Regulating Electric Field Distribution and Improving DC Flashover Voltage of Insulator With EP/SiC Gradient Coating

Basin insulators in gas-insulated switchgears are susceptible to surface charge accumulation owing to the non-uniform electric field, leading to localized electric field distortion and a decrement of surface flashover voltage. This significantly affects the stable operation of ultra-high-voltage systems. In this study, an EP/SiC gradient coating is applied to the surface of basin insulator specimen to enhance its electric flashover performance. This work systematically discusses the effects of coating parameters (number, height, thickness and SiC proportion) on the insulator’s surface electric field. The results indicate that coating parameters significantly affect the surface electric field. Ultimately, a three-layer coating with a thickness of 0.5 mm, SiC doping proportions of 15, 12.5, and 10 wt% from the high- to low-voltage electrodes, and coating heights of 1.1, 2.8, and 11.1 mm is selected. Based on the gradient coating design, insulator samples are prepared, and the distribution of their surface trap and surface charge, and surface discharge voltage are measured. It is found that an appropriate SiC proportion facilitates faster surface charge dissipation and FGM designed sample reduces the maximum electric field. Compared with unmodified insulators, the non-uniform coated insulators exhibit a 17.22% reduction in surface charge density, and DC surface flashover voltage enhancements of 21.89% (20%SF6/80%N2) and 23.67%(10%C4F7N/90%CO2). These findings provide a systematic theoretical foundation for the gradient modification of DC basin insulators and offer a rational design method for effectively improving the insulator flashover voltage.