Electrical Tree Growth Characteristics of Epoxy Resin under Combined Effects of Low Temperature and Mechanical Stress

Due to the uneven thermal expansion, thermal stress will be generated at the epoxy bushing in GIS cable termination at low temperature, which may be the main reason for insulation failures. However, researches on the degradation process of epoxy under low temperature superimposed thermal stress is scarce. Therefore, this paper aims to investigate the effects of combined low temperature and mechanical stress on the electrical tree characteristics of epoxy. The platform with controllable temperature and mechanical stress is built to test the electrical tree characteristics from the range of room temperature to ‐40 °C and 0 to 30 MPa. The partial discharge, the growth rate and the cumulative damage characteristics of electrical tree are analyzed. It is found that, at low temperature, the toughness of the epoxy resin decreases, and the thermal stress will greatly reduce the surface energy for crack expansion, resulting in the electrical tree shows a feature of filamentary electromechanical breakdown. The deterioration process of epoxy shows a rapid expansion like crack, and the time to breakdown is greatly reduced. Making the electrical tree presents filamentary electro-mechanical breakdown, eventually leading to the breakdown failure of cable termination.