Fault Current Bypass and Transient Commutation Current Injection Based Soft Turn-Off DC SSCBs

This paper presents an ultrafast solid-state dc circuit breaker (SSCB) with 1) fault current bypass tripping and 2) transient commutation current injection (TCCI) assisted soft turn-off tripping schemes. It aims to provide two different adjustable tripping schemes to address technical issues in light and heavy fault conditions, respectively. There are four major contributions. First, an improved fault bypass tripping branch is proposed to handle light faults where a low-cost thyristor is paired with metal oxide varistor (MOV) to reduce its voltage stress. Second, an auxiliary TCCI branch is proposed to handle heavy faults, which removes the gate distortion and eliminates power shock of a full-control main switch by achieving soft turnoff at high fault current. Third, the proposed TCCI branch achieves natural self-charging operation, which does not need any external charger. Fourth, the proposed SSCB achieves operating duty of reclosing and reopening following IEEE Std C37.14. The proposed SSCB is validated by experiments of 1) 375 V/44 A with fault bypass scheme and 2) 375 V/ 180 A with TCCI soft tripping scheme. Experimental results also verify an ultrafast response speed of 5.2 µs and 28 µs, respectively.