Electrical Tree Degradation in Epoxy Resin under Bipolar Square Wave Voltage with High Frequency

Electrical tree induced by divergent electric field is detrimental to the safe operation of devices, especially the apparatus like solid state transformers used in smart grids where the epoxy resin is commonly employed as an insulating material that generally has to withstander harsh operating conditions involving bipolar square wave voltage with high frequency. In this study, we investigated the morphology, growing properties, fractal dimension, accumulated damage, initiation proportion and breakdown characteristics of electrical tree in epoxy resin under high-frequency bipolar square wave voltages. The electrical tree grew rapidly with treeing time after a period of slow propagation. The rate of growth, number of branches, fractal dimension, initiation proportion and accumulated damage all increased with voltage magnitude and duty cycle increasing. At 10 kV and frequencies higher than 20 kHz, bubble-like trees appeared due to the decomposition of epoxy resin before breakdown occurred. The intensive partial discharge, proved by luminescence, contributed to the propagation of electrical tree. This research provides valuable insights into the characteristics of electrical trees in epoxy resin under high-frequency bipolar square wave voltages.