Testing of a Liquid Nitrogen Cooled 5-meter, 3000 A Tri-Axial High Temperature Superconducting Cable System

The tri-axial HTS cable design uses three concentric superconducting layers for the phase conductors separated by a cold dielectric material. It offers an efficient HTS cable configuration by reducing the amount of superconductor needed, and placing all three phases in a single cryostat. Ultera and ORNL tested a 5-meter long tri-axial HTS cable and terminations designed to operate at 3 kA ac and 13.2 kV. Test results, including the thermal loads on the system, will be reported. An existing liquid nitrogen skid that circulates subcooled liquid nitrogen through the cable was initially designed for the heat loads on single phase cables at lower current ratings. The refrigeration needed for the 3 kA tri-axial cable configuration made it necessary to upgrade the nitrogen system to increase the cooling capacity. A description of the upgrades and performance of the system is provided.