Cryogenic testing of 100-m superconducting power transmission test facility

The final tests of the cryogenic system designed to cool the test facility for 100 m superconducting, power transmission cables have been completed. Since the completion of previously reported tests in a three-expander configuration, the system was modified to incorporate a fourth turbine placed remotely from the refrigerator at the far end of the load. In this configuration the load, consisting of the superconducting cables and their containment vessel, becomes a long (> 100 m) counterflow heat exchanger with internal heat generation. The results of these tests are presented with discussion of the operation, equipment performance, and possible areas for improvement. The actual operation of the system was quite smooth and required a minimum of manpower. The newly installed automatic control systems on the turbines performed perfectly although, except for speed control, they had little to do. The computers used to monitor the temperatures, pressures, and flows worked very well. It was noted that this system with its large mass of supercritical helium was extremely stable against short-term large perturbations, all of which are damped and disappear into this heat sink. No system or thermo-acoustic oscillations were observed and those temperature oscillations which were observed due to a change inmore » operating mode, etc., were obviously quickly damped and disappeared.« less