Electric Field Regulation of DC-GIS Spacer by Surface Conductivity Gradient Coatings Under Variable Temperature Gradients

The bulk conductivity of the direct current (dc)-gas-insulated switchgear (GIS) spacer increases with temperature, resulting in varying electric field (E-field) distributions across different temperature gradients. In this study, spacers coated with surface conductivity functionally graded materials ( $\sigma $ -SFGMs) are designed and fabricated. The $\sigma $ -SFGM coatings maintain constant conductivity but feature different thickness profiles on recessed and bulging surfaces. Specifically, the coating thickness exhibits a U-shaped distribution on the bulging surface and a decreasing distribution on the recessed surface. Compared to the uniform sample, the maximum E-field strength of the $\sigma $ -SFGM spacer is reduced by 46.2% and 40.2% at ambient temperature and under a temperature difference of 40 ° C, respectively. The dc flashover voltages of the $\sigma $ -SFGM spacer show an improvement ranging from 10.5% to 20.8% under variable temperature gradients.