Abstract
Abstract
Metallized film capacitors (MFCs) are vital in electrical equipment due to their excellent insulation and self-healing properties. However, internal failure under coupled electro-thermal-mechanical stress remains difficult to analyze because of their complex wound multilayer structure. This study employs computed tomography (CT) and three-dimensional reconstruction to visualize the internal structure of MFCs after thermal runaway failure. CT observations suggest that metallic residues in mandrel may migrate into the capacitor during self-healing or breakdown near the mandrel and serve as non-self-healing defects. The observed molten materials and gas cavities further support the proposed formation and expansion of a highly conductive mixture composed of molten polymer and metal-layer fragments during thermal runaway. Comparison of unmolten metallized BOPP films from different radial positions after thermal runaway failure shows pronounced spatially dependent degradation, with the outermost films exhibiting the lowest resistivity and breakdown field strength, likely associated with lower interlayer pressure and weaker mechanical constraint. This finding suggests that regulating interlayer pressure through winding tension or structural optimization may provide a potential strategy for improving the reliability of MFCs under electro-thermal stress.