Development of a highly reliable helium refrigeration system-R&D of a highly reliable helium refrigeration system (conventional type) : Superconducting generator in Japan

The present paper reports the development of the refrigeration system that is applied to 70 MW class superconducting generators. The main subject in developing the refrigeration system for verification tests on site was to develop technology for removing impurities in helium gas, which largely affects its reliability, and to further improve the reliability and efficiency of its main components as screw compressors, turbo expanders, and a low temperature adsorber. Thus this paper deals with its planning and performance testing as well as automatic control in different modes of operation (such as cool-down, steady-state and heat run) and also the reliability analysis. It was verified that the developed refrigeration system demonstrated a higher reliability of 14,637 h mean time between failure, larger than 10,000 h. The total operation time at steady state has reached 9320 h with no failures in the entire testing period.