Role of thermal and electric fields in the failure mechanism of metallized film capacitors: insights from molecular chain dynamics within polymer dielectrics

The seamless integration of modern power systems and renewable energy sources heavily relies on advanced power electronics technologies, with metallized film capacitors (MFCs) playing a pivotal role in this ecosystem. Ensuring the operational efficiency and safety of these systems necessitates a thorough understanding of MFC failure mechanisms. In this study, molecular dynamics and density functional theory are employed to analyze the microscopic parameters governing MFC failure characteristics across a temperature spectrum of 25 °C-105 °C. The investigation is geared toward theoretically assessing MFC failure mechanisms under varying voltage ramp rates. Our findings highlight temperature as the primary influencer of failure characteristics at slower ramp rates (50 and 75 V s⁻¹), where the interplay between carrier transport and intermolecular interaction energy dictates the trend of capacitor failure voltage—a pattern of initial increase followed by decrease with temperature. Conversely, higher voltage ramp rates accentuate the significance of the electric field. At a rapid ramp rate of 900 V s⁻¹, the dominance of the electric field mitigates the impact of temperature, resulting in minimal variation in failure voltage across temperatures. Moreover, under intense electric fields, the reduction in free volume within the polypropylene unit exhibits a rapid decline, significantly constraining the mobility of molecular chains. Consequently, certain segments of these molecular chains exhibit localized alignment and directional movement. The rise in molecular polarity and reduction in energy gap contribute to substantially lower failure voltages compared to slower ramp rates. This study offers robust theoretical insights into comprehending MFC failure characteristics, thereby ensuring their reliable operation in demanding environments.