NERC Petition for Approval of Reliability Standard

NERC Petition for approval of standard 5-4-12.pdf

(Final Rule in RM12-12) Mandatory Reliability Standards for the NPCC Region

NERC Petition for Approval of Reliability Standard

OMB: 1902-0261

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May 4, 2012
VIA ELECTRONIC FILING
Ms. Kimberly D. Bose
Secretary
Federal Energy Regulatory Commission
888 First Street, N.E.
Washington, D.C. 20426
Re: North American Electric Reliability Corporation
Docket No. RR12-___-000
Dear Ms. Bose:
The North American Electric Reliability Corporation (“NERC”) hereby submits
this petition in accordance with Section 215(d) (1) of the Federal Power Act (“FPA”) and
Part 39.5 of the Federal Energy Regulatory Commission’s (“FERC”) regulations seeking
approval of proposed Regional Reliability Standard PRC-006-NPCC-1 — Automatic
Underfrequency Load Shedding, associated Violation Risk Factors (“VRF”) and
Violations Severity Levels (“VSL”), and an implementation plan for PRC-006-NPCC-1.
Upon approval, this standard will only be effective within the Northeast Power
Coordinating Council (“NPCC”) footprint.
The purpose of PRC-006-NPCC-1 is 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, PRC-006-1.

Ms. Kimberly D. Bose
May 4, 2012
Page 2
The proposed Regional Reliability Standard was approved by the NERC Board of
Trustees during its February 9, 2012 meeting. NERC is proposing dual effective dates
for the standard. NERC proposes that for the Eastern Interconnection and 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 Commission’s information, NERC is proposing the following for the 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.
This petition consists of the following:
• this transmittal letter;
• a table of contents for the entire petition;
• a narrative description explaining how the proposed Regional Reliability
Standard meets FERC’s requirements;
• Regional Reliability Standard PRC-006-NPCC-1 — Automatic
Underfrequency Load Shedding and implementation plan, submitted for
approval (Exhibit A);
• the complete development record of the proposed Regional Reliability
Standard (Exhibit B);
• the standard drafting team roster (Exhibit C); and
• the Violation Severity Level and Violation Risk Factor Guideline Analysis
(Exhibit D).

Ms. Kimberly D. Bose
May 4, 2012
Page 3
Please contact the undersigned if you have any questions.
Respectfully submitted,
/s/ Andrew M. Dressel
Andrew M. Dressel
Attorney for North American Electric
Reliability Corporation

UNITED STATES OF AMERICA
BEFORE THE
FEDERAL ENERGY REGULATORY COMMISSION

NORTH AMERICAN ELECTRIC RELIABILITY
CORPORATION

) Docket No. RR12-__-000
)

PETITION OF THE
NORTH AMERICAN ELECTRIC RELIABILITY CORPORATION
FOR APPROVAL OF PROPOSED NPCC REGIONAL RELIABILITY
STANDARD PRC-006-NPCC-1 — AUTOMATIC UNDERFREQUENCY LOAD
SHEDDING

Gerald W. Cauley
President and Chief Executive Officer
3353 Peachtree Road NE
Suite 600, North Tower
Atlanta, GA 30326-1001

Holly A. Hawkins
Assistant General Counsel for Standards and
Critical Infrastructure Protection
North American Electric Reliability
Corporation

David N. Cook
Senior Vice President and General Counsel
North American Electric Reliability
Corporation
1325 G Street, N.W., Suite 600
Washington, D.C. 20005
[email protected]

Andrew M. Dressel
Attorney
North American Electric Reliability
Corporation
1325 G Street, N.W., Suite 600
Washington, D.C. 20005
(202) 400-3000
(202) 393-3998
(202) 393-3955 – facsimile
[email protected]
[email protected]

May 4, 2012

TABLE OF CONTENTS

I. Introduction

II. Notices and Communications

III. Background:

a. Regulatory Framework

b. Basis for Approval of Proposed Regional Reliability Standard

IV. Justification for Approval of Proposed Regional Reliability Standard

a. Basis and Purpose of Standard PRC-006-NPCC-1 - Automatic Underfrequency
Load Shedding

b. Order No. 672 Criteria

c. Additional Order No. 672 Criteria for Regional Reliability Standards

V. Summary of the Regional Reliability Standard Development Proceedings

VI. Conclusion

Exhibit A — PRC-006-NPCC-1 — Automatic Underfrequency Load Shedding Regional Reliability
Standard Proposed and Implementation Plan for Approval
Exhibit B — Complete Development Record of Proposed PRC-006-NPCC-1 Automatic
Underfrequency Load Shedding Regional Reliability Standard
Exhibit C — Standard Drafting Team Roster
Exhibit D — PRC-006-NPCC-1 Violation Severity Level and Violation Risk Factor Analysis

INTRODUCTION
The North American Electric Reliability Corporation (“NERC”) 1 hereby requests

the Federal Energy Regulatory Commission (“FERC”) to approve, in accordance with
Section 215(d)(1) of the Federal Power Act (“FPA”) 2 and Section 39.5 of FERC’s
regulations, 18 C.F.R. § 39.5, proposed Regional Reliability Standard, PRC-006-NPCC-1
included in Exhibit A.
The purpose of PRC-006-NPCC-1 ― Automatic Underfrequency Load Shedding
is 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. UFLS
requirements have been in place at a continent-wide level and within Northeast Power
Coordinating Council, Inc. (“NPCC”) for many years prior to implementation of
federally-mandated reliability standards in 2007.
NERC and NPCC believe that a region-wide and fully coordinated single set of
UFLS requirements is of benefit to achieving an effective and efficient UFLS program,
and their experience has supported that belief. Regional UFLS programs serve “as a last
resort to preserve the Bulk-Power System during a major system failure that could cause
system frequency to collapse.” 3 The NPCC standard adds specificity not contained in the
NERC standard for development and implementation of a UFLS program in the NPCC
1

NERC has been certified by FERC as the Electric Reliability Organization (“ERO”) authorized by Section
215 of the Federal Power Act. FERC certified NERC as the ERO in its order issued July 20, 2006 in
Docket No. RR06-1-000. 116 FERC ¶ 61,062 (2006) (“ERO Certification Order).
2
16 U.S.C. 824o.
3
Mandatory Reliability Standards for the Bulk-Power System, Order No. 693, FERC Stats. & Regs. ¶
31,242 at P 1476, order on reh’g, Order No. 693-A, 120 FERC ¶ 61,053 (2007).

region that effectively arrests declining frequency, assists recovery following
underfrequency events, and provides last resort system preservation measures.
This petition is the first request by NERC for FERC approval of this proposed
Regional Reliability Standard. The Regional Reliability Standard proposed will be in
effect only for applicable registered entities within the NPCC. NERC continent-wide
Reliability Standards do not presently address all of the issues covered in this proposed
Regional Reliability Standard.
NERC specifically requests approval of:
•

Regional Reliability Standard PRC-006-NPCC-1;

•

Associated Violations Risk Factors (“VRF”) and Violation Severity
Levels (“VSL”); and

•

Implementation Plan for PRC-006-NPCC-1.

On February 9, 2012 the NERC Board of Trustees approved PRC-006-NPCC-1
— Automatic Underfrequency Load Shedding. NERC requests that FERC approve this
Regional Reliability Standard and make it effective upon FERC approval for the section
of the NPCC region that lies within the United States, consistent with the proposed
implementation plan. Exhibit A to this filing sets forth the proposed Regional Reliability
Standard and implementation plan. Exhibit B contains the complete Development
Record for the proposed Regional Reliability Standard. Exhibit C includes the standard
drafting team roster. Exhibit D is the Violation Severity Level (“VSL”) and Violation
Risk Factor (“VRF”) guideline analysis.

NERC is also filing the proposed PRC-006-NPCC-1 Regional Reliability
Standard and associated documents with the applicable governmental authorities in
Canada.
II.

NOTICES AND COMMUNICATIONS
Notices and communications with respect to this filing may be addressed to the

following:
Gerald W. Cauley
President and Chief Executive Officer
3353 Peachtree Road NE
Suite 600, North Tower
Atlanta, GA 30326-1001

Holly A. Hawkins
Assistant General Counsel for Standards and
Critical Infrastructure Protection
North American Electric Reliability
Corporation

David N. Cook
Senior Vice President and General Counsel
North American Electric Reliability
Corporation
1325 G Street, N.W., Suite 600
Washington, D.C. 20005
[email protected]

III.

BACKGROUND
a. Regulatory Framework
By enacting the Energy Policy Act of 2005, 4 Congress entrusted FERC with the

duties of approving and enforcing rules to ensure the reliability of the nation’s bulk
power system and with the duties of certifying an ERO that would be charged with
developing and enforcing mandatory Reliability Standards, subject to FERC approval.
Section 215 of the FPA states that all users, owners and operators of the bulk power
system in the United States will be subject to FERC-approved Reliability Standards.
b. Basis for Approval of Proposed Regional Reliability Standard
Section 39.5(a) of FERC’s regulations requires the ERO to file with FERC for its
approval each Reliability Standard that the ERO proposes to become mandatory and
enforceable in the United States and each modification to a Reliability Standard that the
ERO proposes to be made effective. FERC has the regulatory responsibility to approve
standards that protect the reliability of the bulk power system. In discharging its
responsibility to review, approve, and enforce mandatory Reliability Standards, FERC is
authorized to approve those proposed Reliability Standards that meet the criteria detailed
by Congress:
FERC may approve, by rule or order, a proposed reliability standard or
modification to a reliability standard if it determines that the standard is
just, reasonable, not unduly discriminatory or preferential, and in the
public interest. 5
When evaluating proposed Reliability Standards, FERC is expected to give “due
weight” to the technical expertise of the ERO and to the technical expertise of a Regional
Entity organized on an Interconnection-wide basis with respect to a Reliability Standard
4
5

16 U.S.C. § 824o.
16 U.S.C. § 824o(d)(2).

to be applicable within that Interconnection. Order No. 672 provides guidance on the
factors FERC will consider when determining whether proposed Reliability Standards
meet the statutory criteria. 6
A Regional Reliability Standard proposed by a Regional Entity must meet the
same standards that NERC’s Reliability Standards must meet, i.e., the Regional
Reliability Standard must be shown to be just, reasonable, not unduly discriminatory or
preferential, and in the public interest. 7 FERC’s Order No. 672 also requires additional
criteria that a Regional Reliability Standard must satisfy: a regional difference from a
continent-wide Reliability Standard must either be (1) more stringent than the continentwide Reliability Standard (which includes 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. 8
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. As discussed in the Northeast Power Coordinating
Council, Inc. Regional Reliability Standard Development Procedure, 9 NPCC’s standards
are developed according to the following characteristic attributes:
•

Open — The NPCC Regional Reliability Standards Development Procedure
provides any person the ability to participate in the development of a
standard. Any entity that is directly and materially affected by the reliability
of the NPCC’s Bulk Power System has the ability to participate in the

See Rules Concerning Certification of the Electric Reliability Organization; Procedures for the
Establishment, Approval and Enforcement of Electric Reliability Standards, FERC Stats. & Regs., ¶ 31,204
at PP 320-338 (“Order No. 672”), order on reh’g, FERC Stats. & Regs. ¶ 31,212 (2006) (“Order No. 672A”).
7
Section 215(d)(2) of the FPA and 18 C.F.R. §39.5(a).
8
Order No. 672 at P 291.
9
The Northeast Power Coordinating Council, Inc. Regional Reliability Standard Development Procedure is
available at http://www.npcc.org/regStandards/Overview.aspx

development and approval of reliability standards. There are no undue
financial barriers to participation. Participation in the open comment process
is not conditional upon membership in the ERO, NPCC or any organization,
and participation is not unreasonably restricted on the basis of technical
qualifications or other such requirements. NPCC utilizes a website to
accomplish this. Online posting and review of standards and the real time
sharing of comments uploaded to the website allow complete transparency.
•

Inclusive — The NPCC Regional Reliability Standards Development
Procedure provides any person with a direct and material interest the right to
participate by expressing an opinion and its basis, have that position
considered, and appealed through an established appeals process if adversely
affected.

•

Balanced — The NPCC Regional Reliability Standards Development
Procedure has a balance of interests and all those entities that are directly and
materially affected by the reliability of the NPCC’s Bulk Power System are
welcome to participate and shall not be dominated by any two interest
categories and no single interest category shall be able to defeat a matter.
This will be accomplished through the NPCC Bylaws defining eight sectors
(categories) for voting.

•

Fair Due Process — The NPCC Regional Reliability Standards
Development Procedure provides for reasonable notice and opportunity for
public comment. The procedure includes public notice of the intent to
develop a standard, a 45 calendar day public comment period on the proposed
standard request, or standard with due consideration of those public
comments, and responses to those comments will be posted on the NPCC
website. A final draft will be posted for a 30 calendar day pre-balloting
period, and then a ballot of NPCC Members will be conducted. Upon
approval by the NPCC Members, the NPCC Board then votes to approve
submittal of the Regional Standard to NERC.

•

Transparent — All actions material to the development of Regional
Reliability Standards are transparent and information regarding the progress
is posted on the NPCC website as well as through extensive email lists.

Proposed NPCC standards are subject to approval by NERC, as the ERO, and FERC
before becoming mandatory and enforceable under Section 215 of the FPA. 10 As shown
above, the NPCC Regional Reliability Standard was developed in an open, transparent,
and inclusive fashion. During development of the standard, workshops were conducted
jointly with other Regional Entities and NPCC members. The proposed standard is

16 U.S.C. 824o.

widely supported by the NPCC ballot body and regulatory agencies that see this as a
meaningful and necessary step forward in solving a longstanding problem. The standard
was reviewed by NPCC legal counsel for consistency with the provisions and stated goals
of the Federal Power Act and Chapter 39 of FERC’s regulations. 11 As a condition of
NPCC membership, all NPCC Members 12 agree to adhere to the NERC Reliability
Standards in addition to the NPCC Regional Reliability Standards. NERC Reliability
Standards and the NPCC Regional Reliability Standards are both enforced through the
NPCC Compliance Program.
The NPCC drafting team worked closely with its technical committee on UFLS,
the SS-38 Working Group on Inter-Area Dynamics Analysis, as it considered the
technical issues and justifications surrounding the standard.
Additionally, NPCC conducted a number of regional workshops aimed at
informing NPCC Members on the status and background of the standard’s development.
The draft of the standard was posted for a 45 day comment period three times during its
development and the drafting team responded to all comments and technical concerns
that were raised.
NERC conducted two quality reviews of the standard during which formatting
and content issues were corrected. NERC also posted the draft for public consideration
on two occasions after which the drafting team responded to all comments received.
As previously noted, NPCC is a Regional Entity not organized on an
Interconnection-wide basis. Therefore, NERC is not required to rebuttably presume the

18 C.F.R. §39 (2011).
As defined in Section IV.B of the NPCC Corporation By-laws. Available at:
http://www.npcc.org/documents/aboutus/BusPlanBylaws.aspx.
12

proposed standard is just, reasonable, not unduly discriminatory or preferential and in the
public interest.
IV.

JUSTIFICATION FOR APPROVAL OF PROPOSED REGIONAL
RELIABILITY STANDARD
This section summarizes the development of the proposed Regional Reliability

Standard PRC-006-NPCC-1 — Automatic Underfrequency Load Shedding; describes the
reliability objectives to be achieved by the Regional Reliability Standard; explains the
development history of the Regional Reliability Standard; and demonstrates how the
standard meets the Commission’s criteria for approval. NERC, in its analysis and
approval of the proposed Regional Reliability Standard, determined that the standard is
just, reasonable, not unduly discriminatory or preferential, and in the public interest.
The complete development record for the proposed Regional Reliability Standard
is provided in Exhibit C and includes the development and approval process, comments
received during the industry-wide comment period, responses to those comments, ballot
information, and NERC’s evaluation of the proposed standard.
a. Basis and Purpose of Standard PRC-006-NPCC-1 — Automatic
Underfrequency Load Shedding
The proposed Regional Reliability standard, PRC-006-NPCC-1 — Automatic
Underfrequency Load Shedding, will provide regional requirements for Automatic
Underfrequency Load Shedding to applicable entities in NPCC. UFLS requirements
have been in place at a continent-wide level and within NPCC for many years prior to the
implementation of federally mandated reliability standards in 2007. NPCC and its
members believe that a region-wide, fully coordinated single set of UFLS requirements is

necessary to create an effective and efficient UFLS program, and their experience has
supported that belief.
The proposed standard contains 23 requirements that establish UFLS obligations
for entities within the NPCC region. The proposed standard is included in Exhibit A to
this filing.
b. Order No. 672 Criteria
In Order No. 672, the Commission identified the criteria it will use to analyze
Reliability Standards proposed for approval to ensure such standards are just, reasonable,
not unduly discriminatory or preferential, and in the public interest. The discussion
below identifies these factors and explains how the proposed Reliability Standards have
met or exceeded the criteria.
1. Proposed Reliability Standards must be designed to achieve a specified
reliability goal
Order No. 672 at P 321. The proposed Reliability Standard must address a
reliability concern that falls within the requirements of section 215 of the
FPA. That is, it must provide for the reliable operation of Bulk-Power
System facilities. It may not extend beyond reliable operation of such
facilities or apply to other facilities. Such facilities include all those
necessary for operating an interconnected electric energy transmission
network, or any portion of that network, including control systems. The
proposed Reliability Standard may apply to any design of planned
additions or modifications of such facilities that is necessary to provide for
reliable operation. It may also apply to Cybersecurity protection.
The proposed Regional Reliability Standard, PRC-006-NPCC-1 — Automatic
Underfrequency Load Shedding, was developed to provide a Regional Reliability
Standard that ensures the development of an effective UFLS program that preserves the
security and integrity of the bulk power system during declining system frequency events
in coordination with the continent-wide PRC-006-1 Reliability Standard’s requirements.

2. Proposed Reliability Standards must be applicable to users, owners, and
operators of the bulk power system, and not others.
Order No. 672 at P 322. The proposed Reliability Standard may impose a
requirement on any user, owner, or operator of such facilities, but not on
others.
The proposed Regional Reliability Standard is only applicable to Generator
Owners, Planning Coordinators, Distribution Providers, and Transmission Owners within
the NPCC region. These entities are users, owners, or operators of the bulk power
system.
3. Proposed Reliability Standards must consider any other relevant factors.
Order No. 672 at P 323. In considering whether a proposed Reliability
Standard is just and reasonable, we will consider the following general
factors, as well as other factors that are appropriate for the particular
Reliability Standard proposed.
All comments and concerns were addressed using the Northeast Power
Coordinating Council Standards Development Procedure which is consensus-based,
technically sound, and open to the public and bordering entities that may be impacted by
a Regional Reliability Standard. No other factors were identified as necessary for
consideration by the standard drafting team in the development of the proposed Regional
Reliability Standard.
4. Proposed Reliability Standards must contain a technically sound method to
achieve the goal.
Order No. 672 at P 324. The proposed Reliability Standard must be
designed to achieve a specified reliability goal and must contain a
technically sound means to achieve this goal. Although any person may
propose a topic for a Reliability Standard to the ERO, in the ERO’s
process, the specific proposed Reliability Standard should be developed
initially by persons within the electric power industry and community with
a high level of technical expertise and be based on sound technical and
engineering criteria. It should be based on actual data and lessons learned
from past operating incidents, where appropriate. The process for ERO
10

approval of a proposed Reliability Standard should be fair and open to all
interested persons.
The proposed Regional Reliability Standard contains a technically sound means to
achieve this goal. The PRC-006-NPCC-1 drafting team was comprised of power system
engineers with experience in power system protection system design, power system
operations, transmission, and generation. The proposed Regional Reliability Standard
used as its basis the program characteristics defined within NPCC Directory #12
Underfrequency Load Shedding Program Requirements, 13 which contains the criteria that
govern the NPCC Automatic UFLS program as designed by the NPCC Working Group
on Inter-Area Dynamic Analysis (SS-38) and was approved by NPCC’s highest level
technical committee, the Reliability Coordinating Committee (RCC).
The proposed Regional Reliability Standard PRC-006-NPCC-1 was posted for
industry technical comment three times and responses to these comments were evaluated
and incorporated by the drafting team into the standard as appropriate.
5. Proposed Reliability Standards must be clear and unambiguous as to what is
required and who is required to comply.
Order No. 672 at P 325. The proposed Reliability Standard should be
clear and unambiguous regarding what is required and who is required to
comply. Users, owners, and operators of the Bulk-Power System must
know what they are required to do to maintain reliability.
The proposed Regional Reliability Standard establishes clear and unambiguous
requirements for Generator Owners, Planning Coordinators, Distribution Providers, and
Transmission Owners within the NPCC region as detailed below.

NPCC Regional Reliability Reference Directory # 12 Underfrequency Load Shedding Program
Requirements (2009) (“NPCC Directory # 12”). Available at
http://www.theimo.com/imoweb/pubs/ircp/NPCC/Directory_12.pdf.

Requirement R1 requires each Planning Coordinator within the NPCC region to
establish requirements for entities aggregating their UFLS programs for each anticipated
island and requirements for compensatory load shedding as required by the islanding
criteria requirements of the NERC continent-wide Standard PRC-006-1.
Requirement R2 requires each Planning Coordinator to identify to NPCC the
generation facilities within its Planning Coordinator Area necessary to support the UFLS
program performance characteristics within 30 days of completion of its system studies
required by the NERC continent-wide Standard PRC-006-1.
Requirement R3 requires each Planning Coordinator to 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.
Requirement R4 requires each Distribution Provider and Transmission Owner in
the Eastern Interconnection portion of NPCC to 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 PRC-006NPCC-1 Attachment C, Tables 1 through 3, or to 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 PRC-006-NPCC-1 Attachment C, Tables 1 through 3.

Requirement R5 requires 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 to:

5.1

Inform its Planning Coordinator of the need to exceed the stated tolerances
or the number of stages as shown in PRC-006-NPCC-1 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 PRC-006-NPCC-1 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 PRC-006-NPCC-1 Attachment C, Table 2 or Table 3, and in the case of
PRC-006-NPCC-1 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 PRC-006NPCC-1 Attachment C Table 2 or PRC-006-NPCC-1 Attachment C
Table 3.

Requirement R6 requires each Distribution Provider and Transmission Owner in
the Québec Interconnection portion of NPCC to implement an automatic UFLS program
for its Facilities based on the frequency thresholds, slopes, total nominal operating time
and amounts specified in PRC-006-NPCC-1 Attachment C, Table 4 or to 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 PRC-006-NPCC-1
Attachment C, Table 4.
Requirement R7 requires each Distribution Provider and Transmission Owner to
set each underfrequency relay that is part of its region’s UFLS program with a minimum
time delay of 100 ms in the Eastern Interconnection and 200 ms in the Quebec
Interconnection.
Requirement R8 requires each Planning Coordinator to develop and review once
per calendar year settings for the inhibit thresholds to be utilized within its region's UFLS
program.
Requirement R9 requires each Planning Coordinator to 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.
Requirement R10 requires each Distribution Provider and Transmission Owner to
implement the inhibit threshold settings based on the notification provided by the
Planning Coordinator in accordance with Requirement R9.
Requirement R11 requires each Distribution Provider and Transmission Owner to
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 R9.
Requirement R12 requires each Transmission Owner and Distribution Provider to
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.
Requirement R13 requires each Generator Owner to set each generator
underfrequency trip relay, if so equipped, below the appropriate generator
underfrequency trip protection settings threshold curve in PRC-006-NPCC-1 Figure 1,
except as otherwise exempted in Requirements R16 and R19.
Requirement R14 requires each Generator Owner to transmit the generator
underfrequency trip setting and time delay to its Planning Coordinator within 45 days of
the Planning Coordinator’s request.

Requirement R15 requires 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% to:
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 PRC-006-NPCC-1 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 PRC-006-NPCC-1 Figure 1.

Requirement R16 requires 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 PRC-006-NPCC-1 Figure 1 to:
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.

Requirement R17 requires each Planning Coordinator in Ontario, Quebec, and the
Maritime provinces to apply the criteria described in PRC-006-NPCC-1 Attachment A to
determine the compensatory load shedding that is required in Requirement R16 part 16.3
for generating units in its respective NPCC area.
Requirement R18 requires each Generator Owner, Distribution Provider, or
Transmission Owner within the Planning Coordinator area of ISO-NE or the New York
ISO to apply the criteria described in PRC-006-NPCC-1 Attachment B to determine the
compensatory load shedding that is required in Requirement R16 part 16.3 for generating
units in its respective NPCC area.
Requirement R19 requires each Generator Owner of existing nuclear generating
plants with units that have underfrequency relay threshold settings above the Eastern
Interconnection generator tripping curve in PRC-006-NPCC-1 Figure 1, based on their
licensing design basis, to:
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.

Requirement R20 requires each Planning Coordinator to update its UFLS program
database as specified by the NERC UFLS Reliability Standard on UFLS (currently PRC006-1). This database shall include the following information:

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 PRC-006-NPCC-1 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.

Requirement R21 requires each Planning Coordinator to 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, which is currently
PRC-006-1.
Requirement R22 requires each Distribution Provider, Transmission Owner and
Generator Owner to implement the load distribution changes based on the notification
provided by the Planning Coordinator in accordance with Requirement R21.
Requirement R23 requires each Distribution Provider, Transmission Owner and
Generator Owner to 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.
6. Proposed Reliability Standards must include clear and understandable
consequences and a range of penalties (monetary and/or non-monetary) for a
violation
Order No. 672 at P 326. The possible consequences, including range of
possible penalties, for violating a proposed Reliability Standard should be
clear and understandable by those who must comply.
The proposed Regional Reliability Standard includes a Violation Risk Factor
(“VRF”) and at least one Violation Severity Level (“VSL”) for each requirement. The
ranges of penalties for violations will be based on the applicable VRF and VSL and will
be administered based on the sanctions table and supporting penalty determination
process described in the FERC-approved NERC Sanction Guidelines. 14
NPCC developed the VSLs and VRFs proposed for assignment to PRC-006NPCC-1 following applicable NERC and FERC guidance. Exhibit E to this filing
contains the VSL and VRF guideline analysis for PRC-006-NPCC-1.
7. 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.
Order No. 672 at P 327. There should be a clear criterion or measure of
whether an entity is in compliance with a proposed Reliability Standard.
It should contain or be accompanied by an objective measure of
compliance so that it can be enforced and so that enforcement can be
applied in a consistent and non-preferential manner.
Each requirement of PRC-006-NPCC-1 has an associated measure of compliance
that will assist those enforcing the standard in enforcing it in a consistent and nonpreferential manner. The proposed measures are as follows:

NERC Rules of Procedure Appendix 4B. Available at: http://www.nerc.com/page.php?cid=1|8|169.

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. (PRC-006-NPCC-1 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. (PRC-006-NPCC-1 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.

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 PRC-006-NPCC-1
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 PRC-006-NPCC-1
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 PRC-006-NPCC-1 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 R23.
8. 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.
Order No. 672 at P 328. The proposed Reliability Standard does not
necessarily have to reflect the optimal method, or “best practice,” for
achieving its reliability goal without regard to implementation cost or
historical regional infrastructure design. It should however achieve its
reliability goal effectively and efficiently
Regional Reliability Standard PRC-006-NPCC-1 achieves its reliability goal
effectively and efficiently. The standard accomplishes the reliability goal of ensuring the
development of an effective UFLS program in the NPCC region that preserves the
security and integrity of the bulk power system during declining system frequency events
in coordination with the NERC UFLS Reliability Standard characteristics, which is
currently contained in PRC-006-1.

The implementation plan for PRC-006- NPCC-1 (included in Exhibit A) specifies
a six year implementation schedule and provides for annual improvement over that period
in the system performance expected following UFLS operation for an island condition.
Modifications to the program in the first two years are limited to relay setting changes
only. Modifications requiring capital improvements are scheduled to begin in the third
year of the program to provide sufficient time for including expenditures in capital
budgets and procuring equipment.
9. Proposed Reliability Standards cannot be “lowest common denominator,” i.e.,
cannot reflect a compromise that does not adequately protect bulk power system
reliability.
Order No. 672 at P 329. The proposed Reliability Standard must not
simply reflect a compromise in the ERO’s Reliability Standard
development process based on the least effective North American practice
— the so-called “lowest common denominator” — if such practice does
not adequately protect Bulk-Power System reliability. Although [FERC]
will give due weight to the technical expertise of the ERO, [FERC] will
not hesitate to remand a proposed Reliability Standard if [FERC is]
convinced it is not adequate to protect reliability.
This proposed Regional Reliability Standard does not reflect a “lowest common
denominator” approach. PRC-006-NPCC-1 incorporates the UFLS program
recommendations set forth by the SS-38 Working Group on Inter-Area Dynamic
Analysis in assessment studies that were performed after the 2003 Blackout. Contrary to
a “lowest common denominator” approach, the Standard attempts to provide a bridge
between the recommendations of the SS-38 Working Group and the current Registry
Criteria by requiring the Planning Coordinator to identify those generators deemed
critical to the performance of the UFLS program in order for the Regional Entity to
review the status of such units.

10. Proposed Reliability Standards may consider costs to implement for smaller
entities but not at consequence of less than excellence in operating system
reliability.
Order No. 672 at P 330. A proposed Reliability Standard may take into
account the size of the entity that must comply with the Reliability
Standard and the cost to those entities of implementing the proposed
Reliability Standard. However, the ERO should not propose a “lowest
common denominator” Reliability Standard that would achieve less than
excellence in operating system reliability solely to protect against
reasonable expenses for supporting this vital national infrastructure. For
example, a small owner or operator of the Bulk-Power System must bear
the cost of complying with each Reliability Standard that applies to it.
PRC-006-NPCC-1 provides an opportunity for smaller entities to aggregate their
load with other such entities in the same electrical island. This allows each smaller
entity’s respective Planning Coordinator to achieve the desired aggregate outcome within
that island according to the program characteristics.
11. 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 area or approach.
Order No. 672 at P 331. A proposed Reliability Standard should be
designed to apply throughout the interconnected North American BulkPower System, to the maximum extent this is achievable with a single
Reliability Standard. The proposed Reliability Standard should not be
based on a single geographic or regional model but should take into
account geographic variations in grid characteristics, terrain, weather, and
other such factors; it should also take into account regional variations in
the organizational 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.
The proposed Regional Reliability Standard is designed on a regional basis and
will only apply to the NPCC region. It is not intended to be applied throughout North
America.
12. Proposed Reliability Standards should cause no undue negative effect on
competition or restriction of the grid.
25

Order No. 672 at P 332. As directed by section 215 of the FPA, [FERC]
itself will give special attention to the effect of a proposed Reliability
Standard on competition. The ERO should attempt to develop a proposed
Reliability Standard that has no undue negative effect on competition.
Among other possible considerations, a proposed Reliability Standard
should not unreasonably restrict available transmission capability on the
Bulk-Power System beyond any restriction necessary for reliability and
should not limit use of the Bulk-Power System in an unduly preferential
manner. It should not create an undue advantage for one competitor over
another.
This proposed Regional Reliability Standard will not cause undue negative effects
on competition or restriction of the grid. Because this standard will be applied equally
across the NPCC region, PRC-006-NPCC-1 will not negatively affect competition, or
restrict available transmission capability within the NPCC footprint.
13. The implementation time for the proposed Reliability Standards must be
reasonable.
Order No. 672 at P 333. In considering whether a proposed Reliability
Standard is just and reasonable, [FERC] will consider also the timetable
for implementation of the new requirements, including how the proposal
balances any urgency in the need to implement it against the
reasonableness of the time allowed for those who must comply to develop
the necessary procedures, software, facilities, staffing or other relevant
capability.
The implementation plan for the Regional Reliability Standard proposes a phased
in implementation schedule as follows:
For the Eastern Interconnection and Québec Interconnection Portions of NPCC
excluding the Independent Electricity System Operator (“IESO”) Planning Coordinator
Area of NPCC in Ontario, Canada: 15
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
15

Information regarding the implementation plan for the IESO and Québec Interconnection are for the
Commission’s information only.

earlier than Jan 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 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.
The information submitted by NPCC supports the implementation schedule presented.
14. The Reliability Standard development process must be open and fair.
Order No. 672 at P 334. Further, in considering whether a proposed
Reliability Standard meets the legal standard of review, we will entertain
comments about whether the ERO implemented its [FERC]-approved
Reliability Standard development process for the development of the
particular proposed Reliability Standard in a proper manner, especially
whether the process was open and fair. However, we caution that we will
not be sympathetic to arguments by interested parties that choose, for
whatever reason, not to participate in the ERO’s Reliability Standard
development process if it is conducted in good faith in accordance with the
procedures approved by [FERC].
NPCC develops Regional Reliability Standards in accordance with Exhibit C
(Regional Reliability Standards Development Procedure) of its Regional Delegation
Agreement with NERC. The development process is open to any person or entity with a
legitimate interest in the reliability of the bulk power system. NPCC considers the
comments of all stakeholders and an affirmative vote of the stakeholders and the NPCC
Board of Directors are both required to approve a Regional Reliability Standard for
submission to NERC and FERC.

The proposed Regional Reliability Standard has been developed and approved by
industry stakeholders using NPCC’s Regional Reliability Standards Development
Procedure and was approved by the NPCC Board of Directors on November 20, 2011.
The standard was subsequently presented to and approved by the NERC Board of
Trustees February 9, 2012. Therefore, NPCC has utilized its standard development
process in good faith and in a manner that is open and fair. No commenters disagreed
with the open and fair implementation of the NPCC process.
15. Proposed Reliability Standards must balance with other vital public interests.
Order No. 672 at P 335. Finally, we understand that at times development
of a proposed Reliability Standard may require that a particular reliability
goal must be balanced against other vital public interests, such as
environmental, social and other goals. We expect the ERO to explain any
such balancing in its application for approval of a proposed Reliability
Standard.
Neither NERC nor NPCC believes there are competing public interests with the
request for approval of this proposed Regional Reliability Standard. No comments were
received that indicated the proposed standard conflicts with other vital public interests.
Therefore it is not necessary to balance this Regional Reliability Standard against any
other competing public interests.
16. Proposed Reliability Standard must not conflict with prior FERC Rules or
Orders.
Order No. 672 at P 444. A potential conflict between a Reliability
Standard under development and a Transmission Organization function,
rule, order, tariff, rate schedule, or agreement accepted, approved, or
ordered by the Commission should be identified and addressed during the
ERO’s Reliability Standard Development Process.

The proposed PRC-006-NPCC-1 Regional Reliability Standard does not conflict
with any other prior FERC rules or orders and adequately addresses the directives
identified in FERC Order No. 693. 16

NERC has therefore determined that the proposed standard meets the criteria for
consideration and approval as a Reliability Standard.
c. Additional Order No. 672 Criteria for Regional Reliability Standards
FERC’s Order No. 672 also establishes additional criteria that a Regional
Reliability Standard must satisfy: “A regional difference from a continent-wide
Reliability Standard must either be (1) more stringent than the continent-wide Reliability
Standard including a regional difference that addresses matters 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.” 17 The proposed standard satisfies
these additional criteria.
The existing NERC continent-wide standard, PRC-006-1 – Automatic
Underfrequency Load Shedding applies only to Planning Coordinators, Transmission
Owners, and Distribution Providers. The proposed standard, PRC-006-NPCC-1, includes
Generator Owners as applicable entities. The NPCC standard adds specificity not
contained in the NERC standard for development and implementation of a UFLS
program in the NPCC region that effectively arrests declining frequency, assists recovery
following underfrequency events, and provides last resort system preservation measures.
PRC-006-NPCC-1 achieves a coordinated, comprehensive UFLS region-wide consistent

16
17

Order No. 693 at P 1480.
Order No. 672 at P 291.

program within the NPCC Region and provides the regional requirements necessary to
achieve and facilitate the broader program characteristics contained in the requirements
of the NERC UFLS standard. It is designed to work in conjunction with, and augment
the NERC standard by mitigating the consequences of an underfrequency event, 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. The standard also facilitates uniformity, compliance, and
clearly delineates what the applicable entities’ requirements are within the region to
achieve a robust, reliable and effective UFLS program. Thus, the proposed standard
satisfies the additional Order No. 672 criteria for Regional Reliability Standards.
V.

SUMMARY OF THE REGIONAL RELIABILITY STANDARD
DEVELOPMENT PROCEEDINGS
NERC Evaluation: On November 21, 2011, NPCC submitted the proposed

Regional Reliability Standard for evaluation and approval to NERC in accordance with
NERC’s Rules of Procedure and Regional Reliability Standards Evaluation Procedure 18
that was approved by NERC’s Regional Reliability Standards Working Group. NERC
provided its evaluation of the proposed PRC-006-NPCC-1 standard to NPCC on
December 23, 2011, included in Exhibit B, after NERC concluded its 45-day posting of
the standard.
Key Issues:
The NPCC drafting team for PRC-006-NPCC-1 considered and resolved a
number of issues concerning the regional UFLS program and incorporated those
outcomes into the requirements of this standard. The drafting team sought the
18

Regional Reliability Standards Evaluation Procedure, Version 1 (2009). Available at:
http://www.nerc.com/docs/sac/rrswg/NERC_Regional_Reliability_Evaluation_Procedure.pdf.

recommendations of the NPCC SS-38 Working Group in order to ensure that its solutions
to the issues brought forth by commenters and drafting team members were consistent
with maintaining a regional effective program for all of the scenarios considered.
Among the issues resolved were: 1) generator coordination and the administration
of compensatory load shedding for non-conforming generators, 2) participation of small
entities in the regional UFLS program, 3) program tolerances 4) inhibit settings, 5)
generator applicability, and 6) NERC PRC-006-1 coordination.

1) Generator Coordination and Compensatory Load Shedding:
The drafting team established a requirement for all new generators to conform to
the generator tripping curve in the standard, thereby eliminating the problem of nonconforming generators in the future. Existing units that are already interconnected and in
commercial operations that do not conform to the generator tripping curve in the standard
currently obtain compensatory load shedding in accordance with existing NPCC
procedures currently in effect and contained within NPCC Directory#12 Underfrequency
Load Shedding Program Requirements. 19 These procedures are appended to the standard
as attachments and provide the instructions for a non-conforming generator to obtain
compensatory load shedding.
The drafting team also considered the existing nuclear units within NPCC with
under-frequency threshold settings above the generator tripping curve. A requirement
was developed that instructs these units to set the frequency trip setting upper tolerance
as low as possible in accordance with the plant design and licensing limitations and to
transmit the settings and any changes to settings to the Planning Coordinator.
19

NPCC Directory # 12, supra note 12.

2) Small Entity Participation:
The NPCC UFLS program characteristics as developed by the NPCC SS-38
Working Group and implemented by NPCC area Planning Coordinators is designed with
five discrete stages of load shedding (including an anti-stall stage) with approximately
7% of load shedding at each of the program stages. However, many smaller entities
(typically those with less than 100MW) are constrained by facility design but with the
technical support of the NPCC SS-38 group the drafting team developed modified
program stages and tolerances for these smaller entities. The NPCC SS-38 Working
Group modeled these small entity parameters to ensure that the overall regional program
converged using these attributes. Furthermore, these small entity characteristics have
already been incorporated within the regional UFLS criteria and included in NPCC
Directory#12 Underfrequency Load Shedding Program Requirements. 20
3) Program Tolerances:
The drafting team with the support of the NPCC SS-38 Working Group examined
the tolerances that could be permitted when implementing the individual program stages
of load shedding in 7% blocks. NPCC SS-38 recommended that the upper and lower
program tolerances at each stage should be bounded by +/- 0.5% surrounding a nominal
amount of load shed at each stage (7%). This recommendation was incorporated into the
standard and provides entities designing their UFLS programs with some degree of
flexibility when assigning the amount of load to be shed on declining frequency.
4) Inhibit Settings:
The drafting team recognized during the development of the standard that various
inhibit thresholds designed to prevent the misoperation of UFLS relays are employed
20

NPCC Directory # 12, supra note 12.

throughout the region. Although the most common feature is a voltage inhibit, other
inhibit schemes utilizing current and time were also revealed. Additionally, the
application of the voltage inhibit function was not consistent across the region.
Accordingly, the drafting team developed a requirement for each Planning
Coordinator to review and coordinate the development of these thresholds to insure that
they are consistent with the goal of an effective regional UFLS program.
5) Generator Applicability:
The drafting team considered the unique nature of UFLS with respect to the
critical issue of maintaining proper generator coordination for all units determined to be
critical to the support of the UFLS program performance characteristics. The NPCC SS38 Working Group’s assessments and recommendations were developed into a
requirement that will allow the Planning Coordinators to identify generation facilities
within its Planning Coordinator Area that are considered critical to the program’s
performance.
6) Coordination with NERC PRC-006-1.
The NPCC drafting team developed PRC-006-NPCC-1 in a manner that
coordinated with NERC Reliability Standard PRC-006-1 ― Automatic Underfrequency
Load Shedding. In some cases, draft requirements were eliminated from the Regional
Reliability Standard since PRC-006-1 already includes a requirement in place for these
program attributes (e.g. perform a program design assessment every 5 years). In other
cases the requirements in the Regional Standard enhance the existing requirements in the
NERC Standard as a necessary requirement for the Regional program. For example,
NERC PRC- 006-1 has a requirement to “establish islands” and PRC -006-NPCC-1 has a

requirement to “use islands to aggregate load.” In still other cases, the drafting team
developed requirements to be included in the Regional Standard that were not covered in
NERC’s PRC-006-1 and which were critical to the performance of the Regional program,
such as inhibit thresholds and time delay characteristics on UFLS relays.
Violation Risk Factors and Violation Severity Levels:
The proposed Regional Reliability Standard contains both VRFs and VSLs.
VRFs and VSLs are assigned to each requirement in the standard. The VRFs and VSLs
for this standard were developed and reviewed for consistency with NERC and FERC
guidelines. 21 Analyses of the assigned VRFs and VSLs to this standard are included in
Exhibit E.
VI.

CONCLUSION
For the reasons stated above, NERC respectfully requests that FERC approve the

proposed PRC-006-NPCC-1 Regional Reliability Standard and the associated proposed
VRFs and VSLs included in Exhibit A to this filing in accordance with Section 215(d)(1)
of the FPA and Part 39.5 of FERC’s regulations. NERC requests that these approvals be
made effective in accordance with the implementation plan for PRC-006-NPCC-1
included in Exhibit A to this filing.
Respectfully submitted,
/s/ Andrew M. Dressel
Andrew M. Dressel
Attorney for North American Electric
Reliability Corporation

See Order on Violation Risk Factors, 119 FERC ¶ 61,145 (2007) and Order on Violation Severity Levels
Proposed by the Electric Reliability Organization, 123 FERC ¶ 61,284 (2008).

CERTIFICATE OF SERVICE
I hereby certify that I have served a copy of the foregoing document upon all
parties listed on the official service list compiled by the Secretary in this proceeding.
Dated at Washington, D.C. this 4th day of May, 2012.
/s/ Andrew M. Dressel
Andrew M. Dressel
Attorney for North American Electric
Reliability Corporation

Exhibit A
PRC-006-NPCC-1 — Automatic Underfrequency Load Shedding Regional Reliability
Standard Proposed and Implementation Plan for Approval

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
A. Introduction
1.

Title:

Automatic Underfrequency Load Shedding

Number:

PRC-006-NPCC-1

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.

Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.3. Distribution Provider
4.4. Transmission Owner

(Proposed) Effective Date:

To be established.

B. Requirements
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]

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]

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]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
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]

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

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

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
2

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
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]
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]
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]
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]
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]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

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]
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]
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]
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.
4

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

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]
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.

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.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
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]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Figure 1
Thresholds for Setting Underfrequency Trip Protection for Generators

Frequency (Hz)
60

59.5

58.5

57.5

56.5

56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping

0.1

100

Time (sec)

1000

55.5

55
10000

Standard PRC-006-NPCC-1 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.

Standard PRC-006-NPCC-1 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.

Standard PRC-006-NPCC-1 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. 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.
10

Standard PRC-006-NPCC-1 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.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2.

Violation Severity Levels

Requirement
R1

Lower VSL
N/A

Moderate VSL
N/A

High VSL

Severe VSL

Planning Coordinator did not
establish requirements for entities
aggregating their UFLS programs.

Planning Coordinator did not
establish requirements for entities
aggregating their UFLS programs
and did not establish requirements
for compensatory load shedding.

or
Did not establish requirements for
compensatory load shedding.

The Planning Coordinator
identified the generation
facilities within its Planning
Coordinator Area necessary to
support the UFLS program, but
did so more than 30 days but less
than 41 days after completion of
the system studies.

The Planning Coordinator
identified the generation
facilities within its Planning
Coordinator Area necessary to
support the UFLS program, but
did so more than 40 days but less
than 51 days after completion of
the system studies.

The Planning Coordinator
identified the generation facilities
within its Planning Coordinator
Area necessary to support the
UFLS program, but did so more
than 50 days but less than 61 days
after completion of the system
studies.

The Planning Coordinator
identified the generation facilities
within its Planning Coordinator
Area necessary to support the
UFLS program, but did so more
than 60 days after completion of
the system studies.
or
The Planning Coordinator did not
identify the generation facilities
within its Planning Coordinator
Area necessary to support the
UFLS program.

The Planning Coordinator
provided the requested
information, but did so more than
30 days but less than 41 days to
the requesting entity.

The Planning Coordinator
provided the requested
information, but did so more
than 40 days but less than 51
days to the requesting entity.

The Planning Coordinator
provided the requested
information, but did so more than
50 days but less than 61 days to the
requesting entity.

The Planning Coordinator
provided the requested
information, but did so more than
60 days after the request.
or
The Planning Coordinator failed
to provide the requested
information.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

N/A

The Distribution Provider or
Transmission Owner failed to
implement an automatic UFLS
program reflecting normal
operating conditions excluding
outages, for its Facilities or
collectively implemented 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 frequency
thresholds, total nominal
operating time, and amounts
specified in the appropriate
included tables.

N/A

The Distribution Provider or
Transmission Owner did not arm
its load to trip on
underfrequency in order to meet
its minimum obligations and in
doing so exceeded the tolerances
and/or deviated from the number
of stages and frequency set
points of the UFLS program as
specified in the tables contained
in Attachment C, as applicable
depending on their total peak net
Load.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2 only, the need to deviate from
providing two stages of UFLS.

Transmission Owner to comply
with the appropriate table.

N/A

The Distribution Provider or
Transmission Owner in the
Québec Interconnection portion
of NPCC did not 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 did not 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.

N/A

The Distribution Provider or
Transmission Owner failed to set

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
an underfrequency relay that is
part of its region’s UFLS
program as specified in
Requirement 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 days but
less than 41 days of the initial
determination or any subsequent
change to the inhibit thresholds.

N/A

The Planning Coordinator
developed inhibit thresholds as
specified in Requirement R8 but
did not perform the review once
per calendar year.

The Planning Coordinator did
not develop inhibit thresholds as
specified in Requirement R8.

The Planning Coordinator
provided to a Transmission
Owner or Distribution Provider
within its Planning Coordinator
area the applicable inhibit
thresholds more than 40 days but
less than 51 days of the initial
determination or any subsequent
change to the inhibit thresholds.

The Planning Coordinator
provided to a Transmission
Owner or Distribution Provider
within its Planning Coordinator
area the applicable inhibit
thresholds more than 60 days
after the initial determination or
any subsequent change to the
inhibit thresholds.
or
The Planning Coordinator did
not provide to a Transmission
Owner or Distribution Provider
within its Planning Coordinator
area the applicable inhibit
thresholds.

R10

N/A

The Distribution Provider or
Transmission Owner did not
implement the inhibit threshold
based on the notification
provided by the Planning
Coordinator in accordance with
Requirement R9.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

R11

The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 90 days but less
than 101 days after the request
from the Planning Coordinator.

The Distribution Provider or
Transmission Owner developed
and submitted its
implementation plan more than
100 days but less than 111 days
after the request from the
Planning Coordinator.

The Distribution Provider or
Transmission Owner developed
and submitted its implementation
plan more than 110 days but less
than 121 days after the request
from the Planning Coordinator.

The Distribution Provider or
Transmission Owner developed
and submitted its
implementation plan more than
120 days after the request from
the Planning Coordinator.
or
The Distribution Provider or
Transmission Owner did not
develop its implementation plan.

The Transmission Owner or
Distribution Provider did not
provide documentation to its
Planning Coordinator of actual
net load data or updates to the
data that would be shed by the
UFLS relays, as determined by
measuring actual metered load
through the switches that would
be opened by the UFLS relays,
that were armed to shed at each
UFLS stage coincident with their
integrated hourly peak during
the previous year.

R12

R13

N/A

The Generator Owner did not 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.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

R14

The Generator Owner transmitted
the generator underfrequency trip
setting and time delay to its
Planning Coordinator more than
45 days and less than 56 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 days
and less than 66 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
days and less than 76 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 75days
after the Planning
Coordinator’s request.
or

The Generator Owner did not
transmit the generator
underfrequency trip setting and
time delay to its Planning
Coordinator.
R15

N/A

The Generator Owner did not
fulfill the obligation of
Requirement R15; Part 15.1 OR
did not fulfill the obligation of
Requirement R15, Part 15.2.

The Generator Owner did not
fulfill the obligation of
Requirement R15, Part 15.1 and
did not fulfill the obligation of
Requirement R15, Part 15.2.

R16

N/A

The Generator Owner did not
fulfill the obligation of
Requirement R16, Part 16.2.

The Generator Owner did not
fulfill the obligation of
Requirement R16; Part 16.1 OR
did not fulfill the obligation of
Requirement R16, Part 16.3.

The Generator Owner did not
fulfill the obligation of
Requirement R16, Part 16.1 and
did not fulfill the obligation of
Requirement R16, Part 16.3.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

R17

N/A

The Planning Coordinator did
not apply the methodology
described in Attachment A to
determine the compensatory load
shedding that is required.

R18

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.

R19

N/A

The Generator Owner did not
fulfill the obligation of
Requirement R19, Part 19.3.

The Generator Owner did not
fulfill the obligation of
Requirement R19; Part 19.1 OR
did not fulfill the obligation of
Requirement R19, Part 19.2.

The Generator Owner did not
fulfill the obligation of
Requirement R19, Part 19.1 and
did not fulfill the obligation of
Requirement R19, Part 19.2.

R20

The Planning Coordinator did not
have data in its database for one
of the parameters listed in
Requirement 20, Parts 20.1
through 20.5.

The Planning Coordinator did
not have data in its database for
two of the parameters listed in
Requirement 20, Parts 20.1
through 20.5.

The Planning Coordinator did not
have data in its database for three
of the parameters listed in
Requirement 20, Parts 20.1
through 20.5.

The Planning Coordinator did
not have data in its database for
four or more of the parameters
listed in Requirement 20, Parts
20.1 through 20.5.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

R21

N/A

The Planning Coordinator did
not notify a Distribution
Provider, Transmission Owner,
or Generator Owner within its
Planning Coordinator area of
changes to load distribution
needed to satisfy UFLS program
requirements.

R22

N/A

The Distribution Provider,
Transmission Owner, or
Generator Owner did not
implement the load distribution
changes based on the
notification provided by the
Planning Coordinator.

R23

The Distribution Provider.
Transmission Owner or Generator
Owner developed and submitted
its implementation plan more than
90 days but less than 101 days
after the request from the
Planning Coordinator.

The Distribution Provider.
Transmission Owner or
Generator Owner developed and
submitted its implementation
plan more than 100 days but less
than 111 days after the request
from the Planning Coordinator.

The Distribution Provider.
Transmission Owner or
Generator Owner developed and
submitted its implementation
plan more than 120 days after
the request from the Planning
Coordinator.
or
The Distribution Provider.
Transmission Owner or
Generator Owner did not
develop its implementation plan.

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
20

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.

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.

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.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
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
1
Time (s)

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

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 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
1
Operating Time(s)

Load Shed at
Stage as % of TO
or DP Load

Cumulative Load
Shed as % of TO
or DP Load

59.5

0.30

14-25

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.

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
1
(s)

Load Shed at
Stage as % of TO
or DP Load

Cumulative Load
Shed as % of TO
or DP Load

59.5

0.30

28-50

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

UFLS Table 4: Quebec Interconnection

MW
at peak
Rate

Frequency
(Hz)

(*Load must
be fixed at all
times when
above 60% of
peak load..)

Mvar
at peak

Total
Nominal
Operating
2
Time (s)

Threshold Stage 1

–––

58.5

1000*

1000

0.30

Threshold Stage 2

–––

58.0

800*

800

0.30

Threshold Stage 3

–––

57.5

800

0.30

Threshold Stage 4

–––

57.0

800

0.30

–––

59.0

500

20.0

Slope Stage 1

-0.3 Hz/s

58.5

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

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.

Exhibit B
Complete Development Record of Proposed PRC-006-NPCC-1 Automatic Underfrequency
Load Shedding Regional Reliability Standard

Regional Reliability Standards - Under Development

Standard No.

Title

Regional Status

Dates

NERC Status

Northeast Power Coordinating Council (NPCC)

Info (12)
Submit Comments
Comment Form
(11)

11/22/1112/22/11

PRC-006-NPCC1(10)
Implementation
Plan (9)
Comments
Received (8)

Automatic
PRC-006-NPCC- Underfrequency
01
Load Shedding
Program

Consideration of
Comments (7)

NERC Board
Adopted
February 9,
2012

Submit Comments
Comment Form (6)
PRC-006-NPCC-1
(5)

01/11/1102/24/11

Implementation
Plan (4)
Consideration of
Comments (3)
PRC-006-NPCC-1
(2)
Implementation
Plan (1)

PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Implementation Plan

Background:

The purpose of this draft Regional Standard is to ensure the development and maintenance of an effective
and coordinated Automatic Underfrequency Load Shedding program in order to preserve the reliability
and integrity of the bulk power system during declining system frequency events.
In the developing the Implementation Plan for PRC-006-NPCC-01 the Standard Drafting Team
considered the following:
1. The requirements listed in this Regional Standard are intended to cover all aspects of the UFLS
program. The Regional Standard Drafting Team (RSDT) coordinated its development with the
draft NERC UFLS Standard PRC-006. The intent of this Regional Standard is to be more
stringent than the continent wide standard while incorporating specific program characteristics
into the requirements.
2. The Implementation Plan for this standard is based, in part, on the timelines reflected in the
existing and ongoing Implementation Plan for NPCC Directory #12 absent the annual milestones
required by Directory #12.

May 5, 2011

Effective Dates:
Eastern Interconnection & Québec Interconnection Portions of NPCC Excluding the Independent
Electricity System Operator (IESO) Planning Coordinator Area of NPCC in Ontario, Canada.
1. The effective date for requirements R1, R2, R3, R4, R5, R6, R7, R8, and R9 is the first day of the
first calendar quarter following applicable regulatory approval but no earlier than Jan 1, 2016 to allow
for the existing implementation plan to be completed.
2. The effective date for requirements R10 through R27 is the first day of the first calendar quarter
two years following applicable governmental and regulatory approval.

Independent Electricity System Operator (IESO) Planning Coordinator’s Area of NPCC in Ontario,
Canada
1. Effective the first day of the first calendar quarter following applicable governmental and
regulatory approval but no earlier than April 1, 2017.

References:
•
•

2006 Assessment of UFLS Adequacy Part 3 Assessment of Program Modifications.
SS38 Underfrequency Load Shedding Support Studies

NPCC Criteria:
•

•

Directory #12 Underfrequency Load Shedding Program Requirements.
A-7 NPCC Glossary of Terms.

May 5, 2011

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

4.
5.
6.

NPCC Regional Standards Committee (RSC) authorized posting UFLS RSAR
development on August 20, 2008.
UFLS RSAR posted on NPCC website on August 25, 2008.
NPCC Reliability Coordinating Committee (RCC) approved the Task Force on System
Studies (TFSS) as the lead task force to initiate drafting a UFLS Regional Standards on
September 4, 2008.
NPCC UFLS Regional Standard Drafting Team initial meeting on January 27, 2009.
First draft posted on the NPCC Website July 13, 2009 for a 45 day comment period.
Second draft posted on the NPCC Website May 26, 2010 for a 45 day comment period.

Description of Current Draft:
This is the third draft of the proposed standard.
Future Development Plan:
Anticipated Action
1. Post the initial draft of the standard for 45
day comment period.

July 13, 2009 to August 27, 2009

2. Respond to comments on the first posting
and post revised standard and
implementation plan for a 45 day
comment period.

September 2009 to May 2010

3. Respond to comments on the 2nd posting.

July 2010 to October 2010

Obtain RSC approval to move the
standard forward to balloting.

November 2010

Post the standard and implementation
plan for a 30 day pre ballot review.

December 2010

6. Conduct a ten day ballot.

Anticipated Date

May 26, 2010 to July 9th, 2010

December 2010

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Respond to ballot comments and post
revised standard and implementation plan
for a 45 day comment period.

May, 2011.

8. Respond to comments on the 3rd posting.

July 2011

Obtain RSC approval to move the
standard forward to balloting.

August 2011

10. Post the standard and implementation
plan for a 30 day pre ballot review.

August 2011

11. Conduct a ten day ballot.

September 2011

12. Membership Approval.

September 2011.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Definitions of Terms Used in Standard
This section includes all newly defined or revised terms used in the proposed standard. Terms
already defined in the NERC Reliability Standards Glossary of Terms are not repeated here.
New or revised definitions listed below become approved when the proposed standard is
approved. When the standard becomes effective, these defined terms will be removed from the
individual standard and added to the NPCC Glossary.
In the standards, defined terms are indicated with its first letter capitalized.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

A. Introduction
1.

Title:

Automatic Underfrequency Load Shedding

Number:

PRC-006-NPCC-1

Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.3. Distribution Provider
4.4. Transmission Owner

(Proposed) Effective Date:

To be established.

B. Requirements

Each Planning Coordinator shall conduct system studies and/or use real time power
flow data captured from actual system events to identify anticipated islands within the
NPCC region to establish requirements for entities aggregating their UFLS programs in
Requirement R3 and R4 and requirements for compensatory load shedding in
Requirement R18. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]

Each Planning Coordinator shall, in accordance with its system studies, identify to the
Regional Entity the generation facilities within its Planning Coordinator Area
necessary to support the UFLS program performance characteristics. [Violation Risk
Factor: High] [Time Horizon: Long Term Planning]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Each Planning Coordinator shall provide to Transmission Owners, Distribution
Providers, and /or Generator Owners within thirty days upon written request the
information on anticipated islands derived from each Planning Coordinator’s system
studies as determined by Requirement R1 and /or real time power flow data pertinent
to requirements for aggregating UFLS programs and/or providing for compensatory
load shedding. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]

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 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 frequency thresholds,
total nominal operating time, and amounts specified in one of the following tables:
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]
•

Distribution Providers and Transmission Owners with 100 MW or more of peak
net Load shall implement a UFLS program with the following attributes:
UFLS Table 1:

Load Shed at
Stage as %
of TO or DP
Load

Cumulative Load
Shed as %
of TO or DP
Load

UFLS Stage

Frequency
Threshold
(Hz)

59.5

0.30

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

Anti-Stall

59.5

10.0

2–3

29.5 – 31.5

Total Nominal
Operating
Time (s)

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

•

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 Table 2:

UFLS Stage

Frequency
Threshold (Hz)

Total Nominal
Operating Time (s)

Load Shed at
Stage as % of TO
or DP Load

Cumulative Load
Shed as % of TO
or DP Load

59.5

0.30

14-25

59.1

0.30

14-25

28-50

•

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 Table 3:

UFLS Stage

Frequency
Threshold (Hz)

Total Nominal
Operating Time (s)

Load Shed at
Stage as % of TO
or DP Load

Cumulative Load
Shed as % of TO
or DP Load

59.5

0.30

28-50

Each Distribution Provider or Transmission Owner that must arm its load to trip on
under frequency 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 their total peak net Load shall: [Violation Risk
Factor: High] [Time Horizon: Long Term Planning

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

5.1

Inform their Planning Coordinator of the need to exceed the stated
tolerances of UFLS Table 1 if applicable and

5.2

Provide their Planning Coordinator with a technical study that demonstrates
that the Distribution Providers or Transmission Owners specific deviations
from the requirements of UFLS Table 1 will not have a significant adverse
impact on the bulk power system.

5.3

Inform their Planning Coordinator of the need to exceed the stated
tolerances of UFLS Table 2 or Table 3, and in the case of Table 2 only, the
need to deviate from providing two stages of UFLS, if applicable, and

5.4

Provide their 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 Table 2
or Table 3

Each Distribution Provider and Transmission Owner in the Eastern Interconnection
portion of NPCC with peak net Load connected to its Facilities shall ensure that the
total nominal operating time includes the under frequency relay operating time plus
any interposing auxiliary relay operating times, communications time, and the rated
breaker interrupting time, such that: [Violation Risk Factor: High] [Time Horizon:
Long Term Planning]
6.1

The under frequency relay operating time shall be measured from the time
the frequency passes through the frequency threshold set point, using a test
rate of linear frequency decay of 0.2 Hz per second.

6.2

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 if the relay operating time is dependent on the rate of frequency
decay.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Each Distribution Provider and Transmission Owner in the Québec Interconnection
portion of NPCC shall implement an automatic UFLS program for its Facilities 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 the following
table: [Violation Risk Factor: High] [Time Horizon: Long Term Planning]

UFLS Table 4

MW
at peak

Mvar
at peak

Total
Nominal
Operating
Time (s)

Rate

Frequency
(Hz)

Threshold Stage 1

–––

58.5

1000*

1000

0.30

Threshold Stage 2

–––

58.0

800*

800

0.30

Threshold Stage 3

–––

57.5

800

0.30

Threshold Stage 4

–––

57.0

800

0.30

–––

59.0

500

20.0

Slope Stage 1

-0.3 Hz/s

58.5

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

0.30

Threshold Stage 5
(anti-stall)

(*Load must
be fixed at all
times.)

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Each Distribution Provider and Transmission Owner in the Québec Interconnection
portion of NPCC with peak net load connected to its Facilities shall insure that 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.[Violation
Risk Factor: High] [Time Horizon: Long Term Planning]

Each Distribution Provider and Transmission Owner shall set their underfrequency
relays with the following minimum time delay:
9.1

Eastern Interconnection – 100 ms

9.2

Québec Interconnection – 200 ms

[Violation Risk Factor: High] [Time Horizon: Long Term Planning]

R10 Each Planning Coordinator shall develop, implement and maintain a program to
establish the appropriate inhibit thresholds (such as but not limited to voltage, current
and time) to be utilized within its region's UFLS Program to insure that the inhibit
settings do not adversely affect the UFLS program. [Violation Risk Factor: High]
[Time Horizon: Long Term Planning

R11 Each Planning Coordinator shall provide to Transmission Owners and Distribution
Providers within its program area the specific inhibit thresholds applicable to each
Transmission Owner or Distribution Providers within 30 days of the initial
determination of the required inhibit threshold settings or for changes to those
settings. [Violation Risk Factor: High] [Time Horizon: Operations Planning]

R12 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 R11. [Violation Risk Factor: High] [Time Horizon:
Operations Planning]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

R13 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 R11. [Violation Risk
Factor: High] [Time Horizon: Operations Planning]

R14

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 be shed by the UFLS relays at each UFLS
stage coincident with their integrated hourly peak 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]

R15 Each Generator Owner shall set each generator under frequency trip relay, if so
equipped, below the appropriate generator under frequency trip protection settings
threshold curve in Figure 1, except as otherwise exempted in Requirements R18 and
R21. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]

R16 Each Generator Owner shall transmit the generator under frequency trip setting and
time constant to its Planning Coordinator within 45 days of the Planning Coordinator’s
request. [Violation Risk Factor: High] [Time Horizon: Operations Planning]

R17 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]

17.1 Ensure that the generating unit does not trip directly or indirectly for
underfrequency conditions above the appropriate generator tripping
threshold curve in Figure 1.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

17.2 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 under frequency conditions
above the appropriate generator under frequency trip protection settings
threshold curve in Figure 1.
17.3 Transmit the generator underfrequency trip setting and time constant to the
Planning Coordinator.

R18 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]
18.1 Set the underfrequency protection to operate at the lowest frequency
possible as demonstrated by the plant design and licensing limitations..
18.2 Transmit the existing under frequency settings and any changes to the under
frequency settings along with the technical basis for the settings to the
Planning Coordinator.
18.3 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.
R19 Each Planning Coordinator in Ontario, Quebec and the Maritime provinces shall apply
the methodology described in Attachment A to determine the compensatory load
shedding that is required in Requirement R18.3 for generating units in its respective
NPCC area. [Violation Risk Factor: High] [Time Horizon: Long Term Planning]

R20 Each Generator Owner, Distribution Provider or Transmission Owner within the
Planning Coordinator area of ISO-NE or the New York ISO shall apply the
methodology described in Attachment B to determine the compensatory load shedding
that is required in Requirement R18.3 for generating units in its respective NPCC area.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

R21 Each Generator Owner of existing nuclear generating plants with units that have under
frequency relay threshold settings above the Eastern Interconnection generator tripping
curve in Figure 1, based on their licensing design basis, are required to adhere to the
following: [Violation Risk Factor: High] [Time Horizon: Long Term Planning]
21.1

Set the under frequency 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.

21.2

Set the frequency trip setting upper tolerance to no greater than + 0.1 Hz.

21.3

Transmit the initial frequency trip setting and any changes to the setting
and the technical basis for the settings to the Planning Coordinator.

R22 Each Transmission Owner and Distribution Provider shall annually provide, with no
more than 15 months between updates, its UFLS program data to its Planning
Coordinator in accordance with R23 for inclusion in the Planning Coordinator’s data
base. [Violation Risk Factor: Lower] [Time Horizon: Long Term Planning]

R23 Each Planning Coordinator shall develop and maintain its UFLS program data base.
The Planning Coordinator shall update its UFLS program database within four months
of receiving the Requirement R22 information. This data base shall include the
following information: [Violation Risk Factor: Lower] [Time Horizon: Operations
Planning]

23.1

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.

23.2

The buses at which the Load is modeled in the NPCC library power flow
case.

23.3

23.4

The location and amount of additional elements to be switched for voltage
control that are coordinated with UFLS program tripping.

23.5

A list of all UFLS relay inhibit functions along with the corresponding
settings and locations of these relays.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

R24 Each Planning Coordinator shall assess that the NPCC UFLS program requirements
within its Planning Coordinator area are satisfied as implemented by Transmission
Owners, Distribution Providers, and Generator Owners. [Violation Risk Factor: High]
[Time Horizon: Long Term Planning]

R25 Each Planning Coordinator shall notify Distribution Providers, Transmission Owners,
and Generator Owners within its Planning Coordinator area of changes to load
distribution needed to satisfy UFLS program requirements.[Violation Risk Factor:
High] [Time Horizon: Long Term Planning]

R26 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 R25. [Violation Risk Factor:
High] [Time Horizon: Long Term Planning]
R27 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
R25. [Violation Risk Factor: High] [Time Horizon: Operations Planning]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Figure 1
Thresholds for Setting Underfrequency Trip Protection for Generators

Frequency (Hz)
60

59.5

58.5

57.5

56.5

56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping

0.1

100

Time (sec)

1000

55.5

55
10000

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
C. Measures

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.
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 shall have evidence such as
reports, data sheets and other test documentation that demonstrates that it meets
Requirement R6.
M7 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 R7.
M8 Each Distribution Provider and Transmission Owner in the Québec Interconnection
shall have evidence such as reports, data sheets and other test documentation that
demonstrates that it meets Requirement R8.
M9 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 R9.
15

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

M10 Each Planning Coordinator shall have evidence such as reports, system studies or
analysis that demonstrates that it meets Requirement R10.
M11 Each Planning Coordinator 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
test reports, data sheets or other documentation that demonstrates that it meets
Requirement R12.
M13 Each Distribution Provider and Transmission Owner shall provide evidence such as
letters, emails or other dated documentation that demonstrates that it meets
Requirement R13.
M14 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
R14.
M15 Each Generator Owner shall provide evidence such as reports, data sheets,
spreadsheets or other documentation that demonstrates that it meets Requirement R15.
M16 Each Generator Owner shall provide evidence such as emails, letters or other dated
documentation that demonstrates that it meets Requirement R16
M17 Each Generator Owner shall provide evidence such as reports, data sheets,
specifications, memorandum or other documentation that demonstrates that it meets
Requirement R17.

M18 Each Generator Owner with existing non-nuclear units in service prior to the effective
date of this Standard which have under frequency tripping that is not compliant with
Requirement R14 shall provide evidence such as reports, spreadsheets, memorandum
or dated documentation demonstrating that it meets Requirement R18.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

M19 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 R19.
M20 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 R20.
M21 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 R21.

M22 Each Distribution Provider and Transmission Owner shall provide evidence such as
reports, spreadsheets and other dated documentation that demonstrates that it meets
Requirement R22.

M23 Each Planning Coordinator shall provide evidence such as spreadsheets, system
studies, or other documentation that demonstrates that it meets the requirements of
Requirement R23.

M24 Each Planning Coordinator shall provide evidence such as reports, system studies
and/or real time power flow data captured from actual system events that demonstrates
that it meets the requirements of R24.
M25 Each Planning Coordinator shall provide evidence such as emails, memorandum or
other dated documentation that it meets Requirement R25.
M26 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as reports, spreadsheets or other documentation that demonstrates that it
meets Requirement R26.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

M27 Each Distribution Provider, Transmission Owner and Generator Owner shall provide
evidence such as letters, emails or other dated documentation that demonstrates it
meets Requirement R27

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
D. 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, 6,7,8,9,12,13,14, and 22.
The Planning Coordinator shall keep evidence for three calendar years for
Measures 1, 2, 3, 10, 11, 19, 23, 24, and 25.
The Distribution Provider, Transmission Owner, and Generator Owner shall keep
evidences for three calendar years for Measure 20, 26, and 27.
The Generator Owner shall keep evidence for three calendar years for Measures
15,16,17,18, and 21.

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.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
2.

Violation Severity Levels

Requirement

Lower VSL

Moderate VSL

High VSL

Severe VSL

N/A

The Planning Coordinator did not
conduct system studies or use real
time power flow data captured
from actual system events to
identify anticipated islands within
the NPCC region used to establish
requirements for entities
aggregating their UFLS programs,
and requirements for
compensatory load shedding.

N/A

The Planning Coordinator did not
identify the generation facilities
within its Planning Coordinator
Area necessary to support the
UFLS program.

N/A

The Planning Coordinator failed
to provide to Transmission
Owners, Distribution Providers,
and /or Generator Owners within
thirty (30) days upon written
request the information on
anticipated islands derived from
each Planning Coordinator’s
system studies as determined by
Requirement R1 and /or real time
power flow data pertinent to
requirements for aggregating

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
UFLS programs and/or providing
for compensatory load shedding.
R4

N/A

The Distribution Provider or
Transmission Owner did not arm
its load to trip on
underfrequency in order to meet
its minimum obligations and in
doing so exceeded the tolerances
and/or deviated from the number
of stages and frequency set
points of the UFLS program as
specified in the tables contained
in Requirement R4, as applicable
depending on their total peak net
Load.

did not provide the Planning
Coordinator with an analysis
demonstrating that no alternative
load shedding solution is available
that would allow the Distribution

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

N/A

providing two stages of UFLS.

Provider or Transmission Owner to
comply with the appropriate table.

N/A

The Distribution Provider or
Transmission Owner in the Eastern
Interconnection portion of NPCC
with peak net Load connected to its
Facilities shall ensure that 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, but
did not measure the
underfrequency relay operating
time from the time the frequency
passes through the frequency
threshold set point, using a test rate
of linear frequency decay of 0.2 Hz
per second, OR the measurement
and any subsequent testing of the
UFLS relays did not utilize a test
rate of linear frequency decay of
0.2 Hz per second if the relay
operating times is dependent on the
rate of frequency decay.

The Distribution Provider or
Transmission Owner in the
Eastern Interconnection portion
of NPCC with peak net Load
connected to its Facilities did not
ensure that the total nominal
operating time included the
underfrequency relay operating
time plus any interposing
auxiliary relay operating times,
communications time, and the
rated breaker interrupting time.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
R7

N/A

The Distribution Provider or
Transmission Owner did not
implement an automatic UFLS
program for its facilities, or did
not implement collectively by
the mutual agreement with one
or more Distribution Providers
and Transmission Owners within
the same island an aggregated
automatic UFLS program based
on the frequency thresholds,
slopes, total nominal operating
time, and the amounts shown in
the table.

N/A

The Distribution Provider or
Transmission Owner did not
ensure that total nominal
operating time included the
underfrequency relay operating
time plus any interposing
auxiliary relay operating times,
communications time, and the
rated breaker interrupting time,
or the underfrequency relay
operating time was not measured
from the time when the
frequency passes through the
frequency threshold set point.

N/A

The Distribution Provider or
Transmission Owner failed to set
their underfrequency relays with
the minimum time delay
requirement.

R10

N/A

The Planning Coordinator failed
to develop, implement, and
maintain a program to establish
the appropriate voltage inhibit

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
threshold to be used within its
region’s UFLS program.
R11

N/A

The Planning Coordinator failed
to provide to Transmission
Owners and Distribution
Providers within its program
area the specific inhibit
thresholds applicable to each
Transmission Owner or
Distribution Provider within
thirty (30) days of the initial
determination of the required
inhibit threshold settings or for
changes to those settings.

R12

N/A

The Distribution Provider or
Transmission Owner failed to
implement the inhibit threshold
settings based on the notification
provided by the Planning
Coordinator in accordance with
Requirement R11.

R13

N/A

The Distribution Provider or
Transmission Owner shall
develop and submit an
implementation plan within
ninety (90) days of the request
from the Planning Coordinator
for approval by the Planning
Coordinator in accordance with
R11.

R14

The Transmission Owner or
Distribution Provider exceeded
the annual documentation

The Transmission Owner or
Distribution Provider exceeded the
annual documentation submission

The Transmission Owner or
Distribution Provider did not
provide documentation to its

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
submission to its Planning
Coordinator by up to thirty (30)
days, OR exceeded by up to thirty
(30) the fifteen (15) months
between updates provided to its
Planning Coordinator of the
actual net load that would be shed
by the UFLS relays, as
determined by measuring actual
metered load through the switches
that would be opened by the
UFLS relays, that were armed to
shed at each UFLS stage
coincident with their integrated
hourly peak during the previous
year.

submission to its Planning
Coordinator by up to sixty (60)
days, OR exceeded by up to
sixty (60) days the fifteen (15)
months between updates
provided to its Planning
Coordinator of the actual net
load that would be shed by the
UFLS relays, as determined by
measuring actual metered load
through the switches that would
be opened by the UFLS relays,
that were armed to shed at each
UFLS stage coincident with their
integrated hourly peak during
the previous year.

to its Planning Coordinator by up
to ninety (90) days, OR exceeded
by up to ninety (90) the fifteen (15)
months between updates provided
to its Planning Coordinator of the
actual net load that would be shed
by the UFLS relays, as determined
by measuring actual metered load
through the switches that would be
opened by the UFLS relays, that
were armed to shed at each UFLS
stage coincident with their
integrated hourly peak during the
previous year.

Planning Coordinator of actual
net load data or updates to the
data that would be shed by the
UFLS relays, as determined by
measuring actual metered load
through the switches that would
be opened by the UFLS relays,
that were armed to shed at each
UFLS stage coincident with their
integrated hourly peak during
the previous year.

R15

N/A

The Generator Owner failed to
ensure that its generating units
do not trip for underfrequency
conditions above the appropriate
generator underfrequency trip
protection settings threshold
curve unless exempted.

R16

N/A

The Generator Owner did not
transmit the generator
underfrequency trip setting and
time constant to its Planning
Coordinator within forty-five
(45) days of the Planning
Coordinator’s request.

R17

N/A

The Generator Owner did not
transmit the generator
underfrequency trip setting and
time setting to the Planning

The Generator Owner failed to
design auxiliary systems or
devices used for the control and
protection of auxiliary systems

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Coordinator.

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.

R18

N/A

The Generator Owner of existing
non-nuclear units in service prior
to the effective date of this
standard, and which have
underfrequency tripping set to
trip above the curve, did not set
the underfrequency protection to
operate at the lowest frequency
possible as demonstrated by the
plant design and licensing
limitations, OR did not transmit
the initial underfrequency
settings and any changes to the
underfrequency setting s and the
technical basis for those settings
to the Planning Coordinator. OR
did not have compensatory load
shedding that was adequate to
compensate for the loss of their
generator due to early tripping.

R19

N/A

The Planning Coordinator did
not apply the methodology
described in Attachment A to
determine the compensatory load
shedding that is required.

R20

N/A

The Generator Owner,
Distribution Provider, or

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Transmission Owner did not
apply the methodology described
in Attachment B to determine
the compensatory load shedding
that is required.
R21

N/A

R22

The Transmission Owner or
Distribution Provider exceeded
the annual documentation
submission to its Planning
Coordinator by up to thirty (30)
days, OR exceeded by up to thirty
(30) days the fifteen (15) months
between updates provided to its
Planning Coordinator of UFLS
program data.

The Transmission Owner or
Distribution Provider exceeded
the annual documentation
submission to its Planning
Coordinator by up to sixty (60)
days, OR exceeded by up to
sixty (60) days the fifteen (15)
months between updates
provided to its Planning
Coordinator of UFLS program

N/A

The Transmission Owner or
Distribution Provider exceeded the
annual documentation submission
to its Planning Coordinator by up
to ninety (90) days, OR exceeded
by up to ninety (90) days the
fifteen (15) months between
updates provided to its Planning
Coordinator of UFLS program
data.

The Generator Owner of existing
boiling water nuclear generating
plants with units that have
underfrequency relay threshold
settings above the Eastern
Interconnection generator
tripping curve based on their
licensing design basis did not set
the 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., OR reduce
the frequency trip setting
tolerance on those units with
threshold setting tolerances
greater than +0.1Hz., OR did not
transmit the initial frequency trip
settings or any changes to the
settings to the Planning
Coordinator.

The Transmission Owner or
Distribution Provider did not
provide its UFLS program data
or updates to its Planning
Coordinator.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
data.
R23

The Planning Coordinator did not
update its UFLS program data
base within four months of
receiving the requisite
information, or did not have data
for one of the parameters listed in
23.1 through 23.5.

The Planning Coordinator did
not update its UFLS program
data base within four months of
receiving the requisite
information, or did not have data
for two of the parameters listed
in 23.1 through 23.5.

The Planning Coordinator did not
update its UFLS program data base
within four months of receiving the
requisite information, or did not
have data for three of the
parameters listed in 23.1 through
23.5

The Planning Coordinator did
not develop or maintain its
UFLS program data base.

R24

N/A

The Planning Coordinator did
not assess that the NPCC UFLS
program requirements within its
Planning Coordinator area are
satisfied as implemented by
Transmission Owners,
Distribution Providers, and
Generator Owners.

R25

N/A

The Planning Coordinator did
not notify its Distribution
Providers, Transmission
Owners, and Generator Owners
of changes to load distribution
needed to satisfy UFLS program
requirements.

R26

N/A

The Distribution Provider,
Transmission Owner, or
Generator Owner did not
implement the load distribution
changes based on the
notification provided by the
Planning Coordinator.

R27

N/A

The Distribution Provider,
Transmission Owner, or Generator
Owner did not submit an
implementation plan within ninety
(90) days of the request from the

The Distribution Provider,
Transmission Owner, or
Generator Owner did not
develop an implementation plan
at the request of the Planning

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Planning Coordinator.

Coordinator.

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 under frequency 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 under frequency 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 Under frequency 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
31

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.

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 under
frequency 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 Under frequency 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

Standard PRC-006-NPCC-1 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.
2.5The amount of compensatory load shedding shall be equivalent (±5%) to the

Consideration of Comments on PRC-006-NPCC-1 – Frequency Load
Shedding
The Regional Reliability Standard PRC-006-NPCC-1 Frequency Load Shedding Drafting Team
thanks all commenters who submitted comments on the first posting of the PRC-006-NPCC1—Automatic Under frequency Load Shedding. These standards were posted for a 45-day
public comment period from January 11, 2010 through February 24, 2011. The
stakeholders were asked to provide feedback on the standards through a special Electronic
Comment Form. There were 11 sets of comments, including comments 29 different people
from approximately 22 companies representing 9 of the 10 Industry Segments as shown in
the table on the following pages.

http://www.nerc.com/filez/regional_standards/regional_reliability_standards_under_developmen
t.html
If you feel that your comment has been overlooked, please let us know immediately. Our
goal is to give every comment serious consideration in this process! If you feel there has
been an error or omission, you can contact the Vice President and Director of Standards,
Herb Schrayshuen, at 609-452-8060 or at [email protected]. In addition, there is
a NERC Reliability Standards Appeals Process. 1

The appeals process is in the Reliability Standards Development Procedures:
http://www.nerc.com/standards/newstandardsprocess.html.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Index to Questions, Comments, and Responses
1.

Was the proposed standard developed in a fair and open process, using the
associated Regional Reliability Standards Development Procedure? …. ...........5

Does the proposed standard pose an adverse impact to reliability or commerce
in a neighboring region or interconnection? …. ................................................ 7

Does the proposed standard pose a serious and substantial threat to public
health, safety, welfare, or national security? …. ............................................. 12

Does the proposed standard pose a serious and substantial burden on
competitive markets within the interconnection that is not necessary for
reliability? …. ................................................................................................. 14

Does the proposed regional reliability standard meet at least one of the
following criteria? ………………………………………………………………………………..17

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding
The Industry Segments are:
1 — Transmission Owners
2 — RTOs, ISOs
3 — Load-serving Entities
4 — Transmission-dependent Utilities
5 — Electric Generators
6 — Electricity Brokers, Aggregators, and Marketers
7 — Large Electricity End Users
8 — Small Electricity End Users
9 — Federal, State, Provincial Regulatory or other Government Entities
10 — Regional Reliability Organizations, Regional Entities

Group/Individual

Commenter

Organization

Registered Ballot Body Segment
1

Group

Mike Garton

Electric Market Policy

Additional Member Additional Organization

Region

Michael Gildea

Dominion Resources Services, Inc. MRO

Louis Slade

Dominion Resources Services, Inc. SERC

Connie Lowe

Dominion Resources Services, Inc. RFC

Group

Denise Koehn

Bonneville Power Administration

Additional Member Additional Organization
1.

Greg Vassallo

Group

Region

Segment
Selection

Public Service Enterprise Group

Additional Member Additional Organization

BPA, Transmission Customer Service Engineering WECC

Pat Hervochon

Segment
Selection

Region

Segment
Selection

Kenneth Brown

PSE&G

RFC

1, 3

Dominick Grasso

PSEG Fossil

RFC

Peter Dolan

PSEG ER&T

RFC

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Group/Individual

Commenter

Organization

Registered Ballot Body Segment
1

Scott Slickers

PSEG Power NY

NPCC

Eric Schmidt

PSEG ER&T

NPCC

Clint Bogan

Odessa Power Partners ERCOT

Steven Kimmish

PSEG ER&T

Group

Frank Gaffney

ERCOT

Region

Segment
Selection

Timothy Beyrle

Utilities Commission of New Smyrna Beach FRCC

Greg Woessner

Kissimmee Utility Authority

FRCC

Jim Howard

Lakeland Electric

FRCC

Lynne Mila

City of Clewiston

FRCC

Joe Stonecipher

Beaches Energy Services

FRCC

Cairo Vanegas

FPUA

FRCC

Randy Hahn

Ocala Electric Utility

FRCC

Individual

Cynthia S. Bogorad

Transmission Access Policy Study Group

Individual

Michael Lombardi

Northeast Utilities

Individual

J. S. Stonecipher

City of Jacxksonville Beach dba/Beaches
Energy Services

Individual

Dan Rochester

Independent Electricity System Operator

Individual

Don Weaver

New Brunswick System Operator

10.

Individual

Rex Roehl

Indeck Energy Services

11.

Individual

Brian Evans-Mongeon

Utility Services Inc.

Florida Municipal Power Agency

Additional Member Additional Organization

X
X

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

1. Was the proposed standard developed in a fair and open process, using the associated Regional Reliability Standards Development
Procedure?
Summary Consideration:

Organization
Dominion

Yes or No
No

Electric Market Policy

Question 1 Comment
PRC-006-NPCC-1 was filed concurrently at NPCC and NERC. However, the ballot for this standard has not
yet passed at NPCC. Accordingly, this standard is not ripe for NERC consideration. Dominion suggests that
NERC suspend this proceeding until the ballot passes at NPCC, and then reopen this proceeding for further
comments based on the standard as finally approved by NPCC.

Response: Thank you for your comment. As noted in the NERC Regional Reliability Evaluation Procedure the region may request that NERC
consideration of the standard occur concurrent with the anticipated final public comment period in the regional entity's regional standard development
process.

http://www.nerc.com/docs/sac/rrswg/NERC_Regional_Reliability_Evaluation_Procedure.pdf

Bonneville Power Administration

Yes

Transmission Access Policy
Study Group

Yes

Public Service Enterprise Group

As the NPCC process is still ongoing, it is difficult to develop an opinion at this time whether that process was
fair and open.

http://www.nerc.com/docs/sac/rrswg/NERC_Regional_Reliability_Evaluation_Procedure.pdf
Florida Municipal Power Agency

The NPCC process is still ongoing, but it is our understanding that so far it has been fair and open.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 1 Comment

Response: Thank you for your comment.

Northeast Utilities

Yes

City of Jacksonville Beach
dba/Beaches Energy Services

Yes

Yes, This is pretty much what we're doing now with some good success.

Response: Thank you for the comment.
Independent Electricity System
Operator

Yes

New Brunswick System Operator

Yes

Indeck Energy Services

1) None of our generating plants is a member of NPCC. One of them is not large enough to register for
NERC membership and is connected at 34 kV. The pre-ballot review of the regional standard was not
posted for public comment. No comment form is available on the public NPCC website. The letter
announcing a webinar on 1/4/2011 was dated 1/6/2011. The letter also announced an extension of the
comment period from the date of the letter to a week later. The process is patently unfair to generators or
others in NPCC that are not members.

2) The standard improperly extends NERC standards to non-registered entities. NPCC's authority to
implement regional reliability standards issues from its delegation agreement with NERC. NERC has
chosen not to extend registration to entities <20 MW or not connected to the BES.
Response: Thank you for your comment.
1) According to the NPCC Regional Standards Development Procedure the pre ballot review is not intended for comment. Additionally, the NPCC
bylaws promote membership for all registered entities which allow members to actively participate in the development of regional standards.
2)The Regional Standard Drafting Team has reviewed your concerns and notes that the NERC Statement of Registry Criteria does not limit registration
of generation to those greater than 20MVA. However, the applicability in Section 4 has been revised and Attachment C has been removed.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Utility Services Inc.

Yes or No

Question 1 Comment

Yes

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

2. Does the proposed standard pose an adverse impact to reliability or commerce in a neighboring region or
interconnection?
Summary Consideration:

Organization
Dominion

Yes or No
Yes

Question 2 Comment
See comments (item #1) below under Question 5.

Electric Market Policy
Response: Thank you for your comment. Please see the response developed for item#1 Question 5.
Bonneville Power Administration

Public Service Enterprise Group

Florida Municipal Power Agency

No Comment

Yes

FMPA questions the need for the proposed regional standard. A continent-wide UFLS standard has been
drafted and approved by stakeholders and the NERC Board, and will presumably be filed at FERC in the very
near future. That standard is sufficient to protect reliability; the industry should not, at this point in time, be
devoting its scarce resources to developing regional standards on the same subject. Reliability Standard
PRC-006-1 requires Planning Coordinators to develop UFLS programs. It does not require Regional Entities
to develop separate reliability standards.
Furthermore, a regional standard on this topic could place the entities in NPCC under a double jeopardy
threat since all the entities will need to comply with mandatory NERC and Regional Standards. This double
jeopardy threat is exacerbated by the fact that the continent-wide standard requires a periodic review and
potential change to the program every five years whereas the NPCC program locks the UFLS relay settings
into a regional standard that cannot be changed without FERC approval. If those relay settings need to be
changed pursuant to the continent-wide standard, there would be a conflict between the continent-wide
standard and the regional standard that could only be resolved through a revision to one of the standards,
which would have to be FERC-approved to go into effect. In the meantime, entities would have no choice but
to be non-compliant with one of the two standards. NPCC would be better served by being consistent with

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 2 Comment
NERC’s PRC-006-1 and not developing a UFLS program as a regional standard.
.
The draft regional standard’s proposed applicability to Generator Owners--including to small, otherwise
unregisterable generators--highlights the proposed framework’s inappropriateness in the context of continentwide standards. NERC’s PRC-006-1 does not apply to Generator Owners because the frequency protection
set points are being covered in PRC-024-1, which is currently with its SDT. Covering generators in a regional
PRC-006 will result in confusion and a lack of coordination, including the risk of a conflict between the
regional standard and PRC-024-1. If NPCC proceeds down a path of developing a regional standard, at a
minimum, applicability to generators should be removed altogether.

Furthermore, the proposed NPCC UFLS program is not robust enough to serve the overall reliability of the
Eastern Interconnect. The NPCC UFLS program seems to be designed such that a 1% inaccuracy causes
the UFLS program to no longer meet performance requirements. This is far too tight of a tolerance for an
inherently inaccurate analysis and reflects a lack of robustness of the UFLS program. The Eastern
Interconnect would be better protected from an event that causes multiple region instability by a more robust
UFLS program.It seems that one of the primary drivers in designing NPCC’s UFLS program is to cover the
Connecticut island, with roughly 6000 MW of peak load. The SS-38 report titled “Determination of a
Threshold for Generator Applicability” dated November 15, 2010 shows in its Table 1 on Page 3 that there is
only a 1% margin of error in the supply / demand mismatch in the design of the program (or 60 MW).There
are numerous sources of inaccuracy of greater than 1% in the analysis and design of a UFLS program.
Hence, since the proposed UFLS program cannot tolerate a 1% error, it is insufficiently robust to protect
reliability. A UFLS program more robust than that proposed in this regional reliability standard would benefit
other regions in the Eastern Interconnect by helping to defray opportunity for cascading from one region to
another.Examples of sources of inaccuracy greater than 1% include:

1. Load models are nowhere close to 1% accurate. As an industry, we are unavoidably uncertain of the
extent to which electronic and power electronic equipment such as variable speed drives, compact
fluorescent lighting, etc., have penetrated customer premises; we cannot know this because we cannot

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 2 Comment
control customer behavior. In addition, we can only approximate how these devices interact with voltage and
frequency excursions. An inaccurate load model showing that load decreases less by voltage than actual, for
instance, could result in post-disturbance conditions with a far greater than 1% supply/demand mismatch,
outside the NPCC design tolerance. If post-disturbance load is actually 60 MW more than modeled, that
disparity has the same impact as tripping an additional 60 MW of generation.

2. UFLS relays are typically on individual distribution feeders, each of which have different load profiles,
different distributed generation patterns, different levels of important load such as hospitals, and different
levels of electronic and power electronic loads, and are in other ways dissimilar to each other and to the
overall system load pattern. Hence, load diversity with respect to time of day, day of week, time of season,
amount of distributed generation (e.g., generator assistance programs, net-metering and feed-in tariffs),
priority of loads, composition of loads, etc., will result in a larger than 1% inaccuracy in the amount of load
tripped by the UFLS program. If 60 MW too little load is shed, it has the same impact as tripping an additional
60 MW of generation.

3. The continent-wide PRC-006-1 recently approved by the BOT contains a reasonable, but arbitrary
assumption of a 25% supply / demand mismatch. The fact that the NERC standard had to choose a relatively
arbitrary number shows the inexactness of the science of designing a UFLS program. This inexactness runs
counter to a philosophy of designing a UFLS program with only a 1% margin of error; such a UFLS program
lacks the robustness of larger design tolerances.

4. Many more examples exist of inaccuracies inherent in stability studies and UFLS program design greater
than 1%, such as: a) governing systems are difficult and risky to test and their performance characteristic
changes with different operating conditions such as temperature, pressure and power level; and b) the partial
differential equations and numerical methods that describe the stability response of the system are subject to
what mathematicians call “Chaos Theory” and cannot be accurate to within 1%.NPCC mistakenly believes
that a 1% design tolerance can be achieved and uses this mistaken belief to include very small generators in
its UFLS program. As shown above, a 1% design tolerance cannot be achieved due to the very nature of

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 2 Comment
variable load and other variables that cannot be modeled to within a 1% margin of error.The correct approach
is to determine the range of error inherent in the variables used in performing UFLS program design. If a
variable cannot be modeled to within a +/-10% accuracy bandwidth (as is likely the case of loads and load
models), the UFLS program should be designed to be robust enough to tolerate this margin of error. By not
designing the UFLS program with more reasonable design tolerances, the NPCC program creates
unnecessary risk to the reliability of the Eastern Interconnect.

Response: Thank you for your comment. The standard was developed in response to a request from NERC to satisfy FERC Order
693 issued in 2006. At that time, twenty four standards were identified as "fill in the blank" and as a result the FERC directed NERC to modify the
individual standards reliance on the Regional Reliability Organization.
Additionally, of those twenty four standards, four were identified by NERC and the regions to be regionally specific enough to warrant the development of
a regional standard and Under Frequency Load Shedding is one of those four standards.
The remaining comments are beyond the scope of Question#2.

Transmission Access Policy
Study Group

Yes

TAPS questions the need for the proposed regional standard. A continent-wide UFLS standard has been
drafted and approved by stakeholders and the NERC Board, and will presumably be filed at FERC in the very
near future. That standard is sufficient to protect reliability; the industry should not, at this point in time, be
devoting its scarce resources to developing regional standards on the same subject. Reliability Standard
PRC-006-1 requires Planning Coordinators to develop UFLS programs. It does not require Regional Entities
to develop separate UFLS reliability standards.Furthermore, a regional standard on this topic could place the
entities in NPCC under a double jeopardy threat since all the entities will need to comply with mandatory
NERC and Regional Standards. This double jeopardy threat is exacerbated by the fact that the continentwide standard requires a periodic review and potential change to the program every five years whereas the
NPCC program locks the UFLS relay settings into a regional standard that cannot be changed without FERC
approval. If those relay settings need to be changed pursuant to the continent-wide standard, there would be
a conflict between the continent-wide standard and the regional standard that could only be resolved through
a revision to one of the standards, which would have to be FERC-approved to go into effect. In the
meantime, entities would have no choice but to be non-compliant with one of the two standards. NPCC would
be better served by being consistent with NERC’s PRC-006-1 and not developing a UFLS program as a
regional standard. The draft regional standard’s proposed applicability to Generator Owners--including to
small, otherwise unregisterable generators--highlights the proposed framework’s inappropriateness in the
context of continent-wide standards. NERC’s PRC-006-1 does not apply to Generator Owners because the

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 2 Comment
frequency protection set points are being covered in PRC-024-1, which is currently with its SDT. Covering
generators in a regional PRC-006 will result in confusion and a lack of coordination, including the risk of a
conflict between the regional standard and PRC-024-1. If NPCC proceeds down a path of developing a
regional standard, at a minimum, applicability to generators should be removed altogether.Furthermore, the
proposed NPCC UFLS program is not robust enough to serve the overall reliability of the Eastern
Interconnect. The NPCC UFLS program seems to be designed such that a 1% inaccuracy causes the UFLS
program to no longer meet performance requirements. This is far too tight of a tolerance for an inherently
inaccurate analysis and reflects a lack of robustness of the UFLS program. The Eastern Interconnect would
be better protected from an event that causes multiple region instability by a more robust UFLS program.It
seems that one of the primary drivers in designing NPCC’s UFLS program is to cover the Connecticut island,
with roughly 6000 MW of peak load. The SS-38 report titled “Determination of a Threshold for Generator
Applicability” dated November 15, 2010 shows in its Table 1 on Page 3 that there is only a 1% margin of error
in the supply / demand mismatch in the design of the program (or 60 MW).There are numerous sources of
inaccuracy of greater than 1% in the analysis and design of a UFLS program. Hence, since the proposed
UFLS program cannot tolerate a 1% error, it is insufficiently robust to protect reliability. A UFLS program
more robust than that proposed in this regional reliability standard would benefit other regions in the Eastern
Interconnect by helping to defray opportunity for cascading from one region to another.Examples of sources
of inaccuracy greater than 1% include:1. Load models are nowhere close to 1% accurate. As an industry, we
are unavoidably uncertain of the extent to which electronic and power electronic equipment such as variable
speed drives, compact fluorescent lighting, etc., have penetrated customer premises; we cannot know this
because we cannot control customer behavior. In addition, we can only approximate how these devices
interact with voltage and frequency excursions. An inaccurate load model showing that load decreases less
by voltage than actual, for instance, could result in post-disturbance conditions with a far greater than 1%
supply/demand mismatch, outside the NPCC design tolerance. If post-disturbance load is actually 60 MW
more than modeled, that disparity has the same impact as tripping an additional 60 MW of generation.2.
UFLS relays are typically on individual distribution feeders, each of which have different load profiles, different
distributed generation patterns, different levels of important load such as hospitals, and different levels of
electronic and power electronic loads, and are in other ways dissimilar to each other and to the overall system
load pattern. Hence, load diversity with respect to time of day, day of week, time of season, amount of
distributed generation (e.g., generator assistance programs, net-metering and feed-in tariffs), priority of loads,
composition of loads, etc., will result in a larger than 1% inaccuracy in the amount of load tripped by the UFLS
program. If 60 MW too little load is shed, it has the same impact as tripping an additional 60 MW of
generation.3. The continent-wide PRC-006-1 recently approved by the BOT contains a reasonable, but
arbitrary assumption of a 25% supply / demand mismatch. The fact that the NERC standard had to choose a
relatively arbitrary number shows the inexactness of the science of designing a UFLS program. This
inexactness runs counter to a philosophy of designing a UFLS program with only a 1% margin of error; such a
UFLS program lacks the robustness of larger design tolerances.4. Many more examples exist of inaccuracies

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 2 Comment
inherent in stability studies and UFLS program design greater than 1%, such as: a) governing systems are
difficult and risky to test and their performance characteristic changes with different operating conditions such
as temperature, pressure and power level; and b) the partial differential equations and numerical methods
that describe the stability response of the system are subject to what mathematicians call “Chaos Theory” and
cannot be accurate to within 1%.NPCC mistakenly believes that a 1% design tolerance can be achieved and
uses this mistaken belief to include very small generators in its UFLS program. As shown above, a 1%
design tolerance cannot be achieved due to the very nature of variable load and other variables that cannot
be modeled to within a 1% margin of error.The correct approach is to determine the range of error inherent in
the variables used in performing UFLS program design. If a variable cannot be modeled to within a +/-10%
accuracy bandwidth (as is likely the case with respect to loads and load models), the UFLS program should
be designed to be robust enough to tolerate this margin of error. By not designing the UFLS program with
more reasonable design tolerances, the NPCC program creates unnecessary risk to the reliability of the
Eastern Interconnect.

Response: Thank you for your comment. The standard was developed in response to a request from NERC to satisfy FERC Order
693 issued in 2006. At that time, twenty four standards were identified as "fill in the blank" and as a result the FERC directed NERC to modify the
individual standards reliance on the Regional Reliability Organization.
Additionally, of those twenty four standards, four were identified by NERC and the regions to be regionally specific enough to warrant the development of
a regional standard and Under Frequency Load Shedding was one of those four standards.
The remaining comments are beyond the scope of Question#2.

Northeast Utilities

City of Jacxksonville Beach
dba/Beaches Energy Services

Independent Electricity System
Operator

New Brunswick System Operator

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 2 Comment

Yes

The standard's incorporation of generation that is unregistered in the ERO Compliance activities will adversely
impact reliability. The standard proposes to include generation between 1 MVA and the registration criteria.
Without a thorough examination of the impacts of this generation to the compliance, it is unknown how these
"new" registered entities will be dealt with. Further, the standard's requirements in certain ways is
inconsistent with the underlying study that is the basis for the UFLS program. The standard requires differing
curtailment requirements for load versus load being shed for compensatory generation that is above the
curve. Reported data is based upon non-coincidentalized readings while the study is predicated upon
coincidentalized meter readings. The standards expose Registered Entities to double jeopardy when there is
a violation. Compensatory loadshedding can be difficult to achieve when there are no willing players and the
objective creates financial incentives to entities to withhold from negotiations.

Indeck Energy Services
Utility Services Inc.

Response: Thank you for response. The applicability in Section 4 has been revised and Attachment C has been removed.
Additionally, the SS-38 study represents the initial baseline for the Under Frequency program within NPCC. Each PC shall conduct and document a UFLS
design assessment that determines through dynamic simulation whether the UFLS program meets the minimum performance characteristics as defined
in the continent wide draft PRC-006.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

3. Does the proposed standard pose a serious and substantial threat to public health, safety, welfare, or national
security?
Summary Consideration:

Organization

Yes or No

Electric Market Policy

Bonneville Power Administration

Question 3 Comment

Not that we are aware of.
Response: Thank you for your comment.

Transmission Access Policy
Study Group

Public Service Enterprise Group
Florida Municipal Power Agency
Northeast Utilities

City of Jacxksonville Beach
dba/Beaches Energy Services

Independent Electricity System
Operator

New Brunswick System Operator

Indeck Energy Services

Yes

It proposes to drop 50% of load in some islanded areas at frequencies above 58 hz. If they are islanded, they
are no longer a risk to reliability of the system. These islanded areas may be subsidizing the larger areas at
great cost and potential safety risk to these customers.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 3 Comment

Response: Thank you for your response. The results of studies conducted by the NPCC SS38 technical committee showed that the current frequency
response for the islands tested are similar to the responses obtained in Part III of the 2006 UFLS Assessment. Thus the variances proposed by the
Regional Standard Drafting Team (RSDT) for the small load serving entities are acceptable according to the current levels of load served by such entities
on the NPCC system.
SS-38 observed that the draft NPCC standard did not specify an upper limit on the amount of load to be armed for UFLS for LSE’s in Table 2 and 3 of the
draft standard.
SS-38 feels that a cumulative upper limit of 50% would keep the amount of load armed for UFLS by these LSE’s (i.e. 50% at the first stage for Table #3 and
25% each at the first and third stages for Table #2) closer to the original program design while providing latitude to accommodate any constraints due to
the granularity of loads on a limited numbers of feeders.

The data submitted for each Area showed that the amount of load in each of the small LSE categories to be small percentages of the overall peak load for
current day system conditions. It is recognized that these upper limits may require revision if system conditions change and more LSEs are classified.

Utility Services Inc.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

4. Does the proposed standard pose a serious and substantial burden on competitive markets within the
interconnection that is not necessary for reliability?
Summary Consideration:

Organization

Yes or No

Electric Market Policy

Bonneville Power Administration

Public Service Enterprise Group

Transmission Access Policy
Study Group

Yes

Question 4 Comment

In requirement R17, the standard would force generators that do not meet the performance requirements in
the standard (non-conforming generators) to either: 1) make substantial investments to meet performance
requirements imposed on them after they are already interconnected and in commercial operation, or 2) enter
an agreement for compensatory load shedding with one of a limited number of entities that can offer such
service, and with no market to inform pricing of such service. Either option is a significant burden on the
competitiveness of these generators which results in a substantial burden on competitive markets.

Also, as discussed in response to Question 2, the 1% design tolerance desired by the NPCC UFLS program
design team is a flaw in the design itself; hence, with a more reasonable design tolerance, there is no
reliability reason to place this unreasonable burden on small generators.
Compensatory load shedding should NOT be allowed for two reasons: 1) the standards should not force
agreements to be made; and 2) the UFLS program would become a highly complex scheme with settings that
would need to change over time to reflect the status of the non-conforming generator, e.g., if the unit were offline, then too much load would be "armed" to trip, so, those relay settings would need to be changed when
the unit was offline.The complexity of a UFLS program that would have to track the status of non-conforming
generators is staggering. For instance, in order to protect the 1% design tolerance of supply / demand
balance that the drafters of the standard mistakenly believe is important, the UFLS relay settings would need
to change every time the generator changed output. For instance, a non-conforming generator with a capacity
of 300 MW would presumably have 300 MW of compensatory load shedding. If it were running at 200 MW,
then we would want the 300 MW of compensatory load shedding dropped to 200 MW. How would such a

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 4 Comment
thing be possible if we are limited to a finite level of distribution circuits whose load varies minute to minute
with different load patterns, with varying levels of critical loads (e.g., hospitals) and non-critical loads on those
circuits? At what UFLS steps would the compensatory load shedding be adjusted? Would it be multiple
steps? If the generator were providing regulation service, the relay settings would need to change minute by
minute on different circuits depending on actual loads on those circuits. If the ability to make such minute-byminute relay changes were not in place, would the generator be barred from participating in the regulation
service ancillary services market, further burdening competitive markets? Compensatory load shedding is illconceived and highly impractical.The NERC-wide standard recently approved by the BOT takes the correct
approach. Existing non-conforming generators of a sufficient size to matter should be modeled and the UFLS
program be designed in a robust enough fashion to handle the non-conforming generation.

Response: Thank you for your comment. The RSDT acknowledges the technical challenges of administering the compensatory load shedding
program and as a result has developed requirements stating that all new units shall conform to the generator tripping curve.
Additionally, to address your concern regarding generators that are already interconnected and in commercial operation, non conforming
generators either have existing contracts to provide for compensatory load shedding or have mitigated the conditions that would trip the unit
above the appropriate generator tripping curve.
These, requirements are contained as criteria within the approved NPCC Directory #12 and are currently in effect throughout the NPCC region.
Finally, the NPCC technical committee (SS38) developed reviewed and confirmed the use of tolerances as described in the standard. These studies were
reviewed and approved by the NPCC Task Force on System Studies (TFSS) and the Reliability Coordinating Committee (RCC).

Florida Municipal Power Agency

Yes

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 4 Comment
design team is a flaw in the design itself; hence, with a more reasonable design tolerance, there is no
reliability reason to place this unreasonable burden on small generators.Compensatory load shedding should
NOT be allowed for two reasons: 1) the standards should not force agreements to be made; and 2) the UFLS
program would become a highly complex scheme with settings that would need to change over time to reflect
the status of the non-conforming generator; e.g., if the unit were off-line, then too much load would be
"armed" to trip, so, those relay settings would need to be changed when the unit was off-line.The complexity
of a UFLS program that would have to track the status of non-conforming generators is staggering. For
instance, in order to protect the 1% design tolerance of supply / demand balance that the drafters of the
standard mistakenly believe is important, the UFLS relay settings would need to change every time the
generator changed output. For instance, a non-conforming generator with a capacity of 300 MW would
presumably have 300 MW of compensatory load shedding. If it were running at 200 MW, then we would want
the 300 MW of compensatory load shedding dropped to 200 MW. How would such a thing be possible if we
are limited to a finite level of distribution circuits whose load varies minute to minute with different load
patterns, with varying levels of critical loads (e.g., hospitals) and non-critical loads on those circuits? At what
UFLS steps would the compensatory load shedding be adjusted? Would it be multiple steps? If the
generator were providing regulation service, the relay settings would need to change minute by minute on
different circuits depending on actual loads on those circuits. If the ability to make such minute-by-minute
relay changes were not in place, would the generator be barred from participating in the regulation service
ancillary services market, further burdening competitive markets? Compensatory load shedding is illconceived and highly impractical.The NERC-wide standard recently approved by the BOT takes the correct
approach. Existing non-conforming generators of a sufficient size to matter should be modeled and the UFLS
program be designed in a robust enough fashion to handle the non-conforming generation.

Response: Thank you for your comment. The RSDT acknowledges the technical challenges of administering the compensatory load shedding
program and as a result has developed requirements stating that all new units shall conform to the generator tripping curve.
Additionally, to address your concern regarding generators that are already interconnected and in commercial operation, non conforming
generators either have existing contracts to provide for compensatory load shedding or have mitigated the conditions that would trip the unit
above the appropriate generator tripping curve.
These requirements are contained as criteria within the approved NPCC Directory #12 and are currently in effect throughout the NPCC region.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 4 Comment

Finally, the NPCC technical committee (SS38) developed reviewed and confirmed the use of tolerances as described in the standard. These studies were
reviewed and approved by the NPCC Task Force on System Studies (TFSS) and the Reliability Coordinating Committee (RCC).

Northeast Utilities

City of Jacxksonville Beach
dba/Beaches Energy Services

Independent Electricity System
Operator

New Brunswick System Operator

Indeck Energy Services

Yes

The standard imposed a significant burden on the customers of DP's and TO's with less than 100 MW of load
by requiring substantially higher percentages of load reductions at similar frequencies. In addition, this
standard is not necessary for reliability because, and is particularly burdensome, the DP's and TO's with less
than 100 MW's of load are each too small to be a Reportable Disturbance within either the NYISO or ISONE.
How then is reliability improved?
Also, the standard improperly extends its applicability to GO's less than 20 MW and not connected to directly
to the BES. NPCC is delegated its power to develop Regional Standards under the delegation agreement
with NERC. NERC has chosen not to apply its standards to any entities other than Registered Entities.
Therefore, NPCC may not apply the standard to GO's that are not Registered Entities. The publicly available
information does not justify the differences from continent wide standard compared to the burden on
competitive markets.

Response: Thank you for your comment. Entities with less than 100MWs are provided additional flexibility via wider cumulative load shedding bands.
This allowance, supported by technical studies, was provided based on evidence that many smaller entities could not provide the necessary load
shedding without exceeding their requirement based on their limited number of feeders available to be armed.
Additionally, the minimum obligation of these entities is essentially the same of entities greater than 100MWs.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 4 Comment

Finally, the applicability in Section 4 has been revised and Attachment C has been removed.

Utility Services Inc.

Yes

See answer in Q2. Generators whose protection systems trip above the curve are "required" to find load to be
shed. Load could withhold such until financial incentives were offered. It is also possible that compensatory load
might not be found and then the generation would be in violation of the standard. There are no guarantees of
compensatory load shedding in today's competitive horizontal electric markets.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

5. Does the proposed regional reliability standard meet at least one of the following criteria?
• The proposed standard has more specific criteria for the same requirements covered in a continent-wide
standard
• The proposed standard has requirements that are not included in the corresponding continent-wide
reliability standard
• The proposed regional difference is necessitated by a physical difference in the bulk power system.
Summary Consideration:

Organization
Dominion

Electric Market Policy

Yes or No

Question 5 Comment

Yes

Dominion is opposed to NPCC regional reliability standard PRC-006-1, Automatic Underfrequency Load
Shedding, for the following reasons:1. The process by which a Generator Owner would arrange for a
Distribution Provider or Transmission Owner to provide the appropriate amount of compensatory load shed
(Reference Attachment B, Step 2.2) remains unresolved. In previous comments, we noted that Dominion had
polled various Transmission Owners and Distribution Providers and none were willing to offer load shed
service, citing the following:

a. Implementation - load shed service does not currently exist in the Transmission Owner or Distribution
Providers’ tariffs. Requiring them to implement this service, would raise numerous issues, including, but
not limited to the issues of determining which customers’ load is shed to provide this service (retail or
wholesale) and in determining ‘fair value’ for the price of such service. Accordingly, a requirement that
these entities create and manage a new service that is not compelled by the needs of the market, would
have a detrimental impact on commerce.

b. Technical difficulty - (design complexity, difficulty meeting overshoot requirements) - Shedding additional
load equivalent to a non-coordinating generator would be extremely difficult to design and coordinate.
The design would have to account for the real-time status and output of the generator. Otherwise, this
requirement could create more problems than it attempts to solve. For example, consider a load shed
program that is designed assuming the need to shed load equivalent to rated capacity for a noncoordinating generator and a frequency event occurs when this generator is off line. The program sees
the frequency at the trigger level and sheds the load equivalent to the non-coordinating generator.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 5 Comment
However, since that generator wasn’t actually on line, there is no additional loss of generation, but the
MW load equivalent of the generator (that is not designed into the UFLS scheme) is lost anyway. If the
UFLS program then implements the next level of designed reduction of load, this may result in a
subsequent rebound in frequency. This may very well result in overshoot that is more than designed for,
resulting in generator trip from over-frequency. Obviously, the more non-coordinating generators there
are, the more difficult the task of coordination with UFLS schemes becomes and the more widespread the
effects on customers.

2. The Implementation Plan suggests that “the Drafting Team coordinated its development [of NPCC
regional reliability standard PRC-006-1] with the recently approved NERC UFLS Standard PRC-006”.
Dominion is compelled to point out that NERC UFLS Standard PRC-006 has only attained NERC Board
of Trustee approval, has not yet been approved by FERC, and is therefore not enforceable. Since there
is uncertainty as to the FERC outcome, Dominion recommends that NERC suspend its review of
regional reliability standard NPCC regional reliability standard PRC-006-1until continent-wide standards
PRC-006 (Project 2007-01) and PRC-024 (Project 2007-09) are approved by FERC.

d. 3. The applicability of this standard to “Generator Owners with individual generating units or generating
plant/facility <= 1 MVA (nameplate rating) connected at all voltage levels” does not meet the NERC
Statement of Compliance Registry Criteria (Revision 5.0) or the NPCC Compliance Guidance Statement
“Defining Generator Materiality for Registration;” therefore creating a registration gap. Attachment “C”
attempts to close this gap by requiring these facilities to coordinate with NPCC UFLS program
characteristics as mandated by their respective OATT tariff agreements. This appears inappropriate in a
Regional Reliability Standard as enforcement of the OATT tariff resides with FERC, not NERC or the
Regions. Therefore, as acknowledged by NPPC during the January 4, 2011 Webinar, the issue of
registration for generating plants/facilities <= 1 MVA, but < the NERC Registration Criteria remains
unresolved.

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization

Yes or No

Question 5 Comment

Response: Thank you for your comment. The RSDT acknowledges the technical challenges of administering the compensatory load shedding
and as a result has developed requirements stating that all new units shall conform to the generator tripping curve.

NERC has mandated the development of certain regional standards and its development cannot wait until all approvals are obtained on the NERC
continent wide standard. However, the RSDT did coordinate the development of the regional standard with the progress of the continent wide standard.
The Regional Standard Drafting Team has reviewed your concerns and notes that the NERC Statement of Registry Criteria does not limit registration of
generation to those greater than 20MVA. However, the applicability in Section 4 has been revised and Attachment C has been removed.

Bonneville Power Administration

Yes

Transmission Access Policy
Study Group

Yes

Public Service Enterprise Group
Florida Municipal Power Agency
Northeast Utilities

Yes

City of Jacxksonville Beach
dba/Beaches Energy Services

Yes

Independent Electricity System
Operator

Yes

New Brunswick System Operator

Yes

Indeck Energy Services

Consideration of Comments on PRC-006-NPCC-1 Frequency Load Shedding

Organization
Utility Services Inc.

Yes or No

Question 5 Comment

Yes

END OF REPORT

PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Implementation Plan

Background:
The purpose of this draft Regional Standard is to ensure the development and maintenance of an effective
and coordinated Automatic Underfrequency Load Shedding program in order to preserve the reliability
and integrity of the bulk power system during declining system frequency events.
In the developing the Implementation Plan for PRC-006-NPCC-01 the Standard Drafting Team
considered the following:
1. The requirements listed in this Regional Standard are intended to cover all aspects of the UFLS
program. The Drafting Team coordinated its development with the recently approved NERC
UFLS Standard PRC-006. The intent of this Regional Standard is to be more stringent than the
continent wide standard while incorporating specific program characteristics into the
requirements.
2. The Implementation Plan for this standard is the same as the existing and ongoing
Implementation Plan for NPCC Directory #12.
3. The Regional Standard implementation plan will not require adherence to the annual milestones
within the Directory #12 plan. However, entities will be required to be fully compliant by the end
of the existing Directory #12 implementation plan.

Effective Dates:
1. The effective date for requirements R1, R2, R3, R4, R5, R6, R7, and R8 is the first day of the first
quarter following applicable regulatory approval but no earlier than Jan 1, 2016 to allow for the
existing implementation plan to be completed.
2. The effective date for requirements R9 through R26 is the first day of the first quarter two years
following applicable governmental and regulatory approval.

Reference:



2006 Assessment of UFLS Adequacy Part 3 Assessment of Program Modifications.
SS38 Underfrequency Load Shedding Support Study

NPCC Criteria:



Directory #12 Underfrequency Load Shedding Program Requirements.
A-7 NPCC Glossary of Terms.

Implementation Plans:



UFLS Implementation Plan for the Eastern Interconnection Portion of NPCC.
UFLS Implementation Plan for the Québec Interconnection Portion of NPCC.

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Standard Development Roadmap
This section is maintained by the drafting team during the development of the standard and will
be removed when the standard becomes effective.
Development Steps Completed:
1. The Standards Committee approved the SAR for posting on November 21, 2006.
2. SAR posted for comments on November 29, 2006.
3. The Standards Committee appointed a SAR Drafting Team on January 11, 2007.
4. SAR Drafting Team responds to comments, revises SAR and posts for comments on
February 7, 2007.
5. SAR Drafting Team responds to comments on April 20, 2007.
6. Standards Committee approves development of Standard on April 10, 2007.
7. The Standards Committee appointed the Standard Drafting Team on April 10, 2007.
8. The Standards Drafting Team posted draft performance characteristics for comment on
July 2, 2008.
9. Standards Drafting Team responds to comments, revises standard, and posts for
comments on April 15, 2009.
10. Standards Committee approved the Supplemental SAR for posting on October 7, 2009
that expanded the SDT’s scope to include EOP-003-1 but limiting that scope to only
eliminating references to Under-frequency Load Shedding in EOP-003-1.
11. The Standards Drafting Team posted the standard for a third comment period June 11,
2010 – July 16, 2010.
12. The Standard Drafting Team conducted a pre-ballot review of the standard on June 11,
2010 – July 2, 2010
13. The Standard Drafting Team conducted an initial ballot of the standard and non-binding
poll of the VRFs and VSLs on July 8, 2010 – July 17, 2010.
14. The Standard Drafting Team conducted a second ballot of the standard on July 24, 2010 –
August 3, 2010.
15. The Standard Drafting Team conducted a third ballot of the standard September 24October 4, 2010.
Proposed Action Plan and Description of Current Draft:
This is the recirculation ballot period of the proposed standard.
Future Development Plan:
Anticipated Actions

Anticipated Date

1. Request BOT approval

November , 2010

2. File Standard with FERC

December, 2010

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

A. Introduction
1.

Title:

Automatic Underfrequency Load Shedding

Number:

PRC-006-1

Purpose: To establish design and documentation requirements for automatic
underfrequency load shedding (UFLS) programs to arrest declining frequency, assist
recovery of frequency following underfrequency events and provide last resort system
preservation measures.

Applicability:
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
4.3
5.

Transmission Owners that own Elements identified in the UFLS program
established by the Planning Coordinators.

(Proposed) Effective Date:
5.1. The standard, with the exception of Requirement R4, Parts 4.1 through 4.6, is
effective the first day of the first calendar quarter one year after applicable

regulatory approvals.
5.2. Parts 4.1 through 4.6 of Requirement R4 shall become effective and enforceable

one year following the receipt of generation data as required in PRC-024-1, but no
sooner than one year following the first day of the first calendar quarter after
applicable regulatory approvals of PRC-006-1.
B. Requirements
R1.

Each Planning Coordinator shall develop and document criteria, including
consideration of historical events and system studies, to select portions of the Bulk
Electric System (BES), including interconnected portions of the BES in adjacent
Planning Coordinator areas and Regional Entity areas that may form islands. [VRF:
Medium][Time Horizon: Long-term Planning]

R2.

Each Planning Coordinator shall identify one or more islands to serve as a basis for
designing its UFLS program including: [VRF: Medium][Time Horizon: Long-term
Planning]
2.1. Those islands selected by applying the criteria in Requirement R1, and
2.2. Any portions of the BES designed to detach from the Interconnection (planned

islands) as a result of the operation of a relay scheme or Special Protection
System, and
Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding
2.3. A single island that includes all portions of the BES in either the Regional Entity

area or the Interconnection in which the Planning Coordinator’s area resides. If a
Planning Coordinator’s area resides in multiple Regional Entity areas, each of
those Regional Entity areas shall be identified as an island. Planning
Coordinators may adjust island boundaries to differ from Regional Entity area
boundaries by mutual consent where necessary for the sole purpose of producing
contiguous regional islands more suitable for simulation.
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]
3.1. Frequency shall remain above the Underfrequency Performance Characteristic

curve in PRC-006-1 - 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-006-1 - 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:

R4.

3.3.1.

Individual generating units greater than 20 MVA (gross nameplate rating)
directly connected to the BES

3.3.2.

Generating plants/facilities greater than 75 MVA (gross aggregate
nameplate rating) directly connected to the BES

3.3.3.

Facilities consisting of one or more units connected to the BES at a
common bus with total generation above 75 MVA gross nameplate rating.

Each Planning Coordinator shall conduct and document a UFLS design assessment at
least once every five years that determines through dynamic simulation whether the
UFLS program design meets the performance characteristics in Requirement R3 for
each island identified in Requirement R2. The simulation shall model each of the
following: [VRF: High][Time Horizon: Long-term Planning]
4.1. Underfrequency trip settings of individual generating units greater than 20 MVA

(gross nameplate rating) directly connected to the BES that trip above the
Generator Underfrequency Trip Modeling curve in PRC-006-1 - Attachment 1.
4.2. Underfrequency trip settings of generating plants/facilities greater than 75 MVA

(gross aggregate nameplate rating) directly connected to the BES that trip above
the Generator Underfrequency Trip Modeling curve in PRC-006-1 - Attachment
1.

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding
4.3. Underfrequency trip settings of any facility consisting of one or more units

connected to the BES at a common bus with total generation above 75 MVA
(gross nameplate rating) that trip above the Generator Underfrequency Trip
Modeling curve in PRC-006-1 - Attachment 1.
4.4. Overfrequency trip settings of individual generating units greater than 20 MVA

(gross nameplate rating) directly connected to the BES that trip below the
Generator Overfrequency Trip Modeling curve in PRC-006-1 — Attachment 1.
4.5. Overfrequency trip settings of generating plants/facilities greater than 75 MVA

(gross aggregate nameplate rating) directly connected to the BES that trip below
the Generator Overfrequency Trip Modeling curve in PRC-006-1 — Attachment
1.
4.6. Overfrequency trip settings of any facility consisting of one or more units

connected to the BES at a common bus with total generation above 75 MVA
(gross nameplate rating) that trip below the Generator Overfrequency Trip
Modeling curve in PRC-006-1 — Attachment 1.
4.7. Any automatic Load restoration that impacts frequency stabilization and operates

within the duration of the simulations run for the assessment.
R5.

Each Planning Coordinator, whose area or portions of whose area is part of an island
identified by it or another Planning Coordinator which includes multiple Planning
Coordinator areas or portions of those areas, shall coordinate its UFLS program design
with all other Planning Coordinators whose areas or portions of whose areas are also
part of the same identified island through one of the following: [VRF: Medium][Time
Horizon: Long-term Planning]
•

Develop a common UFLS program design and schedule for implementation per
Requirement R3 among the Planning Coordinators whose areas or portions of
whose areas are part of the same identified island, or

•

Conduct a joint UFLS design assessment per Requirement R4 among the
Planning Coordinators whose areas or portions of whose areas are part of the
same identified island, or

•

Conduct an independent UFLS design assessment per Requirement R4 for the
identified island, and in the event the UFLS design assessment fails to meet
Requirement R3, identify modifications to the UFLS program(s) to meet
Requirement R3 and report these modifications as recommendations to the other
Planning Coordinators whose areas or portions of whose areas are also part of the
same identified island and the ERO.

R6.

Each Planning Coordinator shall maintain a UFLS database containing data necessary
to model its UFLS program for use in event analyses and assessments 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]

R7.

Each Planning Coordinator shall provide its UFLS database containing data necessary
to model its UFLS program to other Planning Coordinators within its Interconnection

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

within 30 calendar days of a request. [VRF: Lower][Time Horizon: Long-term
Planning]
R8.

Each UFLS entity shall provide data to its Planning Coordinator(s) according to the
format and schedule specified by the Planning Coordinator(s) to support maintenance
of each Planning Coordinator’s UFLS database. [VRF: Lower][Time Horizon: Longterm Planning]

R9.

Each UFLS entity shall provide automatic tripping of Load in accordance with the
UFLS program design and schedule for application determined by its Planning
Coordinator(s) in each Planning Coordinator area in which it owns assets. [VRF:
High][Time Horizon: Long-term Planning]

R10. Each Transmission Owner shall provide automatic switching of its existing capacitor

banks, Transmission Lines, and reactors to control over-voltage as a result of
underfrequency load shedding if required by the UFLS program and schedule for
application determined by the Planning Coordinator(s) in each Planning Coordinator
area in which the Transmission Owner owns transmission. [VRF: High][Time Horizon:
Long-term Planning]
R11. Each Planning Coordinator, in whose area a BES islanding event results in system

frequency excursions below the initializing set points of the UFLS program, shall
conduct and document an assessment of the event within one year of event actuation to
evaluate: [VRF: Medium][Time Horizon: Operations Assessment]
11.1. The performance of the UFLS equipment,
11.2. The effectiveness of the UFLS program.
R12. Each Planning Coordinator, in whose islanding event assessment (per R11) UFLS

program deficiencies are identified, shall conduct and document a UFLS design
assessment to consider the identified deficiencies within two years of event actuation.
[VRF: Medium][Time Horizon: Operations Assessment]
R13. Each Planning Coordinator, in whose area a BES islanding event occurred that also

included the area(s) or portions of area(s) of other Planning Coordinator(s) in the same
islanding event and that resulted in system frequency excursions below the initializing
set points of the UFLS program, shall coordinate its event assessment (in accordance
with Requirement R11) with all other Planning Coordinators whose areas or portions
of whose areas were also included in the same islanding event through one of the
following: [VRF: Medium][Time Horizon: Operations Assessment]
•

Conduct a joint event assessment per Requirement R11 among the Planning
Coordinators whose areas or portions of whose areas were included in the same
islanding event, or

•

Conduct an independent event assessment per Requirement R11 that reaches
conclusions and recommendations consistent with those of the event assessments
of the other Planning Coordinators whose areas or portions of whose areas were
included in the same islanding event, or

•

Conduct an independent event assessment per Requirement R11 and where the
assessment fails to reach conclusions and recommendations consistent with those

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

of the event assessments of the other Planning Coordinators whose areas or
portions of whose areas were included in the same islanding event, identify
differences in the assessments that likely resulted in the differences in the
conclusions and recommendations and report these differences to the other
Planning Coordinators whose areas or portions of whose areas were included in
the same islanding event and the ERO.
R14. Each Planning Coordinator shall respond to written comments submitted by UFLS

entities and Transmission Owners within its Planning Coordinator area following a
comment period and before finalizing its UFLS program, indicating in the written
response to comments whether changes will be made or reasons why changes will not
be made to the following [VRF: Lower][Time Horizon: Long-term Planning]:
14.1. UFLS program, including a schedule for implementation
14.2. UFLS design assessment
14.3. Format and schedule of UFLS data submittal
C. Measures
M1. Each Planning Coordinator shall have evidence such as reports, or other documentation

of its criteria to select portions of the Bulk Electric System that may form islands
including how system studies and historical events were considered to develop the
criteria per Requirement R1.
M2. Each Planning Coordinator shall have evidence such as reports, memorandums,

e-mails, or other documentation supporting its identification of an island(s) as a basis
for designing a UFLS program that meet the criteria in Requirement R2, Parts 2.1
through 2.3.
M3. Each Planning Coordinator shall have evidence such as reports, memorandums,

e-mails, program plans, or other documentation of its UFLS program, including the
notification of the UFLS entities of implementation schedule, that meet the criteria in
Requirement R3, Parts 3.1 through 3.3.
M4. Each Planning Coordinator shall have dated evidence such as reports, dynamic

simulation models and results, or other dated documentation of its UFLS design
assessment that demonstrates it meets Requirement R4, Parts 4.1 through 4.7.
M5. Each Planning Coordinator, whose area or portions of whose area is part of an island

identified by it or another Planning Coordinator which includes multiple Planning
Coordinator areas or portions of those areas, shall have dated evidence such as joint
UFLS program design documents, reports describing a joint UFLS design assessment,
letters that include recommendations, or other dated documentation demonstrating that
it coordinated its UFLS program design with all other Planning Coordinators whose
areas or portions of whose areas are also part of the same identified island per
Requirement R5.
M6. Each Planning Coordinator shall have dated evidence such as a UFLS database, data

requests, data input forms, or other dated documentation to show that it maintained a
UFLS database for use in event analyses and assessments of the UFLS program per

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Requirement R6 at least once each calendar year, with no more than 15 months
between maintenance activities.
M7. Each Planning Coordinator shall have dated evidence such as letters, memorandums, e-

mails or other dated documentation that it provided their UFLS database to other
Planning Coordinators within their Interconnection within 30 calendar days of a
request per Requirement R7.
M8. Each UFLS Entity shall have dated evidence such as responses to data requests,

spreadsheets, letters or other dated documentation that it provided data to its Planning
Coordinator according to the format and schedule specified by the Planning
Coordinator to support maintenance of the UFLS database per Requirement R8.
M9. Each UFLS Entity shall have dated evidence such as spreadsheets summarizing feeder

load armed with UFLS relays, spreadsheets with UFLS relay settings, or other dated
documentation that it provided automatic tripping of load in accordance with the UFLS
program design and schedule for application per Requirement R9.
M10. Each Transmission Owner shall have dated evidence such as relay settings, tripping

logic or other dated documentation that it provided automatic switching of its existing
capacitor banks, Transmission Lines, and reactors in order to control over-voltage as a
result of underfrequency load shedding if required by the UFLS program and schedule
for application per Requirement R10.
M11. Each Planning Coordinator shall have dated evidence such as reports, data gathered

from an historical event, or other dated documentation to show that it conducted an
event assessment of the performance of the UFLS equipment and the effectiveness of
the UFLS program per Requirement R11.
M12. Each Planning Coordinator shall have dated evidence such as reports, data gathered

from an historical event, or other dated documentation to show that it conducted a
UFLS design assessment per Requirements R12 and R4 if UFLS program deficiencies
are identified in R11.
M13. Each Planning Coordinator, in whose area a BES islanding event occurred that also

included the area(s) or portions of area(s) of other Planning Coordinator(s) in the same
islanding event and that resulted in system frequency excursions below the initializing
set points of the UFLS program, shall have dated evidence such as a joint assessment
report, independent assessment reports and letters describing likely reasons for
differences in conclusions and recommendations, or other dated documentation
demonstrating it coordinated its event assessment (per Requirement R11) with all other
Planning Coordinator(s) whose areas or portions of whose areas were also included in
the same islanding event per Requirement R13.
M14. Each Planning Coordinator shall have dated evidence of responses, such as e-mails and

letters, to written comments submitted by UFLS entities and Transmission Owners
within its Planning Coordinator area following a comment period and before finalizing
its UFLS program per Requirement R14.
D. Compliance

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding
1.

Compliance Monitoring Process
1.1. Compliance Enforcement Authority

Regional Entity
1.2. Data Retention

Each Planning Coordinator and UFLS entity shall keep data or evidence to show
compliance as identified below unless directed by its Compliance Enforcement
Authority to retain specific evidence for a longer period of time as part of an
investigation:
•

Each Planning Coordinator shall retain the current evidence of Requirements
R1, R2, R3, R4, R5, R12, and R14, Measures M1, M2, M3, M4, M5, M12,
and M14 as well as any evidence necessary to show compliance since the last
compliance audit.

•

Each Planning Coordinator shall retain the current evidence of UFLS database
update in accordance with Requirement R6, Measure M6, and evidence of the
prior year’s UFLS database update.

•

Each Planning Coordinator shall retain evidence of any UFLS database
transmittal to another Planning Coordinator since the last compliance audit in
accordance with Requirement R7, Measure M7.

•

Each UFLS entity shall retain evidence of UFLS data transmittal to the
Planning Coordinator(s) since the last compliance audit in accordance with
Requirement R8, Measure M8.

•

Each UFLS entity shall retain the current evidence of adherence with the
UFLS program in accordance with Requirement R9, Measure M9, and
evidence of adherence since the last compliance audit.

•

Transmission Owner shall retain the current evidence of adherence with the
UFLS program in accordance with Requirement R10, Measure M10, and
evidence of adherence since the last compliance audit.

•

Each Planning Coordinator shall retain evidence of Requirements R11, and
R13, and Measures M11, and M13 for 6 calendar years.

If a Planning Coordinator or UFLS entity is found non-compliant, it shall keep
information related to the non-compliance until found compliant or for the
retention period specified above, whichever is longer.
The Compliance Enforcement Authority shall keep the last audit records and all
requested and submitted subsequent audit records.
1.3. Compliance Monitoring and Assessment Processes

•

Compliance Audit

•

Self-Certification

•

Spot Checking

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

•

Compliance Violation Investigation

•

Self-Reporting

•

Complaint

1.4. Additional Compliance Information

Not applicable.

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding
2.
R#
R1

Violation Severity Levels
Lower VSL

N/A

Moderate VSL

High VSL

Severe VSL

The Planning Coordinator
developed and documented criteria
but failed to include the
consideration of historical events,
to select portions of the BES,
including interconnected portions
of the BES in adjacent Planning
Coordinator areas and Regional
Entity areas that may form islands.

The Planning Coordinator
developed and documented criteria
but failed to include the
consideration of historical events
and system studies, to select
portions of the BES, including
interconnected portions of the BES
in adjacent Planning Coordinator
areas and Regional Entity areas,
that may form islands.

The Planning Coordinator failed to
develop and document criteria to
select portions of the BES,
including interconnected portions
of the BES in adjacent Planning
Coordinator areas and Regional
Entity areas, that may form islands.

The Planning Coordinator
identified an island(s) to serve as
a basis for designing its UFLS
program but failed to include two
(2) of the Parts as specified in
Requirement R2, Parts 2.1, 2.2, or
2.3.

The Planning Coordinator
identified an island(s) to serve as
a basis for designing its UFLS
program but failed to include all of
the Parts as specified in
Requirement R2, Parts 2.1, 2.2, or
2.3.

OR
The Planning Coordinator
developed and documented criteria
but failed to include the
consideration of system studies, to
select portions of the BES,
including interconnected portions
of the BES in adjacent Planning
Coordinator areas and Regional
Entity areas, that may form islands.
R2

N/A

The Planning Coordinator
identified an island(s) to serve as
a basis for designing its UFLS
program but failed to include one
(1) of the Parts as specified in
Requirement R2, Parts 2.1, 2.2, or
2.3.

OR
The Planning Coordinator failed to
identify any island(s) to serve as a
basis for designing its UFLS
program.

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

R#
R3

Lower VSL
N/A

Moderate VSL

High VSL

Severe VSL

The Planning Coordinator
developed a UFLS program,
including notification of and a
schedule for implementation by
UFLS entities within its area where
imbalance = [(load — actual
generation output) / (load)], of up to
25 percent within the identified
island(s)., but failed to meet one
(1) of the performance
characteristic in Requirement R3,
Parts 3.1, 3.2, or 3.3 in simulations
of underfrequency conditions.

The Planning Coordinator
developed a UFLS program
including notification of and a
schedule for implementation by
UFLS entities within its area where
imbalance = [(load — actual
generation output) / (load)], of up to
25 percent within the identified
island(s)., but failed to meet two (2)
of the performance characteristic in
Requirement R3, Parts 3.1, 3.2, or
3.3 in simulations of
underfrequency conditions.

The Planning Coordinator
developed a UFLS program
including notification of and a
schedule for implementation by
UFLS entities within its area where
imbalance = [(load — actual
generation output) / (load)], of up to
25 percent within the identified
island(s).,but failed to meet all the
performance characteristic in
Requirement R3, Parts 3.1, 3.2,
and 3.3 in simulations of
underfrequency conditions.
OR
The Planning Coordinator failed to
develop a UFLS program including
notification of and a schedule for
implementation by UFLS entities
within its area

The Planning Coordinator
conducted and documented a
UFLS assessment at least once
every five years that determined
through dynamic simulation
whether the UFLS program design
met the performance
characteristics in Requirement R3
for each island identified in
Requirement R2 but the simulation
failed to include one (1) of the
items as specified in Requirement
R4, Parts 4.1 through 4.7.

The Planning Coordinator
conducted and documented a
UFLS assessment at least once
every five years that determined
through dynamic simulation
whether the UFLS program design
met the performance
characteristics in Requirement R3
for each island identified in
Requirement R2 but the simulation
failed to include two (2) of the
items as specified in Requirement
R4, Parts 4.1 through 4.7.

The Planning Coordinator
conducted and documented a
UFLS assessment at least once
every five years that determined
through dynamic simulation
whether the UFLS program design
met the performance
characteristics in Requirement R3
for each island identified in
Requirement R2 but the simulation
failed to include three (3) of the
items as specified in Requirement
R4, Parts 4.1 through 4.7.

The Planning Coordinator
conducted and documented a
UFLS assessment at least once
every five years that determined
through dynamic simulation
whether the UFLS program design
met the performance
characteristics in Requirement R3
but simulation failed to include four
(4) or more of the items as
specified in Requirement R4,
Parts 4.1 through 4.7.
OR
The Planning Coordinator failed to
conduct and document a UFLS

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Lower VSL

Moderate VSL

High VSL

Severe VSL
assessment at least once every
five years that determines through
dynamic simulation whether the
UFLS program design meets the
performance characteristics in
Requirement R3 for each island
identified in Requirement R2

N/A

The Planning Coordinator, whose
area or portions of whose area is
part of an island identified by it or
another Planning Coordinator
which includes multiple Planning
Coordinator areas or portions of
those areas, failed to coordinate its
UFLS program design through one
of the manners described in
Requirement R5.

N/A

The Planning Coordinator failed to
maintain a UFLS database for use
in event analyses and
assessments of the UFLS program
at least once each calendar year,
with no more than 15 months
between maintenance activities.

The Planning Coordinator provided
its UFLS database to other
Planning Coordinators more than
30 calendar days and up to and
including 40 calendar days
following the request.

The Planning Coordinator provided
its UFLS database to other
Planning Coordinators more than
40 calendar days but less than and
including 50 calendar days
following the request.

The Planning Coordinator provided
its UFLS database to other
Planning Coordinators more than
50 calendar days but less than and
including 60 calendar days
following the request.

The Planning Coordinator provided
its UFLS database to other
Planning Coordinators more than
60 calendar days following the
request.
OR
The Planning Coordinator failed to
provide its UFLS database to other
Planning Coordinators.

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

R#
R8

Lower VSL

Moderate VSL

High VSL

Severe VSL

The UFLS entity provided data to
its Planning Coordinator(s) more
than 5 calendar days but less than
or equal to 10 calendar days
following the schedule specified by
the Planning Coordinator(s) to
support maintenance of each
Planning Coordinator’s UFLS
database.

The UFLS entity provided data to
its Planning Coordinator(s) more
than 10 calendar days but less
than or equal to 15 calendar days
following the schedule specified by
the Planning Coordinator(s) to
support maintenance of each
Planning Coordinator’s UFLS
database.

The UFLS entity provided data to
its Planning Coordinator(s) more
than 15 calendar days but less
than or equal to 20 calendar days
following the schedule specified by
the Planning Coordinator(s) to
support maintenance of each
Planning Coordinator’s UFLS
database.

The UFLS entity provided data to
its Planning Coordinator(s) more
than 20 calendar days following the
schedule specified by the Planning
Coordinator(s) to support
maintenance of each Planning
Coordinator’s UFLS database.
OR
The UFLS entity failed to provide
data to its Planning Coordinator(s)
to support maintenance of each
Planning Coordinator’s UFLS
database.

OR
The UFLS entity provided data to
its Planning Coordinator(s) but the
data was not according to the
format specified by the Planning
Coordinator(s) to support
maintenance of each Planning
Coordinator’s UFLS database.
R9

The UFLS entity provided less than
100% but more than (and
including) 95% of automatic
tripping of Load in accordance with
the UFLS program design and
schedule for application
determined by the Planning
Coordinator(s) area in which it
owns assets.

The UFLS entity provided less than
95% but more than (and including)
90% of automatic tripping of Load
in accordance with the UFLS
program design and schedule for
application determined by the
Planning Coordinator(s) area in
which it owns assets.

The UFLS entity provided less than
90% but more than (and including)
85% of automatic tripping of Load
in accordance with the UFLS
program design and schedule for
application determined by the
Planning Coordinator(s) area in
which it owns assets.

The UFLS entity provided less than
85% of automatic tripping of Load
in accordance with the UFLS
program design and schedule for
application determined by the
Planning Coordinator(s) area in
which it owns assets.

R10

The Transmission Owner provided
less than 100% but more than (and
including) 95% automatic switching
of its existing capacitor banks,
Transmission Lines, and reactors
to control over-voltage if required
by the UFLS program and
schedule for application

The Transmission Owner provided
less than 95% but more than (and
including) 90% automatic switching
of its existing capacitor banks,
Transmission Lines, and reactors
to control over-voltage if required
by the UFLS program and
schedule for application

The Transmission Owner provided
less than 90% but more than (and
including) 85% automatic switching
of its existing capacitor banks,
Transmission Lines, and reactors
to control over-voltage if required
by the UFLS program and
schedule for application

The Transmission Owner provided
less than 85% automatic switching
of its existing capacitor banks,
Transmission Lines, and reactors
to control over-voltage if required
by the UFLS program and
schedule for application
determined by the Planning

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

R11

Lower VSL

Moderate VSL

High VSL

Severe VSL

determined by the Planning
Coordinator(s) in each Planning
Coordinator area in which the
Transmission Owner owns
transmission

Coordinator(s) in each Planning
Coordinator area in which the
Transmission Owner owns
transmission

The Planning Coordinator, in
whose area a BES islanding event
resulting in system frequency
excursions below the initializing set
points of the UFLS program,
conducted and documented an
assessment of the event and
evaluated the parts as specified in
Requirement R11, Parts 11.1 and
11.2 within a time greater than one
year but less than or equal to 13
months of actuation.

The Planning Coordinator, in
whose area a BES islanding event
resulting in system frequency
excursions below the initializing set
points of the UFLS program,
conducted and documented an
assessment of the event and
evaluated the parts as specified in
Requirement R11, Parts 11.1 and
11.2 within a time greater than 13
months but less than or equal to 14
months of actuation.

The Planning Coordinator, in
whose area a BES islanding event
resulting in system frequency
excursions below the initializing set
points of the UFLS program,
conducted and documented an
assessment of the event and
evaluated the parts as specified in
Requirement R11, Parts 11.1 and
11.2 within a time greater than 14
months but less than or equal to 15
months of actuation.

OR
The Planning Coordinator, in
whose area an islanding event
resulting in system frequency
excursions below the initializing set
points of the UFLS program,
conducted and documented an
assessment of the event within one
year of event actuation but failed to
evaluate one (1) of the Parts as
specified in Requirement R11,
Parts11.1 or 11.2.

OR
The Planning Coordinator, in
whose area an islanding event
resulting in system frequency
excursions below the initializing set
points of the UFLS program, failed
to conduct and document an
assessment of the event and
evaluate the Parts as specified in
Requirement R11, Parts 11.1 and
11.2.
OR
The Planning Coordinator, in
whose area an islanding event
resulting in system frequency
excursions below the initializing set
points of the UFLS program,
conducted and documented an

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Lower VSL

Moderate VSL

High VSL

Severe VSL
assessment of the event within one
year of event actuation but failed to
evaluate all of the Parts as
specified in Requirement R11,
Parts 11.1 and 11.2.

R12

N/A

The Planning Coordinator, in which
UFLS program deficiencies were
identified per Requirement R11,
conducted and documented a
UFLS design assessment to
consider the identified deficiencies
greater than 26 months of event
actuation.
OR
The Planning Coordinator, in which
UFLS program deficiencies were
identified per Requirement R11,
failed to conduct and document a
UFLS design assessment to
consider the identified deficiencies.

R13

N/A

Draft 6: October 18, 2010

N/A

The Planning Coordinator, in
whose area a BES islanding event
occurred that also included the
area(s) or portions of area(s) of
other Planning Coordinator(s) in
the same islanding event and that
resulted in system frequency
excursions below the initializing set
points of the UFLS program, failed
to coordinate its UFLS event
assessment with all other Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding
event in one of the manners

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Lower VSL

Moderate VSL

High VSL

Severe VSL
described in Requirement R13

R14

N/A

Draft 6: October 18, 2010

N/A

The Planning Coordinator failed to
respond to written comments
submitted by UFLS entities and
Transmission Owners within its
Planning Coordinator area
following a comment period and
before finalizing its UFLS program,
indicating in the written response to
comments whether changes were
made or reasons why changes
were not made to the items in
Parts 14.1 through 14.3.

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E. Regional Variances
E.A. Regional Variance for the Quebec Interconnection
The following Interconnection-wide variance shall be applicable in the Quebec
Interconnection and replaces, in their entirety, Requirements R3 and R4 and the
violation severity levels associated with Requirements R3 and R4.
E.A.3. Each Planning Coordinator shall develop a UFLS program, including 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]
E.A.3.1. Frequency shall remain above the Underfrequency Performance
Characteristic curve in PRC-006-1 - Attachment 1A, either for 30
seconds or until a steady-state condition between 59.3 Hz and 60.7 Hz
is reached, and
E.A.3.2. Frequency shall remain below the Overfrequency Performance
Characteristic curve in PRC-006-1 - Attachment 1A, either for 30
seconds or until a steady-state condition between 59.3 Hz and 60.7 Hz
is reached, and
E.A.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:
EA.3.3.1. Individual generating unit greater than 50 MVA (gross
nameplate rating) directly connected to the BES
EA.3.3.2. Generating plants/facilities greater than 50 MVA (gross
aggregate nameplate rating) directly connected to the BES
EA.3.3.3. Facilities consisting of one or more units connected to the
BES at a common bus with total generation above 50 MVA
gross nameplate rating.
E.A.4. Each Planning Coordinator shall conduct and document a UFLS design
assessment at least once every five years that determines through dynamic
simulation whether the UFLS program design meets the performance
characteristics in Requirement E.A.3 for each island identified in Requirement
R2. The simulation shall model each of the following; [VRF: High][Time
Horizon: Long-term Planning]
E.A.4.1 Underfrequency trip settings of individual generating units that are
part of plants/facilities with a capacity of 50 MVA or more
individually or cumulatively (gross nameplate rating), directly
connected to the BES that trip above the Generator Underfrequency
Trip Modeling curve in PRC-006-1 - Attachment 1A, and
Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E.A.4.2 Overfrequency trip settings of individual generating units that are part
of plants/facilities with a capacity of 50 MVA or more individually or
cumulatively (gross nameplate rating), directly connected to the BES
that trip below the Generator Overfrequency Trip Modeling curve in
PRC-006-1 - Attachment 2A, and
E.A.4.3 Any automatic Load restoration that impacts frequency stabilization
and operates within the duration of the simulations run for the
assessment.
M.E.A.3. Each Planning Coordinator shall have evidence such as reports, memorandums,
e-mails, program plans, or other documentation of its UFLS program, including
the notification of the UFLS entities of implementation schedule, that meet the
criteria in Requirement E.A.3 Parts E.A.3.1 through EA3.3.
M.E.A.4. Each Planning Coordinator shall have dated evidence such as reports, dynamic
simulation models and results, or other dated documentation of its UFLS design
assessment that demonstrates it meets Requirement E.A.4 Parts E.A.4.1 through
E.A.4.3.

Draft 6: October 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E#
EA3

Lower VSL
N/A

Moderate VSL

High VSL

Severe VSL

The Planning Coordinator developed
a UFLS program, including a
schedule for implementation by
UFLS entities within its area, but
failed to meet one (1) of the
performance characteristic in Parts
E.A.3.1, E.A.3.2, or E.A.3.3 in
simulations of underfrequency
conditions

The Planning Coordinator developed
a UFLS program including a
schedule for implementation by
UFLS entities within its area, but
failed to meet two (2) of the
performance characteristic in Parts
E.A.3.1, E.A.3.2, or E.A.3.3 in
simulations of underfrequency
conditions

The Planning Coordinator developed
a UFLS program including a
schedule for implementation by
UFLS entities within its area, but
failed to meet all the performance
characteristic in Parts E.A.3.1,
E.A.3.2, and E.A.3.3 in simulations
of underfrequency conditions
OR
The Planning Coordinator failed to
develop a UFLS program.

EA4

N/A

The Planning Coordinator conducted
and documented a UFLS
assessment at least once every five
years that determines through
dynamic simulation whether the
UFLS program design meets the
performance characteristics in
Requirement E3 but simulation failed
to include all of the items as
specified in Parts E.A.4.1, E.A.4.2
and E.A.4.3.
OR
The Planning Coordinator failed to
conduct and document a UFLS
assessment at least once every five
years that determines through
dynamic simulation whether the
UFLS program design meets the
performance characteristics in
Requirement E.A.3

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Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E.B.

Regional Variance for the Western Electricity Coordinating Council
The following Interconnection-wide variance shall be applicable in the Western
Electricity Coordinating Council (WECC) and replaces, in their entirety, Requirements
R1, R2, R3, R4, R5, R11, R12, and R13.
E.B.1. Each Planning Coordinator shall participate in a joint regional review with the
other Planning Coordinators in the WECC Regional Entity area that develops and
documents criteria, including consideration of historical events and system
studies, to select portions of the Bulk Electric System (BES) that may form
islands. [VRF: Medium][Time Horizon: Long-term Planning]
E.B.2. Each Planning Coordinator shall identify one or more islands from the regional
review (per E.B.1) to serve as a basis for designing a region-wide coordinated
UFLS program including: [VRF: Medium][Time Horizon: Long-term Planning]
E.B.2.1. Those islands selected by applying the criteria in Requirement E.B.1,
and
E.B.2.2. Any portions of the BES designed to detach from the Interconnection
(planned islands) as a result of the operation of a relay scheme or Special
Protection System.
EB.3. Each Planning Coordinator shall adopt a UFLS program, coordinated across the
WECC Regional Entity area, 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]
E.B.3.1. Frequency shall remain above the Underfrequency Performance
Characteristic curve in PRC-006-1 - Attachment 1, either for 60 seconds
or until a steady-state condition between 59.3 Hz and 60.7 Hz is reached,
and
E.B.3.2. Frequency shall remain below the Overfrequency Performance
Characteristic curve in PRC-006-1 - Attachment 1, either for 60 seconds
or until a steady-state condition between 59.3 Hz and 60.7 Hz is reached,
and
E.B.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:
E.B.3.3.1. Individual generating units greater than 20 MVA (gross
nameplate rating) directly connected to the BES
E.B.3.3.2. Generating plants/facilities greater than 75 MVA (gross
aggregate nameplate rating) directly connected to the BES

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Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E.B.3.3.3. Facilities consisting of one or more units connected to the
BES at a common bus with total generation above 75 MVA
gross nameplate rating.
E.B.4. Each Planning Coordinator shall participate in and document a coordinated UFLS
design assessment with the other Planning Coordinators in the WECC Regional
Entity area at least once every five years that determines through dynamic
simulation whether the UFLS program design meets the performance
characteristics in Requirement E.B.3 for each island identified in Requirement
E.B.2. The simulation shall model each of the following: [VRF: High][Time
Horizon: Long-term Planning]
E.B.4.1. Underfrequency trip settings of individual generating units greater than
20 MVA (gross nameplate rating) directly connected to the BES that trip
above the Generator Underfrequency Trip Modeling curve in PRC-0061 - Attachment 1.
E.B.4.2. Underfrequency trip settings of generating plants/facilities greater than
75 MVA (gross aggregate nameplate rating) directly connected to the
BES that trip above the Generator Underfrequency Trip Modeling curve
in PRC-006-1 - Attachment 1.
E.B.4.3. Underfrequency trip settings of any facility consisting of one or more
units connected to the BES at a common bus with total generation above
75 MVA (gross nameplate rating) that trip above the Generator
Underfrequency Trip Modeling curve in PRC-006-1 - Attachment 1.
E.B.4.4. Overfrequency trip settings of individual generating units greater than 20
MVA (gross nameplate rating) directly connected to the BES that trip
below the Generator Overfrequency Trip Modeling curve in PRC-006-1
— Attachment 1.
E.B.4.5. Overfrequency trip settings of generating plants/facilities greater than 75
MVA (gross aggregate nameplate rating) directly connected to the BES
that trip below the Generator Overfrequency Trip Modeling curve in
PRC-006-1 — Attachment 1.
E.B.4.6. Overfrequency trip settings of any facility consisting of one or more
units connected to the BES at a common bus with total generation above
75 MVA (gross nameplate rating) that trip below the Generator
Overfrequency Trip Modeling curve in PRC-006-1 — Attachment 1.
E.B.4.7. Any automatic Load restoration that impacts frequency stabilization and
operates within the duration of the simulations run for the assessment.
E.B.11. Each Planning Coordinator, in whose area a BES islanding event results in
system frequency excursions below the initializing set points of the UFLS
program, shall participate in and document a coordinated event assessment with
all affected Planning Coordinators to conduct and document an assessment of the
event within one year of event actuation to evaluate: [VRF: Medium][Time
Horizon: Operations Assessment]

Dra ft 6: Oc to b e r 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E.B.11.1. The performance of the UFLS equipment,
E.B.11.2 The effectiveness of the UFLS program
E.B.12.Each Planning Coordinator, in whose islanding event assessment (per E.B.11)
UFLS program deficiencies are identified, shall participate in and document a
coordinated UFLS design assessment of the UFLS program with the other
Planning Coordinators in the WECC Regional Entity area to consider the
identified deficiencies within two years of event actuation. [VRF: Medium][Time
Horizon: Operations Assessment]
M.E.B.1. Each Planning Coordinator shall have evidence such as reports, or other
documentation of its criteria, developed as part of the joint regional review with other
Planning Coordinators in the WECC Regional Entity area to select portions of the
Bulk Electric System that may form islands including how system studies and
historical events were considered to develop the criteria per Requirement E.B.1.
M.E.B.2. Each Planning Coordinator shall have evidence such as reports, memorandums,
e-mails, or other documentation supporting its identification of an island(s), from the
regional review (per E.B.1), as a basis for designing a region-wide coordinated UFLS
program that meet the criteria in Requirement E.B.2 Parts E.B.2.1 and E.B.2.2.
M.E.B.3. Each Planning Coordinator shall have evidence such as reports, memorandums,
e-mails, program plans, or other documentation of its adoption of a UFLS program,
coordinated across the WECC Regional Entity area, including the notification of the
UFLS entities of implementation schedule, that meet the criteria in Requirement E.B.3
Parts E.B.3.1 through E.B.3.3.
M.E.B.4. Each Planning Coordinator shall have dated evidence such as reports, dynamic
simulation models and results, or other dated documentation of its participation in a
coordinated UFLS design assessment with the other Planning Coordinators in the
WECC Regional Entity area that demonstrates it meets Requirement E.B.4 Parts
E.B.4.1 through E.B.4.7.
M.E.B.11.Each Planning Coordinator shall have dated evidence such as reports, data gathered
from an historical event, or other dated documentation to show that it participated in a
coordinated event assessment of the performance of the UFLS equipment and the
effectiveness of the UFLS program per Requirement E.B.11.
M.E.B.12.Each Planning Coordinator shall have dated evidence such as reports, data gathered
from an historical event, or other dated documentation to show that it participated in a
UFLS design assessment per Requirements E.B.12 and E.B.4 if UFLS program
deficiencies are identified in E.B.11.

Dra ft 6: Oc to b e r 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E#
E.B.1

Lower VSL
N/A

Moderate VSL

High VSL

Severe VSL

The Planning Coordinator
participated in a joint regional review
with the other Planning Coordinators
in the WECC Regional Entity area
that developed and documented
criteria but failed to include the
consideration of historical events, to
select portions of the BES, including
interconnected portions of the BES
in adjacent Planning Coordinator
areas, that may form islands

The Planning Coordinator
participated in a joint regional review
with the other Planning Coordinators
in the WECC Regional Entity area
that developed and documented
criteria but failed to include the
consideration of historical events and
system studies, to select portions of
the BES, including interconnected
portions of the BES in adjacent
Planning Coordinator areas, that
may form islands

The Planning Coordinator failed to
participate in a joint regional review
with the other Planning Coordinators
in the WECC Regional Entity area
that developed and documented
criteria to select portions of the BES,
including interconnected portions of
the BES in adjacent Planning
Coordinator areas that may form
islands

OR
The Planning Coordinator
participated in a joint regional review
with the other Planning Coordinators
in the WECC Regional Entity area
that developed and documented
criteria but failed to include the
consideration of system studies, to
select portions of the BES, including
interconnected portions of the BES
in adjacent Planning Coordinator
areas, that may form islands
E.B.2

N/A
N/A

The Planning Coordinator identified
an island(s) from the regional review
to serve as a basis for designing its
UFLS program but failed to include
one (1) of the parts as specified in
Requirement E.B.2, Parts E.B.2.1 or
E.B.2.2

The Planning Coordinator identified
an island(s) from the regional review
to serve as a basis for designing its
UFLS program but failed to include
all of the parts as specified in
Requirement E.B.2, Parts E.B.2.1 or
E.B.2.2
OR
The Planning Coordinator failed to
identify any island(s) from the

Dra ft 6: Oc to b e r 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Lower VSL

Moderate VSL

High VSL

Severe VSL
regional review to serve as a basis
for designing its UFLS program.

E.B.3

N/A

The Planning Coordinator adopted a
UFLS program, coordinated across
the WECC Regional Entity area that
included notification of and a
schedule for implementation by
UFLS entities within its area, but
failed to meet all the performance
characteristic in Requirement E.B.3,
Parts E.B.3.1, E.B.3.2, and E.B.3.3
in simulations of underfrequency
conditions
OR
The Planning Coordinator failed to
adopt a UFLS program, coordinated
across the WECC Regional Entity
area, including notification of and a
schedule for implementation by
UFLS entities within its area.

E.B.4

The Planning Coordinator
participated in and documented a
coordinated UFLS assessment with
the other Planning Coordinators in
the WECC Regional Entity area at
least once every five years that
determines through dynamic
simulation whether the UFLS
program design meets the
performance characteristics in
Requirement E.B.3 for each island
identified in Requirement E.B.2 but
the simulation failed to include one
(1) of the items as specified in
Requirement E.B.4, Parts E.B.4.1

Dra ft 6: Oc to b e r 18, 2010

The Planning Coordinator
participated in and documented a
coordinated UFLS assessment with
the other Planning Coordinators in
the WECC Regional Entity area at
least once every five years that
determines through dynamic
simulation whether the UFLS
program design meets the
performance characteristics in
Requirement E.B.3 for each island
identified in Requirement E.B.2 but
the simulation failed to include two
(2) of the items as specified in
Requirement E.B.4, Parts E.B.4.1

The Planning Coordinator
participated in and documented a
coordinated UFLS assessment with
the other Planning Coordinators in
the WECC Regional Entity area at
least once every five years that
determines through dynamic
simulation whether the UFLS
program design meets the
performance characteristics in
Requirement E.B.3 for each island
identified in Requirement E.B.2 but
the simulation failed to include three
(3) of the items as specified in
Requirement E.B.4, Parts E.B.4.1

The Planning Coordinator
participated in and documented a
coordinated UFLS assessment with
the other Planning Coordinators in
the WECC Regional Entity area at
least once every five years that
determines through dynamic
simulation whether the UFLS
program design meets the
performance characteristics in
Requirement E.B.3 for each island
identified in Requirement E.B.2 but
the simulation failed to include four
(4) or more of the items as specified
in Requirement E.B.4, Parts E.B.4.1

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Lower VSL
through E.B.4.7.

Moderate VSL
through E.B.4.7.

High VSL
through E.B.4.7.

Severe VSL
through E.B.4.7.
OR
The Planning Coordinator failed to
participate in and document a
coordinated UFLS assessment with
the other Planning Coordinators in
the WECC Regional Entity area at
least once every five years that
determines through dynamic
simulation whether the UFLS
program design meets the
performance characteristics in
Requirement E.B.3 for each island
identified in Requirement E.B.2

E.B.11

The Planning Coordinator, in whose
area a BES islanding event resulting
in system frequency excursions
below the initializing set points of the
UFLS program, participated in and
documented a coordinated event
assessment with all Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding event
and evaluated the parts as specified
in Requirement E.B.11, Parts
E.B.11.1 and E.B.11.2 within a time
greater than one year but less than
or equal to 13 months of actuation.

The Planning Coordinator, in whose
area a BES islanding event resulting
in system frequency excursions
below the initializing set points of the
UFLS program, participated in and
documented a coordinated event
assessment with all Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding event
and evaluated the parts as specified
in Requirement E.B.11, Parts
E.B.11.1 and E.B.11.2 within a time
greater than 13 months but less than
or equal to 14 months of actuation.

The Planning Coordinator, in whose
area a BES islanding event resulting
in system frequency excursions
below the initializing set points of the
UFLS program, participated in and
documented a coordinated event
assessment with all Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding event
and evaluated the parts as specified
in Requirement E.B.11, Parts
E.B.11.1 and E.B.11.2 within a time
greater than 14 months but less than
or equal to 15 months of actuation.
OR
The Planning Coordinator, in whose
area an islanding event resulting in
system frequency excursions below
the initializing set points of the UFLS
program, participated in and

Dra ft 6: Oc to b e r 18, 2010

The Planning Coordinator, in whose
area a BES islanding event resulting
in system frequency excursions
below the initializing set points of the
UFLS program, participated in and
documented a coordinated event
assessment with all Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding event
and evaluated the parts as specified
in Requirement E.B.11, Parts
E.B.11.1 and E.B.11.2 within a time
greater than 15 months of actuation.
OR
The Planning Coordinator, in whose
area an islanding event resulting in
system frequency excursions below
the initializing set points of the UFLS
program, failed to participate in and
document a coordinated event

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Lower VSL

Moderate VSL

High VSL

Severe VSL

documented a coordinated event
assessment with all Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding event
within one year of event actuation
but failed to evaluate one (1) of the
parts as specified in Requirement
E.B.11, Parts E.B.11.1 or E.B.11.2.

assessment with all Planning
Coordinators whose areas or portion
of whose areas were also included in
the same island event and evaluate
the parts as specified in
Requirement E.B.11, Parts E.B.11.1
and E.B.11.2.

OR
The Planning Coordinator, in whose
area an islanding event resulting in
system frequency excursions below
the initializing set points of the UFLS
program, participated in and
documented a coordinated event
assessment with all Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding event
within one year of event actuation
but failed to evaluate all of the parts
as specified in Requirement E.B.11,
Parts E.B.11.1 and E.B.11.2.
E.B.12

N/A

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The Planning Coordinator, in which
UFLS program deficiencies were
identified per Requirement E.B.11,
participated in and documented a
coordinated UFLS design
assessment of the coordinated UFLS
program with the other Planning
Coordinators in the WECC Regional
Entity area to consider the identified
deficiencies in greater than two
years but less than or equal to 25
months of event actuation.

The Planning Coordinator, in which
UFLS program deficiencies were
identified per Requirement E.B.11,
participated in and documented a
coordinated UFLS design
assessment of the coordinated UFLS
program with the other Planning
Coordinators in the WECC Regional
Entity area to consider the identified
deficiencies in greater than 25
months but less than or equal to 26
months of event actuation.

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Lower VSL

Moderate VSL

High VSL

Severe VSL
OR
The Planning Coordinator, in which
UFLS program deficiencies were
identified per Requirement E.B.11,
failed to participate in and document
a coordinated UFLS design
assessment of the coordinated UFLS
program with the other Planning
Coordinators in the WECC Regional
Entity area to consider the identified
deficiencies

Dra ft 6: Oc to b e r 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Associated Documents
Version History
Version

Date

Dra ft 6: Oc to b e r 18, 2010

Action

Change Tracking

Complete revision, merging and
updating PRC-006-0, PRC-007-0 and
PRC-009-0

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

PRC-006-1 – Attachment 1
Underfrequency Load Shedding Program
Design Performance and Modeling Curves for
Requirements R3 Parts 3.1-3.2 and R4 Parts 4.1-4.6
Overfrequency Trip Settings
Must Be Modeled for Generators
That Trip Below the Generator
Overfrequency Trip Modeling
Curve

Simulated Frequency Must
Remain Between the
Overfrequency and
Underfrequency Performance
Characteristic Curves

Underfrequency Trip Settings
Must Be Modeled for Generators
That Trip Above the Generator
Underfrequency Trip Modeling
Curve

 Generator Overfrequency Trip Modeling (Requirement R4 Parts 4.4-4.6)
 Overfrequency Performance Characteristic (Requirement R3 Part 3.2)
 Underfrequency Performance Characteristic (Requirement R3 Part 3.1)
 Generator Underfrequency Trip Modeling (Requirement R4 Parts 4.1-4.3)

Curve Definitions
Generator Overfrequency Trip Modeling

Overfrequency Performance Characteristic

t≤2s

t>2s

t≤4s

4 s < t ≤ 30 s

t > 30 s

f = 62.2 Hz

f = -0.686log(t) + 62.41 Hz

f = 61.8 Hz

f = -0.686log(t) + 62.21 Hz

f = 60.7 Hz

Generator Underfrequency Trip Modeling

Underfrequency Performance Characteristic

t≤2s

t>2s

t≤2s

2 s < t ≤ 60 s

t > 60 s

f = 57.8 Hz

f = 0.575log(t) + 57.63 Hz

f = 58.0 Hz

f = 0.575log(t) + 57.83 Hz

f = 59.3 Hz

Dra ft 6: Oc to b e r 18, 2010

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

PRC-006-1 Attachment 1A (Quebec)
Underfrequency Load Shedding Program
Design Performance and Modeling Curves for
Regional
Variances
EA3,E3
Parts
EA3.1-EA3.3
EA4,
EA4.1-EA4.4
Regional
Variances
Parts
E3.1-E3.3and
and
E4 Parts
Parts
E4.1-E4.4

Frequency (Hz)

Overfrequency Trip Settings
Must Be Modeled for Generators
That Trip Below the Generator
Overfrequency Trip Modeling Curve

67
66
65
64
63
62

Simulated Frequency Must
Remain Between the
Overfrequency and
Underfrequency Performance
Characteristic Curves

(30 ; 60.7)
(30 ; 59.3)

60
59
58

(.35 ; 56.7)

0.1

Underfrequency Trip Settings
Must Be Modeled for Generators
That Trip Above the Generator
Underfrequency Trip Modeling Curve
1

57
56
55
100

Time (sec)
Quebec OverFrequency Generator Trip Modeling (Requirement E4.2)

OverFrequency Performance Characteristic (Requirement E3.2)

UnderFrequency Performance Characteristic (Requirement E3.1)

Quebec UnderFrequency Generator Trip Modeling (Requirement E4.1)

Dra ft 6: Oc to b e r 18, 2010

Please use this form to submit comments on the first posting of the Regional Reliability
Standard PRC-006-NPCC-1—Automatic Under frequency Load Shedding. Comments
must be submitted by Feb, 24, 2011. You may submit the completed form using the
electronic comment form posted with the standard. If you have questions please contact
Stephanie Monzon at [email protected] or by telephone at 610-608-8084.
Individual Commenter Information
(Complete this page for comments from one organization or individual.)
Name:
Organization:
Telephone:
E-mail:

NERC
Region

Registered Ballot Body Segment

ERCOT
FRCC
MRO
NPCC
RFC
SERC
SPP
WECC
NA –
Not
Applicable

1 — Transmission Owners

Version 1.0

2 — RTOs and ISOs
3 — Load-serving Entities
4 — Transmission-dependent Utilities
5 — Electric Generators
6 — Electricity Brokers, Aggregators, and Marketers
7 — Large Electricity End Users
8 — Small Electricity End Users
9 — Federal, State, Provincial Regulatory or other Government
Entities
10 — Regional Reliability Organizations and Regional Entities

-1-

Jan. 10, 2011

Automatic Underfrequency Load Shedding PRC-006-NPCC-1

Group Comments (Complete this page if comments are from a group.)
Group Name:
Lead Contact:
Contact Organization:
Contact Segment:
Contact Telephone:
Contact E-mail:
Additional Member Name

Additional Member
Organization

-2-

Region*

Segment*

Automatic Underfrequency Load Shedding PRC-006-NPCC-1

*If more than one Region or Segment applies, indicate the best fit for the purpose of these
comments. Regional acronyms and segment numbers are shown on prior page.
Background Information
A 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.
PRC-006-NPCC-1 ensures the development of an effective automatic under frequency load shedding

(UFLS) program in order to preserve the security and integrity of the bulk power system during declining
system frequency events.
Each NPCC Regional Reliability Standard shall enable or support one or more of the NERC
reliability principles, thereby ensuring that each standard serves a purpose in support of the
reliability of the regional bulk power system. Each of those standards shall also be
consistent with all of the NERC reliability principles, thereby ensuring that no standard
undermines reliability through an unintended consequence. The NERC reliability principles
supported by this standard are the following:

-3-

Automatic Underfrequency Load Shedding PRC-006-NPCC-1
•
•

Reliability Principle 1 — Interconnected bulk electric systems shall be planned and
operated in a coordinated manner to perform reliably under normal and abnormal
conditions as defined in the NERC Standards.
Reliability Principle 2 — The frequency and voltage of interconnected bulk electric
systems shall be controlled within defined limits through the balancing of real and
reactive power supply and demand.

The proposed Northeast Power Coordinating Council (NPCC) Regional Reliability Standard is
not inconsistent with, or less stringent than established NERC Reliability Standards. Once
approved by the appropriate authorities, NPCC Regional Reliability Standard obligates the
NPCC to monitor and enforce compliance, apply sanctions, if any, consistent with any
regional agreements and the NERC rules.
PRC-006-NPCC-1 standard applies to each Transmission Owner, Distribution Provider,
Generator Owner and Planning Coordinator in the NPCC region. The purpose of this standard
is to ensure the development of an effective automatic under frequency load shedding
(UFLS) program in order to preserve the security and integrity of the bulk power system
during declining system frequency events.
The NPCC PRC-006-NPCC-1 standard contains twenty -six main requirements for
applicable entities within the NPCC geographic area. The standard contains the following:
1. Requirement R1 requires that each Planning Coordinator conduct system studies to
identify anticipated islands.
2. Requirement R2 requires that each Planning Coordinator provide information on
anticipated islands to Transmission Owners, Distribution Providers, and Generator
Owners.
3. Requirement R3 requires that each Distribution Provider and Transmission Owner in
the Eastern Interconnection portion of NPCC shall implement an automatic UFLS
program for its Facilities that sheds Load based on frequency thresholds, total
nominal operating time, and amounts specified in Tables 1 through 3.
4. Requirement R4 requires that each Distribution Provider or Transmission Owner that
must arm its load to trip on under frequency in order to meet its minimum
obligations 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 R3 shall provide their Planning Coordinator with the
information in parts 4.1 through 4.4.
5. Requirement R5 requires that each Distribution Provider and Transmission Owner in
the Eastern Interconnection portion of NPCC with peak net Load connected to its
Facilities shall ensure that the total nominal operating time includes the under
frequency relay operating time plus any interposing auxiliary relay operating times,
communications time, and the rated breaker interrupting time as specified in parts
5.1 through 5.2.
6. Requirement R6 requires that each Distribution Provider and Transmission Owner in
the Québec Interconnection portion of NPCC shall implement an automatic UFLS
program for its Facilities that sheds Load based on the frequency thresholds, slopes,
total nominal operating time and amounts specified in Table 4.
7. Requirement R7 requires that each Distribution Provider and Transmission Owner in
the Québec Interconnection portion of NPCC with peak net load connected to its

-4-

Automatic Underfrequency Load Shedding PRC-006-NPCC-1
Facilities shall insure that the total nominal operating time includes the under
frequency relay operating time plus any interposing auxiliary relay operating times,
communications time, and the rated breaker interrupting time.
8. Requirement R8 requires that each Distribution Provider and Transmission Owner set
their under frequency relays with a minimum time delay as specified in parts 8.1 and
8.2.
9. Requirement R9 requires that each Planning Coordinator shall develop, implement
and maintain a program to establish the appropriate inhibit thresholds to be utilized
within its region's UFLS program.
10. Requirement R10 requires that each Planning Coordinator shall provide to
Transmission Owners and Distribution Providers within its program area the specific
inhibit thresholds applicable to each Transmission Owner or Distribution Providers.
11. Requirement R11 requires that 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 R10.
12. Requirement R12 requires that each Distribution Provider and Transmission Owner
shall develop and submit an implementation plan within 90 days of the request from
the Planning Coordinator in accordance with R10.
13. Requirement R13 requires that each Transmission Owner and Distribution Provider
shall annually provide documentation to its Planning Coordinator of the actual net
load that would be shed by the UFLS relays that were armed to shed at each UFLS
stage coincident with their integrated hourly peak during the previous year.
14. Requirement R14 requires that each Generator Owner shall ensure that their
generating units do not trip for under frequency conditions above the appropriate
generator under frequency trip protection settings threshold curve in Figure 1.
15. Requirement R15 requires that each Generator Owner shall transmit the generator
under frequency trip setting and time constant to its Planning Coordinator within 45
days of the Planning Coordinator’s request.
16. Requirement R16 requires that 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 design in
its in generating unit in accordance with parts 16.1 through 16.3.
17. Requirement R17 requires that each Generator Owner of existing non-nuclear units
in service prior to the effective date of this standard that have under frequency
protections set to trip above the curve in Figure 1 shall set its protection, transmit
the setting and obtain compensatory load as specified in parts 17.1 through 17.3.
18. Requirement R18 requires that each Planning Coordinator in Ontario, Quebec and the
Maritime provinces apply the methodology described in Attachment A to determine
the compensatory load shedding that is required in Requirement R17.3.
19. Requirement R19 requires that each Generator Owner, Distribution Provider or
Transmission Owner in ISO-NE and the New York ISO apply the methodology
described in Attachment B to determine the compensatory load shedding that is
required in Requirement R17.3.
20. Requirement R20 requires that each Generator Owner of existing boiling water
reactor nuclear generating plants with units that have under frequency relay
threshold settings above the Eastern Interconnection generator tripping curve in

-5-

Automatic Underfrequency Load Shedding PRC-006-NPCC-1
Figure 1 shall set their under frequency trip settings, and tolerance settings and
transmit the settings as specified in parts 20.1 through 20.3.
21. Requirement R21 requires that each Transmission Owner and Distribution Provider
shall annually provide its UFLS program data to its Planning Coordinator in
accordance with R22 for inclusion in the Planning Coordinator’s data base.
22. Requirement R22 requires that each Planning Coordinator develop, update and
maintain its UFLS program data base as specified in parts 22.1 through 22.5.
23. Requirement R23 requires that each Planning Coordinator shall assess that the UFLS
program requirements within its Planning Coordinator area are satisfied as
implemented by Transmission Owners, Distribution Providers, and Generator Owners
24. Requirement R24 requires that each Planning Coordinator notify its Distribution
Providers, Transmission Owners, and Generator Owners of changes to load
distribution needed to satisfy UFLS program requirements
25. Requirement R25 requires that 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
R24
26. Requirement R26 requires that each Distribution Provider, Transmission Owner and
Generator Owner develop and submit an implementation plan within 90 days of the
request from the Planning Coordinator in accordance with Requirement R25.
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):
Unfair or Closed Process — The regional reliability standard was not developed in
a fair and open process that provided an opportunity for all interested parties to
participate. Although a NERC-approved regional reliability standards development
procedure shall be presumed to be fair and open, objections could be raised
regarding the implementation of the procedure.
Adverse Reliability or Commercial Impact on Other Interconnections — The
regional reliability standard would have a significant adverse impact on reliability or
commerce in other interconnections.
Deficient Standard — The regional reliability standard fails to provide a level of
reliability of the bulk power system such that the regional reliability standard would
be likely to cause a serious and substantial threat to public health, safety, welfare, or
national security.
Adverse Impact on Competitive Markets within the Interconnection — The
regional reliability standard would create a serious and substantial burden on
competitive markets within the interconnection that is not necessary for reliability.
You are not required to answer all questions. Enter all comments in simple text
format.
Insert a “check” mark in the appropriate boxes by double-clicking the gray areas.

-6-

Automatic Underfrequency Load Shedding PRC-006-NPCC-1
1. Was the proposed standard developed in a fair and open process, using the
associated Regional Reliability Standards Development Procedure?
Yes
No

Comments:
2. Does the proposed standard pose an adverse impact to reliability or commerce
in a neighboring region or interconnection?

Yes
No
Comments:
3. Does the proposed standard pose a serious and substantial threat to public
health, safety, welfare, or national security?

Yes
No
Comments:
4. Does the proposed standard pose a serious and substantial burden on
competitive markets within the interconnection that is not necessary for
reliability?

Yes
No
Comments:
5. Does the proposed regional reliability standard meet at least one of the
following criteria?

The proposed standard has more specific criteria for the same requirements
covered in a continent-wide standard

The proposed standard has requirements that are not included in the
corresponding continent-wide reliability standard

The proposed regional difference is necessitated by a physical difference in
the bulk power system.

Yes
No
Comments:

-7-

Consideration of Comments

NPCC Automatic Underfrequency Load Shedding Program
The NPCC Automatic Underfrequency Load Shedding Drafting Team thanks all commenters who
submitted comments on the proposed revisions (clean and redline) to the PRC-006-NPCC-01 standard.
These standards were posted for a 30-day public comment period from November 22, 2011 through
December 22, 2011. Stakeholders were asked to provide feedback on the standards and associated
documents through a special electronic comment form. There were six sets of comments, including
comments from more than 12 different people from approximately nine companies representing five
of the 10 Industry Segments as shown in the table on the following pages.
All submitted comments may be reviewed in their original format on the standard’s project page:
http://www.nerc.com/filez/regional_standards/regional_reliability_standards_under_development.html

If you feel that your comment has been overlooked, please let us know immediately. Our goal is to
give every comment serious consideration in this process! If you feel there has been an error or
omission, you can contact the vice president and director of standards and training, Herb Schrayshuen,
at 404-446-2560 or at [email protected]. In addition, there is a NERC Reliability Standards
Appeals Process.1

The appeals process is in the Reliability Standards Development Procedures: http://www.nerc.com/standards/newstandardsprocess.html.

Index to Questions, Comments, and Responses
1.

Was the proposed standard developed in a fair and open process, using the associated
Regional Reliability Standards Development Procedure? .......................................... 5

Does the proposed standard pose an adverse impact to reliability or commerce in a
neighboring region or interconnection? ................................................................. 7

Does the proposed standard pose a serious and substantial threat to public health,
safety, welfare, or national security? .................................................................. 15

Does the proposed standard pose a serious and substantial burden on competitive
markets within the interconnection that is not necessary for reliability? .................. 16

Does the proposed regional reliability standard meet at least one of the following
criteria? .......................................................................................................... 19

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

The Industry Segments are:
1 — Transmission Owners
2 — RTOs, ISOs
3 — Load-serving Entities
4 — Transmission-dependent Utilities
5 — Electric Generators
6 — Electricity Brokers, Aggregators, and Marketers
7 — Large Electricity End Users
8 — Small Electricity End Users
9 — Federal, State, Provincial Regulatory or other Government Entities
10 — Regional Reliability Organizations, Regional Entities

Group/Individual

Commenter

Organization

Registered Ballot Body Segment
1

Group
Additional Member

Mike Garton
Additional Organization

Dominion

Dominion Resources Services, Inc. MRO

2. Louis Slade

Dominion Resources Services, Inc. SERC

3. Connie Lowe

Dominion Resources Services, Inc. RFC

Group
Additional Member

Annie Lauterbach
Additional Organization

Bonneville Power Administration

Customer Service Engineering WECC 1

2. Laura Oliver

Customer Service Engineering WECC 1

3. Fred Ojima

Transmission Planning

Individual

Michael Falvo

Region Segment Selection

1. Gregory Vasallo

Region Segment Selection

1. Michael Gildea

WECC 1

Independent Electricity System Operator

Group/Individual

Commenter

Organization

Registered Ballot Body Segment
1

Individual

Silvia Parada Mitchell

NextEra Energy

Individual
Individual

Michael Lombardi
John Seelke

Northeast Utilities
PSEG Services Corporation

X
X

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Was the proposed standard developed in a fair and open process, using the associated Regional Reliability Standards
Development Procedure?

Summary Consideration:

Organization

Yes or No

Bonneville Power Administration

Question 1 Comment
BPA thanks you for the opportunity to comment on PRC-006-NPCC-01,
Automatic Underfrequency Load Shedding. BPA has no comments or
concerns at this time as this standard is not applicable to BPA. BPA thanks
you for the opportunity to comment on PRC-006-NPCC-1. BPA has no
comments or concerns at this time as this standard is not applicable to BPA.
Thank you for your comment.

Response:
Independent Electricity System
Operator

Yes

Dominion

Yes

Northeast Utilities

Yes

PSEG Services Corporation

See answer to Q4 below.
Thank you for your comment.
See response to Q4 below.

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 1 Comment

Next Era Energy

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Does the proposed standard pose an adverse impact to reliability or commerce in a neighboring region or interconnection?

Summary Consideration:

Organization
Dominion

Yes or No

Question 2 Comment

Yes

R16.3 and R18 cannot be implemented. As we have stated in previous comments, we
do not agree with the obligation for a non-conforming generator to procure a service
(i.e., load shed) for which we have found no willing provider. It is Dominion’s position
that this portion of the regional standard is not feasible, given no entity will provide
the service a Generator Owner is obligated to procure, which essentially guarantees
that a Generator Owner of a non-conforming generator will not be able to comply
with these requirements.
Thank you for your comment.
The Regional Standard Drafting Team acknowledges the technical challenges of
administering the compensatory load shedding program and as a result has
developed requirements stating that all new units shall conform to the generator
tripping curve.
Additionally, to address your concern regarding generators that are already
interconnected and in commercial operation, non conforming generators either have
existing contracts to provide compensatory load shedding or have mitigated the
conditions that would trip the unit above the appropriate generator curve.
These requirements are contained as criteria within the approved Directory #12 and
are currently in effect throughout the NPCC region.

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 2 Comment
Further, as Dominion noted in previous comments, there are technical difficulties
associated with R16.3 and R18 which would likely have an adverse impact on
reliability. Specifically, shedding additional load equivalent to a non-coordinating
generator would be extremely difficult to design and coordinate. The design would
have to account for the real-time status and output of the generator. Otherwise, this
requirement could create more problems than it attempts to solve. For example,
consider a load shed program that is designed assuming the need to shed load
equivalent to rated capacity for a non-coordinating generator and a frequency event
occurs when this generator is off line. The program sees the frequency at the trigger
level and sheds the load equivalent to the non-coordinating generator. However,
since that generator wasn’t actually on line, there is no additional loss of generation,
but the MW load equivalent of the generator (that is not designed into the UFLS
scheme) is lost anyway. If the UFLS program then implements the next level of
designed reduction of load, this may result in a subsequent rebound in frequency.
This may very well result in overshoot that is more than designed for, resulting in
generator trip from over-frequency. Obviously, the more non-coordinating
generators there are, the more difficult the task of coordination with UFLS schemes
becomes and the more widespread the effects on customers.

The Regional Standard Drafting Team acknowledges the technical challenges of
administering the compensatory load shedding program and as a result has

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 2 Comment
developed requirements stating that all new units shall conform to the generator
tripping curve.
With respect to the possibility of over shedding of load due to existing compensatory
load shedding not matching generation on line, the concern is acknowledged.
However, an average MW output was intended to align the amount of compensatory
load shedding provided with the unit output most likely to be lost if the unit tripped.
It is impossible to ensure a close match between compensatory load shedding and unit
output without real-time arming of UFLS. Adding precision to the amount of
compensatory load shedding that is required will not improve the viability of the
program.
NERC Standard PRC-006-1, Automatic Underfrequency Load Shedding, has been filed
with FERC and a Notice of Potential Rulemaking has been issued for industry
comment (RM11-18). Additionally, under NERC Project 2007-09 Generator
Verification, draft Standard PRC-024-1, Generator Frequency and Voltage Protective
Relay Setting, has the potential to impact the NPCC Regional Standard as it works
through the NERC and FERC approval process. Given the uncertainty of outcome,
there is a potential impact associated with implementation of the Regional Standard
absent FERC approved National Standards. According to the NERC Rules of
Procedure, Section 302 establishes “essential attributes for technically excellent
reliability standards.” Item #9 addresses practicality and states the following:”Each
reliability standard shall establish requirements that can be practically implemented
by the assigned responsible entities within the specified effective date and
thereafter.”Dominion believes the issues previously noted result in a regional
standard that cannot be “practically implemented by the assigned responsibility
entities.”The NPCC Regional Standards Development Procedure in Section II
establishes that “in order to receive the approval of the ERO, the NPCC Reliability

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 2 Comment
Standards Development Process must also achieve the following objectives.”
Specifically:” o No Adverse Impact on Reliability of the Interconnection -An NPCC
Regional Reliability Standard provides a level of bulk power system reliability that is
necessary and adequate to protect public health, safety, welfare, and North American
security and will not have an adverse impact on the reliability of the Interconnection
or other Regions within the Interconnection.”Dominion believes that the technical
difficulties associated with implementing compensating load shedding, if such a
service were available, for non-conforming generators may “have an adverse impact
on the reliability of the Interconnection or other Regions within the
Interconnection.”Therefore, Dominion believes the aforementioned issues must be
resolved prior to approval of this Regional Reliability Standard by NERC and FERC.

The Regional Standard Drafting Team acknowledges the technical challenges of
administering the compensatory load shedding program and as a result has
developed requirements stating that all new units shall conform to the generator
tripping curve.
Additionally, to address your concern regarding generators that are already
interconnected and in commercial operation, non conforming generators either have
existing contracts to provide compensatory load shedding or have mitigated the
conditions that would trip the unit above the appropriate generator curve.
PRC -006-NPCC -1 was developed in response to a request from the ERO to satisfy
FERC Order 693. At that time, 24 standards were identified as ‘fill in the blank’ and as
a result the ERO was ordered to modify the individual standards reliance on the
Regional Reliability Organization.
Additionally, of those 24 standards 4 were identified by the ERO and the regions to
be regionally specific enough to warrant the development of a regional standard and
UFLS is one of those 4 standards.
Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 2 Comment
The Drafting Team made a continual effort to coordinate the standards development
with other related standards that were being drafted concurrently.

Response:
Next Era Energy

Yes

No. R16 requires generators that cannot meet the UFLS curve to have compensatory
load shedding provided by a Distribution Provider (DP). This requirement is fatal
flawed, because this regional reliability standard has inappropriately moved from the
regional reliability organization (RRO) implementing the standard to planning
coordinators, distribution providers, generator owners and transmission owners. The
need for load shedding is not a bottom up analysis. Instead, the need for load
shedding is more appropriately decided collectively by Transmission Planners,
Transmission Operators, Reliability Coordinators and Planning Coordinators. Thus,
the requirement effectively decentralizes the UFLS response, which will only serve to
make the system less reliable.
Thank you for your comment.
The Regional Standard Drafting Team acknowledges the technical challenges of
administering the compensatory load shedding program and as a result has
developed requirements stating that all new units shall conform to the generator
tripping curve.
Additionally, PRC -006-NPCC -1 was developed in response to a request from the ERO
to satisfy FERC Order 693.
At that time, 24 standards were identified as ‘fill in the blank’ and as a result the ERO
was ordered to modify the individual standards reliance on the Regional Reliability
Organization.

Response:
PSEG Services Corporation

Yes

First, the standard lacks the requirement for coordination between Planning
Coordinators (PCs) who have a part of one PC’s island within another PC’s region (R5

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 2 Comment
in NERC PRC-006-1). UFLS program design may require coordination across regional
boundaries as addressed in the NERC standard. R1 in the NPCC standard is NPCCcentric, whereas the power system is not: “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).”

Thank you for your comment.
The Drafting Team made a continual effort to coordinate the standards development
with other related standards that were being drafted concurrently.
Accordingly, Requirement R1 in NERC Standard PRC -006-1 requires a PC to consider
interconnected portions of the BES in adjacent PC areas and Regional Entity areas
that may form islands.
Therefore the requirement to coordinate with adjacent Regional Entities was not
drafted into the NPCC Regional Standard since it is already contained in PRC -006-01.
In addition, R1 is both mistaken and misleading in its reference to the NERC PRC
Standard on UFLS: first, the NERC standard does not address compensatory load
shedding.
The purpose of requirement R1 in the Regional Standard PRC -006-NPCC -1 is to
provide the more specific requirements for utilizing the islands that have been
identified in the NERC Standard.
Accordingly, Generator Owners that trip above the curve in Figure 1 must arrange for
compensatory load shedding as identified by the PC to ensure that adequate
Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 2 Comment
compensatory load shedding is provided in all islands identified in Requirement R1 in
which the unit may operate.

Second, the NERC standard R1 requires PCs “to select portions of the Bulk Electric
System (BES), including interconnected portions of the BES in adjacent Planning
Coordinator areas and Regional Entity areas that may form islands.” While both the
NPCC and the NERC standards require PCs to develop UFLS criteria, the NERC
standard is more expansive in its inclusion of “adjacent Planning Coordinator areas
and Regional Entity areas.” Of course, a regional standard cannot require
coordination with a PC in another region. The NERC standard is superior in that
regard, and therefore the NPCC standard, which lacks this requirement, would be a
detriment to reliability.
With regard to coordination between the NERC standard and the NPCC Regional
Standard, in this case the NERC Standard establishes the broad requirement to
identify islands.
The NPCC Regional Standard establishes the requirements for entities who must
utilize these islands in order to develop a UFLS program.
Second, UFLS programs need to be developed on an Interconnection-wide basis, not
a regional basis. Frequency is an interconnection-specific parameter. This is
recognized in the draft NERC standard BAL-003-1 - Frequency Response and
Frequency Bias Setting, where all Balancing Authorities within an Interconnection
must have a portion of the required Interconnection frequency response.

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 2 Comment
PRC -006-NPCC -1 was developed in response to a request from the ERO to satisfy
FERC Order 693. At that time, 24 standards were identified as ‘fill in the blank’ and as
a result the ERO was ordered to modify the individual standards reliance on the
Regional Reliability Organization.
Additionally, of those 24 standards 4 were identified by the ERO and the regions to
be regionally specific enough to warrant the development of a regional standard and
UFLS is one of those 4 standards.

Response:
Independent Electricity
System Operator

Northeast Utilities

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Does the proposed standard pose a serious and substantial threat to public health, safety, welfare, or national security?

Summary Consideration:

Organization

Yes or No

Dominion

Question 3 Comment
None that can be determined by Dominion.
Thank you for your comment.

Response:
Independent Electricity
System Operator

Northeast Utilities

PSEG Services Corporation

Bonneville Power
Administration
NextEra Energy

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Does the proposed standard pose a serious and substantial burden on competitive markets within the interconnection that is not
necessary for reliability?

Summary Consideration:

Organization

Yes or No

Dominion

Yes

Question 4 Comment
See response provided to Question #2.
Thank you for the comment.

Response:
PSEG Services Corporation

Yes

NERC’s PRC-006-1 does not contain a specific generator performance requirement.
Generators that cannot meet the underfrequency operational assumption in
Attachment 1 of the standard are modeled “as is” by the Planning Coordinator in
accordance with R4, and the UFLS calculated with their actual underfrequency
generator performance parameters must be provided by UFLS entities (Transmission
Owners and Distribution Providers). However, NPCC’s draft standard proposes
specific generator performance requirements on existing in NYISO and ISO-NE -see
Attachment B referenced in R18. In addition, it would require existing Generator
Owner’s to obtain compensatory UFLS for the early tripping of their generator’s
which cannot meet their specific performance requirements - see R16.3. This
compensatory UFLS would be provided by Transmission Owners or Distribution
Providers, but the Generator Owner would be required to obtain it. Although not
directly stated in this regional standard, the presumption is that Generator Owners
would be required to compensate their providers for their compensatory UFLSPSEG
objects to this aspect (compensatory UFLS) of the draft regional standard for several

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 4 Comment
reasons. First, the added cost to existing Generation Owners whose generators do
not meet the draft standard’s performance requirements will impact the
competitiveness of these generators since they must bear an added cost of acquiring
compensatory UFLS that other generators will not. This violates the NPCC Regional
Standards Development Procedure, which adheres to NERC’s market principles - see
p. 9 of the procedure. The NERC market principles state, in part, that “A reliability
standard shall not give any market participant an unfair competitive advantage.”
Thank you for the comment.
In accordance with NERC requirements and NPCC criteria an assessment of the NPCC
UFLS program attributes is required to be performed by NPCC technical committees.
Careful coordination of UFLS parameters is necessary to meet the performance
requirements of the program and generator performance during frequency excursion
is essential to maintaining the programs adequacy.
Second, the requirement that existing Generator Owners acquire compensatory UFLS
to make up for their generators underfrequency performance is completely absent in
the Reliability Functional model description of a Generator Owner’s functions. By
contrast, a Distribution Provider is assigned the task of “providing] and
implement[ing] load-shed capability,” a result that makes sense since Distribution
Providers.
The Regional Standard Drafting Team acknowledges the technical challenges of
administering the compensatory load shedding program and as a result has
developed requirements stating that all new units shall conform to the generator
tripping curve.
Non conforming generators that are already interconnected and in commercial
operation, either have existing contracts to provide compensatory load shedding or
have mitigated the conditions that would trip the unit above the appropriate

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 4 Comment
generator curve.
With regard to the concern regarding the functional model responsibilities, existing
arrangements to provide compensatory load shedding are acceptable to meet the
standards requirements and no new generation shall be permitted to arrange such
agreements in lieu of adhering to the UFLS program parameters.

Response:
Northeast Utilities

Independent Electricity
System Operator

Bonneville Power
Administration
NextEra Energy

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Does the proposed regional reliability standard meet at least one of the following criteria?
• The proposed standard has more specific criteria for the same requirements covered in a continent-wide standard
• The proposed standard has requirements that are not included in the corresponding continent-wide reliability standard
• The proposed regional difference is necessitated by a physical difference in the bulk power system.

Summary Consideration:

Organization
Dominion

Yes or No

Question 4 Comment

Yes

NERC Standard PRC-006-1, Automatic Underfrequency Load Shedding, has been filed
with FERC and a Notice of Potential Rulemaking has been issued for industry
comment (RM11-18). Additionally, under NERC Project 2007-09 Generator
Verification, draft Standard PRC-024-1, Generator Frequency and Voltage Protective
Relay Setting, has the potential to impact the NPCC Regional Standard as it works
through the NERC and FERC approval process. Given the uncertainty of outcome,
there is a potential impact associated with implementation of the Regional Standard
absent FERC approved National Standards.
Thank you for the comment.
PRC -006-NPCC -1 was developed in response to a request from the ERO to satisfy
FERC Order 693. At that time, 24 standards were identified as ‘fill in the blank’ and as
a result the ERO was ordered to modify the individual standards reliance on the
Regional Reliability Organization.
The Drafting Team made a continual effort to coordinate the standards development
with other related standards that were being drafted concurrently.

Response:

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization
PSEG Services Corporation

Yes or No
Yes

Question 4 Comment
While there are more specific criteria and more requirements, the standard has the
deficiencies cited in Q2 and Q4 above.
Thank you for the comment.
Please see responses to Q2 and Q4 above.
ADDITIONAL COMMENTS not addressed in any prior questions: The standard may
violate the market principle that states “Standards shall not define an adequate
amount of, or require expansion of, bulk power system resources or delivery
capability.” Delivery capability of a generator includes the frequency range over
which it can safely and reliably produce MVA output. As written the standard defines
adequacy of delivery capability and also would require Generator Owners of units
that cannot meet that adequacy requirement to either increase their generators’
underfrequency response capability or acquire compensatory UFLS, presumably at
their cost. This violates the market principle.
Thank you for the comment.
In accordance with NERC requirements and NPCC criteria an assessment of the NPCC
UFLS program attributes is required to be performed by NPCC technical committees.
Careful coordination of UFLS parameters is necessary to meet the performance
requirements of the program and generator performance during frequency excursion
is essential to maintaining the programs adequacy.

Response:
Independent Electricity

Yes

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Organization

Yes or No

Question 4 Comment

System Operator
Northeast Utilities

Yes

Bonneville Power
Administration
NextEra Energy
END OF REPORT

Consideration of Comments: NPCC Automatic Underfrequency Load Shedding Program

Individual or group. (6 Responses)
Name (3 Responses)
Organization (3 Responses)
Group Name (3 Responses)
Lead Contact (3 Responses)
Question 1 (4 Responses)
Question 1 Comments (6 Responses)
Question 2 (5 Responses)
Question 2 Comments (6 Responses)
Question 3 (4 Responses)
Question 3 Comments (6 Responses)
Question 4 (4 Responses)
Question 4 Comments (6 Responses)
Question 5 (4 Responses)
Question 5 Comments (6 Responses)
Individual
Michael Falvo
Independent Electricity System Operator
Yes
No
No
No
Yes
Group
Compliance & Responsibility
Silvia Parada Mitchell
Yes
No. R16 requires generators that cannot meet the UFLS curve to have compensatory load shedding provided by a
Distribution Provider (DP). This requirement is fatal flawed, because this regional reliability standard has
inappropriately moved from the regional reliability organization (RRO) implementing the standard to planning
coordinators, distribution providers, generator owners and transmission owners. The need for load shedding is not a
bottom up analysis. Instead, the need for load shedding is more appropriately decided collectively by Transmission
Planners, Transmission Operators, Reliability Coordinators and Planning Coordinators. Thus, the requirement
effectively decentralizes the UFLS response, which will only serve to make the system less reliable.

Individual
Michael Lombardi
Northeast Utilities
Yes
No
No

No
Yes
Group
Dominion
Mike Garton
Yes
Yes
R16.3 and R18 cannot be implemented. As we have stated in previous comments, we do not agree with the obligation
for a non-conforming generator to procure a service (i.e., load shed) for which we have found no willing provider. It is
Dominion’s position that this portion of the regional standard is not feasible, given no entity will provide the service a
Generator Owner is obligated to procure, which essentially guarantees that a Generator Owner of a non-conforming
generator will not be able to comply with these requirements. Further, as Dominion noted in previous comments, there
are technical difficulties associated with R16.3 and R18 which would likely have an adverse impact on reliability.
Specifically, shedding additional load equivalent to a non-coordinating generator would be extremely difficult to design
and coordinate. The design would have to account for the real-time status and output of the generator. Otherwise, this
requirement could create more problems than it attempts to solve. For example, consider a load shed program that is
designed assuming the need to shed load equivalent to rated capacity for a non-coordinating generator and a
frequency event occurs when this generator is off line. The program sees the frequency at the trigger level and sheds
the load equivalent to the non-coordinating generator. However, since that generator wasn’t actually on line, there is no
additional loss of generation, but the MW load equivalent of the generator (that is not designed into the UFLS scheme)
is lost anyway. If the UFLS program then implements the next level of designed reduction of load, this may result in a
subsequent rebound in frequency. This may very well result in overshoot that is more than designed for, resulting in
generator trip from over-frequency. Obviously, the more non-coordinating generators there are, the more difficult the
task of coordination with UFLS schemes becomes and the more widespread the effects on customers. NERC Standard
PRC-006-1, Automatic Underfrequency Load Shedding, has been filed with FERC and a Notice of Potential
Rulemaking has been issued for industry comment (RM11-18). Additionally, under NERC Project 2007-09 Generator
Verification, draft Standard PRC-024-1, Generator Frequency and Voltage Protective Relay Setting, has the potential to
impact the NPCC Regional Standard as it works through the NERC and FERC approval process. Given the uncertainty
of outcome, there is a potential impact associated with implementation of the Regional Standard absent FERC
approved National Standards. According to the NERC Rules of Procedure, Section 302 establishes “essential attributes
for technically excellent reliability standards.” Item #9 addresses practicality and states the following: “Each reliability
standard shall establish requirements that can be practically implemented by the assigned responsible entities within
the specified effective date and thereafter.” Dominion believes the issues previously noted result in a regional standard
that cannot be “practically implemented by the assigned responsibility entities.” The NPCC Regional Standards
Development Procedure in Section II establishes that “in order to receive the approval of the ERO, the NPCC Reliability
Standards Development Process must also achieve the following objectives.” Specifically: “• No Adverse Impact on
Reliability of the Interconnection —An NPCC Regional Reliability Standard provides a level of bulk power system
reliability that is necessary and adequate to protect public health, safety, welfare, and North American security and will
not have an adverse impact on the reliability of the Interconnection or other Regions within the Interconnection.”
Dominion believes that the technical difficulties associated with implementing compensating load shedding, if such a
service were available, for non-conforming generators may “have an adverse impact on the reliability of the
Interconnection or other Regions within the Interconnection.” Therefore, Dominion believes the aforementioned issues
must be resolved prior to approval of this Regional Reliability Standard by NERC and FERC.
No
None that can be determined by Dominion.
Yes
See response provided to Question #2.
Yes
NERC Standard PRC-006-1, Automatic Underfrequency Load Shedding, has been filed with FERC and a Notice of
Potential Rulemaking has been issued for industry comment (RM11-18). Additionally, under NERC Project 2007-09
Generator Verification, draft Standard PRC-024-1, Generator Frequency and Voltage Protective Relay Setting, has the
potential to impact the NPCC Regional Standard as it works through the NERC and FERC approval process. Given the
uncertainty of outcome, there is a potential impact associated with implementation of the Regional Standard absent
FERC approved National Standards.
Individual
John Seelke
PSEG Services Corporation

No
See answer to Q4 below.
Yes
First, the standard lacks the requirement for coordination between Planning Coordinators (PCs) who have a part of one
PC’s island within another PC’s region (R5 in NERC PRC-006-1). UFLS program design may require coordination
across regional boundaries as addressed in the NERC standard. R1 in the NPCC standard is NPCC-centric, whereas
the power system is not: “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).” In addition, R1 is both mistaken and misleading in its reference to
the NERC PRC Standard on UFLS: first, the NERC standard does not address compensatory load shedding. Second,
the NERC standard R1 requires PCs “to select portions of the Bulk Electric System (BES), including interconnected
portions of the BES in adjacent Planning Coordinator areas and Regional Entity areas that may form islands.” While
both the NPCC and the NERC standards require PCs to develop UFLS criteria, the NERC standard is more expansive
in its inclusion of “adjacent Planning Coordinator areas and Regional Entity areas.” Of course, a regional standard
cannot require coordination with a PC in another region. The NERC standard is superior in that regard, and therefore
the NPCC standard, which lacks this requirement, would be a detriment to reliability. Second, UFLS programs need to
be developed on an Interconnection-wide basis, not a regional basis. Frequency is an interconnection-specific
parameter. This is recognized in the draft NERC standard BAL-003-1 – Frequency Response and Frequency Bias
Setting, where all Balancing Authorities within an Interconnection must have a portion of the required Interconnection
frequency response.
No
Yes
NERC’s PRC-006-1 does not contain a specific generator performance requirement. Generators that cannot meet the
underfrequency operational assumption in Attachment 1 of the standard are modeled “as is” by the Planning
Coordinator in accordance with R4, and the UFLS calculated with their actual underfrequency generator performance
parameters must be provided by UFLS entities (Transmission Owners and Distribution Providers). However, NPCC’s
draft standard proposes specific generator performance requirements on existing in NYISO and ISO-NE –see
Attachment B referenced in R18. In addition, it would require existing Generator Owner’s to obtain compensatory UFLS
for the early tripping of their generator’s which cannot meet their specific performance requirements – see R16.3. This
compensatory UFLS would be provided by Transmission Owners or Distribution Providers, but the Generator Owner
would be required to obtain it. Although not directly stated in this regional standard, the presumption is that Generator
Owners would be required to compensate their providers for their compensatory UFLS PSEG objects to this aspect
(compensatory UFLS) of the draft regional standard for several reasons. First, the added cost to existing Generation
Owners whose generators do not meet the draft standard’s performance requirements will impact the competitiveness
of these generators since they must bear an added cost of acquiring compensatory UFLS that other generators will not.
This violates the NPCC Regional Standards Development Procedure, which adheres to NERC’s market principles –
see p. 9 of the procedure. The NERC market principles state, in part, that “A reliability standard shall not give any
market participant an unfair competitive advantage.” Second, the requirement that existing Generator Owners acquire
compensatory UFLS to make up for their generators underfrequency performance is completely absent in the
Reliability Functional model description of a Generator Owner’s functions. By contrast, a Distribution Provider is
assigned the task of “provid[ing] and implement[ing] load-shed capability,” a result that makes sense since Distribution
Providers.
Yes
While there are more specific criteria and more requirements, the standard has the deficiencies cited in Q2 and Q4
above. ADDITIONAL COMMENTS not addressed in any prior questions: The standard may violate the market principle
that states “Standards shall not define an adequate amount of, or require expansion of, bulk power system resources
or delivery capability.” Delivery capability of a generator includes the frequency range over which it can safely and
reliably produce MVA output. As written the standard defines adequacy of delivery capability and also would require
Generator Owners of units that cannot meet that adequacy requirement to either increase their generators’
underfrequency response capability or acquire compensatory UFLS, presumably at their cost. This violates the market
principle.
Group
Bonneville Power Administration
Annie Lauterbach
BPA thanks you for the opportunity to comment on PRC-006-NPCC-01, Automatic Underfrequency Load Shedding.
BPA has no comments or concerns at this time as this standard is not applicable to BPA. BPA thanks you for the
opprotunity to comment on PRC-006-NPCC-1. BPA has no comments or concerns at this time as this standard is not
applicable to BPA.

PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
Implementation Plan
Background:

Effective Dates:
Eastern Interconnection & Québec Interconnection Portions of NPCC Excluding the Independent
Electricity System Operator (IESO) Planning Coordinator Area of NPCC in Ontario, Canada.
1. 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 Jan 1, 2016 to allow for
the existing implementation plan to be completed.
2. 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.

References:



2006 Assessment of UFLS Adequacy Part 3 Assessment of Program Modifications.
SS38 Underfrequency Load Shedding Support Studies

NPCC Criteria:



Directory #12 Underfrequency Load Shedding Program Requirements.
A-7 NPCC Glossary of Terms.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

4.
5.
6.
7.

Description of Current Draft:
This is the third draft of the proposed standard.
Future Development Plan:
Anticipated Action

Anticipated Date

1. Post the initial draft of the standard for 45
day comment period.

July 13, 2009 to August 27, 2009

2. Respond to comments on the first posting
and post revised standard and
implementation plan for a 45 day
comment period.

September 2009 to May 2010

3. Respond to comments on the 2nd posting.

July 2010 to October 2010

4. Obtain RSC approval to move the
standard forward to balloting.

November 2010

December 2010

Post the standard and implementation
plan for a 30 day pre ballot review.

May 26, 2010 to July 9th, 2010

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

6. Conduct a ten day ballot.

December 2010

May, 2011.

Respond to ballot comments and post
revised standard and implementation plan
for a 45 day comment period.

8. Respond to comments on the 3rd posting.

July 2011

9. Obtain RSC approval to move the
standard forward to balloting.

August 2011

10. Post the standard and implementation
plan for a 30 day pre ballot review.

August 2011

11. Conduct a ten day ballot.

September 2011

12. Membership Approval.

September 2011.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

A. Introduction
1.

Title:

Automatic Underfrequency Load Shedding

Number:

PRC-006-NPCC-1

Applicability:
4.1. Generator Owner
4.2. Planning Coordinator
4.3. Distribution Provider
4.4. Transmission Owner

(Proposed) Effective Date:

To be established.

B. Requirements

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]
R2

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

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]

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

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

5.4

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]

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]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

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]

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]

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]

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]

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

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]
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]

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.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

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.

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

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.

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding

Figure 1
Thresholds for Setting Underfrequency Trip Protection for Generators

Frequency (Hz)
60

59.5

58.5

57.5

56.5

56
Eastern Interconnection Generator Tripping
Quebec Interconnection Generator Tripping

0.1

100

Time (sec)

1000

55.5

55
10000

Standard PRC-006-NPCC-1 Automatic Underfrequency Load Shedding
C. Measures

M2. Each Planning Coordinator shall have evidence such as dated documentation that

Standard PRC-006-NPCC-1 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.