Hybrid high-speed DC circuit breaker using charge-storage diode

Arcless DC-circuit interruption with metallic contacts is accomplished by the hybrid combination of a mechanical switch, a sold state device (power diode) and a varistor. The load current is carried by the mechanical switch. Before opening the contacts, the diode is charged by a high current pulse in forward direction. When the contacts open the diode short-circuits the fault current in its reverse direction until the charge accumulated in the diode is depleted. By this time the contacts have to be separated to withstand the now fast increasing voltage. With the hybrid high-speed circuit breaker switching currents of 275 ampere at 1250 volts were achieved with delay times of 80 microseconds