Status
PRC-026-1 – Relay Performance During Stable Power Swings was adopted by the Board of Trustees December 17, 2014.
Background
The March 18, 2010, FERC Order No. 733, approved Reliability Standard PRC-023-1 – Transmission Relay Loadability. In this Order, FERC directed NERC to address three areas of relay loadability that include modifications to the approved PRC-023-1, developing a new Reliability Standard to address generator protective relay loadability, and another Reliability Standard to address the operation of protective relays due to stable power swings. This project’s SAR addresses these directives and establishes a three-phased approach to standard development.
This Phase 3 of the project is focused on developing a new Reliability Standard, PRC-026-1 – Stable Power Swing Relay Loadability, to address protective relay operations due to stable power swings. This Reliability Standard will establish requirements aimed at preventing protective relays from operating unnecessarily due to stable power swings by requiring the use of protective relay systems that can differentiate between faults and stable power swings and, when necessary, phases-out relays that cannot meet this requirement.
Phase 2 was focused on developing a new Reliability Standard, PRC-025-1 – Generator Relay Loadability, to address generator protective relay loadability which is currently awaiting regulatory approval.
Phase 1 was focused on making the specific modifications to PRC-023-1 and was completed in the approved Reliability Standard PRC-023-2, which became mandatory on July 1, 2012.
Purpose/Industry NeedThe Commission observed that PRC-023-1 does not address stable power swings, and pointed out that currently available protection applications and relays, such as pilot wire differential, phase comparison and blinder-blocking applications and relays, and impedance relays with non-circular operating characteristics, are demonstrably less susceptible to operating unnecessarily because of stable power swings. Given the availability of alternatives, the Commission stated that the use of protective relay systems that cannot differentiate between faults and stable power swings constitutes miscoordination of the protection system and is inconsistent with entities’ obligations under existing Reliability Standards.
In this Final Rule the Commission decided not to direct the ERO to modify PRC-023-1 to address stable power swings. However, because both NERC and the U.S.-Canada Power System Outage Task Force have identified undesirable relay operation due to stable power swings as a reliability issue, the Commission directed the ERO to develop a Reliability Standard that requires use of protective relay systems that can differentiate between faults and stable power swings and, when necessary, phases out protective relays that cannot meet this requirement.
