Metallised polypropylene film capacitors (MPPFCs) are widely used in power electronics and are generally degraded by elevated temperatures. This work aims to determine the relationships between the structural changes of MPPFC and the microstructural variations of the PP film during the thermal ageing of MPPFC at 100°C for 38 days. The capacitance of MPPFC has a slight decrease during thermal ageing. However, the breakdown voltage of the MPPFC decreases by 39.4% by the ageing. The partial discharge (PD) number of MPPFC increases linearly with ageing time. The tear-down analysis of the MPPFC reveals that the molecular structure of the PP film has not been altered but has led to molecular chain scission and the generation of some polar fragments/groups. Meanwhile, the relative permittivity of the PP films rises as the ageing time increases. Moreover, thermal ageing causes the conversion of aluminum to alumina in the metallised electrode, which is hydrophilic for polar groups and leads to an adhesion effect between the metallised electrodes and the PP film. Contact angle measurements prove that the surface hydrophilicity of the PP sample increased after thermal ageing. Therefore, the PD/breakdown voltage in the MPPFC increases/decreases due to the uneven adhesion of the metallised PP film.

中文翻译：

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重温金属化聚丙烯薄膜电容器的热老化：从器件到介电薄膜

金属化聚丙烯薄膜电容器 (MPPFC) 广泛用于电力电子设备，并且通常会因高温而退化。这项工作旨在确定 MPPFC 在 100°C 下热老化 38 天期间结构变化与 PP 薄膜微观结构变化之间的关系。MPPFC 的电容在热老化过程中略有下降。然而，随着老化，MPPFC 的击穿电压下降了 39.4%。MPPFC 的局部放电 (PD) 数随老化时间线性增加。MPPFC 的拆卸分析表明，PP 薄膜的分子结构没有改变，但导致分子链断裂和一些极性片段/基团的产生。同时，PP薄膜的相对介电常数随着老化时间的增加而升高。而且，热老化导致金属化电极中的铝转化为氧化铝，这对极性基团具有亲水性，并导致金属化电极和 PP 薄膜之间的粘附效应。接触角测量证明 PP 样品的表面亲水性在热老化后增加。因此，MPPFC 中的 PD/击穿电压由于金属化 PP 薄膜的不均匀附着而增加/减少。