The Influence of Variable Frequency Voltage and Temperature on Breakdown of Epoxy Insulation Square Wave

The breakdown characteristics and mechanism of solid insulation under high frequency non sinusoidal, high dv/dt, multi harmonic and high temperature conditions is one of the key issues in the design and application of high power density solid-state transformers. In this paper, the breakdown characteristics of epoxy resin film for solid-state transformer under variable frequency voltage and temperature are studied. Firstly, a high frequency and high temperature breakdown test platform was built to test the breakdown voltage and current of epoxy samples under different conditions. Then, the effects of frequency, temperature and dv/dt on the high frequency non sinusoidal breakdown of epoxy insulation were studied. The experimental results show that under the bipolar square wave, the breakdown strength (E_b) of epoxy resin film decreases with the increase of frequency, and the rate of breakdown field strength decreases with the increase of frequency; With the increase of temperature, the breakdown field strength of epoxy resin increases first and then decreases; Next, the influence of different dv/dt on the breakdown field strength of epoxy samples was analyzed. It was found that high dv/dt reduced the breakdown field strength of epoxy, and the dv/dt of 80kV/μs E_b was 7.74% lower than that of 30kV/μs E_b. Finally, combined with the free volume breakdown theory, the reasons for the change of the breakdown performance of epoxy insulation were analyzed. This paper provides theoretical and experimental basis for insulation design and reliability of high-power solid-state transformer.