Variation of Breakdown Voltage of a Positive-point/Plane Gap with Applied Voltage Waveshape

Abstract

IN recent years it has become a well-known experimentally observed fact^1–5 that the breakdown voltages of certain non-uniform field gaps are strongly dependent on the shape of the applied voltage impulses. For positive-point negative-plane gaps it has generally been found that, for standard double exponential applied voltage impulses and with gap spacings of 1–5 m, the breakdown voltage decreases with increasing rise-time, for rise-times of 100–200 µsec, beyond which it increases again. The magnitude of the effect increases with increase of gap-length and for a 5-m gap, for example, the breakdown voltage at the minimum can be as little as 50 per cent of that for a 1-µsec rise-time impulse.