Inductance ratio of flat type fault current limiter with high Tc superconducting disks

We have proposed a flat type of the superconducting fault current limiter (FCL) which is a modified version of a magnetic shielding type of the fault current limiter. The flat type FCL basically consists of a pancake coil and doughnut-like form high Tc superconductor (HTS) disk, each of which works as a primary winding and a secondary one-turn winding, respectively. In order to clarify the static current-limiting performance of the flat type FCL, the magnetic field analyses were carried out for the small modules of the FCL. The inductance values of the FCL in the superconducting state and normal-conducting state of the HTS disk, L-0 and L-limit, were calculated and their ratio L-limit/L-0 was estimated. The high performance of the FCL must be brought about by the large inductance ratio. It was confirmed that lower L-0 was derived by sandwiching the pancake primary winding with two HTS disks and by using thin spacer between them, and larger L-limit is produced by connecting the built-up pancake primary windings in series. This suggests that a full-scale FCL may be designed and produced by building up many modules whose pancake winding is sandwiched with the HTS disks.