Arc modes of intermediate-frequency vacuum arc with axial magnetic field

Vacuum circuit breaker has advantages of low maintenance cost and high reliability. It reaches the priority in aviation field. This paper focuses on the arc modes of intermediate-frequency (400Hz-800Hz) vacuum arc in commercial-type vacuum interrupters with axial magnetic field (AMF) contacts. With high speed photography in conjunction with voltage-current characteristics, three different arc modes can be identified. The arc-mode evolution starts with initial free-expansion of cone-type arc column. Afterwards, the vacuum arc converts into the split constricted arc. The constricted arc is twisted and with a number of cathode spots around it. Meanwhile the constricted arc tends to diffuse and moves towards the periphery of contacts. The arc voltage has a transient peak during the second stage. The arc maintains the diffuse arc after current reaches the peak value. The arc column stops expanding and has a rapid decrease in both arc voltage and light intensity. The initial change rate of arc voltage and the arc voltage at current peak increase with the increasing frequency at a fixed current. It correlates with the increased electrons emitted from cathode at higher current frequency.