Effect of trap density/depth on space charge transport and electric field distribution in polypropylene films

Metallized polypropylene film capacitors are subjected to the combined action of strong direct current electric field and high temperature thermal field for a long time in the service process, which leads to the accumulation of space charge in the medium of polypropylene film, resulting in local electrical field distortion, material aging and even breakdown phenomenon, and ultimately lead to the degradation of electrical insulation performance and failure. Based on this, the space charge and electric field distribution and charge transport mechanism in polypropylene film were simulated by using the bipolar charge transport model, and the charge transport characteristics under different electric fields were analyzed by parameterization. The simulation results show that when the external field is 100 kV/mm, the trap parameters become larger, and the injected homo polar charges are captured by a large number of traps within 1μm near the interface of the film, forming a thin charge layer, and there is no space charge in the film. When the applied electric field is high (200 kV/mm), the trap density/depth become larger to inhibit the space charge injection and conduction in the polypropylene film. It indicates that at room temperature, when the external electric field is low, the space charge distribution is mainly regulated by trap parameters. When applied electric field is high, the electric field plays a dominant role in the process of charge transport, and the charge conduction ability becomes stronger, and the regulation effect of trap parameters will be weakened.