Optimization Design of Grounding Sealing Structure of 220kV GIS Basin Insulator

The surface flashover of basin insulator is an important factor causing SF6 gas insulated switchgear (GIS) equipment failure. The main cause of surface flashover is the local electric field distortion caused by unreasonable structural design, defects, foreign matters and surface charge accumulation. Thus, the optimization of insulator electric field structure design is very important. Generally, the permissible value of electric field strength focuses on the shielding electrode surface and insulator surface in the structure design. Previous studies have not paid enough attention to the electric field distribution at the grounding terminal. This paper studies the influence of two methods on the surface electric field strength distribution of grounding terminal, one is setting a gas gap on the contact surface between basin insulator and shell flange, and the other one is inserting a shielding ring into insulator near grounding flange. The results show that changing the height of gas gap, radial distance and radius of shielding ring could effectively optimize the electric field distribution, but the optimization effect of shielding ring is better than that of gas gap. The shielding ring could suppress the maximum electric field strength at grounding area from 29.36kV/mm to 6.71kV/mm, while the gas gap could only suppress it to 14.24kV/mm. For 220kV GIS basin insulator, the height is recomanded as 2mm when using the method of setting gas gap, and a radial distance of 170mm and a radius of 3mm is recommended for shielding ring. Therefore, it is suggested to choose the grounding shielding ring to optimize the electric field distribution of 220kV GIS basin insulator.