Search

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 o and L limit , were calculated and their ratio L limit/L o was estimated. The high performance of the FCL must be brought about by the large inductance ratio. It was confirmed that lower L o was derived by sandwiching the pancake primary winding with two HTS disks and by using thin spacer between them, and larger L limit a 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.

To cope with the increase in electric power demand and provide an alternative technology to conventional electric power transmission cables, it is hoped that high-temperature superconducting (HTS) cables would be developed. A protective layer has been adopted in HTS cables as a countermeasure against short-circuit current. This protective layer is established in parallel, and is connected to the HTS cable at both ends of the cable. However, this protective layer is not effective for quenching the local degradation of HTS wire in the overload-current domain, which slightly exceeds the rated current in real cables with lengths of several km. Therefore, of concern is the possibility in which the generation of bubbles via an exothermic reaction affecting the electrical insulation, when local quenching occurs. In a 500-m HTS power cable, we applied an external magnetic field to a part of the HTS cable, and the superconducting cable was locally quenched. Quench propagation features and electrical insulation characteristics based on this enforced quenching were determined experimentally.

The 500 m high temperature superconducting (HTS) cable developed by the Super-ACE (R&D of fundamental technologies for superconducting ac power equipment) project included copper layers as protection against short circuit current. The design policy was that liquid nitrogen would not vaporize when it was exposed to the short circuit current of 31.5 kA with 0.5 s. In order to establish the design policy, we have made nine 10 m samples with the same construction of the 500 m HTS cable and set three cables in the liquid nitrogen vessel. Both of balanced fault of three-line grounding (3LG) and unbalanced faults of one line grounding (1LG) and two-line grounding (2LG) have been set and fault currents have been applied to the HTS cables. After each fault, the critical current has been measured and we have confirmed no variation of Ic before and after each fault. HTS cables have not been damaged mechanically by the fault current of 31.5 kA with 0.5 s.

Sr/sub 1-x/Nd/sub x/CuO/sub y/ thin films were grown by both RF magnetron sputtering and laser ablation on SrTiO/sub 3/