Influence of thickness on field distortion due to space charge migration in LDPE sheet

Influence of thickness in LDPE sheet on electrical field distortion and transient external current under dc step voltage are studied. Temporal change in space charge distribution in LDPE sheets of 100, 200 and 300 mum in thickness are measured by PEA method with evaporated A1 electrode or semiconduction rubber electrode under a mean applied field of 1 MV/cm. No temporal changes in space charge distribution are observed for 100 mum-thick-sheet with A1-anode/A1-cathode system. The external current exponentially decreases within a few minutes and then it keeps a constant value. For 300 mum-thick-sheet, however, positive charges from anode are penetrated deeply, so that the maximum field strength becomes much higher than the mean field strength. When semiconduction rubber is used as anode, field distortion due to positive-packet penetration is observed clearly even for 200 mum. The relation between packet-moving and current-increasing will be discussed.