Reliability Standard PRC-006-1

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

Title:

Automatic Underfrequency Load Shedding

2.

Number:

PRC-006-1

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:
4.1. Planning Coordinators
4.2. UFLS entities shall mean all entities that are responsible for the ownership,

operation, or control of UFLS equipment as required by the UFLS program
established by the Planning Coordinators. Such entities may include one or more
of the following:
4.2.1 Transmission Owners
4.2.2 Distribution Providers
4.3
5.

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

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

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

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

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

R2.

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

islands) as a result of the operation of a relay scheme or Special Protection
System, and

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

area or the Interconnection in which the Planning Coordinator’s area resides. If a
Planning Coordinator’s area resides in multiple Regional Entity areas, each of
those Regional Entity areas shall be identified as an island. Planning
Coordinators may adjust island boundaries to differ from Regional Entity area
boundaries by mutual consent where necessary for the sole purpose of producing
contiguous regional islands more suitable for simulation.
R3.

Each Planning Coordinator shall develop a UFLS program, including notification of
and a schedule for implementation by UFLS entities within its area, that meets the
following performance characteristics in simulations of underfrequency conditions
resulting from an imbalance scenario, where an imbalance = [(load — actual
generation output) / (load)], of up to 25 percent within the identified island(s). [VRF:
High][Time Horizon: Long-term Planning]
3.1. Frequency shall remain above the Underfrequency Performance Characteristic

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

curve in PRC-006-1 - Attachment 1, either for 60 seconds or until a steady-state
condition between 59.3 Hz and 60.7 Hz is reached, and
3.3. Volts per Hz (V/Hz) shall not exceed 1.18 per unit for longer than two seconds

cumulatively per simulated event, and shall not exceed 1.10 per unit for longer
than 45 seconds cumulatively per simulated event at each generator bus and
generator step-up transformer high-side bus associated with each of the following:

R4.

3.3.1.

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

3.3.2.

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

3.3.3.

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

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

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

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

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

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

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

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

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

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

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

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



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



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

R6.

Each Planning Coordinator shall maintain a UFLS database containing data necessary
to model its UFLS program for use in event analyses and assessments of the UFLS
program at least once each calendar year, with no more than 15 months between
maintenance activities. [VRF: Lower][Time Horizon: Long-term Planning]

R7.

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

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

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

R9.

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

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

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

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

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

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

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



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



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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

letters, to written comments submitted by UFLS entities and Transmission Owners
within its Planning Coordinator area following a comment period and before finalizing
its UFLS program per Requirement R14.
D. Compliance
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1.

Compliance Monitoring Process
1.1. Compliance Enforcement Authority

Regional Entity
1.2. Data Retention

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

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



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



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



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



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



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



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

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



Compliance Audit



Self-Certification



Spot Checking

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

Compliance Violation Investigation



Self-Reporting



Complaint

1.4. Additional Compliance Information

Not applicable.

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2.
R#
R1

Violation Severity Levels
Lower VSL

N/A

Moderate VSL

High VSL

Severe VSL

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

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

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

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

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

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

N/A

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

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

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R#
R3

Lower VSL
N/A

Moderate VSL

High VSL

Severe VSL

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

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

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

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

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Standard PRC-006-1 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

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

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

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Standard PRC-006-1 — Automatic Underfrequency Load Shedding

R#
R8

Lower VSL

Moderate VSL

High VSL

Severe VSL

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

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

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

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

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

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

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

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

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

R10

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

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

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

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

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Standard PRC-006-1 — Automatic Underfrequency Load Shedding

R#

R11

Lower VSL

Moderate VSL

High VSL

Severe VSL

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

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

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

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

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

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

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

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

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

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

Draft 6: October 18, 2010

13

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

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

R12

N/A

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

R13

N/A

Draft 6: October 18, 2010

N/A

N/A

The Planning Coordinator, in
whose area a BES islanding event
occurred that also included the
area(s) or portions of area(s) of
other Planning Coordinator(s) in
the same islanding event and that
resulted in system frequency
excursions below the initializing set
points of the UFLS program, failed
to coordinate its UFLS event
assessment with all other Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding
event in one of the manners
14

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

R#

Lower VSL

Moderate VSL

High VSL

Severe VSL
described in Requirement R13

R14

N/A

Draft 6: October 18, 2010

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.

15

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E. Regional Variances
E.A. Regional Variance for the Quebec Interconnection
The following Interconnection-wide variance shall be applicable in the Quebec
Interconnection and replaces, in their entirety, Requirements R3 and R4 and the
violation severity levels associated with Requirements R3 and R4.
E.A.3. Each Planning Coordinator shall develop a UFLS program, including a schedule
for implementation by UFLS entities within its area, that meets the following
performance characteristics in simulations of underfrequency conditions
resulting from an imbalance scenario, where an imbalance = [(load — actual
generation output) / (load)], of up to 25 percent within the identified island(s).
[VRF: High][Time Horizon: Long-term Planning]
E.A.3.1. Frequency shall remain above the Underfrequency Performance
Characteristic curve in PRC-006-1 - Attachment 1A, either for 30
seconds or until a steady-state condition between 59.3 Hz and 60.7 Hz
is reached, and
E.A.3.2. Frequency shall remain below the Overfrequency Performance
Characteristic curve in PRC-006-1 - Attachment 1A, either for 30
seconds or until a steady-state condition between 59.3 Hz and 60.7 Hz
is reached, and
E.A.3.3. Volts per Hz (V/Hz) shall not exceed 1.18 per unit for longer than two
seconds cumulatively per simulated event, and shall not exceed 1.10
per unit for longer than 45 seconds cumulatively per simulated event at
each generator bus and generator step-up transformer high-side bus
associated with each of the following:
EA.3.3.1. Individual generating unit greater than 50 MVA (gross
nameplate rating) directly connected to the BES
EA.3.3.2. Generating plants/facilities greater than 50 MVA (gross
aggregate nameplate rating) directly connected to the BES
EA.3.3.3. Facilities consisting of one or more units connected to the
BES at a common bus with total generation above 50 MVA
gross nameplate rating.
E.A.4. Each Planning Coordinator shall conduct and document a UFLS design
assessment at least once every five years that determines through dynamic
simulation whether the UFLS program design meets the performance
characteristics in Requirement E.A.3 for each island identified in Requirement
R2. The simulation shall model each of the following; [VRF: High][Time
Horizon: Long-term Planning]
E.A.4.1 Underfrequency trip settings of individual generating units that are
part of plants/facilities with a capacity of 50 MVA or more
individually or cumulatively (gross nameplate rating), directly
connected to the BES that trip above the Generator Underfrequency
Trip Modeling curve in PRC-006-1 - Attachment 1A, and
Draft 6: October 18, 2010

16

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

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

Draft 6: October 18, 2010

17

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E#
EA3

Lower VSL
N/A

Moderate VSL

High VSL

Severe VSL

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

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

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

EA4

N/A

The Planning Coordinator conducted
and documented a UFLS
assessment at least once every five
years that determines through
dynamic simulation whether the
UFLS program design meets the
performance characteristics in
Requirement E.A.3 but simulation
failed to include one (1) of the items
as specified in Parts E.A.4.1, E.A.4.2
or E.A.4.3.

The Planning Coordinator conducted
and documented a UFLS
assessment at least once every five
years that determines through
dynamic simulation whether the
UFLS program design meets the
performance characteristics in
Requirement E3 but simulation failed
to include two (2) of the items as
specified in Parts E.A.4.1, E.A.4.2 or
E.A.4.3.

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

Draft 6: October 18, 2010

18

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E.B.

Regional Variance for the Western Electricity Coordinating Council
The following Interconnection-wide variance shall be applicable in the Western
Electricity Coordinating Council (WECC) and replaces, in their entirety, Requirements
R1, R2, R3, R4, R5, R11, R12, and R13.
E.B.1. Each Planning Coordinator shall participate in a joint regional review with the
other Planning Coordinators in the WECC Regional Entity area that develops and
documents criteria, including consideration of historical events and system
studies, to select portions of the Bulk Electric System (BES) that may form
islands. [VRF: Medium][Time Horizon: Long-term Planning]
E.B.2. Each Planning Coordinator shall identify one or more islands from the regional
review (per E.B.1) to serve as a basis for designing a region-wide coordinated
UFLS program including: [VRF: Medium][Time Horizon: Long-term Planning]
E.B.2.1. Those islands selected by applying the criteria in Requirement E.B.1,
and
E.B.2.2. Any portions of the BES designed to detach from the Interconnection
(planned islands) as a result of the operation of a relay scheme or Special
Protection System.
EB.3. Each Planning Coordinator shall adopt a UFLS program, coordinated across the
WECC Regional Entity area, including notification of and a schedule for
implementation by UFLS entities within its area, that meets the following
performance characteristics in simulations of underfrequency conditions resulting
from an imbalance scenario, where an imbalance = [(load — actual generation
output) / (load)], of up to 25 percent within the identified island(s). [VRF:
High][Time Horizon: Long-term Planning]
E.B.3.1. Frequency shall remain above the Underfrequency Performance
Characteristic curve in PRC-006-1 - Attachment 1, either for 60 seconds
or until a steady-state condition between 59.3 Hz and 60.7 Hz is reached,
and
E.B.3.2. Frequency shall remain below the Overfrequency Performance
Characteristic curve in PRC-006-1 - Attachment 1, either for 60 seconds
or until a steady-state condition between 59.3 Hz and 60.7 Hz is reached,
and
E.B.3.3. Volts per Hz (V/Hz) shall not exceed 1.18 per unit for longer than two
seconds cumulatively per simulated event, and shall not exceed 1.10 per
unit for longer than 45 seconds cumulatively per simulated event at each
generator bus and generator step-up transformer high-side bus associated
with each of the following:
E.B.3.3.1. Individual generating units greater than 20 MVA (gross
nameplate rating) directly connected to the BES
E.B.3.3.2. Generating plants/facilities greater than 75 MVA (gross
aggregate nameplate rating) directly connected to the BES

Draft 6: October 18, 2010

19

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

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

Draft 6: October 18, 2010

20

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

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

Draft 6: October 18, 2010

21

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E#
E.B.1

Lower VSL
N/A

Moderate VSL

High VSL

Severe VSL

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

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

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

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

N/A
N/A

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

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

Draft 6: October 18, 2010

22

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E#

Lower VSL

Moderate VSL

High VSL

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

E.B.3

N/A

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

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

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

E.B.4

The Planning Coordinator
participated in and documented a
coordinated UFLS assessment with
the other Planning Coordinators in
the WECC Regional Entity area at
least once every five years that
determines through dynamic
simulation whether the UFLS
program design meets the
performance characteristics in
Requirement E.B.3 for each island
identified in Requirement E.B.2 but
the simulation failed to include one
(1) of the items as specified in
Requirement E.B.4, Parts E.B.4.1
Draft 6: October 18, 2010

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

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

The Planning Coordinator
participated in and documented a
coordinated UFLS assessment with
the other Planning Coordinators in
the WECC Regional Entity area at
least once every five years that
determines through dynamic
simulation whether the UFLS
program design meets the
performance characteristics in
Requirement E.B.3 for each island
identified in Requirement E.B.2 but
the simulation failed to include four
(4) or more of the items as specified
in Requirement E.B.4, Parts E.B.4.1
23

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E#

Lower VSL
through E.B.4.7.

Moderate VSL
through E.B.4.7.

High VSL
through E.B.4.7.

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

E.B.11

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

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

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

Draft 6: October 18, 2010

The Planning Coordinator, in whose
area a BES islanding event resulting
in system frequency excursions
below the initializing set points of the
UFLS program, participated in and
documented a coordinated event
assessment with all Planning
Coordinators whose areas or
portions of whose areas were also
included in the same islanding event
and evaluated the parts as specified
in Requirement E.B.11, Parts
E.B.11.1 and E.B.11.2 within a time
greater than 15 months of actuation.
OR
The Planning Coordinator, in whose
area an islanding event resulting in
system frequency excursions below
the initializing set points of the UFLS
program, failed to participate in and
document a coordinated event
24

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E#

Lower VSL

Moderate VSL

High VSL

Severe VSL

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

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

E.B.12

N/A

Draft 6: October 18, 2010

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

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

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

25

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

E#

Lower VSL

Moderate VSL

High VSL

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

Draft 6: October 18, 2010

26

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

Associated Documents
Version History
Version

Date

1

Draft 6: October 18, 2010

Action

Change Tracking

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

27

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

PRC-006-1 – Attachment 1
Underfrequency Load Shedding Program
Design Performance and Modeling Curves for
Requirements R3 Parts 3.1-3.2 and R4 Parts 4.1-4.6
63

62

60

Frequency (Hz)

61

59

58

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

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

Draft 6: October 18, 2010

28

Standard PRC-006-1 — Automatic Underfrequency Load Shedding

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

Frequency (Hz)

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

67
66
65
64
63
62
61

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

(30 ; 60.7)

60

(30 ; 59.3)
59
58

(.35 ; 56.7)

0.1

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

10

57
56
55
100

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

OverFrequency Performance Characteristic (Requirement E3.2)

UnderFrequency Performance Characteristic (Requirement E3.1)

Quebec UnderFrequency Generator Trip Modeling (Requirement E4.1)

Draft 6: October 18, 2010

29