Analysis of Vacuum Arc Phenomena in Instability Region and the Effects on Cathode Spot

The aim of this paper is to clarify the instability phenomena in VCB when the interrupting current is relatively small. As well known, the instabilities are occasionally observed during a small current interruption, especially with parallel circuits to VCB. We consider that the instability phenomena are mainly related to cathode spot conditions. This paper gives experiments and analysis results focusing on physical parameter. Followings three investigating methods are shown, 1) Experiments based on the conditions of the electrode and measurements cathode spot size 2) Observing cathode spots by a simple way and analyzing the metallic elements around cathode spot 3) Theoretical calculating on by physical equations.