Numerical Simulation of Partial Discharge in Air-Polyimide Insulation under High Frequency Electrical Stress

Partial discharge is one of the main reasons leading to premature failure of high-frequency power equipment insulation. However, there is still a lack of complete understanding on the development rules of partial discharge process. In order to inquiry the evolution of partial discharge, a set of simplified but effective reactions was used to describe all reactions of air discharge. On this basis, a non-equilibrium plasma model of air-polyimide partial discharge under the sphere-plate electrode structure was presented with fluid dynamic theory. This model solved the continuity equations for charged species and the electron energy balance equation, coupled with Poisson's equation. Then, the temporal and spatial evolution laws of the charged particle density, surface charge density and discharge current during the discharge process were obtained. Accordingly, the influence of voltage amplitude and frequency on partial discharge was also studied and revealed. The results indicate that the process of partial discharge is mainly controlled by the change of air gap voltage, and the superposition effect of electric field and external electric field caused by charge accumulation on the dielectric surface is significant. At the moment of discharge, electrons, positive and negative ions are mainly concentrated near the cathode sheath which leads to serious distortion of the air gap electric field. The number of discharges in a single cycle is positively correlated with the voltage amplitude and negatively correlated with the voltage frequency.