Breakdown Improvement of PP Films under DC Supercomposed Harmonic Voltages

In this paper, novel polypropylene (PP) films were designed for metallized film capacitors (MFCs) by crystallization control. Modified PP films were doped with a kind of organic additives, which had a well dispersion in PP and could promote the crystallization process. The change of micro morphologies in films was confirmed by thermal measurements. Besides, the doping content was optimized based on the breakdown experiments under DC voltage. When the content was 0.03 wt%, the breakdown strength of modified films was 584.8 kV/mm, an increase of 19.57 % compared with that of the pure PP. The amplitude and frequency of harmonics were taken into consideration in actual operation of the capacitor in converter valves. The optimized film showed stable advantages in breakdown properties without increasing the conduction loss. This work can provide a reference for the performance improvement of PP films for MFCs.