Long time range breakdown in polymeric insulating films subjected to step voltage

The breakdown time lags for five kinds of polymeric insulating films subjected to a step voltage were measured in the minute range at room temperature. The time-lag distributions were classified into two types, exponential and normal distributions. Low-density polyethylene (LDPE), polystyrene (PS), and polypropylene (PP) belong to the exponential distribution class while polycarbonate (PC) and ethylene-vinylacetate copolymer (EVA) belong to the normal distribution class, although the time lags in the nanosecond range were exponentially distributed in all specimens. The exponential distribution in LDPE, PS, and PP suggests that breakdowns are caused by a stochastic mechanism, such as an avalanche breakdown. The normal distribution of time lag in PC and EVA implies that some physical processes proceed slowly after the application of the voltage until a breakdown occurs.<>