On December 19, 2024, FERC issued a Notice of Proposed Rulemaking (NOPR) to approve the addition of the newly defined term “Ride-through” to the North American Electric Reliability Corporation (NERC) Glossary of Terms and to approve the proposed Protection and Control (PRC) Reliability Standards PRC-024-4 (Frequency and Voltage Protection Settings for Synchronous Generators, Type 1 and 2 Wind Resources, and Synchronous Condensers) and PRC-029-1 (Frequency and Voltage Ride-through Requirements for Inverter-Based Resources (IBR)). According to FERC, these reliability standards are intended to address reliability gaps associated with IBRs tripping or entering momentary cessation in aggregate. The new rules will ensure that IBRs are able to “ride through” frequency and voltage excursions, such as faults on the transmission or sub-transmission system. In the NOPR, FERC seeks comments on the proposed rules and the need for informational filings that would help FERC analyze the impact of proposed exemptions in the rules for certain IBRs.
NERC filed the two PRC standards and the “ride-through” definition with FERC on November 4, 2024, in response to the Commission’s Order No. 901. Reliability Standards to Address Inverter-Based Resources, Order No. 901, 185 FERC ¶ 61,042 (2023). In Order No. 901, FERC found that some IBRs “are not configured or programmed to support grid voltage and frequency in the event of a system disturbance, and, as a result, will reduce power output, exhibit momentary cessation, or trip in response to variations in system voltage or frequence.” According to FERC, these issues are amplified when IBRs act in the aggregate. The standards FERC directed in Order No. 901 are intended to require registered IBRs to ride-through certain system disturbances and to protect IBR equipment similar to mechanisms used by synchronous generation resources. The specific proposed Reliability Standards include the following:
PRC-024-4 Requirements
PRC-024-4 is designed to “ensure that protection of synchronous generators, type 1 and type 2 wind resources, and synchronous condensers do not cause tripping during defined frequency and voltage excursions in support” of the Bulk-Power System. The proposed changes maintain voltage and frequency setting requirements for synchronous generators, synchronous condensers and type 1 and type 2 wind resources and removes the performance-based requirements for IBR functionality, which are instead included in proposed PRC-029. Based on NERC’s proposed definition of IBRs in the Glossary of Terms (proposed in a separate filing pending in Docket No. RD25-1) type 1 and type 2 wind resources are not considered IBRs because they operate as asynchronous resources.
PRC-029 Requirements
PRC-029-1 is intended to “ensure that IBRs Ride-through disturbances to support the Bulk-Power System . . . during and after defined frequency and voltage excursions.” NERC’s IBR definition includes resources such as solar photovoltaic, type 3 and type 4 wind, battery storage systems and fuel cell devices. Under the proposed PRC-029, IBRs must meet or exceed Ride-through requirements in accordance with the “must Ride-through zone” as specified in the Institute of Electrical and Electronics Engineers (IEEE) standard 2800-2022, except under four conditions: (i) the IBR needed to disconnect to clear a fault, (ii) the voltage at the high-side of the transformer went outside acceptable hardware limitations, (iii) 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, or (iv) the Volts per Hx at the high-side of the transformer exceed 1.1 per unit for longer than 45 seconds or exceed 1.18 per unit for longer than 2 seconds.
PRC-029 allows existing IBRs that are already in operation prior to the effective date of the standard to seek an exemption to the voltage and ride-through requirements if hardware replacements would be needed for compliance. Entities would have twelve months from the effective date of PRC-029-1 to request an exemption.
Ride-Through Definition
In PRC-029-1, the term “Ride-through” means “the plant/facility remains connected and continues to operate through voltage or frequency system disturbances.”
Proposed Informational Filings
In addition to the reliability standards and definition, the NOPR also proposed to require NERC to submit two informational filings detailing exemption requests by generator owners of legacy IBRs from frequency and/or voltage Ride-through requirements to get a better understanding of the practical implications of the exemptions as proposed. FERC seeks comment on all aspects of the proposed approvals.
Entities are requested to submit comments within 60 days after the NOPR is published in the Federal Register. Reply comments are due 90 days after the publication of the NOPR in the Federal Register. FERC’s Order is available here, Reliability Standards for Frequency and Voltage Protection Settings and Ride-Through for Invertor-Based Resources, 189 FERC ¶ 61,212 (2024) (NOPR).