NEW Standard Authorization Request for PRC-024

By Allegra Jones, NERC Reliability Specialist

NERC has decided to revamp the way compliance is achieved for PRC-024. The current PRC-024 standard, titled Frequency and Voltage Protection Settings for Generating Resources, is set to transition to revision 3 (PRC-024-3) on October 1st, 2022. However, NERC is already planning the demise of PRC-024-3 in the new Standard Authorization Request (SAR) titled Generator Ride-Through Standard (PRC-024-3 Replacement). The SAR, released on 4/28/2022, calls for a replacement or overhaul of PRC-024-3. According to the SAR, NERC believes the PRC-024 standard is “serving little to no value for ensuring BPS-connected inverter-based resources remain connected and supporting the BPS during grid disturbances.” In other words, NERC believes that PRC-024 as currently enforced fails to support reliability. Further, NERC believes that “the systemic tripping and reductions of inverter-based resources, in addition to notable concurrent tripping or performance from synchronous generating resources poses a risk to BPS reliability that must be addressed in a timely manner.” According to NERC, the time to act is now regardless of the upcoming “improvements” provided in PRC-024-3.

The SAR, proposes to retire PRC-024-3 and replace it with a performance-based ride-through standard that “ensures generators remain connected to the BPS during system disturbances.” The goal of the project will be to overhaul or replace PRC-024-3 with a performance-based standard focused on “riding-through” disturbances to ensure generation assets remain connected. The new standard will include requirements to ensure that protection and controls failing to “ride-through” system events must be analyzed, addressed with a corrective action plan, and reported to the appropriate entities (GOP, TOP, RC, or BA). At a glance, this calls to mind the ways in which NERC’s Misoperation Identification standard, PRC-004, is currently managed: analysis, corrective actions and mandatory reporting. The SAR aims to address the root cause of BES Events and power reductions. Momentary cessation, which means to cease the injection of current, will be deemed unacceptable performance during BES disturbances. Legacy type inverter-based facilities using momentary cessation can expect to receive an exemption, while newer resources will not. When the SAR is implemented, the terms “Ride-Through” and “Momentary Cessation” will be added to the NERC Glossary of Terms.

The current version of PRC-024 is focused solely on voltage and frequency protection settings. Entities are required, per the standard, to ensure that their units do not trip within specified “no trip zones” regarding voltage (per unit) and frequency. According to NERC, many asset owners have “misconstrued” the purpose of PRC-024 and used incorrect protection settings which ultimately pose a risk to the reliability of the Bulk Power System rather than safeguarding it. The goal of the new standard will be to mitigate system performance during disturbances. To do so, Generator Owners may expect to upgrade their equipment in order to analyze generating asset performance, but the costs are expected to be minimal.

The project created as a result of the new PRC-024 SAR will specify the protections and controls in scope including all generator protections (synchronous and inverter-based). Per the SAR, “protections and controls directly focused on the generator and its prime mover (e.g., overspeed, power-load imbalance, overvoltage, phase jump, overcurrent) or plant-level (e.g., voltage, current, frequency, phase, etc.) have posed notable risks to BES reliability and should be addressed directly in this standard.”