The present paper reports the development of the highly reliable refrigeration system (three types), which is applied for 70 MW class superconducting generators. R & D of the oil-free turbo type: In the turbo type of advanced refrigeration system, a complete oil free 80 K cold compressor was developed. Moreover, the cold compressor driven by a coaxial turbine was developed to enhance the system efficiency and to save space. R&D of the oil-free screw type: In the oil-free screw rotors, taper rotors were planned to maintain a radial clearance between male and female rotors and the casing, to compensate their thermal deformation because of the heat of compression. Moreover, a seal technique was established that used a magnetic fluid and gas seals to prevent lubricating oil from bearings and the timing gear chamber into the rotor housing, under a higher rotational speed of 25,000 rpm. © 2002 Elsevier Science Ltd. All rights reserved.
Asakura, H., Saji, N., Yoshinaga, S., Ishizawa, T., Ikeuchi, M., Yanagi, H., … Kitagawa, K. (2002). Development of a highly reliable helium refrigeration system - R & D of a highly reliable helium refrigeration system (oil-free type). Cryogenics, 42(3–4), 203–208. https://doi.org/10.1016/S0011-2275(02)00030-9