Decay Modes of Anode Surface Temperature After Current Zero in Vacuum Arcs—Part II: Theoretical Study of Dielectric Recovery Strength

Anode surface temperature after current zero has a great impact on the interruption capacity of a vacuum interrupter. The objective of this paper is to theoretically investigate the relation between breakdown voltages and anode surface temperature after current zero. A heat conduction model was adopted to describe the temperature development of the anode, taking account of phase transition and evaporation. The breakdown voltages in certain metal vapor densities were obtained by the Particle-in-Cell/Monte Carlo collision (PIC-MCC) method. Finally, the Paschen curve for copper vapor was obtained using the PIC-MCC method and verified by the theoretical model. Moreover, the minimum breakdown voltage, 30 V, was obtained at a density of 1.3 × 10²²/m³ with a gap of 10 mm, which corresponded to a surface temperature of 1983 K. In order to ensure a successful interruption, anode surface temperature should not be higher than 1983 K at current zero, and the melting time should be kept as short as possible.

I. Introduction

Anode surface temperature after interrupting a high-current vacuum arc has a significant impact on the decay of metal vapor density after current zero, which dominates the interruption capacity of a vacuum interrupter [1]–[3]. A breakdown may occur if the surface is still hot in a postarc dielectric recovery process. In order to achieve a successful interruption, the surface temperature has to be reduced to a certain level so that the contact gap rapidly recovers to a vacuum condition. For low-current interruptions, anode surface temperature is quite low because the vacuum arc is emitted from cathode spots on the cathode contact, and the anode acts as a passive absorber. For high-current interruptions, however, a stationary anode spot appears on the anode surface, which inputs energy into the surface, locally resulting in overheating. Thus, excess metal vapor is continuously generated from the anode spot even after current zero. The higher the anode surface temperature is, the more the metal vapor that will be evaporated into the contact gap of the vacuum circuit breaker (VCB). Therefore, it is necessary to keep the anode surface temperature low and avoid heating the surface locally.