Mechanical Stress Distribution in Epoxy Encapsulation of 500kV Prefabricated HVDC Cable Joint under Extreme Cold Weather

Integral prefabricated joint is widely used for the HVDC cable connection. As an important part, the epoxy encapsulation plays a role in supporting the main body of the cable accessories and maintaining the interface pressure. HVDC cable accessories operating in high latitude regions usually face an extreme low temperature environment of- 10
^o
C to- 30
^o
C or even lower. The maximum temperature of internal metal conductor can reach 90
^o
C, but the thermal expansion coefficient of epoxy materials is significantly higher than that of metal materials. Under the condition of temperature gradient, a stress concentration is formed at the epoxy-metal interface, which leads to cracking at the epoxy-metal interface, thus causing discharge breakdown failure, which seriously affects the safe operation of the power grid. In this paper, the full-sized model of a 500kV HVDC cable prefabricated joint was built in the COMSOL Multiphysics. The influence of extreme cold conditions on the mechanical stress distribution and cracking risk of epoxy encapsulation structural parts of DC cable joints are simulated and studied, and the coupling characteristics of temperature gradient and mechanical stress distribution of epoxy encapsulation structural parts under extreme temperature rise are analyzed. Results show that the cold weather can generate huge stress concentration without load current, which can be close to the mechanical strength of epoxy resin composite. While this situation can be relieved with load current.