Cryostat for 66 kV/750 A high-Tc superconducting fault current limiter magnet

This paper describes a design and experimental results of a sub-cooled nitrogen cryostat for 66 kV/750 A high T_c superconducting (HTS) fault current limiter (FCL) magnet. Six unit coils were designed to be operated in sub-cooled nitrogen at around 65 K. Three sets of Gifford-McMahon (GM) cryocooler were used for cooling liquid nitrogen in the cryostat. Experimental results of cooling down and temperature uniformity in the vessel at current flowing tests of the magnet were reported. A design for high voltage insulation in a liquid nitrogen vessel and an experimental result of overvoltage test of the cryostat were also reported. This work is as a part of the Super-conductive AC Equipment (Super-ACE) project presently being performed, an AC magnet for a FCL is being developed (Yazawa et al., (2001), Yazawa et al., (2002) and Sakai et al. (2000)).