ELECTRICAL BREAKDOWN TIME-DELAY AND BREAKDOWN PROPAGATION VELOCITY INPOLYPROPYLENE UNDER A HIGHLY NONUNIFORM FIELD CONDITION

The electrical breakdown phenomenon in polypropylene for point-to-plan e gap configuration has been investigated using a photo-optical curren t-measuring technique and a 760 ns rectangular high-voltage pulse gene rator. The waveform of prebreakdown current in polyethylene is essenti ally the same as that in liquid nitrogen. A linear relation to formati ve time delay and gap spacing is obtained for gap lengths greater than some critical value, indicating a constant propagation velocity in th is region. The velocity is deduced to be 1.7 km s-1 for a positive poi nt at 60 kV. This value is coincident with that of polyethylene, and c lose to that of a longitudinal wave in polypropylene at 193 K.