Influence of vacuum arc behavior on current interrupting limit of spiral contact

The authors observed the behavior of an arc on spiral contacts using a high-speed video camera, and found three periods of arc motion. These periods consist of a slow arc period immediately after the arc ignition where the arc begins to move gradually at less than 10 m/s, an acceleration period, and a high speed period where the arc rotates faster than 50 m/s. The duration of the slow arc period and the speed during the high speed period showed a dependence on the shape of the contact. Their results were as follows: (1) the spiral contact with a short slow arc period has high interrupting capability; (2) there is a borderline between successful and failed interruption in the electric charge transferred into the contact during the slow arc period; and (3) the borderline depends on the contact material. From these results, they conclude that the transferred electric charge during the slow arc period influences the state of the gap at the current zero.