Particle Detection in Vacuum Interrupter: Preliminary

While interrupting the large current in vacuum circuit breaker, the surface temperature of both electrodes will rise due to the arc current Joule heating process; the surface profile gets rough due to the vacuum arc burning on electrodes nonuniformly; and protrusions are simultaneously generated, which may potentially lead to late discharge. In this paper, the random discharge after current zero is reported, and the particle phenomenon is observed as considered to be responsible for the late discharge phenomenon previously. The authors develop a synthetic experiment system, which consists of current source, voltage source, control units, and the observation system. The high-speed video camera is used to record the particle motion in the interelectrode space. Using this system, the motion of small particles is tracked. From the particle information in each frame, the size and speed of the particle are calculated to be within 160 mu m and 100 m/s, respectively; the charge quantity of small particles is derived as less than 10(-11) C. Furthermore, the surface field enhancement factor is deduced from the particle detachment model, which lays in hundred orders. Since observed particles cannot directly lead to the observed current, possible reasons for the late discharge would be Townsend type metal vapor discharge, and the vapor comes from high-temperature electrode surface and protrusions.