Evaluation of Lapped Tape Electrical Insulation for Gaseous Helium Cooled High Temperature Superconducting Power Cables

The discrepancy between the observed enhancement of the intrinsic dielectric strength of helium gas by mixing hydrogen and the performance of High Temperature Superconducting (HTS) cables in the mixtures at cryogenic temperatures was investigated by systematically varying the insulation system design. Finite element analysis of the electric field enhancements and experimental verification of model cables with varying electrical insulation designs in pure helium and helium-hydrogen mixtures are reported. Triple points formed at the interfaces of the ground layer, the lapped tape insulation, and the gas medium were identified as the culprits. It was concluded that eliminating the micro gaps between the insulating and ground layers and adding stress cones are necessary to achieve high partial discharge inception voltage (PDIV) in HTS cables cooled with a helium gas medium. The results reported and the conclusions drawn pave a path for high power density distribution networks necessary for the electrification of aviation and ships.