Measurement of Electrode Surface Temperature and Post-Arc Current in Vacuum Interrupter

In vacuum interrupters, plasma remains between the electrodes after the current zero because of arcs generated by the interruption of short-circuit current. This residual plasma consisting of ions, electrons, and metal vapor affects the insulation recovery process after the short-circuit current interruption. The ion and electron densities can be attributed to the post-arc current and the electrode surface temperature. Therefore, direct measurement of the post-arc current and electrode surface temperature is crucial for a fundamental understanding of the insulation recovery process after the short-circuit current interruption. In this study, a prototype spiral electrode was mounted in a vacuum chamber, and the electrode surface temperature and the post-arc current were measured. The electrode was made of Cu-Cr material, and the interruption current above 10–24 kArms was applied. The electrode surface temperature was measured two-dimensionally using a two-color pyrometer method. The melting area increased with an increase in the interruption current above 20 kArms. The post-arc current and its charge also increased with increasing the interruption current, but they did not increase as dramatically as the melting area.

I. Introduction

Vacuum interrupters are widely used for circuit breakers (CBs) in medium-voltage power systems. The vacuum interrupter has a pair of electrodes inside it and is capable of interrupting fault currents of several tens of kA. A schematic of the current interruption is shown in Fig. 1. Before current zero, arc plasma is generated between the electrodes. During this period, the temperature of the anode becomes high because of the heat load of the arc. Fig. 1.

Schematic of current interruption. (a) Before current zero. (b) Immediately after current zero.