Commutation of Current in a Hybrid DC Switch

Hybrid DC switches have been intensively studied because of the increasing demand for DC power distribution systems. A hybrid switch consists of high-speed mechanical contacts, semiconductor power devices, and metal– oxide varistor elements. Make arcs are suppressed from occurring by turning on the power device connected in parallel before closing the contacts. In the opening period, the contact voltage increases and microsecond make arcs occur intermittently during the rise of contact voltage exceed the boiling voltage of the contact material. The arc voltage turns on the power device and subsequently the circuit current commutates from the contacts to the power device. The DC current is interrupted by the power device with varistors. Although the duration of make arcs was a few 10 m s, the contact surface was degraded and the insulation strength decreased up to 20% in 1 kA DC commutation.