Moisture Induced Weight Gain Relation to Capacitance Loss Characteristic of Film Capacitors under Harsh Enviroment

The ambient moisture would diffuse into the film capacitor under the humid environment. The corrosion of electrodes would occur under ac voltage stress with the participation of the moisture, which results in a decrease of the capacitance. Thus, the moisture ingress is harmful to long-term reliable operation of film capacitors. In this paper, the process of moisture ingress is analyzed based on the Fick’s second law. An accelerated aging is carried out for two types of film capacitors to obtain the capacitance change and the weight gain. A staged fitting analysis is used to describe the capacitance change curves of capacitor samples. The effect of the moisture ingress on the lifetime of film capacitors is studied. The results indicate that the encapsulating material which provides better moisture resistance can slow down the electrode corrosion and significantly improve the lifetime of the film capacitors.