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. System benefits include: . Significantly lower arc flash energy for downstream faults; Faster backup clearing times for a feeder relay/breaker failure; Reduction of motor starter dropouts due to fault produced voltage dips; Improved system stability . Improvement in utility´s CAIDI reliability index; Reduced stress on switchgear breakers; Overall lower capital costs on new construction (switchgear, cables etc.). This paper demonstrates relay setting changes on typical single ended and MTM arrangement with and without applying the ET-FCL. Impacts on incident energy reduction, backup clearing times, dynamic system stability and voltage dips will be discussed.