Liquid Nitrogen (LN2) is used as the cryogen and is part of the dielectric insulation system in most high temperature superconducting (HTS) power cables. However, in electric propulsion systems for transportation, using LN2 is not feasible due to asphyxiation concerns in the event of a leak in a confined space. Gaseous helium (GHe) has been proposed as an alternate cryogen to relieve this asphyxiation concern. GHe has benefits such as a wider operating temperature range and versatility for a centralized cryogenic cooling system for multiple devices which could potentially reduce the overall weight of the superconducting system. The drawback is that GHe has a lower dielectric strength compared to LN2, which limits its use to low-medium voltage applications. A hybrid cryogen HTS cable was proposed using LN2 as the dielectric media and GHe as the cryogen of an HTS cable to solve the limitations and issues associated with each cryogen and explained in this paper. A 1-m prototype cable that used LN2 as the cryogen and dielectric was fabricated and dielectric breakdown measurements were performed on it to establish a baseline on what to be expected from the hybrid cryogen HTS cable.

Large electric transportation systems such as electric aircraft and electric ships have been designed with multiple high temperature superconducting (HTS) power cables as part of superconducting power distribution network, and a good electric insulation for the power cables is a critical design requirement needed to be considered. This is because terminations in HTS cable represent a location of significant electrical and thermal stresses and needs to be addressed to reduce the substantial heat load that might be introduced into the cryogenic system. The use of a warm dielectric termination is seen as a potential solution to reduce the electrical standoffs required as part of the design and allow for a high-power dense termination design. A warm dielectric termination design using commercially off-the-shelf ceramic breaks as electrical breaks is explored and withstand and partial discharge measurements are performed to determine the viability of the design concept.