Prc-006-5

PRC-006-5 — Automatic Underfrequency Load Shedding

A. Introduction
1.
Title:
Automatic Underfrequency Load Shedding
2.

Number:

3.

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.

4.

Applicability:

PRC-006-5

4.1. Planning Coordinators
4.2. UFLS entities shall mean all entities that are responsible for the ownership,
operation, or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators. Such entities may include one or
more of the following:
4.2.1 Transmission Owners
4.2.2 Distribution Providers
4.2.3 UFLS-Only Distribution Providers
4.3. Transmission Owners that own Elements identified in the UFLS program
established by the Planning Coordinators.
5.

Effective Date:
See Implementation Plan

B. Requirements and Measures
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]

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.
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

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PRC-006-5 — Automatic Underfrequency Load Shedding

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
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.
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.
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-006-5 - 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-006-5 - 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:
• Individual generating units greater than 20 MVA (gross nameplate rating)
directly connected to the BES
• Generating plants/facilities greater than 75 MVA (gross aggregate nameplate
rating) directly connected to the BES
• Facilities consisting of one or more units connected to the BES at a common
bus with total generation above 75 MVA gross nameplate rating.

M3. Each Planning Coordinator shall have evidence such as reports, memorandums,
e-mails, program plans, or other documentation of its UFLS program, including the
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PRC-006-5 — Automatic Underfrequency Load Shedding

notification of the UFLS entities of implementation schedule, that meet the criteria in
Requirement R3, Parts 3.1 through 3.3.
R4.

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-006-5 - 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-006-5 - Attachment 1.
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-006-5 - 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-006-5 — 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-006-5 — 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-006-5 — Attachment 1.
4.7. Any automatic Load restoration that impacts frequency stabilization and operates
within the duration of the simulations run for the assessment.

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.
R5.

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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: High][Time
Horizon: Long-term Planning]

PRC-006-5 — Automatic Underfrequency Load Shedding
•

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.

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.
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]

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
Requirement R6 at least once each calendar year, with no more than 15 months
between maintenance activities.
R7.

Each Planning Coordinator shall provide its UFLS database containing data necessary to
model its UFLS program to other Planning Coordinators within its Interconnection
within 30 calendar days of a request. [VRF: Lower][Time Horizon: Long-term Planning]

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.
R8.

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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: Long-term
Planning]

PRC-006-5 — Automatic Underfrequency Load Shedding

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.
R9.

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

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 implementation, including any Corrective Action Plan,
per Requirement R9.
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
implementation, including any Corrective Action Plan, as 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]
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 implementation, including any Corrective Action Plan, per Requirement R10.
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.
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.
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]

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PRC-006-5 — Automatic Underfrequency Load Shedding

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.
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 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.

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.
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]:

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PRC-006-5 — Automatic Underfrequency Load Shedding

14.1. UFLS program, including a schedule for implementation
14.2. UFLS design assessment
14.3. Format and schedule of UFLS data submittal
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.
R15. Each Planning Coordinator that conducts a UFLS design assessment under
Requirement R4, R5, or R12 and determines that the UFLS program does not meet the
performance characteristics in Requirement R3, shall develop a Corrective Action Plan
and a schedule for implementation by the UFLS entities within its area. [VRF:
High][Time Horizon: Long-term Planning]
15.1. For UFLS design assessments performed under Requirement R4 or R5, the
Corrective Action Plan shall be developed within the five-year time frame
identified in Requirement R4.
15.2. For UFLS design assessments performed under Requirement R12, the Corrective
Action Plan shall be developed within the two-year time frame identified in
Requirement R12.
M15. Each Planning Coordinator that conducts a UFLS design assessment under
Requirement R4, R5, or R12 and determines that the UFLS program does not meet the
performance characteristics in Requirement R3, shall have a dated Corrective Action
Plan and a schedule for implementation by the UFLS entities within its area, that was
developed within the time frame identified in Part 15.1 or 15.2.

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PRC-006-5 — Automatic Underfrequency Load Shedding

C. Compliance
1.

Compliance Monitoring Process
1.1. Compliance Enforcement Authority
As defined in the NERC Rules of Procedure, “Compliance Enforcement Authority”
(CEA) means NERC or the Regional Entity in their respective roles of monitoring
and enforcing compliance with the NERC Reliability Standards.
1.2. Evidence 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, R14, and R15, Measures M1, M2, M3, M4, M5, M12,
M14, and M15 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.

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PRC-006-5 — Automatic Underfrequency Load Shedding

1.3. Compliance Monitoring and Assessment Processes:
Compliance Audit
Self-Certification
Spot Checking
Compliance Violation Investigation
Self-Reporting
Complaints
1.4. Additional Compliance Information
None

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PRC-006-5 — Automatic Underfrequency Load Shedding

Violation Severity Levels
R#
R1

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

The Planning Coordinator
identified an island(s) to serve

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

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PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL

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.

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.

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

R3

N/A

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
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PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL
including notification of and a
schedule for implementation by
UFLS entities within its area

R4

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
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

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PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL

R5

N/A

N/A

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.

R6

N/A

N/A

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.

R7

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

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PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL
The Planning Coordinator failed
to provide its UFLS database to
other Planning Coordinators.

R8

The UFLS entity provided data
to its Planning Coordinator(s)
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.

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

The UFLS entity provided less
than 85% of automatic tripping
of Load in accordance with the
UFLS program design and
schedule for implementation,

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

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

OR
The UFLS entity failed to provide
data to its Planning
Coordinator(s) to support
maintenance of each Planning
Coordinator’s UFLS database.

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PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL

program design and schedule
for implementation, including
any Corrective Action Plan, as
determined by the Planning
Coordinator(s) area in which
it owns assets.

and schedule for
implementation, including any
Corrective Action Plan, as
determined by the Planning
Coordinator(s) area in which it
owns assets.

and schedule for
implementation, including any
Corrective Action Plan, as
determined by the Planning
Coordinator(s) area in which it
owns assets.

including any Corrective Action
Plan, as 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 overvoltage if required by the
UFLS program and schedule
for implementation, including
any Corrective Action Plan, as
determined by the Planning
Coordinator(s) in each
Planning Coordinator area in
which the Transmission
Owner owns transmission.

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 overvoltage if required by the
UFLS program and schedule
for implementation, including
any Corrective Action Plan, as
determined by the Planning
Coordinator(s) in each
Planning Coordinator area in
which the Transmission
Owner owns transmission.

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 overvoltage if required by the UFLS
program and schedule for
implementation, including any
Corrective Action Plan, as
determined by the Planning
Coordinator(s) in each
Planning Coordinator area in
which the Transmission Owner
owns transmission.

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
implementation, including any
Corrective Action Plan, as
determined by the Planning
Coordinator(s) in each Planning
Coordinator area in which the
Transmission Owner owns
transmission.

R11

The Planning Coordinator, in
whose area a BES islanding
event resulting in system
frequency excursions below
the initializing set points of

The Planning Coordinator, in
whose area a BES islanding
event resulting in system
frequency excursions below
the initializing set points of

The Planning Coordinator, in
whose area a BES islanding
event resulting in system
frequency excursions below
the initializing set points of the

The Planning Coordinator, in
whose area a BES islanding event
resulting in system frequency
excursions below the initializing
set points of the UFLS program,
Page 15 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

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 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.

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.

Severe VSL
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 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 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
assessment of the event within
one year of event actuation but
failed to evaluate all of the Parts

Page 16 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL
as specified in Requirement R11,
Parts 11.1 and 11.2.

R12

R13

N/A

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 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 R11,
conducted and documented a
UFLS design assessment to
consider the identified
deficiencies greater than 25
months but less than or equal
to 26 months of event
actuation.

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.

N/A

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

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.

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PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL
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 described in
Requirement R13

R14

N/A

N/A

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.

R15

N/A

The Planning Coordinator
determined, through a UFLS
design assessment performed
under Requirement R4, R5, or
R12, that the UFLS program
did not meet the performance
characteristics in Requirement

The Planning Coordinator
determined, through a UFLS
design assessment performed
under Requirement R4, R5, or
R12, that the UFLS program
did not meet the performance
characteristics in Requirement

The Planning Coordinator
determined, through a UFLS
design assessment performed
under Requirement R4, R5, or
R12, that the UFLS program did
not meet the performance
characteristics in Requirement
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PRC-006-5 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL

R3, and developed a
Corrective Action Plan and a
schedule for implementation
by the UFLS entities within its
area, but exceeded the
permissible time frame for
development by a period of
up to 1 month.

R3, and developed a
Corrective Action Plan and a
schedule for implementation
by the UFLS entities within its
area, but exceeded the
permissible time frame for
development by a period
greater than 1 month but not
more than 2 months.

R3, but failed to develop a
Corrective Action Plan and a
schedule for implementation by
the UFLS entities within its area.
OR
The Planning Coordinator
determined, through a UFLS
design assessment performed
under Requirement R4, R5, or
R12, that the UFLS program did
not meet the performance
characteristics in Requirement
R3, and developed a Corrective
Action Plan and a schedule for
implementation by the UFLS
entities within its area, but
exceeded the permissible time
frame for development by a
period greater than 2 months.

Page 19 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

D. Regional Variances
D.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.
Rationale for Requirement D.A.3:
There are two modifications for requirement D.A.3 :
1. 25% Generation Deficiency : Since the Quebec Interconnection has no potential
viable BES Island in underfrequency conditions, the largest generation deficiency
scenarios are limited to extreme contingencies not already covered by RAS.
Based on Hydro-Québec TransÉnergie Transmission Planning requirements, the
stability of the network shall be maintained for extreme contingencies using a case
representing internal transfers not expected to be exceeded 25% of the time.
The Hydro-Québec TransÉnergie defense plan to cover these extreme contingencies
includes two RAS (RPTC- generation rejection and remote load shedding and TDST a centralized UVLS) and the UFLS.
2. Frequency performance curve (attachment 1A) : Specific cases where a small
generation deficiency using a peak case scenario with the minimum requirement of
spinning reserve can lead to an acceptable frequency deviation in the Quebec
Interconnection while stabilizing between the PRC-006-2 requirement (59.3 Hz) and
the UFLS anti-stall threshold (59.0 Hz).
An increase of the anti-stall threshold to 59.3 Hz would correct this situation but would
cause frequent load shedding of customers without any gain of system reliability.
Therefore, it is preferable to lower the steady state frequency minimum value to 59.0
Hz.
The delay in the performance characteristics curve is harmonized between D.A.3 and
R.3 to 60 seconds.
Rationale for Requirements D.A.3.3. and D.A.4:
The Quebec Interconnection has its own definition of BES. In Quebec, the vast
majority of BES generating plants/facilities are not directly connected to the BES. For
simulations to take into account sufficient generating resources D.A.3.3 and D.A.4
need simply refer to BES generators, plants or facilities since these are listed in a
Registry approved by Québec’s Regulatory Body (Régie de l’Énergie).

D.A.3. 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 each of these extreme events:

Page 20 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

•

Loss of the entire capability of a generating station.

•

Loss of all transmission circuits emanating from a generating station,
switching station, substation or dc terminal.

•

Loss of all transmission circuits on a common right-of-way.

•

Three-phase fault with failure of a circuit breaker to operate and correct
operation of a breaker failure protection system and its associated breakers.

•

Three-phase fault on a circuit breaker, with normal fault clearing.

•

The operation or partial operation of a RAS for an event or condition for
which it was not intended to operate.

[VRF: High][Time Horizon: Long-term Planning]
D.A.3.1.

Frequency shall remain above the Underfrequency Performance
Characteristic curve in PRC-006 - Attachment 1A, either for 60
seconds or until a steady-state condition between 59.0 Hz and 60.7
Hz is reached, and

D.A.3.2.

Frequency shall remain below the Overfrequency Performance
Characteristic curve in PRC-006 - Attachment 1A, either for 60
seconds or until a steady-state condition between 59.0 Hz and 60.7
Hz is reached, and

D.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 Quebec BES generator bus and associated generator
step-up transformer high-side bus

M.D.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 D.A.3 Parts D.A.3.1 through
D.A.3.3.
D.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 D.A.3 for each island identified in Requirement
R2. The simulation shall model each of the following; [VRF: High][Time
Horizon: Long-term Planning]
D.A.4.1

Underfrequency trip settings of individual generating units that are
part of Quebec BES plants/facilities that trip above the Generator
Page 21 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

Underfrequency Trip Modeling curve in PRC-006 - Attachment 1A,
and
D.A.4.2

Overfrequency trip settings of individual generating units that are
part of Quebec BES plants/facilities that trip below the Generator
Overfrequency Trip Modeling curve in PRC-006 - Attachment 1A,
and

D.A.4.3

Any automatic Load restoration that impacts frequency stabilization
and operates within the duration of the simulations run for the
assessment.

M.D.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 D.A.4
Parts D.A.4.1 through D.A.4.3.

Page 22 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

D#
DA3

Lower VSL
N/A

Moderate VSL

High VSL

The Planning Coordinator
developed a UFLS program,
including notification of and a
schedule for implementation by
UFLS entities within its area, but
failed to meet one (1) of the
performance characteristic in
Parts D.A.3.1, D.A.3.2, or D.A.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, but
failed to meet two (2) of the
performance characteristic in
Parts D.A.3.1, D.A.3.2, or D.A.3.3
in simulations of underfrequency
conditions

Severe VSL
The Planning Coordinator
developed a UFLS program
including notification of and a
schedule for implementation by
UFLS entities within its area, but
failed to meet all the
performance characteristic in
Parts D.A.3.1, D.A.3.2, and
D.A.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.

DA4

N/A

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
D.A.3 but the simulation failed
to include one (1) of the items as

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
D.A.3 but the simulation failed to
include two (2) of the items as

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
D.A.3 but the simulation failed to
include all of the items as

Page 23 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

D#

Lower VSL

Moderate VSL
specified in Parts D.A.4.1,
D.A.4.2 or D.A.4.3.

High VSL

Severe VSL

specified in Parts D.A.4.1, D.A.4.2
or D.A.4.3.

specified in Parts D.A.4.1, D.A.4.2
and D.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
D.A.3

Page 24 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

D.B.

Regional Variance for the Western Electricity Coordinating Council
The following Interconnection-wide variance shall be applicable in the Western
Interconnection and replaces, in their entirety, Requirements R1 through R5, and R11
through R15.
As used in the RV, Planning Coordinator is specific to those Planning Coordinators
providing Planning Coordinator service(s) to entities within the Western
Interconnection, regardless of where the Planning Coordinator is located.
D.B.1. Each Planning Coordinator shall participate in a joint regional review with the
other Planning Coordinators 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]
M.D.B.1. Each Planning Coordinator will have evidence such as reports, or other
documentation of its criteria, developed as part of the joint regional review
with other Planning Coordinators 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 D.B.1.
D.B.2. Each Planning Coordinator shall identify one or more islands from the regional
review (per D.B.1) to serve as a basis for designing a Western Interconnectionwide coordinated UFLS program including: [VRF: Medium][Time Horizon: Longterm Planning]
D.B.2.1. Those islands selected by applying the criteria in Requirement D.B.1,
and
D.B.2.2. Any portions of the BES designed to detach from the Western
Interconnection (planned islands) as a result of the operation of a
relay scheme or Remedial Action Scheme.
M.D.B.2. Each Planning Coordinator will have evidence such as reports, memorandums,
e-mails, or other documentation supporting its identification of an island(s),
from the regional review (per D.B.1), as a basis for designing a Western
Interconnection-wide coordinated UFLS program meeting the criteria in
Requirement D.B.2 Parts D.B.2.1 and D.B.2.2.
D.B.3. Each Planning Coordinator shall adopt a UFLS program, coordinated across the
Western Interconnection, 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]
D.B.3.1.

Frequency shall remain above the Underfrequency Performance
Characteristic curve in PRC-006-5 - Attachment 1, either for 60
Page 25 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

seconds or until a steady-state condition between 59.3 Hz and 60.7
Hz is reached, and
D.B.3.2.

Frequency shall remain below the Overfrequency Performance
Characteristic curve in PRC-006-5 - Attachment 1, either for 60
seconds or until a steady-state condition between 59.3 Hz and 60.7
Hz is reached, and

D.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:
D.B.3.3.1. Individual generating units greater than 20 MVA (gross
nameplate rating) directly connected to the BES
D.B.3.3.2. Generating plants/facilities greater than 75 MVA (gross
aggregate nameplate rating) directly connected to the
BES
D.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.

M.D.B.3. Each Planning Coordinator will have evidence such as reports, memorandums,
e-mails, program plans, or other documentation of its adoption of a UFLS
program, coordinated across the Western Interconnection, including the
notification of the UFLS entities of implementation schedule meeting the
criteria in Requirement D.B.3 Parts D.B.3.1 through D.B.3.3.
D.B.4. Each Planning Coordinator shall participate in and document a coordinated
UFLS design assessment with the other Planning Coordinators in the Western
Interconnection at least once every five years that determines through dynamic
simulation whether the UFLS program design meets the performance
characteristics in Requirement D.B.3 for each island identified in Requirement
D.B.2. The simulation shall model each of the following: [VRF: High][Time
Horizon: Long-term Planning]
D.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-006-5 - Attachment 1.

D.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-006-5 - Attachment 1.

Page 26 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

D.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-006-5 Attachment 1.

D.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-006-5 — Attachment 1.

D.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-006-5 — Attachment 1.

D.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-006-5 —
Attachment 1.

D.B.4.7.

Any automatic Load restoration that impacts frequency stabilization
and operates within the duration of the simulations run for the
assessment.

M.D.B.4. Each Planning Coordinator will 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
demonstrating that it meets Requirement D.B.4 Parts D.B.4.1 through D.B.4.7.
D.B.5. through D.B.10. Reserved
D.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]
D.B.11.1. The performance of the UFLS equipment,
D.B.11.2 The effectiveness of the UFLS program

M.D.B.11. Each Planning Coordinator will 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 D.B.11.

Page 27 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

D.B.12.

Each Planning Coordinator, in whose islanding event assessment (per D.B.11)
UFLS program deficiencies are identified, shall participate in and document a
coordinated UFLS design assessment of the UFLS program with all other Planning
Coordinators in the Western Interconnection to consider the identified
deficiencies within two years of event actuation. [VRF: Medium][Time Horizon:
Operations Assessment]

M.D.B.12. Each Planning Coordinator will 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 D.B.12 and D.B.4 if
UFLS program deficiencies are identified in D.B.11.

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PRC-006-5 — Automatic Underfrequency Load Shedding

D#
D.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 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 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 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

The Planning Coordinator
identified an island(s) from the

The Planning Coordinator
identified an island(s) from the

OR
The Planning Coordinator
participated in a joint regional
review with the other Planning
Coordinators 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
D.B.2

N/A

N/A

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PRC-006-5 — Automatic Underfrequency Load Shedding

D#

Lower VSL

Moderate VSL

High VSL

Severe VSL

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 D.B.2, Parts D.B.2.1
or D.B.2.2

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

D.B.3

N/A

The Planning Coordinator
adopted a UFLS program,
coordinated across the Western
Interconnection that included
notification of and a schedule for
implementation by UFLS entities
within its area, but failed to meet
one (1) of the performance
characteristic in Requirement
D.B.3, Parts D.B.3.1, D.B.3.2, or
D.B.3.3 in simulations of
underfrequency conditions

The Planning Coordinator
adopted a UFLS program,
coordinated across the Western
Interconnection that included
notification of and a schedule for
implementation by UFLS entities
within its area, but failed to meet
two (2) of the performance
characteristic in Requirement
D.B.3, Parts D.B.3.1, D.B.3.2, or
D.B.3.3 in simulations of
underfrequency conditions

The Planning Coordinator
adopted a UFLS program,
coordinated across the Western
Interconnection 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
D.B.3, Parts D.B.3.1, D.B.3.2, and
D.B.3.3 in simulations of
underfrequency conditions
OR
The Planning Coordinator failed
to adopt a UFLS program,

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PRC-006-5 — Automatic Underfrequency Load Shedding

D#

Lower VSL

Moderate VSL

High VSL

Severe VSL
coordinated across the Western
Interconnection , including
notification of and a schedule for
implementation by UFLS entities
within its area.

D.B.4

The Planning Coordinator
participated in and
documented a coordinated
UFLS assessment with the other
Planning Coordinators across
the Western Interconnection at
least once every five years that
determines through dynamic
simulation whether the UFLS
program design meets the
performance characteristics in
Requirement D.B.3 for each
island identified in Requirement
D.B.2 but the simulation failed
to include one (1) of the items
as specified in Requirement
D.B.4, Parts D.B.4.1 through
D.B.4.7.

The Planning Coordinator
participated in and documented
a coordinated UFLS assessment
with the other Planning
Coordinators across the Western
Interconnection at least once
every five years that determines
through dynamic simulation
whether the UFLS program
design meets the performance
characteristics in Requirement
D.B.3 for each island identified in
Requirement D.B.2 but the
simulation failed to include two
(2) of the items as specified in
Requirement D.B.4, Parts D.B.4.1
through D.B.4.7.

The Planning Coordinator
participated in and documented
a coordinated UFLS assessment
with the other Planning
Coordinators across the Western
Interconnection at least once
every five years that determines
through dynamic simulation
whether the UFLS program
design meets the performance
characteristics in Requirement
D.B.3 for each island identified in
Requirement D.B.2 but the
simulation failed to include three
(3) of the items as specified in
Requirement D.B.4, Parts D.B.4.1
through D.B.4.7.

The Planning Coordinator
participated in and documented
a coordinated UFLS assessment
with the other Planning
Coordinators across the Western
Interconnection at least once
every five years that determines
through dynamic simulation
whether the UFLS program
design meets the performance
characteristics in Requirement
D.B.3 for each island identified in
Requirement D.B.2 but the
simulation failed to include four
(4) or more of the items as
specified in Requirement D.B.4,
Parts D.B.4.1 through D.B.4.7.
OR
The Planning Coordinator failed
to participate in and document a
coordinated UFLS assessment
with the other Planning
Coordinators across the Western
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PRC-006-5 — Automatic Underfrequency Load Shedding

D#

Lower VSL

Moderate VSL

High VSL

Severe VSL
Interconnection at least once
every five years that determines
through dynamic simulation
whether the UFLS program
design meets the performance
characteristics in Requirement
D.B.3 for each island identified in
Requirement D.B.2

D.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 D.B.11, Parts
D.B.11.1 and D.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 D.B.11, Parts
D.B.11.1 and D.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 D.B.11, Parts
D.B.11.1 and D.B.11.2 within a
time greater than 14 months but
less than or equal to 15 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 D.B.11, Parts
D.B.11.1 and D.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

The Planning Coordinator, in
whose area an islanding event

OR

Page 32 of 40

PRC-006-5 — Automatic Underfrequency Load Shedding

D#

Lower VSL

Moderate VSL

High VSL
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
one (1) of the parts as specified
in Requirement D.B.11, Parts
D.B.11.1 or D.B.11.2.

Severe VSL
excursions below the initializing
set points of the UFLS program,
failed to participate in and
document a coordinated event
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 D.B.11,
Parts D.B.11.1 and D.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 D.B.11, Parts
D.B.11.1 and D.B.11.2.

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PRC-006-5 — Automatic Underfrequency Load Shedding

D#
D.B.12

Lower VSL
N/A

Moderate VSL

High VSL

Severe VSL

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

The Planning Coordinator, in
which UFLS program deficiencies
were identified per Requirement
D.B.11, participated in and
documented a coordinated UFLS
design assessment of the
coordinated UFLS program with
the other Planning Coordinators
across the Western
Interconnection to consider the
identified deficiencies in greater
than 26 months of event
actuation.
OR
The Planning Coordinator, in
which UFLS program deficiencies
were identified per Requirement
D.B.11, failed to participate in
and document a coordinated
UFLS design assessment of the
coordinated UFLS program with
the other Planning Coordinators
across the Western
Interconnection to consider the
identified deficiencies

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PRC-006-5 — Automatic Underfrequency Load Shedding

E. Associated Documents
Version History
Version

Date

Action

Change Tracking

0

April 1, 2005

Effective Date

New

1

May 25, 2010

Completed revision, merging and
updating PRC-006-0, PRC-007-0 and
PRC-009-0.

1

November 4, 2010

Adopted by the Board of Trustees

1

May 7, 2012

FERC Order issued approving PRC006-1 (approval becomes effective
July 10, 2012)

1

November 9, 2012

2

November 13, 2014

FERC Letter Order issued accepting
the modification of the VRF in R5
from (Medium to High) and the
modification of the VSL language in
R8.
Adopted by the Board of Trustees

Revisions made under
Project 2008-02:
Undervoltage Load
Shedding (UVLS) &
Underfrequency Load
Shedding (UFLS) to address
directive issued in FERC
Order No. 763.
Revisions to existing
Requirement R9 and
R10 and addition of
new Requirement
R15.

2

March 4, 2015

3

August 10, 2017

3

September 5, 2017

FERC Order issued approving PRC006-2. Docket No. RD15-2-000
Adopted by the NERC Board of
Trustees
FERC Order issued approving PRC006-3.

Revisions to the Regional
Variance for the Quebec
Interconnection.

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PRC-006-5 — Automatic Underfrequency Load Shedding

4

February 6, 2020

Adopted by NERC Board of Trustees

5

August 20, 2020

Adopted by NERC Board of Trustees

Revisions under Project
2017-07
In Version 5: 1)
Requirements R14 and R15
were added to the list of
Requirements not
applicable to the Western
Interconnection (WI), 2)
use of “Planning
Coordinator” (PC) was
made specific to PCs
providing services within
the WI, regardless of
where the PC is located, 3)
non-substantive changes
were made conforming the
document and styles to the
newest NERC conventions
and templates, and 4)
references to Version 3
were updated to Version 5.

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PRC-006-5 — Automatic Underfrequency Load Shedding

PRC-006-5 – 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
63

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

62

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

60

59

58

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

57
0.1

1

Time (sec)

10

100

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

Page 37 of 40

Frequency (Hz)

61

PRC-006-5 — Automatic Underfrequency Load Shedding
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

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PRC-006-5 — Automatic Underfrequency Load Shedding

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PRC-006-5 — Automatic Underfrequency Load Shedding

Rationale:
During development of this standard, text boxes were embedded within the standard to explain
the rationale for various parts of the standard. Upon BOT approval, the text from the rationale
text boxes was moved to this section.
Rationale for R9:
The “Corrective Action Plan” language was added in response to the FERC directive from Order
No. 763, which raised concern that the standard failed to specify how soon an entity would
need to implement corrections after a deficiency is identified by a Planning Coordinator (PC)
assessment. The revised language adds clarity by requiring that each UFLS entity follow the
UFLS program, including any Corrective Action Plan, developed by the PC.
Also, to achieve consistency of terminology throughout this standard, the word “application”
was replaced with “implementation.” (See Requirements R3, R14 and R15)
Rationale for R10:
The “Corrective Action Plan” language was added in response to the FERC directive from Order
No. 763, which raised concern that the standard failed to specify how soon an entity would
need to implement corrections after a deficiency is identified by a PC assessment. The revised
language adds clarity by requiring that each UFLS entity follow the UFLS program, including any
Corrective Action Plan, developed by the PC.
Also, to achieve consistency of terminology throughout this standard, the word “application”
was replaced with “implementation.” (See Requirements R3, R14 and R15)
Rationale for R15:
Requirement R15 was added in response to the directive from FERC Order No. 763, which
raised concern that the standard failed to specify how soon an entity would need to implement
corrections after a deficiency is identified by a PC assessment. Requirement R15 addresses the
FERC directive by making explicit that if deficiencies are identified as a result of an assessment,
the PC shall develop a Corrective Action Plan and schedule for implementation by the UFLS
entities.
A “Corrective Action Plan” is defined in the NERC Glossary of Terms as, “a list of actions and an
associated timetable for implementation to remedy a specific problem.” Thus, the Corrective
Action Plan developed by the PC will identify the specific timeframe for an entity to implement
corrections to remedy any deficiencies identified by the PC as a result of an assessment.

Page 40 of 40