Prc-24-4

PRC-024-4.pdf

FERC-725G, RD25-1-000, RD25-2-000, RD25-3-000; RM25-3 Mandatory Reliability Standards for the Bulk-Power System: PRC Rel Stds.

PRC-24-4

OMB: 1902-0252

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PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type
2 Wind Resources, and Synchronous Condensers

A. Introduction
1.

Title:

Frequency and Voltage Protection Settings for Synchronous Generators,
Type 1 and Type 2 Wind Resources, and Synchronous Condensers

Number:

PRC-024-4

Purpose:

To assure that protection of synchronous generators, type 1 and type 2
wind resources, and synchronous condensers do not cause tripping
during defined frequency and voltage excursions in support of the Bulk
Power System (BPS).

Applicability:
4.1. Functional Entities:
4.1.1. Generator Owners that apply protection listed in Sections 4.2.1 or 4.2.2.
4.1.2. Transmission Owners that apply protection listed in Section 4.2.2.
4.1.3. Transmission Owners (in the Quebec Interconnection only) that own a
BES generator step-up (GSU) transformer or main power transformer
(MPT) 1 and apply protection listed in Section 4.2.1.
4.1.4. Planning Coordinators (in the Quebec Interconnection only)
4.2. Facilities 2:
4.2.1 Frequency, voltage, and volts per hertz protection (whether provided by
relaying or functions within associated control systems) that respond to
electrical signals and: (i) directly trip the generating resource(s); or (ii)
provide signals to the generating resource(s) to trip; and are applied to
the following:
4.2.1.1

Bulk Electric System (BES) synchronous generators.

4.2.1.2

BES GSU transformer(s) for synchronous generators.

4.2.1.3

High-side of the synchronous generator-connected unit
auxiliary transformer 3 (UAT) installed on BES generating
resource(s).

4.2.1.4

Individual dispersed power producing type 1 or type 2 wind
resource(s) identified in the BES Definition, Inclusion I4.

For the purpose of this standard, the MPT is the power transformer that steps up voltage from multiple small synchronous
generators (e.g. multiple small hydro generators connecting to a common bus) or from a type 1 or type 2 wind resource
collector station to transmission voltage .
2 It is not required to install or activate the protections described in Facilities Section 4.2.
3 These transformers are variously referred to as station power UAT, or station service transformer(s) used to provide overall
auxiliary power to the synchronous generators. This UAT is the transformer connected on the generator bus between the low
side of the GSU and the generator terminal.
1

Page 1 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type
2 Wind Resources, and Synchronous Condensers

4.2.1.5

Elements that are designed primarily for the delivery of
capacity from multiple synchronous generators connecting to
a common bus or individual dispersed power producing type 1
or type 2 wind resources identified in the BES Definition,
Inclusion I4, to the point where those resources aggregate to
greater than 75 MVA.

4.2.1.6

MPT of multiple synchronous generators connecting to a
common bus or MPT of individual dispersed power producing
type 1 or type 2 wind resources as identified in the BES
Definition, Inclusion I4.

4.2.2 Frequency, voltage, and volts per hertz protection (whether provided by
relaying or functions within associated control systems) that respond to
electrical signals and: (i) directly trip transmission connected synchronous
condensers; or (ii) provide signals to trip transmission connected
synchronous condenser and are applied to the following:
4.2.2.1

BES synchronous condensers

4.2.2.2

BES step-up transformer(s) for synchronous condensers.

4.2.2.3

High-side of the synchronous condenser-connected unit
auxiliary transformer (UAT).

4.2.3 Exemptions: Protection on all auxiliary equipment within the
synchronous generator, type 1 or type 2 wind resource, or synchronous
condenser Facility.
5.

Effective Date: See Implementation Plan for PRC-024-4

Page 2 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type
2 Wind Resources, and Synchronous Condensers

B. Requirements and Measures
R1.

Each Generator Owner and Transmission Owner shall set applicable frequency
protection 4 in accordance with PRC-024-4 Attachment 1 such that the applicable
protection does not cause the Facility to which it is applied to trip within the “no trip
zone” during a frequency excursion with the following exceptions: [Violation Risk
Factor: Medium] [Time Horizon: Long-term Planning]
•

Applicable frequency protection may be set to trip within a portion of the “no
trip zone” for documented and communicated regulatory or equipment
limitations in accordance with Requirement R3.

M1. Each Generator Owner and Transmission Owner shall have evidence that the
applicable frequency protection has been set in accordance with Requirement R1,
such as dated setting sheets, calibration sheets, calculations, or other documentation.
R2.

Each Generator Owner and Transmission Owner shall set applicable voltage
protection 5 in accordance with PRC-024-4 Attachment 2, such that the applicable
protection does not cause the Facility to which it is applied to trip within the “no trip
zone” during a voltage excursion at the high-side of the GSU or MPT, subject to the
following exceptions: [Violation Risk Factor: Medium] [Time Horizon: Long-term
Planning]
•

If the Transmission Planner allows less stringent voltage protection settings than
those required to meet PRC-024-4 Attachment 2, then the Generator Owner or
Transmission Owner may set its protection within the voltage recovery
characteristics of a location-specific Transmission Planner’s study.

•

Applicable voltage protection may be set to trip during a voltage excursion
within a portion of the “no trip zone” for documented and communicated
regulatory or equipment limitations in accordance with Requirement R3.

M2. Each Generator Owner and Transmission Owner shall have evidence that applicable
voltage protection has been set in accordance with Requirement R2, such as dated
setting sheets, voltage-time boundaries, calibration sheets, coordination plots,
dynamic simulation studies, calculations, or other documentation.
R3.

Each Generator Owner and Transmission Owner shall document each known
regulatory or equipment limitation 6 that prevents its Facility, with applicable
frequency or voltage protection from meeting the protection setting criteria in
Requirements R1 or R2, including (but not limited to) study results, experience from
an actual event, or manufacturer’s advice. [Violation Risk Factor: Lower] [Time
Horizon: Long-term Planning]

Frequency, voltage, and volts per hertz protection (whether provided by relaying or functions within associated control
systems) that respond to electrical signals and: (i) directly trip the synchronous generator(s), type 1 or type 2 wind resource(s),
or synchronous condenser(s); or (ii) provide signals to trip the same Facilities.
5 Ibid.
6 Excludes limitations caused by the setting capability of the frequency, voltage, and volts per hertz protective relays applied to
the synchronous generator(s), type 1 and type 2 wind resource(s), and synchronous condenser(s). This does not exclude
limitations originating in the equipment protected by the relay(s).
4

Page 3 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type
2 Wind Resources, and Synchronous Condensers

3.1. The Generator Owner and Transmission Owner shall communicate the
documented regulatory or equipment limitation, or the removal of a previously
documented regulatory or equipment limitation, to its Planning Coordinator and
Transmission Planner within 30 calendar days of any of the following:
•

Identification of a regulatory or equipment limitation.

•

Repair of the equipment causing the limitation that removes the limitation.

•

Replacement of the equipment causing the limitation with equipment that
removes the limitation.

•

Creation or adjustment of an equipment limitation caused by consumption of
the cumulative turbine life-time frequency excursion allowance.

M3. Each Generator Owner and Transmission Owner shall have evidence that it has
documented and communicated any known regulatory or equipment limitations that
resulted in an exception to Requirements R1 or R2 in accordance with Requirement
R3, such as a dated email or letter that contains such documentation as study results,
experience from an actual event, or manufacturer’s advice.
R4.

Each Generator Owner and Transmission Owner shall provide its applicable protection
settings associated with Requirements R1 and R2 to the Planning Coordinator or
Transmission Planner that models the associated Facility within 60 calendar days of
receipt of a written request for the data and within 60 calendar days of any change to
those previously requested settings unless directed by the requesting Planning
Coordinator or Transmission Planner that the reporting of protection setting changes
is not required. [Violation Risk Factor: Lower] [Time Horizon: Operations Planning]

M4. Each Generator Owner and Transmission Owner shall have evidence that it
communicated applicable protection settings in accordance with Requirement R4,
such as dated emails, correspondence or other evidence and copies of any requests it
has received for that information.

Page 4 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type
2 Wind Resources, and Synchronous Condensers

C. Compliance
1.

Compliance Monitoring Process
1.1. Compliance Enforcement Authority: “Compliance Enforcement Authority”
means NERC or the Regional Entity, or any entity as otherwise designated by an
Applicable Governmental Authority, in their respective roles of monitoring
and/or enforcing compliance with mandatory and enforceable Reliability
Standards in their respective jurisdictions.
1.2. Evidence Retention: The following evidence retention period(s) identify the
period of time an entity is required to retain specific evidence to demonstrate
compliance. For instances where the evidence retention period specified below
is shorter than the time since the last audit, the Compliance Enforcement
Authority may ask an entity to provide other evidence to show that it was
compliant for the full-time period since the last audit.
The applicable 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.
•

The Generator Owner and Transmission Owner shall keep data or evidence
of Requirements R1 through R4 for five years or until the next audit,
whichever is longer.

•

If a Generator Owner or Transmission Owner is found non-compliant, the
Generator Owner or Transmission Owner shall keep information related to
the non-compliance until mitigation is complete and approved for the time
period specified above, whichever is longer.

1.3. Compliance Monitoring and Enforcement Program: As defined in the NERC
Rules of Procedure, “Compliance Monitoring and Enforcement Program” refers
to the identification of the processes that will be used to evaluate data or
information for the purpose of assessing performance or outcomes with the
associated Reliability Standard.

Page 5 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type 2 Wind Resources, and Synchronous
Condensers

Violation Severity Levels
R#

Violation Severity Levels

Lower VSL

Moderate VSL

High VSL

R1.

N/A

R2.

N/A

R3.

The Generator Owner or
Transmission Owner
documented the known nonprotection system equipment
limitation that prevented it
from meeting the criteria in
Requirement R1 or R2 and
communicated the
documented limitation to its
Planning Coordinator and
Transmission Planner more
than 30 calendar days but less
than or equal to 60 calendar
days of identifying the
limitation.

The Generator Owner or
Transmission Owner
documented the known nonprotection system equipment
limitation that prevented it
from meeting the criteria in
Requirement R1 or R2 and
communicated the
documented limitation to its
Planning Coordinator and
Transmission Planner more
than 60 calendar days but less
than or equal to 90 calendar
days of identifying the
limitation.

The Generator Owner or
Transmission Owner
documented the known nonprotection system equipment
limitation that prevented it
from meeting the criteria in
Requirement R1 or R2 and
communicated the
documented limitation to its
Planning Coordinator and
Transmission Planner more
than 90 calendar days but less
than or equal to 120 calendar
days of identifying the
limitation.

Severe VSL
The Generator Owner or
Transmission Owner failed to
set its applicable frequency
protection so that it does not
trip according to Requirement
R1.
The Generator Owner or
Transmission Owner failed to
set its applicable voltage
protection so that it does not
trip according to Requirement
R2.
The Generator Owner or
Transmission Owner failed to
document any known nonprotection system equipment
limitation that prevented it
from meeting the criteria in
Requirement R1 or R2.
OR
The Generator Owner or
Transmission Owner failed to
communicate the documented
limitation to its Planning
Coordinator and Transmission
Planner within 120 calendar

Page 6 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type 2 Wind Resources, and Synchronous
Condensers
Violation Severity Levels

Lower VSL

Moderate VSL

High VSL

Severe VSL
days of identifying the
limitation.

R4.

The Generator Owner or
Transmission Owner provided
its protection settings more
than 60 calendar days but less
than or equal to 90 calendar
days of any change to those
settings.

The Generator Owner or
Transmission Owner provided
its protection settings more
than 90 calendar days but less
than or equal to 120 calendar
days of any change to those
settings.

The Generator Owner or
Transmission Owner provided
its protection settings more
than 120 calendar days but less
than or equal to 150 calendar
days of any change to those
settings.

The Generator Owner or
Transmission Owner failed to
provide its protection settings
within 150 calendar days of any
change to those settings.

The Generator Owner or
Transmission Owner provided
protection settings more than
60 calendar days but less than
or equal to 90 calendar days of
a written request.

The Generator Owner or
Transmission Owner provided
protection settings more than
90 calendar days but less than
or equal to 120 calendar days
of a written request.

The Generator Owner or
Transmission Owner or
provided protection settings
more than 120 calendar days
but less than or equal to 150
calendar days of a written
request.

The Generator Owner or
Transmission Owner failed to
provide protection settings
within 150 calendar days of a
written request.

Page 7 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type
2 Wind Resources, and Synchronous Condensers

D. Regional Variances
D.A.

Variance for the Quebec Interconnection

This Variance replaces Requirement R2 of the continent-wide standard in its entirety
and adds a new requirement, Requirement D.A.5., applicable to Planning
Coordinators in the Quebec Interconnection.
This Variance replaces continent-wide Requirement R2 in its entirety with the
following:
D.A.2.

Each Generator Owner and Transmission Owner shall set applicable
voltage protection 7 in accordance with PRC-024 Attachment 2A, such
that the applicable protection does not cause the Facility to which it is
applied to trip within the “no trip zone” during a voltage excursion at the
high-side of the GSU or MPT, subject to the following exceptions:
[Violation Risk Factor: Medium] [Time Horizon: Long-term Planning]
•

For newly designated strategic power plants, applicable protections
must comply with the high voltage durations for such plants within 48
calendar months of the notification made pursuant to Requirement
D.A.5. During this transition period, voltage protections must at least
comply with the high voltage durations for “all power plants”.

•

Applicable voltage protection may be set to trip during a voltage
excursion within a portion of the “no trip zone” of PRC-024
Attachment 2A for documented and communicated regulatory or
equipment limitations in accordance with Requirement R3.

•

If the Transmission Planner allows less stringent voltage protection
settings than those required to meet PRC-024 Attachment 2A, then
the Generator Owner or Transmission Owner may set its protection
within the voltage recovery characteristics of a location-specific
Transmission Planner’s study.

M.D.A.2. Each Generator Owner and Transmission Owner shall have evidence that
applicable voltage protection has been set in accordance with
Requirement R2, such as dated setting sheets, voltage-time boundaries,
calibration sheets, coordination plots, dynamic simulation studies,
calculations, or other documentation.
This Variance adds the following Requirement:
D.A.5

Each Planning Coordinator shall designate, at least once every five
calendar years, the strategic power plants that must comply with
Attachment 2A and notify, within 30 calendar days of its designation,

Page 8 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type
2 Wind Resources, and Synchronous Condensers

each Generator Owner or Transmission Owner that owns facilities 8 in the
strategic power plants. [Violation Risk Factor: Medium] [Time Horizon:
Long-term planning]
M.D.A.5

Each Planning Coordinator shall have evidence that it designated, at least
once every five calendar years, strategic power plants in accordance with
Requirement D.A.5, Part 5 and shall have dated evidence that each
Generator Owner or Transmission Owner has been notified in accordance
with Requirement D.A.5, part 5.2. Evidence may include, but is not
limited to letters, emails, electronic files, or hard copy records
demonstrating transmittal of information.

Facilities in the strategic power plants include facilities with synchronous generator(s) from the generator up to and including
the MPT or GSU.
8

Page 9 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type 2 Wind Resources, and Synchronous
Condensers

Violation Severity Levels

This Variance adds a VSL for D.A.5 and modifies the VSL for R2 as follows:
R#
D.A.2.

Violation Severity Levels
Lower
VSL
N/A

Moderate VSL

High VSL

Severe VSL

N/A

The Generator Owner or Transmission
Owner failed to set its applicable
voltage protection so that it does not
trip in accordance with Requirement
D.A.2.
OR

D.A.5.

N/A

The Planning Coordinator designated
strategic power plants at least once
every five calendar years but notified
each Generator Owner or Transmission
Owner that owns facilities in the
strategic power plants between 31
days and 45 days after its designation.

The Generator Owner or Transmission
Owner set its applicable voltage
protection in accordance with
Requirement D.A.2 but, for strategic
power plants, failed to do so within 48
months of notification.
The Planning Coordinator failed to
designate, at least once every five
years, the strategic power plants that
must comply with Attachment 2A.
OR
The Planning Coordinator failed to
notify, each Generator Owner or
Transmission Owner that owns
facilities in the strategic power plants
or notified them more than 60 days
after its designation.

E. Associated Documents
Implementation Plan

Page 10 of 20

PRC-024-4 —Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type
2 Wind Resources, and Synchronous Condensers

Version History
Version

Date

Action

Change Tracking

May 9, 2013

Adopted by the NERC Board of
Trustees

March 20, 2014

FERC Order issued approving PRC024-1. (Order becomes effective on
7/1/16.)

February 12, 2015

Adopted by the NERC Board of
Trustees

Standard revised in
Project 2014-01:
Applicability revised to
clarify application of
requirements to BES
dispersed power
producing resources

May 29, 2015

FERC Letter Order in Docket No.
RD15-3-000 approving PRC-024-2

Modifications to adjust
the applicability to
owners of dispersed
generation resources.

February 6, 2020

Adopted by the NERC Board of
Trustees

Standard revised in
Project 2018-04

July 9, 2020

FERC Letter Order approved PRC0243. Docket No. RD20-7-000

July 17, 2020

Effective Date

10/1/2022

August 2, 2024

Revisions made by the 2020-02
Drafting Team

Revision accounts for
changes with PRC-029-1
as part of Milestone 2 of
NERC’s work plan to
address FERC Order No.
901.

October 8, 2024

Adopted by the NERC Board of
Trustees

Standard revised in
Project 2020-02

Page 11 of 20

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

Attachment 1

(Frequency No Trip Boundaries by Interconnection 9)

Frequency (Hz)

63
62
61
60
No Trip Zone*

59
58
57

0.1

100

1000

10000

Time (Sec)
Figure 1: Eastern Interconnection Boundaries
* The area outside the "No Trip Zone" is not a "Must Trip Zone."
Table 1: Frequency Boundary Data Points - Eastern Interconnection
High Frequency Duration

Low Frequency Duration

Frequency (Hz)

Minimum Time (Sec)

Frequency (Hz)

Minimum Time (sec)

≥61.8
≥60.5

Instantaneous 10
10(90.935-1.45713*f)

≤57.8
≤59.5

Instantaneous11
10(1.7373*f-100.116)

<60.5

Continuous operation

> 59.5

Continuous operation

The figures do not visually represent the “no trip zone” boundaries before 0.1 seconds and after 10,000 seconds. The
Frequency Boundary Data Points Table defines the entirety of the “no trip zone” boundaries.
10 Frequency is calculated over a window of time. While the frequency boundaries include the option to trip instantaneously for
frequencies outside the specified range, this calculation should occur over a time window. Typical window/filtering lengths are
three to six cycles (50 – 100 milliseconds). Instantaneous trip settings based on instantaneously calculated frequency
measurement is not permissible.
9

Page 12 of 20

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

Frequency (Hz)

62
61
60
59

No Trip Zone*

58
57
56

0.1

100

1000

10000

Time (Sec)
Figure 2: Western Interconnection Boundaries
* The area outside the "No Trip Zone" is not a "Must Trip Zone."

Table 2: Frequency Boundary Data Points – Western Interconnection
High Frequency Duration

Low Frequency Duration

Frequency (Hz)

Minimum Time (Sec)

Frequency (Hz)

Minimum Time (sec)

≥61.7
≥61.6
≥60.6
<60.6

Instantaneous11
30
180
Continuous operation

≤57.0
≤57.3
≤57.8
≤58.4
≤59.4

Instantaneous11
0.75
7.5
30
180

>59.4

Continuous operation

Page 13 of 20

Frequency (Hz)

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

67
66
65
64
63
62
61
60
59
58
57
56
55

No Trip Zone*

0.1

100

1000

10000

Time (Sec)
Figure 3: Quebec Interconnection Boundaries
* The area outside the "No Trip Zone" is not a "Must Trip Zone."
Table 3: Frequency Boundary Data Points – Quebec Interconnection
High Frequency Duration

Low Frequency Duration

Frequency (Hz)

Minimum Time (Sec)

Frequency (Hz)

Minimum Time (Sec)

>66.0

Instantaneous11

<55.5

Instantaneous11

≥63.0

≤56.5

0.35

≥61.5

≤57.0

≥60.6

660

≤57.5

<60.6

Continuous operation

≤58.5

≤59.4

660

>59.4

Continuous operation

Page 14 of 20

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

Frequency (Hz)

63
62
61
60

No Trip Zone*

59
58
57

0.1

100

1000

10000

Time (Sec)
Figure 4: ERCOT Interconnection Boundaries
* The area outside the "No Trip Zone" is not a "Must Trip Zone."
Table 4: Frequency Boundary Data Points – ERCOT Interconnection
High Frequency Duration

Low Frequency Duration

Frequency (Hz)

Minimum Time (Sec)

Frequency (Hz)

Minimum Time (sec)

≥61.8

Instantaneous11

≤57.5

Instantaneous11

≥61.6

≤58.0

≥60.6

540

≤58.4

<60.6

Continuous operation

≤59.4

540

>59.4

Continuous operation

Page 15 of 20

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

PRC-024 — Attachment 2

Voltage (per unit)8

(Voltage No-Trip Boundaries – Eastern, Western, and ERCOT Interconnections)

1.30
1.25
1.20
1.15
1.10
1.05
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00

The Voltage No Trip Zone ends at 4
seconds for applicability to PRC-024

No Trip Zone*

0.5

1.5

2.5

Time (sec)

High Voltage Duration

3.5

Low Voltage Duration

Figure 5: Voltage No-Trip Boundaries – Eastern, Western, and ERCOT
Interconnections
* The area outside the "No Trip Zone" is not a "Must Trip Zone."

Table 5: Voltage Boundary Data Points
High Voltage Duration

Low Voltage Duration

Voltage (per unit)

Minimum Time (sec)

Voltage (per unit)

Minimum Time (sec)

≥1.200
≥1.175
≥1.15
≥1.10
<1.10

0.00
0.20
0.50
1.00
4.00

<0.45
<0.65
<0.75
<0.90
≥ 0.90

0.15
0.30
2.00
3.00
4.00

Page 16 of 20

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

Attachment 2: Voltage Boundary Clarifications – Eastern, Western,
and ERCOT Interconnections
Boundary Details:

1. Unless otherwise specified by the Transmission Planner, the per unit voltage base for
these boundaries is the nominal transmission system voltage (e.g., 100 kV, 115 kV, 138
kV, 161 kV, 230 kV, 345 kV, 400 kV, 500 kV, 765 kV, etc.).
2. The values in the table represent the minimum time durations allowed for specified
voltage excursion thresholds.
3. When evaluating volts per hertz protection, either assume a system frequency of 60
Hertz or the magnitude of the high voltage boundary can be adjusted in proportion to
deviations of frequency below 60 Hertz.
4. Voltages in the boundaries assume RMS fundamental frequency phase-to-ground or
phase-to-phase per unit voltage.
5. For applicability to PRC-024, the “no trip zone” ends at 4 seconds.
Evaluating Protection Settings:

The voltage values in the Attachment 2 voltage boundaries are voltages at the high-side of the
GSU/MPT. For resources with multiple stages of step up to reach interconnecting voltage, this is
the high-side of the transformer with a low side below 100kV and a high-side 100kV or above.
When evaluating protection settings, consider the voltage differences between where the
protection is measuring voltage and the high-side of the GSU/MPT. A steady state calculation or
dynamic simulation may be used.
If using a steady state calculation or dynamic simulation, use the following conditions when
evaluating protection settings:
a. The most probable real and reactive loading conditions for the synchronous generator,
type 1 or 2 wind resources, or synchronous condenser under study.
b. All installed wind resource reactive support (e.g., static VAR compensators, synchronous
condensers, capacitors) equipment is available and operating normally.
c. Account for the actual tap settings of transformers between the generator terminals or
the collector station and the high-side of the GSU/MPT.
d. For dynamic simulations, the synchronous generator or condenser automatic voltage
regulator is in automatic voltage control mode with associated limiters in service.

Page 17 of 20

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

PRC-024— Attachment 2A

(Voltage No-Trip Boundaries – Quebec Interconnection)

1.5

Positive-sequence Voltage (per unit)

1.4

1.25
1.20
1.15
1.10
1.0

"No Trip Zone" *

0.90
0.85
0.75

0.25

0
0 0.1
0.033

0.15

2.5

0.5

300

Time (sec)
Low Voltage/High Voltage Duration – Synchronous Generators and Condensers
High Voltage Duration - Strategic Power Plants

Figure 6: Voltage No-Trip Boundaries – Quebec Interconnection
* The area outside the “No Trip Zone” is not a “Must Trip Zone.”

Page 18 of 20

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

Table 6: High Voltage Boundary Data Points – Quebec Interconnection
High Voltage Duration for all
Synchronous Generators and
Condensers

High Voltage Duration for strategic
Power Plants

Voltage (per unit)

Minimum Time (sec)

Voltage (per unit)

Minimum Time (sec)

-->1.40
>1.25
>1.20
>1.15
>1.10
≤1.10

--0.033
0.10
2.00
30
300
continuous

>1.50
>1.40
>1.25
>1.20
>1.15
>1.10
≤1.10

0.033
0.10
2.50
5.00
30
300
continuous

Table 7: Low Voltage Boundary Data Points – Quebec Interconnection
Low Voltage Duration for all
Synchronous Generators and
Condensers

Voltage (per unit)

Minimum Time (sec)

<0.25
<0.75
<0.85
<0.90
≥0.90

0.15
1.00
2.00
30
continuous

Page 19 of 20

PRC-024-4 Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind,
and Synchronous Condensers

Attachment 2A: Voltage Boundary Clarifications – Quebec
Interconnection
Boundary Details:

1. The per unit voltage base for these boundaries is the nominal operating voltage (e.g.,
120 kV, 161 kV, 230 kV, 315 kV, 735 kV, etc.).
2. The values in the table represent the minimum time durations allowed for specified
voltage excursion thresholds.
3. When evaluating volts per hertz protection, either assume a system frequency of 60
Hertz or the magnitude of the high voltage boundary can be adjusted in proportion to
deviations of frequency below 60 Hertz.
4. Voltages in the Quebec Interconnection boundaries assume positive-sequence values.
Evaluating Protection Settings:

The voltage values in the Attachment 2A voltage boundaries are voltages at the high-side of the
GSU/MPT. For resources with multiple stages of step up to reach interconnecting voltage, this is
the high-side of the transformer that connects to the interconnecting voltage. When evaluating
protection settings, consider the voltage differences between where the protection is
measuring voltage and the high-side of the GSU/MPT. A steady state calculation or dynamic
simulation may be used.
If using a steady state calculation or dynamic simulation, use the following conditions when
evaluating protection settings:
a. The most probable real and reactive loading conditions for the unit under study.
b. All installed generating plant reactive support (e.g., static VAR compensators,
synchronous condensers, capacitors) equipment is available and operating normally.
c. Account for the actual tap settings of transformers between the generator terminals
and the high-side of the GSU/MPT.
d. For dynamic simulations, the automatic voltage regulator is in automatic voltage control
mode with associated limiters in service.

Page 20 of 20

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