Simulation study on breakdown evolution of tri-post insulator under electric-mechanical-thermal stresses in 1100 kV HVAC-GIL

Abstract

Due to the presence of electric-mechanical-thermal stress, inner cracks and reduced adhesion strength between metal and epoxy can cause the breakdown of a tri-post insulator in the GIL. In this study, a simulation model was developed to investigate the breakdown evolution of the tri-post insulator subjected to combined electrical, mechanical, and thermal stresses. Various temperature gradients and defect positions were considered, along with the application of an AC voltage of 1100 kV. At room temperature, the tri-post insulator undergoes considerable residual internal stress of up to 35 MPa, primarily concentrated around the conductor and inserts, thereby accelerating the breakdown process. The temperature gradient across the insulator post has a notable impact on breakdown characteristics. Specifically, when the conductor temperature increases from 25 °C to 125 °C, the breakdown time of the insulator with the HV side defect increases by 83.1 %, while the damaged area reduces by 41.9 %. This is attributed to the release of the residual internal stress and the reduction of strain energy. When the defect is located at the GND side, the breakdown channel forms more rapidly, and the impact of temperature gradient on the breakdown process is weakened, because the tensile stress is high but the temperature is low around the GND inserts. The outcomes of this study are hoped to enhance understanding and enable the prediction of insulation breakdown behaviors in practical projects.