Study on surface discharge of polyimide at high frequency

Power electronic transformer (PET) can realize the flexible transformation of AC and DC voltage, which has a wide application prospect in the fields of renewable distributed power grid and large AC-DC power grid flexible interconnection. PET is mainly gas-solid insulation, while surface discharge is one of the main causes of gas-solid insulation failure. Polyimide, the insulation material of power electronic transformer, bears high frequency voltage for a long time, and its insulation is more prone to failure than power frequency voltage. In order to study the surface discharge characteristics of air polyimide interface at high frequency, experiments based on needle plate electrode model were carried out, and a simulation model based on fluid dynamics was built. By comparing the experimental results with the simulation results, the development law of surface discharge process is explored, the causes of negative half wave and positive half wave forming polarity effect are obtained, and the reasons of different polarity effects in power frequency and high frequency are analyzed.