Effect of interlayer air on performance of dry-type metalized film capacitor in DC, AC and pulsed applications

The metalized film capacitor can work under a high electric field due to its self-healing characteristic. Firstly, this study indicates that inter-layer air is one of the most important factors which influence the process of self-healing. The interlayer air not only increases the duration of self-healing process, but also increases the self-healing energy and self-healing area. The interlayer air between the outer layers is more than that between the inner layers, so the self-healing area in the outer layer is larger than that in the inner layer. Secondly, H₂O and O₂ in the air are the necessary conditions of electrochemical corrosion. So if the capacitor is used in ac or pulsed applications, electrochemical corrosion will occur in the aluminum electrode. The product of electrochemical corrosion is alumina (Al₂O₃), which leads to capacitance loss. For the safety film capacitor, electrochemical corrosion, which is caused by the air along the segmented gap causes electrode recession, resulting in rapid decrease of the capacitance. This paper provides three methods: wrap strengthening, heat treatment and end-sealing after vacuum to exclude or decrease the interlayer air. The experimental results show that all three methods can improve the lifetime of the capacitor to some extent.