In this study, a method for evaluating the breakdown of PP films under complex stresses is presented. The effects and mechanism of thermal aging treatment, DC superimposed harmonics on the breakdown properties of the pure PP and five different modified films are analyzed. The breakdown strength of aged PP film is decreased, and the performance 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 the films under DC superimposed harmonic voltage is slightly lower than the test data 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.

Capacitor,Polypropylene Film,Thermal Ageing;,breakdown strength