Pattern identification of dielectric breakdown of polypropylene film for dielectric failure prediction of high energy density capacitor

With the rapid development of high energy density capacitor, polypropylene (PP) film has superior chemical corrosion-resistant, mechanical properties, insulation performance and breakdown field, and it is extensively used in the high energy density capacitors. But the dielectric reliability of polypropylene film is a critical factor affecting the operating reliability, even the lifetime of high energy density capacitor. In this paper, PP films with different thickness were employed as the specimens and polarized for different time. The capacitance, dielectric loss and volume resistances of PP films were measured after different polarization time. The dielectric breakdown tests of PP films were carried out using bias DC voltage after different polarization time. The images of breakdown craters were captured through applying a monocular-video-zoom microscope. Based on the image processing technology, both breakdown area and carbonized area of breakdown craters were statistically analyzed. Obtained results revealed that with increasing the thickness, the breakdown voltage increases, but the breakdown area and carbonized area decrease. As the polarization time increases, the dielectric constant, dielectric loss, volume resistance and breakdown voltage all decrease as well as the breakdown area and carbonized area.