Energy storage performance of BOPP films subjected to impact stress for pulse power capacitors

Abstract Pulse capacitors are indispensable components in electromagnetic energy equipment, and they are subjected to very high electric fields during operation. However, the high electric field generates significant electro-induced impact forces, which can adversely affect the film dielectric inside the capacitor. In this study, biaxially oriented polypropylene (BOPP) film, the most widely used dielectric material in pulse capacitors, is selected as the focus of investigation. The impact stresses under varying electric field are calculated and simulated, the changes in the dielectric and energy storage properties of the film before and after exposure to stresses are systematically analyzed. The experimental results show that dielectric loss and direct current conductivity are increased after being subjected to impact stress. The breakdown strength was reduced by up to 33.1%, discharge energy density and charge-discharge efficiency were reduced from 4.62 J/cm3 and 88.36% at 700 kV/mm to 0.86 J/cm3 and 32.85% at 500 kV/mm. The reason for the change in performance can be attributed to the impact stress with strong energy, which severely disrupts the ordered molecular chain and stable spheroid structure of the film, resulting in a large number of defects. As a result, the energy level and density of the deep trap are reduced, and carrier migration and charge accumulation are intensified. This work provides a reference for exploring the influence of impact stress on the insulation failure of BOPP films, and also shows the direction for revealing the performance degradation mechanism of pulsed capacitors in extreme environments.