66 kV/1 kA high-Tc superconducting fault current limiter magnet

One of the items included in the Super-conductive AC Equipment (Super-ACE) project, being performed from 2000 to 2004, is development of a 66 kV/1 kA class high-Tc superconducting (HTS) fault current limiter (FCL) magnet. This research focuses on fundamental technical items essential for a 66 kV class fault current limiter, that is, high current-capacity, high voltage-insulation, and sub-cooled nitrogen cooling. This paper describes the design of the magnet and the test results obtained. The magnet mainly consists of a vacuum vessel, a nitrogen bath, a pair of current leads, cryocoolers, and six sets of coils wound with Bi2223 tape. The rated current of the magnet is 750 Ap. The insulation voltage of the magnet is of the 66 kV class. In the final year of the project, all six sets of the coils are set connected in the cryostat and evaluation tests have been implemented. In the cooling test, sub-cooled nitrogen of 65 K was obtained, with homogenous temperature distribution in the cryogen. The rated current of 750 Ap was successfully obtained for both direct and alternating current tests. In addition, the magnet passed the simultaneous current and voltage application test. Finally, the dielectric test results showed that the magnet satisfied the insulation for 66 kV apparatus in the Japanese Electrotechnical Committee Standard (JEC) standard.