Space charge dynamics in LDPE films immediately before breakdown

Space charge dynamics in low-density polyethylene (LDPE) films were observed by the pulsed electroacoustic (PEA) method during breakdown tests at various temperatures. In order to investigate the intrinsic electrical breakdown, the applied electric field was increased to 300 kV/mm in 150 ms, and kept constant until breakdown of the specimens, or 300 ms at the longest. Space charge profiles were measured at 1 ms intervals. A significant positive charge propagating into the sample was observed only immediately before the breakdown at 90/spl deg/C. These measurements revealed that the positive charge behavior is strongly related to the breakdown phenomena.