{"id":1238,"date":"2020-08-13T12:09:38","date_gmt":"2020-08-13T12:09:38","guid":{"rendered":"https:\/\/www.trccompanies.com\/insights\/nerc-issues-lessons-learned-on-misoperations-due-to-mixing-relay-technologies\/"},"modified":"2024-12-12T15:59:02","modified_gmt":"2024-12-12T15:59:02","slug":"nerc-issues-lessons-learned-on-misoperations-due-to-mixing-relay-technologies","status":"publish","type":"news-and-insights","link":"https:\/\/www.trccompanies.com\/fr\/insights\/nerc-issues-lessons-learned-on-misoperations-due-to-mixing-relay-technologies\/","title":{"rendered":"NERC Issues Lessons Learned on Misoperations Due to Mixing Relay Technologies"},"content":{"rendered":"\n\n
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On July 10, 2020 NERC released new Lessons Learned guidance to address situations where multiple composite protection systems have misoperated as a result of mixing protective relay technologies at the remote terminals of directional comparison blocking (DCB) schemes. This technical information will help utilities improve the reliability of the Bulk Power System.<\/p>\n

One of the most challenging situations for mixing of technologies occurs when a relay system based on microprocessors is used at one terminal and an older electromechanical relay system is used at the opposite terminal of a transmission system. Often, only one terminal of a DCB system is upgraded to microprocessor-based relays due to reasons including different ownership of terminals, budget constraints, and emergency replacements. Relay timing and directional coordination is critical in DCB schemes and may be overlooked when relay technology varies between terminals.<\/p>\n

DCB protection systems with electromechanical relays are high speed protective schemes that use very fast phase and ground fault detectors to transmit or \u201cstart\u201d a blocking signal by opening contacts. Opening contacts to start a blocking signal allows quicker operation by minimizing the time required to overcome inertia in electromechanical relays. It is common to have this blocking signal transmission initiated within a quarter cycle of the start of a fault in electromechanical DCB protection schemes.<\/p>\n

NERC points out that mixing electromechanical and microprocessor relay technologies can introduce timing problems. The electromechanical relay can send a blocking signal fast enough for the remote microprocessor terminal to detect and block tripping for external faults. However, the microprocessor relay at the remote terminal may not send a blocking signal until after the electromechanical terminal relay(s) have initiated the trip, thus causing the electromechanical end to incorrectly trip. This is a misoperation of the protection scheme which is reportable and requires investigation under NERC standards.<\/p>\n <\/div>\n

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Resources<\/h4>\n