High field conduction and space charge formation in polypropylene film

High-field conduction and space-charge formation in polypropylene (PP) film at high temperatures was studied by measuring charging and discharge currents. The electric-field dependence of the charging current was divided into three regions: the low-, the medium-, and the high-field region. In the high-field region, the increase of the charging current with electric field is depressed from the Schottky line, and anomalous discharging currents which flow in the same direction as the charging currents were observed. The appearance depended on the anode metal rather than the cathode and was most remarkable under the condition of an Au anode and Al cathode. The breakdown tests were also made at 100°C with different combinations of electrode metals. The samples with the Au anode showed a lower breakdown strength than those with the Al anode. These processes may be caused by the hetero-space charge formation near the anode