Results-based Standard

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

A. Introduction
1. Title:

Frequency and Voltage Ride-through Requirements for Inverter-based
Resources

2. Number:

PRC-029-1

3. Purpose:

To ensure that IBRs Ride-through to support the Bulk Power System (BPS)
during and after defined frequency and voltage excursions.

4. Applicability:
4.1

Functional Entities:
4.1.1. Generator Owner

4.2

Facilities:
4.2.1. Bulk Electric System (BES) IBRs
4.2.2. Non-BES IBRs that either have or contribute to an aggregate nameplate
capacity of greater than or equal to 20 MVA, connected through a system
designed primarily for delivering such capacity to a common point of
connection at a voltage greater than or equal to 60 kV.

Effective Date: See Implementation Plan for Project 2020-02 – PRC-029-1
Standard-only Definition: None

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

B. Requirements and Measures
R1.

Each Generator Owner shall ensure the design and operation is such that each IBR
meets or exceeds Ride-through requirements, in accordance with the “must Ridethrough 1 zone” as specified in Attachment 1, except in the following conditions:
[Violation Risk Factor: High] [Time Horizon: Operations Assessment]
•

The IBR needed to electrically disconnect in order to clear a fault;

•

The voltage at the high-side of the main power transformer 2 went outside an
accepted hardware limitation, in accordance with Requirement R4;

•

The instantaneous positive sequence voltage phase angle change is more than
25 electrical degrees at the high-side of the main power transformer and is
initiated by a non-fault switching event on the transmission system 3; or

•

The Volts per Hz (V/Hz) at the high-side of the main power transformer exceed
1.1 per unit for longer than 45 seconds or exceed 1.18 per unit for longer than
2 seconds.

M1. Each Generator Owner shall have evidence to demonstrate the design of each IBR will
adhere to Ride-through requirements, as specified in Requirement R1. Examples of
evidence may include, but are not limited to dynamic simulations, studies, plant
protection settings, and control settings design evaluation. Each Generator Owner shall
retain evidence of actual disturbance monitoring (i.e., sequence of event recorder,
dynamic disturbance recorder, and fault recorder) to demonstrate that the operation
of each IBR did adhere to Ride-through requirements, as specified in Requirement R1.
If the Generator Owner choose to utilize Ride-through exemptions that occur within
the “must Ride-through zone” and are caused by non-fault initiated phase jumps of
greater than 25 electrical degrees, then each Generator Owner shall also retain
evidence of actual disturbance monitoring (i.e., sequence of event recorder, dynamic
disturbance recorder, and fault recorder) data to demonstrate that the IBR failed to
Ride-through during a phase jump of greater than or equal to 25 electrical degrees, and
documentation from their Transmission Planner, Reliability Coordinator, Planning
Coordinator, or Transmission Operator that a non-fault initiated switching event
occurred.
R2. Each Generator Owner shall ensure the design and operation is such that the voltage
performance for each IBR adheres to the following during a voltage excursion, unless a
documented hardware limitation exists in accordance with Requirement R4. [Violation
Risk Factor: High] [Time Horizon: Operations Assessment]
2.1.

While the voltage at the high-side of the main power transformer remains within
the continuous operation region as specified in Attachment 1, each IBR shall:

1 Includes no tripping associated with phase lock loop loss of synchronism.

2 For the purpose of this standard, the main power transformer is the power transformer that steps up voltage from the

collection system voltage to the nominal transmission/interconnecting system voltage for IBRs. In case of IBR connecting via a
dedicated Voltage Source Converter High Voltage Direct Current (VSC-HVDC), the main power transformer is the main power
transformer on the receiving end.
3 Current blocking mode may be used for non-fault initiated phase jumps greater than 25 degrees in order to prevent tripping.
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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

2.1.1 Continue to deliver the pre-disturbance level of Real Power or available
Real Power 4, whichever is less. 5
2.1.2 Continue to deliver Reactive Rower up to its Reactive Power limit and
according to its controller settings.
2.1.3 Prioritize Real Power or Reactive Power when the voltage is less than
0.95 per unit, the voltage is within the continuous operating region, and
the IBR cannot deliver both Real Power and Reactive Power due to a
current limit or Reactive Power limit, unless otherwise specified through
other mechanisms by an associated Transmission Planner, Planning
Coordinator, Reliability Coordinator, or Transmission Operator.
2.2.

2.3.

While voltage at the high-side of the main power transformer is within the
mandatory operation region as specified in Attachment 1, each IBR shall
exchange current, up to the maximum capability to provide voltage support, on
the affected phases during both symmetrical and asymmetrical voltage
disturbances, either under 6:
•

Reactive Power priority by default; or

•

Real Power priority if required through other mechanisms by an associated
Transmission Planner, Planning Coordinator, Reliability Coordinator, or
Transmission Operator.

While voltage at the high-side of the main power transformer is within the
permissive operation region, as specified in Attachment 1, each IBR may operate
in current blocking mode if necessary to avoid tripping. Otherwise, each IBR shall
follow the requirements for the mandatory operation region in Requirement
R2.2.
2.3.1 If an IBR enters current blocking mode, it shall restart current exchange
in less than or equal to five cycles of positive sequence voltage returning
to a continuous operation region or mandatory operation region.

2.4.

Each IBR shall not itself cause voltage at the high-side of the main power
transformer to exceed the applicable high voltage thresholds and time durations
in its response as voltage recovers from the mandatory or permissive operation
regions to the continuous operation region.

2.5.

Each IBR shall restore Real Power output to the pre-disturbance or available
level 7 (whichever is lesser) within 1.0 second when the voltage at the high-side
of the main power transformer returns from the mandatory operation region or

4 “Available Real Power" refers to changes of facility Real Power output attributed to factors such as weather patterns, change

of wind, and change in irradiance, but not changes of facility Real Power attributed to IBR tripping in whole or part.

5 Except if this would occur during a frequency excursion. The Real Power response should recover in accordance with the

primary frequency controller.
6 In either case and if required, the magnitude of Real Power and reactive current shall be as specified by the Transmission
Planner, Planning Coordinator, Reliability Coordinator, or Transmission Operator.
7 “Available Real Power" refers to changes of facility Real Power output attributed to factors such as weather patterns, change
of wind, and change in irradiance, but not changes of facility Real Power attributed to IBR tripping in whole or part.
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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

permissive operation region (including operating in current blocking mode) to
the continuous operation region, as specified in Attachment 1, unless an
associated Transmission Planner, Planning Coordinator, Reliability Coordinator,
or Transmission Operator requires a lower post-disturbance Real Power level
requirement or requires a different post-disturbance Real Power restoration
time through other mechanisms. 8
M2. Each Generator Owner shall have evidence to demonstrate the design of each IBR will
adhere to requirements, as specified in Requirement R2. Examples of evidence may
include, but are not limited to dynamic simulations, studies, plant protection settings,
and control settings design evaluation. Each Generator Owner shall also retain evidence
of actual disturbance monitoring (i.e., sequence of event recorder, dynamic disturbance
recorder, and fault recorder) data to demonstrate that the operation of each IBR did
adhere to performance requirements, as specified in Requirement R2, during each
voltage excursion measured at the high-side of the main power transformer. Regarding
R2.1.3, R2.2, and R2.5, the Generator Owner shall retain evidence of receiving such
performance requirements, (e.g., email exchange, contract information) if the
Transmission Planner, Transmission Operator, Reliability Coordinator, or Planning
Coordinator has required the Generator Owner through other mechanisms to follow
performance requirements other than those in Requirement R2 (e.g., ramp rates,
Reactive Power prioritization).
R3. Each Generator Owner shall ensure the design and operation is such that each IBR
meets or exceeds Ride-through requirements during a frequency excursion event
whereby the System frequency remains within the “must Ride-through zone” according
to Attachment 2 and the absolute rate of change of frequency (RoCoF) 9 magnitude is
less than or equal to 5 Hz/second, unless a documented hardware limitation exists in
accordance with Requirement R4. [Violation Risk Factor: High] [Time Horizon:
Operations Assessment]
M3. Each Generator Owner shall have evidence to demonstrate the design of each IBR will
adhere to Ride-through requirements, as specified in Requirement R3. Examples of
evidence may include, but are not limited to dynamic simulations, studies, plant
protection settings, and control settings design evaluation. Each Generator Owner shall
also retain evidence of actual disturbance monitoring (i.e., sequence of event recorder,
dynamic disturbance recorder, and fault recorder) data to demonstrate the operation
of each IBR did adhere to Ride-through requirements, as specified in Requirement R3,
during each frequency excursion event measured at the high-side of the main power
transformer.
R4. Each Generator Owner identifying an IBR that is in-service by the effective date of PRC029-1, has known hardware limitations that prevent the IBR from meeting Ride-through
criteria as detailed in Requirements R1-R3, and requires an exemption from specific
8 Except if this would occur during a frequency excursion. The Real Power response should recover in accordance with the

primary frequency controller.
9 Rate of change of frequency (RoCoF) is calculated as the average rate of change for multiple calculated system frequencies for
a time period of greater than or equal to 0.1 second. RoCoF is not calculated during the fault occurrence and clearance.
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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

Ride-through criteria shall: 10 [Violation Risk Factor: Lower] [Time Horizon: Long-term
Planning]
4.1.

Document information supporting the identified hardware limitation no later
than 12 months following the effective date of PRC-029-1. This documentation
shall include:
4.1.1 Identifying information of the IBR (name and facility number);
4.1.2 Which aspects of Ride-through requirements that the IBR would be
unable to meet and the capability of the hardware due to the limitation;
4.1.3 Identification of the specific piece(s) of hardware causing the limitation;
4.1.4 Technical documentation verifying the limitation is due to hardware that
would need to be physically replaced to meet all Ride-through criteria,
and that the limitation cannot be remedied by software updates or
setting changes; and
4.1.5 Information regarding any plans to remedy the hardware limitation (such
as an estimated date).

4.2.

Provide a copy of the information detailed in Requirement R4.1, except for any
material considered by the original equipment manufacturer to be proprietary
information, to the associated Planning Coordinator(s), Transmission Planner(s),
Transmission Operator(s), Reliability Coordinator(s), and the Compliance
Enforcement Authority (CEA) no later than 12 months following the effective
date of PRC-029-1. 11
4.2.1 Provide any response for additional information requested by the
associated Planning Coordinator(s), Transmission Planner(s),
Transmission Operator(s), Reliability Coordinator(s), and the CEA to the
requestor within 90 days of the request.
4.2.2 Provide a copy of the acceptance of a hardware limitation by the CEA to
the associated Planning Coordinator(s), Transmission Planner(s),
Transmission Operator(s), and Reliability Coordinator(s) within 90 days
of receiving the acceptance. 12

4.3.

Each Generator Owner with a previously accepted limitation that replaces the
hardware causing the limitation shall document and communicate such a
hardware change to the associated Planning Coordinator(s), Transmission
Planner(s), Transmission Operator(s), and Reliability Coordinator(s) within 90
days of the hardware change.

10 The exemption requests for a non-US Registered Entity should be implemented in a manner that is consistent with, or under

the direction of, the applicable governmental authority or its agency in the non-US jurisdiction.

11 To the extent the original equipment manufacturer considers any material to be proprietary, the Generator Owner is

required to share this proprietary material only with the CEA.
12 Acceptance by the CEA is verification that the information provided includes all information listed in Requirement R4.1.
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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

4.3.1 When existing hardware causing the limitation is replaced, the
exemption for that Ride-through criteria no longer applies.
M4. Each Generator Owner submitting for an exemption for an IBR that is in-service by the
effective date of PRC-029-1, shall have evidence of submission to the CEA consistent
with the information listed in Requirement R4.1. Each Generator Owner shall have
evidence of communicated copies of each submission in accordance with Requirement
R4.2 and to the associated entities described in Requirement R4.2. Acceptable types of
evidence for submittals include, but are not limited to, meeting minutes, agreements,
copies of procedures or protocols in effect, or email correspondence. Acceptable types
of evidence for a hardware limitation may include, but is not limited to damage curves
provided by the original equipment manufacturer. Each Generator Owner that receives
a request for additional information under Requirement R4.2.1 shall have evidence of
providing that information within 90 days. Each Generator Owner that replaces
hardware at an IBR that is directly associated with an accepted exemption and that
hardware is the cause for the limitation, shall have evidence of communicating the
hardware change to the associated entities described in Requirement R4.3 within 90
days of the hardware replacement.

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

C. Compliance
1.

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

Each Generator Owner shall retain evidence with Requirements R1, R2, and
R3 in this standard for 36 calendar months or the date of the last audit,
whichever is greater.

•

Each Generator Owner shall retain evidence with Requirement R4 in this
standard for five calendar years or the date of the last audit, whichever is
greater.

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

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

Violation Severity Levels
R#

Violation Severity Levels
Lower VSL

Moderate VSL

High VSL

Severe VSL

R1.

The Generator Owner failed to
ensure the design capability of
each applicable IBR to
Ride-through in accordance
with Attachment 1, except for
those conditions identified in
Requirement R1.

N/A

N/A

The Generator Owner failed to
ensure each applicable IBR
adhered to Ride-through
requirements in accordance
with Attachment 1, except for
those conditions identified in
Requirement R1.

R2.

The Generator Owner failed to
ensure the design capability of
each applicable IBR to adhere
to performance requirements
during voltage excursions, as
specified in Requirement R2,
unless a documented
hardware limitation exists in
accordance with Requirement
R4.

N/A

N/A

The Generator Owner failed to
ensure each applicable IBR
adhered to performance
requirements during voltage
excursions, as specified in
Requirement R2, unless a
documented hardware
limitation exists in accordance
with Requirement R4.

R3.

The Generator Owner failed to
ensure the design capability of
each applicable IBR to
Ride-through in accordance
with Attachment 2, unless a
documented hardware
limitation exists in accordance
with Requirement R4.

N/A

N/A

The Generator Owner failed to
ensure each applicable IBR
adhered to Ride-through
requirements in accordance
with Attachment 2, unless a
documented hardware
limitation exists in accordance
with Requirement R4.

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

Violation Severity Levels

R#
R4.

Lower VSL

Moderate VSL

High VSL

Severe VSL

The Generator Owner
provided a copy to the
applicable entities as detailed
in Requirement R4.2 more
than 12 months, but less than
or equal to 15 months after
the effective date of
Requirement R4.

The Generator Owner
provided a copy to the
applicable entities as detailed
in Requirement R4.2 more
than 15 months, but less than
or equal to 18 months after
the effective date of
Requirement R4.

The Generator Owner
provided a copy to the
applicable entities as detailed
in Requirement R4.2 more
than 18 months, but less than
or equal to 24 months after
the effective date of
Requirement R4.

The Generator Owner failed to
document complete
information for IBR identified
with known hardware
limitations that prevent the
IBR from meeting Ridethrough criteria as detailed in
Requirements R1, R2, or R3.

OR

OR

OR

OR

The Generator Owner failed to
respond to the applicable
entities as detailed in
Requirement R4.2.1 more than
90 days but less than or equal
to 120 days after receiving a
request for additional
information by an entity listed
in Requirement R4.2.1.

The Generator Owner failed to
respond to the applicable
entities as detailed in
Requirement R4.2.1 more than
120 days, but less than or
equal to 150 days after
receiving a request for
additional information by an
entity listed in Requirement
R4.2.1.

The Generator Owner failed to
respond to the applicable
entities as detailed in
Requirement R4.2.1 more than
150 days but less than or equal
to 180 days after receiving a
request for additional
information by an entity listed
in Requirement R4.2.1.

The Generator Owner failed to
provide a copy to the
applicable entities as detailed
in Requirement R4.2 within 24
months after the effective
date of Requirement R4.

OR
The Generator Owner failed to
respond to the applicable
entities as detailed in
Requirement R4.2.2 more than
90 days but less than or equal
to 120 days after receiving the
acceptance of a hardware
limitation by the CEA.
OR

OR
The Generator Owner failed to
respond to the applicable
entities as detailed in
Requirement R4.2.2 more than
120 days but less than or equal
to 150 days after receiving the
acceptance of a hardware
limitation by the CEA.

OR
The Generator Owner failed to
respond to the applicable
entities as detailed in
Requirement R4.2.2 more than
150 days but less than or equal
to 180 days after receiving the
acceptance of a hardware
limitation by the CEA.
OR

OR
The Generator Owner failed to
respond to the applicable
entities as detailed in
Requirement R4.2.1 more than
180 days after receiving a
request for additional
information by an entity listed
in Requirement R4.2.1.
OR
The Generator Owner failed to
respond to the applicable

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

R#

Violation Severity Levels
Lower VSL
The Generator Owner with a
previously communicated
hardware limitation that
replaces the documented
limiting hardware but failed to
document and communicate
the change to its Planning
Coordinator(s), Transmission
Planner(s), Transmission
Operator(s), Reliability
Coordinator(s), and CEA more
than 90 calendar days but less
than or equal to 120 calendar
days after the change to the
hardware.

Moderate VSL
OR
The Generator Owner with a
previously communicated
hardware limitation that
replaces the documented
limiting hardware but failed to
document and communicate
the change to its Planning
Coordinator(s), Transmission
Planner(s), Reliability
Coordinator(s), Transmission
Operator(s), and CEA more
than 120 calendar days but
less than or equal to 150
calendar days after the change
to the hardware.

High VSL
The Generator Owner with a
previously communicated
hardware limitation that
replaces the documented
limiting hardware but failed to
document and communicate
the change to its Planning
Coordinator(s), Transmission
Planner(s), Reliability
Coordinator(s), Transmission
Operator(s), and CEA more
than 150 calendar days but
less than or equal to 180
calendar days after the change
to the hardware.

Severe VSL
entities as detailed in
Requirement R4.2.2 more than
180 days after receiving the
acceptance of a hardware
limitation by the CEA.
The Generator Owner with a
previously communicated
hardware limitation that
replace the documented
limiting hardware but failed to
document and communicate
the change to its Planning
Coordinator(s), Transmission
Planner(s), Transmission
Operator(s),Reliability
Coordinator(s), and CEA more
than 180 days after the change
to the hardware.

D. Regional Variances
None.

E. Associated Documents
Implementation Plan .

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

Version History
Action

Change
Tracking

Version

Date

1

October 8, 2024

Draft 4 approved by the NERC Board of
Trustees

Developed under
Project 2020-02

1

October 16, 2024

Draft 4 errata approved by the Standards
Committee

Approved errata

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

Attachment 1: Voltage Ride-Through Criteria

Table 1: Voltage Ride-through Requirements for AC-Connected Wind IBR 13
Voltage
(per unit) 14

Operation Region

Minimum RideThrough Time (sec)

> 1.20

N/A 15

N/A

≥ 1.10

Mandatory Operation Region

1.0

> 1.05

Continuous Operation Region

1800

≤ 1.05 and ≥ 0.90

Continuous Operation Region

Continuous

< 0.90

Mandatory Operation Region

3.00

< 0.70

Mandatory Operation Region

2.50

< 0.50

Mandatory Operation Region

1.20

< 0.25

Mandatory Operation Region

0.16

< 0.10

Permissive Operation Region

0.16

Table 2: Voltage Ride-through Requirements for All Other IBR
Voltage
(per unit) 16

Operation Region

Minimum RideThrough Time (sec)

> 1.20

N/A 17

N/A

> 1.10

Mandatory Operation Region

1.0

> 1.05

Continuous Operation Region

1800

≤ 1.05 and ≥ 0.90

Continuous Operation Region

Continuous

< 0.90

Mandatory Operation Region

6.00

< 0.70

Mandatory Operation Region

3.00

< 0.50

Mandatory Operation Region

1.20

< 0.25

Mandatory Operation Region

0.32

< 0.10

Permissive Operation Region

0.32

1. Table 1 applies to type 3 and type 4 wind IBR or hybrid IBR that include wind, unless
connected via a dedicated Voltage Source Converter - High Voltage Direct Current
(VSC-HVDC) transmission facility.
2. Table 2 applies to all other IBR types not covered in Table 1; including, but not limited
to, the following facilities:

13 Type 3 and type 4 wind resources directly connected to the AC Transmission System.
14 Refer to bullet #4 below.

15 These conditions are referred to as the “may Ride-through zone”.
16 Refer to bullet #4 below.

17 These conditions are referred to as the “may Ride-through zone”.

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

a. IBR, regardless of their energy resource, interconnecting via a dedicated VSCHVDC transmission facility.
b. Other IBR or hybrid IBR consisting of photovoltaic (PV) and BESS.
3. The applicable voltage for VSC-HVDC system with a dedicated connection to an IBR is
on the AC side of the transformer(s) that is (are) used to connect the VSC-HVDC
system to the interconnected transmission system.
4. The voltage base for per unit calculation is the nominal phase-to-ground or phase-tophase transmission system voltage unless otherwise defined by the Planning
Coordinator, Transmission Planner, or Transmission Owner.
5. The applicable voltage for Tables 1 and 2 is identified as the voltage max/min of phaseto-neutral or phase-to-phase fundamental root mean square (RMS) voltage at the
high-side of the main power transformer.
6. Tables 1 and 2 are only applicable when the frequency is within the “must
Ride-through zone” as specified in Figure 1 of Attachment 2.
7. At any given voltage value, each IBR shall Ride-through unless the time duration at
that voltage has exceeded the specified minimum Ride-through time duration. If the
voltage is continuously varying over time, it is necessary to add the duration within
each band of Tables 1 and 2 over any 10 second time period.
8. The specified duration of the mandatory operation regions and the permissive
operation regions in Tables 1 and 2 is cumulative over one or more disturbances
within any 10 second time period.
9. The IBR may trip for more than four deviations of the applicable voltage at the highside of the main power transformer outside of the continuous operation region within
any 10 second time period.
10. Instantaneous trip settings based on instantaneously calculated voltage
measurements with less than filtering lengths of one cycle (16.6 millisecond) are not
permissible.
11. The “must Ride-through zone” is the combined area of the mandatory operating
regions, the continuous operating regions, and the permissive operating region. All
area outside of these operating regions is referred to as the “may Ride-through zone”.

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PRC-029-1 – Frequency and Voltage Ride-through Requirements for Inverter-based Resources

Attachment 2: Frequency Ride-Through Criteria
Table 3: Frequency Ride-through Capability Requirements
System Frequency (Hz)

Minimum Ride-Through
Time (sec)

> 61.8

May trip

> 61.2

299

≤ 61.2 and ≥ 58.8

Continuous

< 58.8

299

< 57.0

May trip

1. Frequency measurements are taken at the high-side of the main power transformer.
2. Frequency is measured over a period of time (typically 3-6 cycles) to calculate system
frequency at the high-side of the main power transformer.
3. Instantaneous or single points of measurement may not be used in the determination of
control settings.
4. At any given frequency value, each IBR shall Ride-through unless the time duration at that
frequency has exceeded the specified minimum ride-through time duration.
5. The specified durations of Table 3 are cumulative over one or more disturbances within a
10-minute time period.
63

May Ride-through Zone

62

Frequency (Hz)

61

Must Ride-through Zone

60

59

58

May Ride-through Zone

57

56

0

100

200

300
299

400

500

600

700

800

900

∞
1000

Time (seconds)

Figure 1: PRC-029 Frequency Ride-through Requirements
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