Investigation on influence of current interruption on V-t characteristics of vacuum interrupters

To identify the influence of current interruption on the insulation strength of vacuum interrupters (VIs), the V-t characteristics of VIs were measured from nano seconds to several micro seconds range before and after current interruption. The breakdown voltage increased after the current interruption for VIs of Cu-Cr contacts. The field emission current of contacts were also measured before and after the current interruption, and the change of the field enhancement factor β was investigated by Fowler-Nordheim (F-N) analysis. The analysis indicated that the surface condition was improved by the current interruption, which can explain the improvement of breakdown voltage. It also turned out that the impulse voltage application during the V-t characteristics measurement had a considerable influence on the surface condition.