hinder restoration to a
normal condition.
FERC VRF Guideline 1
Consistency with Blackout Report
Emergency operations, protection systems
and their coordination, system modeling
and data exchange, and clearer criteria for
operationally critical facilities
FERC VRF Guideline 2
Consistency within a Reliability Standard
Not applicable. There are no subRequirement VRFs in the Regional
Reliability Standard.
FERC VRF Guideline 3
Consistency among Reliability Standards
The proposed VRF is consistent with
other FERC-approved VRFs in different
Reliability Standards that address similar
reliability goals. Specifically, the
proposed VRF of “High” is consistent
with the VRF of “High” in PRC-006-3
Requirement R15, which requires the
Planning Coordinator to develop a
corrective action plan and schedule if the
UFLS program does not meet the required
performance characteristics.
FERC VRF Guideline 4
Consistency with NERC Definition of
VRFs
The team relied on NERC’s definition of a
high risk requirement.
17
VRF Justifications for PRC-006-NPCC-2 Requirement R13
FERC VRF Guideline 5
Treatment of Requirements that comingle
more than one obligation
The Requirement refers to a separate
Requirement with a VRF of “Lower” that
require entities to provide UFLS island
boundaries within 30 days of a request,
but retains a VRF of “High” that requires
entities to set underfrequency protections
and arrange compensatory load shedding
that is adequate to compensate for the loss
of generator(s) that is within the UFLS
island identified by the referenced
Requirement. Thus, the VRF of the
higher risk reliability objective was not
watered down to reflect the lower risk
level associated with the lower risk
reliability objective.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
14. PRC-006-NPCC-2 Requirement R14. Proposed Requirement R14 carries forward
currently effective PRC-006-NPCC-1 Requirement R17 substantively unchanged,
updating only the numbering of the requirement and the number of a referenced
requirement.
VRF Justification: The VRF of “High” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
18
15. PRC-006-NPCC-2 Requirement R15. Proposed Requirement R15 carries forward
currently effective PRC-006-NPCC-1 Requirement R18 substantively unchanged,
updating only the numbering of the requirement and the number of a referenced
requirement.
VRF Justification: The VRF of “High” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
16. PRC-006-NPCC-2 Requirement R16. Proposed Requirement R16 carries forward
currently effective PRC-006-NPCC-1 Requirement R19 substantively unchanged,
updating only the numbering of the requirement and the number of a Figure referenced
in the requirement.
VRF Justification: The VRF of “High” did not change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard.
VSL Justification: The VSLs did not substantively change from the previously FERCapproved PRC-006-NPCC-1 Regional Reliability Standard. Only minor revisions were
made.
19
| File Type | application/pdf |
| Author | NERC Legal (ST) |
| File Modified | 2019-12-23 |
| File Created | 2019-12-23 |