Feasibility Analysis of ɛ-Graded Spacer for HVAC Superconducting GHe Insulated Pipelines

The gaseous helium (GHe) circulation has become an option as cryogen in superconducting cables with the large demands for higher power density, but the traditional insulation design limits the voltage ratings of GHe-cooled cables. This paper designed a superconducting GHe insulated pipeline (S-GIL) that referred to the insulation design of gas insulated lines (GIL). In order to uniform the E-field distribution and reduce the occurrence of flashover in HVAC S-GIL, the ?-graded spacer with spatially nonuniform permittivity distribution has been extensively researched. The iterative method was employed to optimize the permittivity profile of cone-type spacers. As the iterative times increases, the E-field distribution along the spacer surface becomes increasingly uniform, but the E-field concentration appears in the spacer bottom. After six iterations, the E-field distribution and permittivity distribution have converged to the optimum. Compared with the ɛ-uniform spacer, the ɛ-graded spacer has slightly higher leakage current that increases with the iterative times in the previous four iterations and then keeps unchanged basically.