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 SF6/N2 and C4F7N/CO2 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 C4F7N/CO2 mixture than in SF6/N2 mixture. The surface charge density decreases with the increase of gas pressure, and the charge density in C4F7N/CO2 mixture is slightly higher than that in SF6/N2 mixture. The surface charge distribution in C4F7N/CO2 mixture is more irregular than in SF6/N2 mixture, and the regularity increases with the rise of gas pressure and decreases with the rise of applied voltage.