Epoxy Bushing Breakdown Caused by Uneven Thermal Stress in Cable Termination Under Extremely Cold Weather

In this article, a simulation model of 110 kV cable termination based on COMSOL is established, and electro thermal coupling characteristics at different temperatures are simulated. Obvious uneven thermal stress distribution inside the termination is found at temperatures below $- 20~^{\circ }$ C, due to the difference in thermal expansion coefficients between different materials. Stress concentration at the interface between the metal insert and epoxy resin occurs. Tensile stress along the direction of the electric field in the epoxy increases as the temperature decreases, with a maximum value of 66.7 MPa at $- 40~^{\circ }$ C. The electrical treeing and partial discharge (PD) characteristics are investigated in epoxy resin under various thermal stress conditions. It is found that the electrical tree growth is accelerated under low temperatures, which is attributed to the increase in thermal stress and decrease in the toughness of the epoxy bushing. In such circumstances, the electrical tree growth rate is greatly increased, frequently accompanied by a sudden enhancement in PDs and expansion of deterioration channels, which is proved by a phase field model considering the induced thermal stress.