Triggered discharges with high arc voltages in a vacuum interrupter

Studies of nonsustained disruptive discharges (NSDD), isolated cases of which can occur in vacuum interrupters, are presented. They indicate lateral discharges between the cathode and shield, which can initiate a brief discharge between the contacts. To facilitate the study of such discharges, they were triggered by a surface discharge induced by a spark gap, built into the side of the cathode, and observed with a high-speed film camera and an image-converter camera. The tests showed a cathode spot after igniting. The electrons emitted here first charge the shield negatively and are directed toward the anode. The discharge burns at a high voltage, with currents ranging from 10 to 100 A. After a period of up to 400μs, the current demand increases abruptly; an arc discharge occurs between the contacts and discharges the capacitances near the switch. The contact gap undergoes a rapid dielectric recovery, and the restored voltage is maintained