Space Charge and Trap Distributions and Charge Dynamic Migration Characteristics in Polypropylene under Strong Electric Field

Abstract

Space charge accumulation in the polypropylene will accelerate the aging of the material and lead to the degradation of its insulation performance. In the work, space charge distribution, current conduction characteristics, thermally stimulated depolarization current (TSDC) and surface potential decay (SPD) characteristics of polypropylene (PP) under strong electric field are measured and analyzed, and the bulk trap and surface trap parameters are extracted. Further, the charge transport model of PP is established to study the charge dynamic transport physical processes and characteristics under strong electric field. The experimental results show that the charge accumulation amount in PP under the action of negative polarity electric field is higher than that of positive polarity electric field, about one order of magnitude. and the corresponding trap energy levels are 0.84 eV and 0.81 eV, which both belong to deep traps. There are two obvious charge density peaks on the PP surface, which are 2.60 × 1020·eV−1·m−3 and 3.66 × 1020·eV−1·m−3, respectively, and the corresponding surface trap energy levels are 0.86 eV and 0.97 eV. The simulation results show that with the extension of the applied voltage time, the injected charges by the electrode gradually migrate to the bulk of the material and eventually the positive and negative charges are offset at the middle position. The local electric field caused by the accumulation of interfacial charges will weaken the original electric field, while the local electric field caused by the accumulation of the bulk charges will strengthen the original electric field, resulting in the distortion of the internal electric field.