Cryostat vacuum thermal considerations for HTS power transmission cable systems

The use of high-temperature superconducting (HTS) materials for power transmission cable applications is being realized in several utility demonstration projects. Both room-temperature and cold-dielectric cable systems rely on a vacuum cryostat to keep the ambient thermal loads at a minimum. For long-term installations, operating 30 years or longer, the thermal-insulating vacuum pressure may increase in sections of a long length installation. Even if only a small section of the total length of the HTS cable system is affected, localized heating of the cable may reduce the performance of the HTS cable system. A study is presented of the effects of degraded vacuum levels on the operation of HTS cables for different cryogenic thermal insulation systems.