The influence of bridged slots on arc behavior in spiral type vacuum interrupter

Slots of a spiral type contact play an important role to generate radial magnetic field in vacuum interrupter. Radial magnetic field is one of the sources of arc driving force. Radial magnetic field type vacuum interrupter has to move constricted arc to protect contact surface from melting by high-temperature arc. Arc can move via interaction between magnetic field density of radial magnetic field and current density of the current flowing through arc (F = j × B). But as the number of interruption tests increases, contacts become melted by arc and fill slots more and more with melted contact volume. Namely, the spiral type contacts become butt type contacts slowly. Then, arc control ability of contacts will be declined considerably. But there have been few reports on this phenomenon. In this paper, arc behavior was investigated by means of arc photographs and arc voltages acquired from current interruption tests with long arcing time. Especially, the influence of bridged slots on arc behavior was dealt with.