Estimation on LN2 Level and Condensation of Insulation Gas in HTS Power Cable Termination

The terminations of high-temperature superconducting (HTS) power cables help supply current between the cryogenic HTS power cable and the room temperature power system while maintaining electrical insulation. This involves a cryogenic section with circulating liquid nitrogen (LN2) for cooling the HTS power cable and temperature gradient section with level interface formed by thermal equilibrium and an ambient section with current leads and insulation gases such as nitrogen and sulfur hexafluoride (SF6). The level of LN2 varies depending on the structure of the termination and the operation conditions, and this may further affect the temperature of the ambient section that is installed at the upper end of the cryogenic section. As the level of LN2 increases, the temperature of the insulation gas decreases and condenses, resulting in a significant decrease in the dielectric strength. Therefore, it is crucial to estimate the level of LN2 while designing the termination for HTS power cable. In this study, the LN2 level of the termination was estimated according to heat load and the operating conditions to avoid dielectric breakdown of insulation gas are proposed using a commercial thermo-fluid network analysis tool, SINDA/FLUINT.