Streak Camera Observations of Partial Discharg Polyethylene under Fast Impulse Voltage Stress

Abstract

Samples of polyethylene with electrical trees at the tip of a needle radius/9 mm gap) molded into the material were subjected to voltage impulses of between 50 and 85 kV (20 ns/2 /spl mu/s). The light emitted from the partial discharges was recorded with a streak camera. Light was emitted for less than 20 ns for a positive impulse of 70 kV. The recorded light was located in the region of the electrical tree and the "length" of the recorded light increased with the growth of the tree. There was degradation of the emitting region after many impulses, except in one branch. The rate of growth of the electrical tree leading to final breakdown depends also on the mechanical stress applied sample.