Space charge and external circuit current measurements in LDPE films during breakdown tests

Space charge dynamics in low density polyethylene films were observed by the pulsed electroacoustic (PEA) method throughout breakdown tests at various temperatures. To clarify the relationship between space charge and breakdown, we developed a PEA system with a current measurement unit. The applied voltage was increased up to 300 kV mm-1 in 150 ms to investigate a short time breakdown. Space charge profiles were measured at 1 ms intervals, and the external current was simultaneously measured. A significant positive charge propagating into the specimen was observed immediately before the breakdown at 90°C. These measurements revealed that the positive charge behaviour is strongly related to the breakdown.