Related Files
Status:
PRC‐023‐3 became effective on October 1, 2014.
PRC-025‐1 became effective on October 1, 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 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 power swings. This project’s SAR addresses these directives and establishes a three-phased approach to standard development.
Phase 2 is focused on developing a new Reliability Standard, PRC-025-1 – Generator Relay Loadability, to address generator protective relay loadability. This Reliability Standard establishes requirements for the Generator Operator functional entity to set protective relays at a level such that generating units do not trip during system disturbances that are not damaging to the generator thereby unnecessarily removing the generator from service.
Phase 1 was focused on making the specific modifications to PRC-023-1 and was completed in the approved PRC-023-2 Reliability Standard, which became mandatory on July 1, 2012. Phase 3, which will follow this project, will focus on developing requirements that address protective relay operations due to stable power swings.
Purpose/Industry Need:
During analysis of many of the major disturbances in the last 25 years on the North American interconnected power system, generators have been found to have tripped for conditions that did not apparently pose a direct risk to those generators and associated equipment within the time period where the tripping occurred. This unnecessary tripping has often been evaluated to have extended the scope and/or duration of that disturbance. This was noted, in detail, to be a serious issue in the August 2003 “blackout’ in the northeastern North American continent.
During the recoverable phase of a disturbance, the disturbance may exhibit a “voltage disturbance” behavior pattern, where system voltage is widely depressed. In order to support the system during this phase of a disturbance, this standard establishes criteria for setting load-responsive relays such that individual generators may provide Reactive Power within their dynamic capability during transient time periods to help the system recover from that voltage disturbance. Premature or unnecessary tripping of generators during this period can deepen the severity of the voltage disturbance due to removal of dynamic Reactive Power, and change the character of the disturbance such that it is less recoverable.
All comments should be forwarded to sarcomm@nerc.net.
