AC LOSS REDUCTION OF A 6.6KV SUPERCONDUCTING FAULT CURRENT LIMITER

The authors have been investigating a 6.6kV superconducting fault curr ent limiter (SCFCL) for use in power distribution system. For practica l application, heat load at 4.2 K must be reduced to a level which can be compensated by a small refrigerator. This paper describes AC loss reduction of a SCFCL coil, which is comprised of a conductor and junct ions. The conductor is a cable of double-twisted multi-filament NbTi s trands in a high-resistivity CuNi matrix. The filament diameter in str ands and the filament twist pitch were reduced for AC loss reduction. Current junctions made of copper generate eddy current loss because an alternating magnetic field is applied on them by the conductor. It wa s confirmed experimentally that cylindrical-shaped junctions effective ly reduced the loss. A total coil loss of 0.8 W at 1 kA has been achie ved, which value is sufficiently low for the development of a closed c ryostat of superconducting fault current limiter compensated by a smal l refrigerator.