Surface Electrode Degradation Features of Metalized Film Capacitors: Considering Self-Healing and Flashover Discharge

Abstract

Metallized film capacitors (MFCs) play a crucial role in photovoltaic (PV) power inverters, electric vehicles, and other devices. Current researches on the capacitance loss of ac filter MFCs have predominantly focused on metal corrosion, with limited attention to the critical factor of surface electrode degradation caused by different types of discharge—the movement and release of charges due to the localized insulation failure within MFCs. This work investigates the discharge characteristics of metalized films based on the partial discharge (PD) characteristics of pure polypropylene film samples. The findings reveal that the self-healing (SH) waveform in metallized films is similar to surface flashover, with a duration of 0.7–1 $\mu $ s and a dominant frequency of 3–4 MHz. SH, flashover around SH points, and margin flashover are the types of discharge that lead to electrode evaporation, collectively termed capacitance-reducing discharge (CRD). The PD inception voltage (PDIV) for the metallized film is 329 V, while the CRD inception voltage (CRDIV) is 753 V. The coupling effect among CRDs exacerbates capacitance reduction and compromises the performance of MFCs. Investigation into the energy characteristics of CRD reveals that the discharge energy WD is confidently correlated with the root mean squares (rms) voltage URMS. The exponent n in W $_{D}~\sim $ U $_{\text {RMS}}^{n}$ dependence is 2.044, lower than measured under dc voltage. This study has both theoretical and experimental significance in comprehensively analyzing surface electrode degradation features in ac filter MFCs.