The influence of the cathode melted layer on vacuum insulation

The objective of this paper is to determine the influence of the depth of cathode melted layer on vacuum gap's insulation. A pair of rod-plane electrode was used. A DC arcing circuit produced different depth melted layer on the rod anode through different arcing time, which were 10ms, 46ms and 73ms respectively. Then the vacuum gap was adjusted at 1mm to measure the breakdown voltage. Positive polarity standard 1.2/50μs lighting impulse voltage was applied by a basic up-down method and the rod was the cathode. Experimental results revealed that the breakdown probability distribution followed a Weibull distribution when the breakdown voltage saturated. The 50% breakdown voltage U50 of different arcing time 0ms, 10ms, 46ms, 73ms corresponded to 55.6kV, 73.3kV, 75.5kV, 77.9kV, respectively. The U50 with the melted layers increased 37% at least. However, the U50 with various depth of melted layers were similar. Therefore, the melted layer does improve the breakdown voltage but the depth of melted layer has no influence on the breakdown voltage.