Testing of a prototype high temperature superconducting current lead

A prototype helium vapor-cooled current lead employing a ceramic high temperature superconductor was designed and tested. The lead which has a nominal current rating of 1 kA consists of copper and a ceramic superconductor sections and was designed for operation in 300 K/4.2 K temperature range. A single monolithic bismuth-based superconductor (BSCCO-2212) was used in the superconductor section. Extensive testing of the current lead was carried out to determine its performance such as steady-state boil-off rates at various operating currents, transient characteristics of the lead under zero-flow condition, and the effects of repetitive current cycling. At 1000 A operating current, the lead was found to require a steady-state helium vapor cooling flow rate equivalent to a liquid helium boil-off rate of 0.98 l/hr, an over 40% reduction from the conventional all copper lead. Cut-off of helium vapor flow for 230 seconds poses no overheating problem and no performance degradation was observed after 1000 cycles of repetitive current cycling between 0 and 1000 A. A very low contact joint resistance, 17 n/spl Omega/ for carrying 1000 A, was also observed at the 4.2 K lead terminal.<>