Current commutation in a medium voltage hybrid DC circuit breaker using 15 kV vacuum switch and SiC devices

Analysis and experimental study of current commutation in an ultra-fast, current limiting, hybrid DC circuit breaker for medium voltage applications is reported in this paper. The hybrid DCCB consists a fast acting 15 kV mechanical switch, a low voltage commutating switch, a single 15 kV Silicon Carbide Emitter Turn Off Thyristor (ETO) device, and a stack of MOVs. The proof-of-concept prototype is able to conduct 45 A normal current and interrupt a maximum of more than 100 A fault current at medium voltage level in less than 4 milliseconds, which is one order of magnitude faster compared to conventional mechanical circuit breakers that typically take 40-100 ms. This paper has presented the operation principle of a hybrid DC circuit breaker and analyzed the current commutation process. Based on the analysis, guidelines are given in the paper to select and design the commutating switch.