Degradation Mechanisms of Polypropylene Film Under Coupled Electrical and Mechanical Stress During Frequent Charge-Discharge Cycles

The polypropylene film insulation medium limits the performance of pulse capacitors, which are the main energy storage component of pulse power supplies and electromagnetic transmission systems. The deteriorating mechanism of electrical and mechanical multi-field coupling in pulse repetitive charge-discharge cycles is still unknown, despite the fact that the majority of current research focuses on the aging of polypropylene films under steady state settings. This study involved constructing a multi-physics field testing system to reveal the degradation mechanism of polypropylene films when subjected to pulse conditions and pressure. The research found that repeated charging and discharging, as well as increased pressure, would lead to a decline in the electrical performance of the polypropylene films. Increased pressure caused changes in the microstructure of the BOPP films, thereby enhancing conductivity. While the dielectric constant increased within a small range, polarization loss also increased, reducing charging and discharging efficiency and energy storage density. The DC breakdown field strength of the PP- 0 sample was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$595 \text{kV} / \text{mm}$</tex>, whereas that of the PP-8 sample was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$482 \text{kV} / \text{mm}$</tex>, representing a 19 % decrease. This study provides a basis for improving the performance of polypropylene films.