Surface Charge Accumulation of Zoning-Coating GIS Insulator in Different Gas Atmospheres

Zoning-coating that deposits various functional coating materials on different surface regions of insulators installed in gas-insulated switchgear (GIS) has been recognized as a promising method to suppress surface charge accumulation. This article reports on the surface charge accumulation on the zoning-coating insulator in various gas atmospheres. A downsized disk insulator and a coaxial electrode system are designed to investigate the charge behavior under dc voltage of - 10, - 20, and - 30 kV. The insulator is placed in the enclosed chamber, which is filled with 0.1, 0.2 and 0.3 mPa SF _{6} /N _{2} and C _{4} F _{7} N/CO _{2} mixture. After being charged by HVDC, the surface charge is measured by a kelvin-type probe, and the accumulation mechanism as well as the regularity of charge distribution are demonstrated. The results indicate that homo-charges are accumulated on the nonplanar region and hetero-charges are mainly accumulated on the planar region of the insulator in the mixtures. With the increase of the applied voltage, the charge density rises and it is higher in C _{4} F _{7} N/CO _{2} mixture than in SF _{6} /N _{2} mixture. The surface charge density decreases with the increase of gas pressure, and the charge density in C _{4} F _{7} N/CO _{2} mixture is slightly higher than that in SF