Arc Behavior of Intermediate-Frequency Vacuum Arc on Axial Magnetic Field Contacts

A 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 behavior of intermediate-frequency (400, 650, and 800 Hz) vacuum arc in commercial-type vacuum interrupters with axial magnetic field contacts. With high-speed photography and volt-ampere characteristics, three different arc modes were identified: free-expansion arc column, transition arc, and diffuse arc. At the transition arc mode, the arc column is constricted, twisted, and fast moving, with an increasing number of cathode spots around it, and accompanied by an appreciable arc voltage noise at higher current. At a given current, the arc column is more constricted at higher current frequencies during this stage. The arc voltage increases with the increasing frequency regardless of the arc voltage noise; it implies a larger instantaneous energy input in shorter arc durations. Anode behavior was observed to further investigate the increased instantaneous energy input. It showed that the transient spot on the anode during the transition arc mode becomes a major source of anode erosion, although the anode erosion is slight at very high current. The instantaneous energy input, defined as mean power input, increases with current frequency, and it correlates with the constricted arc column at higher frequency. This explains the anode erosion that happened in short durations in our experiments and others.