Experimental study on insulation properties of epoxy casting resins using high-frequency square waveforms

Although the transmission efficiency of high-voltage high-frequency transformers improve as the rated frequency increases, their insulation performance is severely affected. Through a high-frequency experimental platform, insulation tests on epoxy casting resins are carried out using high-frequency square wave signals. Subsequently, the variations of discharge inception and flashover voltages with frequency were analyzed based on the Secondary Electron Emission Avalanche (SEEA) model. The breakdown characteristics of epoxy casting resins are studied based on the Weibull distribution analysis and inverse power function model. Finally, an insulation test standard is proposed based on the breakdown characteristics of epoxy casting resins for dry-type HV-HF transformers. The results show that, the flashover voltages are noticeably reduced with the increase of frequency while the discharge inception is hardly affected by frequency. Moreover, the drop in breakdown voltages and insulation lifetime shortening are caused by high-frequency thermal effects. Also, the applied voltages of epoxy resin cast dry-type HV-HF transformers are recommended to be 3.27 to 3.49 times their maximum operating voltages in 1 min applied withstand tests. The applied voltages of the induced withstand tests should be 2.20 to 2.52 times their maximum operating voltages.