Film Capacitor Degradation under Electrical and Thermal Stresses Based on Capacitance Loss

With the rise of temperature and voltage, the electrode oxidation of film capacitors under AC voltage becomes more significant. This paper focuses on the effects of AC voltage amplitude and temperature on capacitor degradation. An electrothermal aging model is first proposed based on oxidation kinetics. A temperature-humidity-bias (THB) accelerated aging test is carried out for two types of film capacitors from different manufacturers under a variety of electrical and thermal stresses. The results indicate that the effect of voltage is more significant than that of temperature. The capacitance loss of encapsulated film capacitors could be divided into the linear stage and acceleration stage. The duration of the former one is determined by the moisture ingress process in the encapsulation and decreases with the increasing temperature, while it changes little with voltage. This work would enable a better understanding of the effect mechanism of AC voltage and temperature on the film capacitor degradation caused by electrode oxidation, and can be used for lifetime estimation to enhance the reliability of the system.