Recovery Times of Vaccum Interrupters Which have Stationary Anode Spots

With rectangular power current waves recovery times of a vacuum interrupter with copper-based button contacts were measured. They were found to increase from 7 , μat 250 A to 630 μs at 12 kAp, where a stationary anode spot had formed. With a stationary anode spot present recovery time was also approximately proportional to current pulse duration. An attempt was made to explain the long recovery times by evaporation from the highly heated anode after the current had ceased. In addition, some high-speed photographic observations were made on the formation of stationary anode spots.