Effect of electrode surface roughness on electrical breakdown in high voltage apparatus

This paper considers the statistical theory of electrical breakdowns in high voltage (HV) devices. The extended probability distribution of breakdown is deduced for nonuniform gaps. The breakdown of high voltage apparatus is sensitive to local irregularity of the electric field which may result from the presence of defects such, as surface roughness. The surface roughness leads to existence of localized microscopic projection with local electric field strength at the projection top larger than the average field at the electrode surface. The link between parameters determining the probability of electrical breakdown and the parameters determining microscopic geometry of electrode surface is obtained. In this paper a simplified breakdown model is used as a basis for statistical treatment. According to the model the breakdown proceeds if the electric field strength at the projection top exceeds the critical value. The method of dielectric strength calculation for HV devices using a simplified model of breakdown is presented. The paper gives an example of calculation of the breakdown voltage for vacuum switch TVS-43. Results of calculations are compared with available experimental data and Weibull distribution.