Space-charge characteristics of modified high-density polyethylene for DC cables

Modified high-density polyethylene (m-HDPE) is a candidate for high-voltage solid DC cable insulation. Based on the space-charge measurements on thick modified HDPE samples (1.5 mm), it was reported that modified HDPE contained relatively small amount of space charge and showed high breakdown strength. We measured space-charge distribution in thin m-HDPE samples (50 /spl mu/m) by using the laser-induced-pressure-pulse method in order to clarify effects of charge injection on the space-charge characteristics and electrical conduction. The samples with Au electrodes showed positive home space charge at room temperature but negative charge became dominant at higher temperature. These charges are due to injection from the electrode. The space-charge behaviour at voltage polarity reversal suggested that these space charges affected the breakdown characteristics. The samples with a semiconducting layer showed space-charge and conduction characteristics different from those with metal electrodes. The change was partly attributed to the diffusion of impurities during the hot-press process for applying the semiconducting layer.