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PRC-024-4
Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and Type 2 Wind Resources, and Synchronous Condensers
PRC-024-4 requires Generator Owners and Transmission Owners to set the frequency, voltage and volts per hertz protection applied to synchronous generators, type 1 and type 2 wind resources and synchronous condensers so that it does not trip the Facility inside the no trip zones of Attachments 1 and 2, except for documented and communicated regulatory or equipment limitations and, for voltage protection, settings within a location-specific Transmission Planner study where the Transmission Planner allows less stringent settings. It replaced PRC-024-3 on October 1, 2026, and inverter-based resources are no longer in its scope; their ride-through requirements are in PRC-029-2.
Who it applies to
- Generator Owners that apply frequency, voltage or volts per hertz protection (by relaying or by functions within associated control systems) that trips, or signals to trip, BES synchronous generators, their BES GSU transformers, the high side of the generator-connected unit auxiliary transformer, individual type 1 or type 2 wind resources identified through BES Inclusion I4, Elements designed primarily to deliver capacity from multiple synchronous generators on a common bus or from those wind resources up to the point where they aggregate to more than 75 MVA, and the main power transformer for those resources.
- Generator Owners and Transmission Owners that apply that protection to BES synchronous condensers, their BES step-up transformers and the high side of the synchronous condenser-connected unit auxiliary transformer.
- Quebec Interconnection only: Transmission Owners that own a BES GSU or main power transformer and apply the protection above, and Planning Coordinators, under Regional Variance D.A.
- Protection on auxiliary equipment within the Facility is exempt. The standard does not require installing or activating any of these protections.
Key dates
- October 1, 2026: effective date. PRC-024-3 was retired immediately before it.
- Within 30 calendar days of identifying a limitation or its removal: communicate the regulatory or equipment limitation, or its removal, to the Planning Coordinator and Transmission Planner. The 30 days run from identifying the limitation, from a repair or replacement that removes it, or from a limitation created or adjusted by consumption of the cumulative turbine life-time frequency excursion allowance (R3.1).
- Within 60 calendar days of a written request or a settings change: provide the R1 and R2 protection settings to the Planning Coordinator or Transmission Planner that asked for them, and report any change to previously requested settings (R4).
Source
NERC PRC-024-4 (standard page)October 4, 2026
Requirements
What each requirement asks for, in plain English.
R1 · Frequency protection settings
What it means. Set applicable frequency protection in accordance with Attachment 1 so that it does not cause the Facility to trip within the no trip zone during a frequency excursion. Attachment 1 gives separate boundaries for the Eastern, Western, Quebec and ERCOT Interconnections, and the area outside the no trip zone is not a must trip zone. Frequency is calculated over a window of time; instantaneous trip settings based on instantaneously calculated frequency are not permissible. The only exception is a regulatory or equipment limitation documented and communicated under R3.
Evidence an auditor expects. Dated setting sheets, calibration sheets, calculations or other documentation showing the frequency protection is set per R1.
R2 · Voltage protection settings
What it means. Set applicable voltage protection in accordance with Attachment 2 so that it does not cause the Facility to trip within the no trip zone during a voltage excursion at the high side of the GSU or main power transformer. If the Transmission Planner allows less stringent settings, the protection may be set within the voltage recovery characteristics of a location-specific Transmission Planner study, and a documented and communicated limitation under R3 is also an exception. In the Quebec Interconnection, Regional Variance D.A.2 replaces R2 and uses Attachment 2A.
Evidence an auditor expects. Dated setting sheets, voltage-time boundaries, calibration sheets, coordination plots, dynamic simulation studies, calculations or other documentation.
R3 · Document and communicate limitations
What it means. Document each known regulatory or equipment limitation that prevents the Facility from meeting R1 or R2, with support such as study results, experience from an actual event or manufacturer's advice. Limitations caused by the setting capability of the protective relays themselves do not count; limitations originating in the protected equipment do. Communicate the limitation, or its removal, to the Planning Coordinator and Transmission Planner within 30 calendar days of identifying it, of a repair or replacement that removes it, or of a limitation created or adjusted by consumption of the cumulative turbine life-time frequency excursion allowance.
Evidence an auditor expects. A dated email or letter to the Planning Coordinator and Transmission Planner containing the documentation, such as study results, event experience or manufacturer's advice.
R4 · Provide settings on request
What it means. Provide the protection settings associated with R1 and R2 to the Planning Coordinator or Transmission Planner that models the Facility within 60 calendar days of a written request, and within 60 calendar days of any change to those previously requested settings, unless the requester says changes need not be reported.
Evidence an auditor expects. Dated emails, correspondence or other evidence of the transmittal, and copies of the requests received.
For inverter-based plants
PRC-024-4 does not apply to inverter-based resources: its implementation plan says the revision removed IBRs from its applicable facility types, and IBR ride-through is now addressed in PRC-029-2.
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