Dielectric recovery strength after vacuum arc extinctions

Anode surface temperature after interrupting a vacuum arc has a significant impact on the interruption capacity of a vacuum circuit breaker (VCB) because it dominates metal vapor evaporation. The objective of this paper is to theoretically investigate the relationship between breakdown voltages and anode surface temperatures after current zero. A heat transfer model was established to describe the temperature development on an anode surface, taking account of phase transition processes. The contact material was copper. Moreover, PIC-MCC was adopted to simulate the breakdown voltages in a range of metal vapor density. The calculated results verified the two decay modes of anode surface temperature after current zero proposed by our experiments. The metal vapor density evaporated from an anode surface was positive correlated with its temperature. The breakdown voltage was negative correlated with the anode temperature. A higher surface temperature results in a higher probability of breakdown. Thus, it is better to keep the initial surface temperature at current zero below a certain value.

I. Introduction

Surface temperature after interrupting a high current has a significant impact on the interruption capacity of a vacuum circuit breaker(VCB) [1]–[3]. In particular, the anode surface will evaporate a great deal of metal vapor and droplets if the surface is heated to a high temperature, maybe above the melting point of the material, making interruptions more difficult. Moreover, anode surface temperature is closely related to vacuum arc modes. As Miller's classification of anode phenomena in vacuum arcs [4], anode modes consist of diffuse arc, footpoint, anode spot, and intense arc. Furthermore, he related the anode modes with different surface temperatures. For example, a footpoint will appear on an anode if the surface temperature exceeds the anode material's melting point and anode spot mode is associated with the boiling point. Furthermore, the surface temperature has a clear physical meaning, and can be observed quantitively comparing arc photography. Therefore, the researches on anode surface temperature will gain insight into vacuum arc and also dielectric recovery after current zero.