Frequency and Voltage Requirements for IBRs and Upcoming PRC-029

Federal Energy Regulatory Commission (FERC) Order 901 required inverter-based resource (IBR) related ride-through performance requirements be established to support the Bulk Electric System (BES) during and after defined frequency and voltage excursions. The current North American Electric Reliability Corporation (NERC) Standard in effect for frequency and voltage protection settings is PRC-024-3. Upon regulatory approval by FERC, two distinct Standards will become applicable—PRC-024-4 and PRC-029-1.  

These new frequency and voltage protection settings have distinct applicability. The revised PRC-024-4 applies to synchronous generators, type 1 and type 2 wind resources, and synchronous condensers. The new PRC-029-1 institutes frequency and voltage ride-through requirements for IBRs that will be applicable to Generator Owners (GOs) with IBRs once it is effective. The applicable IBRs will include both BES Facilities as well as non-BES IBRs that contribute to an aggregate nameplate capacity of at least 20MVA and are connected to a common point of connection greater than or equal to 60 kV. PRC-029-1 R1 and Attachment 1 of the Standard specify a voltage “must ride-through zone” for the IBRs. Requirement R2 outlines in subparts R2.1 through R2.5 the detailed design and operation criteria that each IBR must adhere to during a voltage excursion to maintain reliability. Similarly, ride-through requirements during a frequency excursion are outlined in Requirement R3 and Attachment 2, which includes both a frequency table and graph of the must ride-through zone.

Like PRC-024, PRC-029-1 will also account for the fact that there may be some unique situations in which a resource is unable to meet the ride-through criteria. PRC-029-1 R4 addresses situations in which a GO has an IBR with a hardware limitation that prevents it from meeting R1-R3 criteria and for which the GO needs an exemption. Under R4.1 and R4.2, the GO shall document and submit any identified hardware limitations it has within 12 months following the effective date of the Standard.

Ultimately, the separation of IBRs voltage and frequency protection requirements into their own unique Reliability Standard will address IBR ride-through capabilities. It will also enable Compliance Monitoring and Enforcement Program (CMEP) personnel and industry to account for the changing generation mix and improve reliability of the BES. As industry awaits the final regulatory approval for both PRC-029-1 and PRC-024-4, Responsible Entities should familiarize themselves with these Standards to ensure they are prepared to meet the compliance requirements once they become effective. Additional information can be found on the NERC Project Page Project 2020-02 Modifications to PRC-024 (Generator Ride-through).