Improving relay protection levels in medium voltage switchgear

This paper demonstrates the impacts of an electronically triggered fault current limiter (ET-FCL) on typical single-ended and main-tie-main (MTM) medium voltage (MV) switchgear arrangements. The fast acting (less than 1 ms) ET-FCL described in this paper effectively opens the normally-closed tie connection between two mains, thereby disconnecting one of the sources to the fault. An ultra-fast opening of the tie connection simplifies protection coordination by not having to coordinate the main breaker relay with the tie breaker relay at maximum fault levels.