Reliability Standard PRC-023-2

Standard PRC-023-2 — Transmission Relay Loadability
A. Introduction
1. Title: Transmission Relay Loadability
2. Number:

PRC-023-2

3. Purpose: Protective relay settings shall not limit transmission loadability; not interfere with
system operators’ ability to take remedial action to protect system reliability and; be set to
reliably detect all fault conditions and protect the electrical network from these faults.
4. Applicability
4.1. Functional Entity
4.1.1 Transmission Owners with load-responsive phase protection systems as described in
PRC-023-2 - Attachment A, applied to circuits defined in 4.2.1 (Circuits Subject to
Requirements R1 – R5).
4.1.2 Generator Owners with load-responsive phase protection systems as described in
PRC-023-2 - Attachment A, applied to circuits defined in 4.2.1 (Circuits Subject to
Requirements R1 – R5).
4.1.3 Distribution Providers with load-responsive phase protection systems as described in
PRC-023-2 - Attachment A, applied to circuits defined in 4.2.1(Circuits Subject to
Requirements R1 – R5), provided those circuits have bi-directional flow capabilities.
4.1.4 Planning Coordinators
4.2. Circuits
4.2.1 Circuits Subject to Requirements R1 – R5
4.2.1.1 Transmission lines operated at 200 kV and above.
4.2.1.2 Transmission lines operated at 100 kV to 200 kV selected by the Planning
Coordinator in accordance with R6.
4.2.1.3 Transmission lines operated below 100 kV that are part of the BES and
selected by the Planning Coordinator in accordance with R6.
4.2.1.4 Transformers with low voltage terminals connected at 200 kV and above.
4.2.1.5 Transformers with low voltage terminals connected at 100 kV to 200 kV
selected by the Planning Coordinator in accordance with R6.
4.2.1.6 Transformers with low voltage terminals connected below 100 kV that are part
of the BES and selected by the Planning Coordinator in accordance with R6.
4.2.2 Circuits Subject to Requirement R6
4.2.2.1 Transmission lines operated at 100 kV to 200 kV and transformers with low
voltage terminals connected at 100 kV to 200 kV
4.2.2.2 Transmission lines operated below100 kV and transformers with low voltage
terminals connected below 100 kV that are part of the BES
5.

Effective Dates

The effective dates of the requirements in the PRC-023-2 standard corresponding to the applicable
Functional Entities and circuits are summarized in the following table:

Approved by the Board of Trustees: March 10, 2011

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Standard PRC-023-2 — Transmission Relay Loadability

Effective Date
Applicability

Jurisdictions where
Regulatory Approval is
Required

Jurisdictions where
No Regulatory
Approval is Required

Each Transmission Owner, Generator
Owner, and Distribution Provider with
transmission lines operating at 200 kV
and above and transformers with low
voltage terminals connected at 200 kV
and above, except as noted below.
• For Requirement R1, criterion 10.1,
to set transformer fault protection
relays on transmission lines
terminated only with a transformer
such that the protection settings do
not expose the transformer to fault
level and duration that exceeds its
mechanical withstand capability
• For supervisory elements as
described in PRC-023-2 - Attachment
A, Section 1.6

First day of the first
calendar quarter, after
applicable regulatory
approvals

First calendar quarter
after Board of
Trustees adoption

First day of the first
calendar quarter 12
months after applicable
regulatory approvals

First day of the first
calendar quarter 12
months after Board
of Trustees adoption

First day of the first
calendar quarter 24
months after applicable
regulatory approvals

First day of the first
calendar quarter 24
months after Board
of Trustees adoption

•

Later of the first day of
the first calendar
quarter after applicable
regulatory approvals of
PRC-023-2 or the first
day of the first
calendar quarter 39
months following
applicable regulatory
approvals of PRC-023-1
(October 1, 2013)

Later of the first day
of the first calendar
quarter after Board
of Trustees adoption
of PRC-023-2 or July
1, 2011 1

Later of the first day of
the first calendar
quarter 39 months
following notification
by the Planning
Coordinator of a
circuit’s inclusion on a

Later of the first day
of the first calendar
quarter 39 months
following notification
by the Planning
Coordinator of a
circuit’s inclusion on

Requirement

R1

For switch-on-to-fault schemes as
described in PRC-023-2 - Attachment
A, Section 1.3

Each Transmission Owner, Generator
Owner, and Distribution Provider with
circuits identified by the Planning
Coordinator pursuant to Requirement R6

1 July 1, 2011 is the first day of the first calendar quarter 39 months following the Board of Trustees February 12,
2008 approval of PRC-023-1.

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Standard PRC-023-2 — Transmission Relay Loadability
Effective Date
Requirement

Applicability

Each Transmission Owner, Generator
Owner, and Distribution Provider with
transmission lines operating at 200 kV
and above and transformers with low
voltage terminals connected at 200 kV
and above
Each Transmission Owner, Generator
Owner, and Distribution Provider with
circuits identified by the Planning
Coordinator pursuant to Requirement R6

R2 and R3

Approved by the Board of Trustees: March 10, 2011

Jurisdictions where
Regulatory Approval is
Required

Jurisdictions where
No Regulatory
Approval is Required

list of circuits subject to
PRC-023-2 per
application of
Attachment B, or the
first day of the first
calendar year in which
any criterion in
Attachment B applies,
unless the Planning
Coordinator removes
the circuit from the list
before the applicable
effective date

a list of circuits
subject to PRC-023-2
per application of
Attachment B, or the
first day of the first
calendar year in
which any criterion in
Attachment B
applies, unless the
Planning Coordinator
removes the circuit
from the list before
the applicable
effective date

First day of the first
calendar quarter after
applicable regulatory
approvals

First day of the first
calendar quarter
after Board of
Trustees adoption

Later of the first day of
the first calendar
quarter 39 months
following notification
by the Planning
Coordinator of a
circuit’s inclusion on a
list of circuits subject to
PRC-023-2 per
application of
Attachment B, or the
first day of the first
calendar year in which
any criterion in
Attachment B applies,
unless the Planning
Coordinator removes
the circuit from the list
before the applicable
effective date

Later of the first day
of the first calendar
quarter 39 months
following notification
by the Planning
Coordinator of a
circuit’s inclusion on
a list of circuits
subject to PRC-023-2
per application of
Attachment B, or the
first day of the first
calendar year in
which any criterion in
Attachment B
applies, unless the
Planning Coordinator
removes the circuit
from the list before
the applicable
effective date

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Standard PRC-023-2 — Transmission Relay Loadability
Effective Date
Applicability

Jurisdictions where
Regulatory Approval is
Required

Jurisdictions where
No Regulatory
Approval is Required

R4

Each Transmission Owner, Generator
Owner, and Distribution Provider that
chooses to use Requirement R1 criterion
2 as the basis for verifying transmission
line relay loadability

First day of the first
calendar quarter six
months after applicable
regulatory approvals

First day of the first
calendar quarter six
months after Board
of Trustees adoption

R5

Each Transmission Owner, Generator
Owner, and Distribution Provider that
sets transmission line relays according to
Requirement R1 criterion 12

First day of the first
calendar quarter six
months after applicable
regulatory approvals

First day of the first
calendar quarter six
months after Board
of Trustees adoption

R6

Each Planning Coordinator shall conduct
an assessment by applying the criteria in
Attachment B to determine the circuits in
its Planning Coordinator area for which
Transmission Owners, Generator
Owners, and Distribution Providers must
comply with Requirements R1 through R5

First day of the first
calendar quarter 18
months after applicable
regulatory approvals

First day of the first
calendar quarter 18
months after Board
of Trustees adoption

Requirement

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Standard PRC-023-2 — Transmission Relay Loadability

B. Requirements
R1.

Each Transmission Owner, Generator Owner, and Distribution Provider shall use any one of
the following criteria (Requirement R1, criteria 1 through 13) for any specific circuit terminal
to prevent its phase protective relay settings from limiting transmission system loadability
while maintaining reliable protection of the BES for all fault conditions. Each Transmission
Owner, Generator Owner, and Distribution Provider shall evaluate relay loadability at 0.85 per
unit voltage and a power factor angle of 30 degrees. [Violation Risk Factor: High] [Time
Horizon: Long Term Planning].
Criteria:
1. Set transmission line relays so they do not operate at or below 150% of the highest seasonal
Facility Rating of a circuit, for the available defined loading duration nearest 4 hours
(expressed in amperes).
2. Set transmission line relays so they do not operate at or below 115% of the highest seasonal
15-minute Facility Rating 2 of a circuit (expressed in amperes).
3. Set transmission line relays so they do not operate at or below 115% of the maximum
theoretical power transfer capability (using a 90-degree angle between the sending-end and
receiving-end voltages and either reactance or complex impedance) of the circuit
(expressed in amperes) using one of the following to perform the power transfer
calculation:
•

An infinite source (zero source impedance) with a 1.00 per unit bus voltage at each
end of the line.

•

An impedance at each end of the line, which reflects the actual system source
impedance with a 1.05 per unit voltage behind each source impedance.

4. Set transmission line relays on series compensated transmission lines so they do not operate
at or below the maximum power transfer capability of the line, determined as the greater of:
•

115% of the highest emergency rating of the series capacitor.

•

115% of the maximum power transfer capability of the circuit (expressed in
amperes), calculated in accordance with Requirement R1, criterion 3, using the full
line inductive reactance.

5. Set transmission line relays on weak source systems so they do not operate at or below
170% of the maximum end-of-line three-phase fault magnitude (expressed in amperes).
6. Set transmission line relays applied on transmission lines connected to generation stations
remote to load so they do not operate at or below 230% of the aggregated generation
nameplate capability.
7. Set transmission line relays applied at the load center terminal, remote from generation
stations, so they do not operate at or below 115% of the maximum current flow from the
load to the generation source under any system configuration.

2

When a 15-minute rating has been calculated and published for use in real-time operations, the 15-minute rating
can be used to establish the loadability requirement for the protective relays.

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Standard PRC-023-2 — Transmission Relay Loadability
8. Set transmission line relays applied on the bulk system-end of transmission lines that serve
load remote to the system so they do not operate at or below 115% of the maximum current
flow from the system to the load under any system configuration.
9. Set transmission line relays applied on the load-end of transmission lines that serve load
remote to the bulk system so they do not operate at or below 115% of the maximum current
flow from the load to the system under any system configuration.
10. Set transformer fault protection relays and transmission line relays on transmission lines
terminated only with a transformer so that the relays do not operate at or below the greater
of:
•

150% of the applicable maximum transformer nameplate rating (expressed in
amperes), including the forced cooled ratings corresponding to all installed
supplemental cooling equipment.

•

115% of the highest operator established emergency transformer rating

10.1

Set load responsive transformer fault protection relays, if used, such that the
protection settings do not expose the transformer to a fault level and duration that
exceeds the transformer’s mechanical withstand capability3.

11. For transformer overload protection relays that do not comply with the loadability
component of Requirement R1, criterion 10 set the relays according to one of the
following:
•

Set the relays to allow the transformer to be operated at an overload level of at least
150% of the maximum applicable nameplate rating, or 115% of the highest operator
established emergency transformer rating, whichever is greater, for at least 15
minutes to provide time for the operator to take controlled action to relieve the
overload.

•

Install supervision for the relays using either a top oil or simulated winding hot spot
temperature element set no less than 100° C for the top oil temperature or no less
than 140° C for the winding hot spot temperature 4.

12. When the desired transmission line capability is limited by the requirement to adequately
protect the transmission line, set the transmission line distance relays to a maximum of
125% of the apparent impedance (at the impedance angle of the transmission line) subject
to the following constraints:
a. Set the maximum torque angle (MTA) to 90 degrees or the highest supported by the
manufacturer.
b. Evaluate the relay loadability in amperes at the relay trip point at 0.85 per unit
voltage and a power factor angle of 30 degrees.

3

As illustrated by the “dotted line” in IEEE C57.109-1993 - IEEE Guide for Liquid-Immersed Transformer
Through-Fault-Current Duration, Clause 4.4, Figure 4
4

IEEE standard C57.91, Tables 7 and 8, specify that transformers are to be designed to withstand a winding hot spot
temperature of 180 degrees C, and Annex A cautions that bubble formation may occur above 140 degrees C.

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Standard PRC-023-2 — Transmission Relay Loadability
c. Include a relay setting component of 87% of the current calculated in Requirement
R1, criterion 12 in the Facility Rating determination for the circuit.
13. Where other situations present practical limitations on circuit capability, set the phase
protection relays so they do not operate at or below 115% of such limitations.
R2.

Each Transmission Owner, Generator Owner, and Distribution Provider shall set its out-of-step
blocking elements to allow tripping of phase protective relays for faults that occur during the
loading conditions used to verify transmission line relay loadability per Requirement R1.
[Violation Risk Factor: High] [Time Horizon: Long Term Planning]

R3.

Each Transmission Owner, Generator Owner, and Distribution Provider that uses a circuit
capability with the practical limitations described in Requirement R1, criterion 6, 7, 8, 9, 12, or
13 shall use the calculated circuit capability as the Facility Rating of the circuit and shall obtain
the agreement of the Planning Coordinator, Transmission Operator, and Reliability Coordinator
with the calculated circuit capability. [Violation Risk Factor: Medium] [Time Horizon: Long
Term Planning]

R4.

Each Transmission Owner, Generator Owner, and Distribution Provider that chooses to use
Requirement R1 criterion 2 as the basis for verifying transmission line relay loadability shall
provide its Planning Coordinator, Transmission Operator, and Reliability Coordinator with an
updated list of circuits associated with those transmission line relays at least once each calendar
year, with no more than 15 months between reports. [Violation Risk Factor: Lower] [Time
Horizon: Long Term Planning]

R5.

Each Transmission Owner, Generator Owner, and Distribution Provider that sets transmission
line relays according to Requirement R1 criterion 12 shall provide an updated list of the
circuits associated with those relays to its Regional Entity at least once each calendar year, with
no more than 15 months between reports, to allow the ERO to compile a list of all circuits that
have protective relay settings that limit circuit capability. [Violation Risk Factor: Lower]
[Time Horizon: Long Term Planning]

R6.

Each Planning Coordinator shall conduct an assessment at least once each calendar year, with
no more than 15 months between assessments, by applying the criteria in Attachment B to
determine the circuits in its Planning Coordinator area for which Transmission Owners,
Generator Owners, and Distribution Providers must comply with Requirements R1 through R5.
The Planning Coordinator shall: [Violation Risk Factor: High] [Time Horizon: Long Term
Planning]
6.1

Maintain a list of circuits subject to PRC-023-2 per application of Attachment B,
including identification of the first calendar year in which any criterion in Attachment
B applies.

6.2

Provide the list of circuits to all Regional Entities, Reliability Coordinators,
Transmission Owners, Generator Owners, and Distribution Providers within its
Planning Coordinator area within 30 calendar days of the establishment of the initial
list and within 30 calendar days of any changes to that list.

C. Measures
M1. Each Transmission Owner, Generator Owner, and Distribution Provider shall have evidence
such as spreadsheets or summaries of calculations to show that each of its transmission relays
is set according to one of the criteria in Requirement R1, criterion 1 through 13 and shall have
evidence such as coordination curves or summaries of calculations that show that relays set per
criterion 10 do not expose the transformer to fault levels and durations beyond those indicated
in the standard. (R1)

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Standard PRC-023-2 — Transmission Relay Loadability
M2. Each Transmission Owner, Generator Owner, and Distribution Provider shall have evidence
such as spreadsheets or summaries of calculations to show that each of its out-of-step blocking
elements is set to allow tripping of phase protective relays for faults that occur during the
loading conditions used to verify transmission line relay loadability per Requirement R1. (R2)
M3. Each Transmission Owner, Generator Owner, and Distribution Provider with transmission
relays set according to Requirement R1, criterion 6, 7, 8, 9, 12, or 13 shall have evidence such
as Facility Rating spreadsheets or Facility Rating database to show that it used the calculated
circuit capability as the Facility Rating of the circuit and evidence such as dated
correspondence that the resulting Facility Rating was agreed to by its associated Planning
Coordinator, Transmission Operator, and Reliability Coordinator. (R3)
M4. Each Transmission Owner, Generator Owner, or Distribution Provider that sets transmission
line relays according to Requirement R1, criterion 2 shall have evidence such as dated
correspondence to show that it provided its Planning Coordinator, Transmission Operator, and
Reliability Coordinator with an updated list of circuits associated with those transmission line
relays within the required timeframe. The updated list may either be a full list, a list of
incremental changes to the previous list, or a statement that there are no changes to the
previous list. (R4)
M5. Each Transmission Owner, Generator Owner, or Distribution Provider that sets transmission
line relays according to Requirement R1, criterion 12 shall have evidence such as dated
correspondence that it provided an updated list of the circuits associated with those relays to its
Regional Entity within the required timeframe. The updated list may either be a full list, a list
of incremental changes to the previous list, or a statement that there are no changes to the
previous list. (R5)
M6. Each Planning Coordinator shall have evidence such as power flow results, calculation
summaries, or study reports that it used the criteria established within Attachment B to
determine the circuits in its Planning Coordinator area for which applicable entities must
comply with the standard as described in Requirement R6. The Planning Coordinator shall
have a dated list of such circuits and shall have evidence such as dated correspondence that it
provided the list to the Regional Entities, Reliability Coordinators, Transmission Owners,
Generator Owners, and Distribution Providers within its Planning Coordinator area within the
required timeframe.
D. Compliance
1.

Compliance Monitoring Process
1.1. Compliance Monitoring Responsibility
•
•

For entities that do not work for the Regional Entity, the Regional Entity shall serve as
the Compliance Enforcement Authority.
For functional entities that work for their Regional Entity, the ERO shall serve as the
Compliance Enforcement Authority.

1.2. Data Retention
The Transmission Owner, Generator Owner, Distribution Provider and Planning Coordinator
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:

Approved by the Board of Trustees: March 10, 2011

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Standard PRC-023-2 — Transmission Relay Loadability
The Transmission Owner, Generator Owner, and Distribution Provider shall each retain
documentation to demonstrate compliance with Requirements R1 through R5 for three
calendar years.
The Planning Coordinator shall retain documentation of the most recent review process
required in R6. The Planning Coordinator shall retain the most recent list of circuits in its
Planning Coordinator area for which applicable entities must comply with the standard, as
determined per R6.
If a Transmission Owner, Generator Owner, Distribution Provider or Planning Coordinator is
found non-compliant, it shall keep information related to the non-compliance until found
compliant or for the time specified above, whichever is longer.
The Compliance Monitor shall keep the last audit record and all requested and submitted
subsequent audit records.
1.3. Compliance Monitoring and Assessment Processes
•

Compliance Audit

•

Self-Certification

•

Spot Checking

•

Compliance Violation Investigation

•

Self-Reporting

•

Complaint

1.4. Additional Compliance Information
None.

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Standard PRC-023-2 — Transmission Relay Loadability

2.

Violation Severity Levels:

Requirement
R1

Lower
N/A

Moderate
N/A

High
N/A

Severe
The responsible entity did not use
any one of the following criteria
(Requirement R1 criterion 1
through 13) for any specific circuit
terminal to prevent its phase
protective relay settings from
limiting transmission system
loadability while maintaining
reliable protection of the Bulk
Electric System for all fault
conditions.
OR
The responsible entity did not
evaluate relay loadability at 0.85
per unit voltage and a power factor
angle of 30 degrees.

R2

N/A

N/A

N/A

The responsible entity failed to
ensure that its out-of-step blocking
elements allowed tripping of phase
protective relays for faults that
occur during the loading
conditions used to verify
transmission line relay loadability
per Requirement R1.

R3

N/A

N/A

N/A

The responsible entity that uses a
circuit capability with the practical
limitations described in
Requirement R1 criterion 6, 7, 8,
9, 12, or 13 did not use the
calculated circuit capability as the
Facility Rating of the circuit.
OR

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Standard PRC-023-2 — Transmission Relay Loadability

Requirement

Lower

Moderate

High

Severe
The responsible entity did not
obtain the agreement of the
Planning Coordinator,
Transmission Operator, and
Reliability Coordinator with the
calculated circuit capability.

R4

N/A

N/A

N/A

The responsible entity did not
provide its Planning Coordinator,
Transmission Operator, and
Reliability Coordinator with an
updated list of circuits that have
transmission line relays set
according to the criteria
established in Requirement R1
criterion 2 at least once each
calendar year, with no more than
15 months between reports.

R5

N/A

N/A

N/A

The responsible entity did not
provide its Regional Entity, with
an updated list of circuits that have
transmission line relays set
according to the criteria
established in Requirement R1
criterion 12 at least once each
calendar year, with no more than
15 months between reports.

R6

N/A

The Planning Coordinator used the
criteria established within
Attachment B to determine the
circuits in its Planning Coordinator
area for which applicable entities
must comply with the standard and
met parts 6.1 and 6.2, but more
than 15 months and less than 24
months lapsed between
assessments.

The Planning Coordinator used the
criteria established within
Attachment B to determine the
circuits in its Planning Coordinator
area for which applicable entities
must comply with the standard and
met parts 6.1 and 6.2, but 24
months or more lapsed between
assessments.

The Planning Coordinator failed to
use the criteria established within
Attachment B to determine the
circuits in its Planning Coordinator
area for which applicable entities
must comply with the standard.

Approved by the Board of Trustees: March 10, 2011

OR
The Planning Coordinator used the
criteria established within

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Standard PRC-023-2 — Transmission Relay Loadability

Requirement

Lower

Moderate

High

OR
The Planning Coordinator used the
criteria established within
Attachment B at least once each
calendar year, with no more than
15 months between assessments to
determine the circuits in its
Planning Coordinator area for
which applicable entities must
comply with the standard and met
6.1 and 6.2 but failed to include
the calendar year in which any
criterion in Attachment B first
applies.
OR
The Planning Coordinator used the
criteria established within
Attachment B at least once each
calendar year, with no more than
15 months between assessments to
determine the circuits in its
Planning Coordinator area for
which applicable entities must
comply with the standard and met
6.1 and 6.2 but provided the list of
circuits to the Reliability
Coordinators, Transmission
Owners, Generator Owners, and
Distribution Providers within its
Planning Coordinator area
between 31 days and 45 days after
the list was established or updated.
(part 6.2)

Approved by the Board of Trustees: March 10, 2011

OR
The Planning Coordinator used the
criteria established within
Attachment B at least once each
calendar year, with no more than
15 months between assessments to
determine the circuits in its
Planning Coordinator area for
which applicable entities must
comply with the standard and met
6.1 and 6.2 but provided the list of
circuits to the Reliability
Coordinators, Transmission
Owners, Generator Owners, and
Distribution Providers within its
Planning Coordinator area
between 46 days and 60 days after
list was established or updated.
(part 6.2)

Severe
Attachment B, at least once each
calendar year, with no more than
15 months between assessments to
determine the circuits in its
Planning Coordinator area for
which applicable entities must
comply with the standard but
failed to meet parts 6.1 and 6.2.
OR
The Planning Coordinator used the
criteria established within
Attachment B at least once each
calendar year, with no more than
15 months between assessments to
determine the circuits in its
Planning Coordinator area for
which applicable entities must
comply with the standard but
failed to maintain the list of
circuits determined according to
the process described in
Requirement R6. (part 6.1)
OR
The Planning Coordinator used the
criteria established within
Attachment B at least once each
calendar year, with no more than
15 months between assessments to
determine the circuits in its
Planning Coordinator area for
which applicable entities must
comply with the standard and met
6.1 but failed to provide the list of
circuits to the Reliability
Coordinators, Transmission

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Standard PRC-023-2 — Transmission Relay Loadability

Requirement

Lower

Moderate

High

Severe
Owners, Generator Owners, and
Distribution Providers within its
Planning Coordinator area or
provided the list more than 60 days
after the list was established or
updated. (part 6.2)
OR
The Planning Coordinator failed to
determine the circuits in its
Planning Coordinator area for
which applicable entities must
comply with the standard.

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Standard PRC-023-2 — Transmission Relay Loadability
E. Regional Differences
None
F. Supplemental Technical Reference Document
1. The following document is an explanatory supplement to the standard. It provides the technical
rationale underlying the requirements in this standard. The reference document contains
methodology examples for illustration purposes it does not preclude other technically comparable
methodologies
“Determination and Application of Practical Relaying Loadability Ratings,” Version 1.0, June
2008, prepared by the System Protection and Control Task Force of the NERC Planning
Committee, available at:
http://www.nerc.com/fileUploads/File/Standards/Relay_Loadability_Reference_Doc_Clean_Fina
l_2008July3.pdf
.
Version History
Version

Date

Action

Change Tracking

1

February 12, 2008

Approved by Board of Trustees

New

1

March 19, 2008

Corrected typo in last sentence of Severe VSL
for Requirement 3 — “then” should be “than.”

Errata

1

March 18, 2010

Approved by FERC

1

Filed for approval
April 19, 2010

Changed VRF for R3 from Medium to High;
changed VSLs for R1, R2, R3 to binary Severe
to comply with Order 733

Revision

2

March 10, 2011
approved by Board
of Trustees

Revised to address initial set of directives from
Order 733

Revision (Project
2010-13)

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Standard PRC-023-2 — Transmission Relay Loadability
PRC-023 — Attachment A
1. This standard includes any protective functions which could trip with or without time delay, on load
current, including but not limited to:
1.1. Phase distance.
1.2. Out-of-step tripping.
1.3. Switch-on-to-fault.
1.4. Overcurrent relays.
1.5. Communications aided protection schemes including but not limited to:
1.5.1

Permissive overreach transfer trip (POTT).

1.5.2

Permissive under-reach transfer trip (PUTT).

1.5.3

Directional comparison blocking (DCB).

1.5.4

Directional comparison unblocking (DCUB).

1.6. Phase overcurrent supervisory elements (i.e., phase fault detectors) associated with currentbased, communication-assisted schemes (i.e., pilot wire, phase comparison, and line current
differential) where the scheme is capable of tripping for loss of communications.
2. The following protection systems are excluded from requirements of this standard:
2.1. Relay elements that are only enabled when other relays or associated systems fail. For
example:
•

Overcurrent elements that are only enabled during loss of potential conditions.

•

Elements that are only enabled during a loss of communications except as noted in
section 1.6

2.2. Protection systems intended for the detection of ground fault conditions.
2.3. Protection systems intended for protection during stable power swings.
2.4. Generator protection relays that are susceptible to load.
2.5. Relay elements used only for Special Protection Systems applied and approved in accordance
with NERC Reliability Standards PRC-012 through PRC-017 or their successors.
2.6. Protection systems that are designed only to respond in time periods which allow 15 minutes or
greater to respond to overload conditions.
2.7. Thermal emulation relays which are used in conjunction with dynamic Facility Ratings.
2.8. Relay elements associated with dc lines.
2.9. Relay elements associated with dc converter transformers.

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Standard PRC-023-2 — Transmission Relay Loadability
PRC-023 — Attachment B
Circuits to Evaluate

•
•

Transmission lines operated at 100 kV to 200 kV and transformers with low voltage terminals
connected at 100 kV to 200 kV.
Transmission lines operated below 100 kV and transformers with low voltage terminals
connected below 100 kV that are part of the BES.

Criteria
If any of the following criteria apply to a circuit, the applicable entity must comply with the standard for
that circuit.
B1. The circuit is a monitored Facility of a permanent flowgate in the Eastern Interconnection, a
major transfer path within the Western Interconnection as defined by the Regional Entity, or a
comparable monitored Facility in the Québec Interconnection, that has been included to address
reliability concerns for loading of that circuit, as confirmed by the applicable Planning
Coordinator.
B2. The circuit is a monitored Facility of an IROL, where the IROL was determined in the planning
horizon pursuant to FAC-010.
B3. The circuit forms a path (as agreed to by the Generator Operator and the transmission entity) to
supply off-site power to a nuclear plant as established in the Nuclear Plant Interface
Requirements (NPIRs) pursuant to NUC-001.
B4. The circuit is identified through the following sequence of power flow analyses 5 performed by the
Planning Coordinator for the one-to-five-year planning horizon:
a. Simulate double contingency combinations selected by engineering judgment, without
manual system adjustments in between the two contingencies (reflects a situation where a
System Operator may not have time between the two contingencies to make appropriate
system adjustments).
b. For circuits operated between 100 kV and 200 kV evaluate the post-contingency loading, in
consultation with the Facility owner, against a threshold based on the Facility Rating assigned
for that circuit and used in the power flow case by the Planning Coordinator.
c. When more than one Facility Rating for that circuit is available in the power flow case, the
threshold for selection will be based on the Facility Rating for the loading duration nearest
four hours.
d. The threshold for selection of the circuit will vary based on the loading duration assumed in
the development of the Facility Rating.

5

Past analyses may be used to support the assessment if no material changes to the system have occurred since the
last assessment

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Standard PRC-023-2 — Transmission Relay Loadability
i.

If the Facility Rating is based on a loading duration of up to and including four hours,
the circuit must comply with the standard if the loading exceeds 115% of the Facility
Rating.

ii.

If the Facility Rating is based on a loading duration greater than four and up to and
including eight hours, the circuit must comply with the standard if the loading
exceeds 120% of the Facility Rating.

iii.

If the Facility Rating is based on a loading duration of greater than eight hours, the
circuit must comply with the standard if the loading exceeds 130% of the Facility
Rating.

e. Radially operated circuits serving only load are excluded.
B5. The circuit is selected by the Planning Coordinator based on technical studies or assessments,
other than those specified in criteria B1 through B4, in consultation with the Facility owner.
B6. The circuit is mutually agreed upon for inclusion by the Planning Coordinator and the Facility
owner.

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