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

We observed the behavior of an are on spiral contacts using a high-speed video camera, and found three periods of are motion, These periods consist of a Slow Are Period immediately after the arc: ignition where the are begins to move gradually at less than 10m/s, an Acceleration Period, and a Nigh Speed Period where the are rotates faster than 50 m/s. The duration of the Slow Are Period and the speed during the Nigh Speed Period showed a dependence on the shape of the contact. Our results were as follows. (1) The spiral contact with a short Slow Are 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 Are Period. (3) The borderline depends on the contact material. From these results, we conclude that the transferred electric charge during the Slow Are Period influences the state of the gap at the current zero.