Helium Gas Cooled and Insulated Superconducting Coaxial Dipole Cable for Electric Transport

The design concept, electric field distribution models, fabrication, and experimental characterization of a coaxial superconducting gas-insulated dipole line [dipole superconducting gas-insulated line (SGIL)] are discussed. Two different insulating spacers were explored to study the effect of the permittivity mismatch between the insulator material and the gas medium on the maximum electric field strength. Results of the experiments conducted at 77 and 300 K under gas pressures up to 2 MPa are discussed. The dipole SGIL design developed showed promising results in breakdown strength. It was found that compact design coupled with permittivity mismatches causes high electric field concentrations that lead to corona discharge activity below the target operating voltage. Potential design solutions for the SGIL to address the high electric field stress at the triple points that cause localized corona discharge activity in the gaseous cryogen are discussed. Future SGIL designs must address the large permittivity mismatch between gaseous helium (GHe) and the insulator spacers to minimize the electric field stresses. Design optimizations need to consider the tradeoffs between the power density requirements and the operating voltage of superconducting dipole cables on electric aircraft and ships.