Breakdown in Compressed HE/SF6 Gas Mixtures in Uniform Field

The breakdown strengths in uniform field were calculated for helium/SF6 mixtures at pressures up to 300 kPa for smooth electrodes, and compared with measured values. The effect on discharge thresholds in He/SF6 mixtures due to the polarity of an artificial protrusion and due to irradiation of the gap was investigated. The results obtained from this study show that the calculation of the breakdown levels in He/SF6 mixtures from the pure gases has not given satisfactory agreement with measured values. An empirical equation which expresses the limiting value of Ep (E= electric field, p=pressure) for the mixtures was derived as a function of the ratio of the partial pressures of He and SF6.