Evaluation of breakdown properties of polypropylene films under multiple stresses for DC capacitors

In this study, a method to evaluate the breakdown properties of PP films under complex stresses is presented. The effects of the thermal aging experiment, DC superimposed harmonics on the breakdown strength of the pure and five different modified PP films are discussed. The breakdown strength of aged PP film is decreased, and breakdown properties of PP film based on the crystallization control is slightly better than that of organic-inorganic nano-hybrid addition composite films. The breakdown strength of all films under the DC superimposed harmonic voltage is slightly lower than that under pure DC. As the harmonic amplitude or frequency increases, such effect will be amplified. Among all modified films, the PP composite film based on micro-addition of organic accelerator has the highest breakdown strength. The research results can provide a reference for the property evolution law, improvement method and evaluation system of polypropylene films suitable for DC capacitors in converter valve halls.