Space charge dynamics in LDPE films immediately before breakdown

Space charge dynamics in low-density polyethylene (LDPE) films were observe d by the pulsed electroacoustic (PEA) method during breakdown tests at vari ous temperatures. In order to investigate the intrinsic electrical breakdow n, the applied electric field was increased to 300 kV/mm in 150 ms, and kep t constant until breakdown of the specimens, or 300 ms at the longest. Spac e charge profiles were measured at 1 ms intervals. A significant positive c harge propagating into the sample was observed only immediately before the breakdown at 90 degreesC. These measurements revealed that the positive cha rge behavior is strongly related to the breakdown phenomena.