ABSTRACT The operating temperature of metallised polypropylene film capacitors (MPPFCs) has been steadily increasing. The polypropylene (PP) dielectric film undergoes severe degradation at high temperature constraining system reliability. In this study, accelerated thermal ageing experiments were performed to assess the long‐term thermal stability of electron‐beam‐crosslinked polypropylene (EIPP) films. The effects of ageing at 125°C for up to 600 h on the chemical structure and dielectric properties of pristine PP and EIPP were systematically investigated. For pristine PP, intensified oxidative degradation at high temperature induces molecular chain scission leading to decreased crystallinity and degraded dielectric performance. In contrast, EIPP forms a compact spherulitic morphology and a stable crosslinked network effectively restraining chain mobility and oxygen diffusion. After 600 h of ageing, EIPP exhibits a 53.8% longer oxidation induction time, an electrical conductivity that is only 28.1% of that of pristine PP and a 56.5% enhancement in maximum energy storage density compared with pristine PP. These results demonstrate that electron‐beam‐induced crosslinking significantly improves the long‐term thermal stability of PP films, providing a promising pathway for high‐temperature capacitors used in high‐voltage direct current systems and DC–DC converters.
Zhang et al. (Thu,) studied this question.