Repetitive Phenomena in Dielectrics

Insulating systems employing polyethylene terephthalate and polypropylene were tested for dielectric strength and time-to -break under pulsed and ramped voltages in the pulsewidth range of 0.2 to 5 ¿s with risetimes of 20 ns to 5 ps at a repetition rate of 500 pps. The dependence of dielectric strength and time-to-break on pulse shape was examined, with the result that none of the systems demonstrated a dependence within the specified range. It is demonstrated that this result, along with the observations made during the experiments, suggest that streamer breakdown occurred in some of the systems while thermal breakdown occurred in the others.