Investigations on Initial Self-Healing Failure Probability of AC Metalized Film Capacitors

Self-healing failure in metallized film capacitors (MFCs) is adverse to their lifetime and will affect the stability of systems. The probability of initial self-healing failure of MFCs is influenced by various factors. In this article, an experimental setup is established to obtain the initial self-healing failure probability of MFCs under ac voltage, and the effects of interlayer pressure, temperature, film thickness and voltage on the initial self-healing failure probability are studied. The results reveal that, with the interlayer pressure increases from 200 kPa to 900 kPa, the probability of initial self-healing failure decreases first and then increases, reaching the minimum value at 600 kPa. With the temperature increases from 20 °C to 70 °C, the probability of initial self-healing failure decreases first and then increases, reaching the minimum value at 50 °C. The probability of initial self-healing failure is negatively correlated with the thickness of the film within the range of 7 μm to 10 μm. The probability of initial self-healing failure is positively correlated with voltage within the range of 1150 V to 1350 V. In the design and manufacture of MFCs, to reduce the initial self-healing failure probability, steps should be taken to improve interlayer pressure for the outer layer of cylindrical capacitor elements to 600 kPa, such as increasing the turns of wrapped film outside and optimizing heat treatment processes. For flat elements, applying a pressure of 600 kPa is appropriate; measures should be taken to control the internal temperature of MFCs close to 50 °C; thicker film can reduce the probability of initial self-healing failure; under the present design field strength, the initial self-healing failure probability of the MFCs is relatively low, and the design field strength is reasonable. The research results can provide reference for the design of MFCs.