Sub‐Cooled Nitrogen Cryostat for 66 kV/750A Superconducting Fault Current Limiter Magnet

As a part of the Super‐conductive AC Equipment (Super‐ACE) project presently being performed, an AC magnet for a fault current limiter (FCL) is being developed. The goal of the project is the development of 66 kV/750A High Tc Superconducting (HTS) FCL magnet, which is composed of six HTS coils operating at around 65 K. This paper describes a design of a sub‐cooled nitrogen cryostat for the FCL magnet. Three sets of Gifford‐McMahon (GM) cryocooler were used for cooling liquid nitrogen in the cryostat. Experimental results of cooling down and temperature stability during current flowing tests of the magnet were reported in this paper. The sub‐cooled nitrogen of 65 K was successfully obtained in the vessel with 2.6 m3 in volume. And the temperature uniformity was observed in both of the cooling down process and the coil energizing process.