High field AC dissipation current waveforms of an oxidized polypropylene film superposed by DC ramp voltage

To investigate the AC conduction mechanisms, the dissipation current waveforms superposed by DC ramp voltage of an OPP sample were observed. The main conclusions are as follows; (1) At room temperature, tan δ, and dissipation current waveforms did not depend on the superposed DC ramp voltage. The shapes of dissipation current waveforms were almost sinusoidal for the oxidized polypropylene film sample. (2) In the high-temperature and high-field region, tan δ and dissipation current waveforms were affected by the superposition of DC ramp voltage. The shapes of dissipation current waveforms were different between the positive and the negative half cycle. The loss current is enhanced around a positive peak with superposition of positive DC high-field and vice versa. However, if the magnitude of DC field is smaller than the peak level of AC field component or if the temperature is lower, the superposed DC field makes no significant changes for the dielectric loss property