Space Charge Measurements in Thin Bilayer BOPP Films by Thermal Pulse Method

In this paper, space charge accumulation in bilayer dielectrics composed of two metalized biaxially oriented polypropylene (BOPP) films thermally coupled by thin heat transfer oil (dibenzyltoluene, DBT) is investigated by thermal pulse method. An improved thermal pulse method for in-situ double-sided measurements is proposed to achieve higher spatial resolution. The accumulation and decay of the injected space charge is monitored after the laminated films being subjected to DC applied field of 150 V/µm at various temperatures from 25°C to 70 °C. Experimental results show that both charge injection rate and migration are sensitive to the operated temperature. Bipolar space charge injection is the rule, but negative charge becomes dominant as the injection rate asymmetry enhances with the elevated temperature. The interface between the films acts as a potential barrier to space charge transport at relative low temperature and the effect of the potential barrier appears weaken as the temperature rises. Therefore, the maximum electrical field by accumulated space charge is approximately 80 V/µm and the internal interface has little impact at 70°C.