R&D of high reliability refrigeration system for superconducting generators

Super-GM (Engineering Research Association for Superconductive Generation Equipment and Materials) is grappling with R&D for 70 MW class superconducting generator (Model Machine), refrigeration system, superconducting wires for the generator and other applications, as the first step of the research for applying superconductivity technology to electric power apparatuses. Main problems to be solved in the development of the refrigeration system are to enhance the reliability of major components such as compressors and turbo expanders in addition to thorough removal of oil and impurity gas generated from lubricating oil. Main results obtained are that an oil injection type screw compressor has been found to have a reliability corresponding to more than 70,000 hours in terms of MTBF, and a technique to remove impurities to less than 0.1 ppm developed. Furthermore, oil free screw and turbo compressors promise even higher reliability.