Crystallization Morphology-Dependent Breakdown Strength of Polypropylene Films for Converter Valve Capacitor

In this paper, a novel modification method of polypropylene (PP) films is proposed in the field of metallized film capacitors for converter valves. An organic crystallization accelerator with good dispersion improves the micromorphology of PP films. The doping content of the organic crystallization accelerator is optimized based on breakdown experiments under DC voltage. The DC breakdown strength is 584.8 kV/mm, an increase of 19.6%, compared with that of the original film. Under DC, DC superimposed harmonics, and DC superimposed pulse voltages, the modified PP film has successfully withstood the tests, showing stable advantages in breakdown properties without increasing the conduction loss. Trap analysis and theoretical modeling were performed to clarify the mechanism of improving electrical performances based on crystallization control. The entanglement layer introduced by the organic crystallization accelerator helps to expand the crystal area, resulting in deep trap sites and limitation of carrier migration. This research can provide a reference for the PP performance optimization for metallized film capacitors of converter valves.