Accelerated Degradation Testing and Failure Mechanism Analysis of Metallized Film Capacitors for AC Filtering

Film capacitors for ac filtering play a crucial role in various industrial applications, such as wind power and traction systems. However, current research lacks studies on the aging and failure analyses of high-power ac film capacitors subjected to realistic stresses. This article addresses this gap by presenting degradation testing and failure analysis of metallized film capacitors employed in megawatt (MW) power converters for ac filtering purposes. First, accelerated aging tests are performed on ac filter capacitors based on realistic stresses for more than 3500 h. Testing results on electrothermal parameters are recorded, and derivative models of parameter aging are obtained. The analysis reveals that electrochemical corrosion is the primary aging factor, with negligible capacitance reduction until catastrophic failure occurs. Further investigation, including temperature rise results and microstructure evaluation, indicates that the melting of the dielectric film is a crucial precursor to catastrophic failure. Finally, the possible degradation and failure mechanisms for this type of ac filtering capacitors are summarized. The observations provide a new perspective on the possible failure mechanisms and condition monitoring of film capacitors in ac filtering applications.