Arcless Commutation of a Hybrid DC Breaker by Contact Voltage of Molten Metal Bridge

DC circuit breakers (DCCBs) have been intensively studied because of increasing demand for dc power transmission. A hybrid dc circuit breaker that consists of mechanical switches, semiconductor devices, and metal-oxide varistor elements is a promising device to provide low contact resistance and fast interruption. Semiconductor devices are turned on by the sustaining voltage of arc discharge generated between the metal contacts of the mechanical switch. Though the arc duration time in the hybrid DCCB is shorter than that in classical mechanical CBs, the arc causes contact erosion. In this report, an arcless commutation is described that uses the molten metal bridge voltage at the opening stage of the contacts. The magnitude of the molten bridge voltage is just enough to turn on SiC-MOSFET devices under specific conditions. Arcless commutation and interruption of dc current were observed with an Ag-W vacuum contact and SiC-MOSFETs at current values of 78-140 A.