Packet-like space charges and conduction current in polyethylene cable insulation

Packet-like space-charge behavior in polyethylene for cable insulation was studied by utilizing the laser-induced pressure-pulse technique. Space charge observation under various conditions showed that the charge packet was formed in the specimen doped with antioxidant, especially when the specimen is oxidized. Periodic formation and transport of charge packets led to a small current oscillation. The charge packet seemed to be formed in the bulk, and the internal field of 1.2 to 1.4 MV/cm, in the region where the packet was formed was periodically enhanced from 2 to 2.5 MV/cm by space-charge accumulation. This suggests that the packet formation is caused by carrier generation under the highly enhanced field. The antioxidant deteriorated by oxidation was shown to be a possible origin of the carrier generation.