Experimental Study on the Damage Mechanism of High-Frequency Partial Discharge of Multilayer PI Films under Repetitive Electrical Stress

Partial discharge (PD)is an important factor leading to insulation degradation and failure of solid-state transformer (SST). To accurately evaluate the effect of voltage frequency on partial discharge characteristics under high-frequency sinusoidal waveforms, a high-frequency PD test system is designed. Considering the structural characteristics of the turn-to-turn insulation of SST, a three-layer polyimide (PI) laminated insulation model was designed, and PD tests on the samples at different frequencies were carried out using the pulse current method. This paper focuses specifically on the lifetime and discharge characteristics of the specimen, including maximum and average discharge amplitude, total number of discharges, and number of discharges per cycle or per second. Based on these data, the correlation law between voltage frequency and insulation lifetime was obtained, and the microstructure of damaged PI was also obtained, and the damage mechanism of PI at high-frequency was investigated. The results of the study provide a theoretical basis for the application of PI in electrical insulation.