Tomotaka Yano

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.

The impact of capacitive switching condition on vacuum breakdown phenomena

In the case of switching capacitive loads, breakdown electric field of vacuum interrupter tends to decrease because contacts of vacuum interrupter are damaged by large making current. In this paper, the authors investigated the decreased breakdown electric field from the following two viewpoints. First, the relation between breakdown electric field and condition of opening operation was investigated. The breakdown electric field was invariant regardless of whether mechanical impact of opening operation was applied. On the other hand, the breakdown electric field tended to increase when opening operation was carried out with long arc time. These results indicate that the field emission mainly determine the breakdown phenomena. Secondly, the relation between breakdown electric field and making current was investigated. On the whole, the larger the amplitude of making current became, the lower breakdown electric field tended to be. However, the breakdown electric field was exceptionally high when the generation time of making current arc was long. This is because arc of making current diffused rapidly.