Cryogenic benefits of a 70 Ka high temperature superconductor current lead

A 70 kA high temperature superconductor current lead (HTS-CL) was developed, built partly together with industry and tested at this current level at the Forschungszentrum Karlsruhe in 2004 and 2005. The HTS-CL consists of three main parts, the cold end for the connection to the bus bar at 4.5 K, the HTS part operating in the temperature range from 4.5 K to 65 K and a copper heat exchanger (HEX) in the temperature range from 65 K to room temperature. The lead was designed for a He inlet temperature to the HEX of 50 K but was also tested with a He inlet temperature of 4.5 K and 80 K. In a further step, a test with direct LN2 cooling with and without sub-atmospheric pressure operation was successfully performed up to a current of 75 kA. The operation at a temperature level above 4.5 K reduces the required power consumption of the cryoplant by a factor of 1.3 in case of 80 K He inlet temperature and up to a factor of 3.0 for 50 K He and direct LN2 cooling. Details of these operation modes including the advantages of the cryogenic system will be outlined.