Influence of Polarization and Non-Uniform Electric Field on Failure Characteristics of Polypropylene Film

Polypropylene (PP) film is widely used in the high energy density capacitors due to its excellent electrical properties. However, polarization and non-uniform electric field have great impact on the dielectric reliability of PP films, which were investigated in this paper focusing on the failure characteristics. By using the polarization and depolarization current method, the polarization tests of PP films with different thickness were conducted to reveal the variation of the capacitance, dielectric loss and volume resistivity. The accumulation of space charge was measured based on PEA method, and then the trap density and trap depth of PP films at different polarization levels were calculated. Finally, the DC breakdown properties at non-uniform electric field were analyzed based on the breakdown voltage and the quantitative indication of breakdown craters. Obtained results reveal that the increasing polarization degree causes the decrease in the volume resistivity, the increase in the polarization current, dielectric constant and dielectric loss. In addition, the trap density and trap depth both increase that promote the accumulation of space charge. The breakdown voltage, failure area and angular second moment of breakdown craters show the increasing tendency with the increase of the electric-field uniformity, but the decreasing tendency with increasing polarization degree.