Electric Field Relaxation of HVDC GIL Spacer With Surface Conductivity Gradient Material (σ-SFGM) Using Electrospinning Technology

This study discusses the application of the surface conductivity gradient materials ( $\sigma $ -SFGMs) for relaxing the electric field concentration around the epoxy-based spacer in high-voltage direct current gas-insulated transmission lines (HVDC GIL). Based on the ±500-kV HVDC GIL model, the iterative method is applied to optimize the thickness gradients of the $\sigma $ -SFGM layers on convex and concave surfaces of the basin-type spacer. It is proven that the $\sigma $ -SFGM layers can significantly suppress the electric field distortion around the high voltage electrode by increasing the homopolar charges and reducing the heteropolar charges on both spacer surfaces. To fabricate the $\sigma $ -SFGM spacer, a thickness-graded layer of high conductivity is formed on a truncated cone-type spacer by electrospinning. Experimental test results show that the application of $\sigma $ -SFGM exhibits a promoting effect of about 11.5% on the dc flashover voltage of the cone-type spacer. The $\sigma $ -SFGM spacer can withstand over ten thermal-shock cycles, indicating that the $\sigma $ -SFGM layer fabricated by electrospinning is more reliable than that fabricated by dip coating.