Research on Discharge Characteristic of Metallized Film Capacitors Based on Electrical and Acoustic Signals

Metallized film capacitors (MFCs) are widely used in the modular multilevel converters (MMCs) in HVDC systems due its high reliability. During the operation of MFCs, there are some self-healing discharge signals and partial discharge signals. It is necessary to clarify the discharge characteristics of MFC. In this study, a direct current breakdown voltage test platform was built to obtain the breakdown field strength of the MFC films. The characteristic breakdown field strengths of films from MFCs at different deterioration states were analyzed by Weibull distribution. Additionally, the ultrasonic method was applied to investigate the discharge characteristic during the operation of MFCs. The results reveal that with the deterioration of MFC, the characteristic breakdown field strength of the metallized film decreases, the discharge frequency during MFC operation increases and the energy distribution of the discharge ultrasonic signal becomes more dispersed.