Breakdown of SF/sub 6/ in non-uniform field gaps under combined DC fast oscillating impulse and standard lightning impulse voltages

Abstract

Breakdown and voltage-time characteristics of nonuniform field gaps in compressed SF/sub 6/ gas were studied using a point-to-plane electrode arrangement. Combined voltages, consisting of very fast transient (VFT) overvoltage and standard lightning impulse (SLI) voltage superimposed upon DC voltage, were applied. The experimental gas pressure ranged from 100 to 500 kPa. The results presented show that the magnitude and the polarity of the direct voltage, as well as the gas pressure, influence the corona discharge and the breakdown characteristics. It was found that the breakdown voltages under the VFT are higher than the corresponding values obtained under SLI voltages. At the higher gas pressures, the voltage-time characteristics of VFT fall below those for SLI. >