Effects of Low Temperature on the Thermal Stress Distribution of GIS Cable Termination

In recent years, there are many GIS termination failures occur at low temperature. The breakdown of epoxy bushing is one of the main features. It is inferred that the operation condition of epoxy bushing has changed at low temperature, but its evolution process is unclear. In order to explore the evolution process, simulation model of a 110kV GIS cable terminal based on COMSOL is established, and the thermal stress distribution in epoxy bushing at different temperatures is simulated. It is found that, with temperature decreases, the difference in thermal expansion coefficients of the materials results in stress concentration at the metal insert/epoxy interface, as well as increased tensile stress along the direction of the electric field in the epoxy bushing. At -40 °C, the thermal stress is concentrated at the metal insert, where defects are easy to occur. Moreover, due to the assembly constraints of GIS terminations, there is a transition from compression stress to tensile stress in the epoxy bushing at low temperatures. This transition further distorts the stress distribution, resulting in defects and further leading to insulation deterioration.