Improved charging behaviors and flashover voltage of polypropylene film based on surface molecular structure modification

Abstract

The elevated temperature in operating capacitors speeds up the transportation of charges and causes the flashover to occur easily. Direct fluorination was used to modify the polypropylene film applied as capacitor dielectric, and behaviors of surface charging and flashover voltage at different temperatures were investigated. The surface morphology, functional groups and elemental composition of polypropylene film before and after modification treatment were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray analysis (EDAX), respectively. The surface charging behaviors were analyzed by the surface potential decay (SPD) method at temperature varying from 293 to 353 K. The flashover voltage was analyzed by the view of surface charge and trap characteristics. A thin layer of fluorination which changed the surface state of polypropylene film was formed, which can effectively inhibit the surface charge injection and accumulation at different temperatures. Shallow traps were introduced by the surface molecular structure modification, which was confirmed by the simulation of three-dimensional (3D) electrostatic potential and density of states (DOS). The modification of surface molecular structure, which suppresses the accumulation of surface charge leading to the inhibited distortion of electric field, effectively increased the flashover voltage at different temperatures.