Failure mechanism and life estimate of metallized film capacitor under high temperature and humidity

Studying the failure mechanism of thin film capacitors is of great significance to improve the service safety and life of capacitors. In this paper, firstly, the accelerated aging test and failure mechanism analysis under conditions of high temperature and high humidity were carried out. Secondly, the life prediction models were established based on the experimental data. The results showed that at 120 °C or higher, the polypropylene (PP) film of the capacitor shrank and degraded, and the electrode was damaged. The contact with oxygen caused the electrode oxidation and the capacitor failed. Under the high humidity (>69 % relative humidity, RH) service environment, water molecules and oxygen kept intruding into the interior of the capacitor, causing electrochemical corrosion and damaging the Al Zn layer on the capacitor film. Based on the life data of test samples, the life estimate models were established and the parameter values were calculated. In the temperature failure mode, the failure activation energy Ea = 1.48 eV, and under the humidity failure mode, the humidity coefficient n = 4. • The failure of MFC under temperature and humidity conditions were studied. • Detailed failure mechanism under different conditions were proposed. • Reliability models and the parameter estimation are proposed. • The proposed method can provide a lifetime estimation for services.