Electro-optical measurement of prebreakdown current and breakdown time lag in polyethylene using nano-second rectangular pulse voltage

Electrical breakdown phenomena in polyethylene for the point-to-plane gap configuration were investigated using a photooptical current measuring technique and a 760-ns rectangular high-voltage pulse. The waveform of the prebreakdown current in polyethylene was essentially the same as those in liquid dielectrics. Discharge from the positive point was more intense and faster than that from the negative point in longer gap spacing. A linear relationship to formative time lag and gap spacing was observed for gap length greater than some critical value, which indicates a constant propagation velocity in this region. The velocities are deduced to be 1.7 km/s for a point positive 50-kV and 0.38 km/s for a 60-kV negative point. These values agree with those for liquid dielectrics