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In order to limit fault current from an accident in power grid, many research groups have developed resistive superconducting fault current limiters (SFCLs) with a bifilar solenoid and a bifilar pancake types. Comparing with a bifilar solenoid type, a bifilar pancake type has the advantage of its volume, but it has problems such as recovery and insulation of SFCLs. To eliminate the drawback of these two types, in this paper, a new type of coil that is an oval-shaped SFCL, have proposed. This type consists of inner and outer layers which are connected in parallel. A small-scale sample coil was fabricated and experiments for both a short circuit test and recovery characteristic test were performed in liquid nitrogen. Experimental results were compared with two types of coils; the bifilar solenoid and bifilar pancake coil. Consequently, we confirmed the feasibility of an oval-shaped type.

To design a large scale superconducting fault current limiter (SFCL) for power grids, a single long-length YBCO coated conductor (CC) wire is preferred. However this single YBCO CC wire can cause a problem of unequal voltage distribution between the parts on the long wire at quench by the faults. Inhomogeneous critical current of the YBCO CCs in the SFCL is a possibility. Furthermore, sub-cooled liquid nitrogen (LN2) condition is usually used to increase current capacity of the SFCL. However, this sub-cooled condition can worsen the inhomogeneity between the YBCO CCs. Therefore, it is important to understand the relation between the unequal voltage distribution and the inhomogeneous critical currents in the single long length YBCO CC. In this paper, experiments with the same single YBCO CC wire were conducted in various temperature conditions, LN2 and sub-cooled LN2 . In both experiments, the critical currents and voltage distributions generated by faults at short-circuit tests were measured. It was observed that the inhomogeneous condition impacts on the unequal voltage distribution.

This study deals with a conceptual design for a high temperature superconductor (HTS) coil fabricated with YBCO wire in a prototype HTS-electromagnet (HTS-EM) model for the electromagnetic suspension (EMS)-based Maglev. Because the size of the HTS coil and the power it consumes during operation are very critical factors in designing the HTS-EM, we focused on the number of coil turns and the operating conditions needed to generate the required magneto-motive force (MMF) effectively. The winding geometry of the sample HTS coil with the largest Ic value was selected for use in this study. To determine the operating condition corresponding to the number of coil turns, we produced the operating profile for the load current of DC current source and the Ic value of HTS coil. From the profile, the optimal number of coil turns to minimize the operating power is determined to be in the range of 1200 to 1400 turns. And the HTS coil should be operated with the current of 37 to 43 A at the cooling temperature of 73 to 76 K.

A resistive superconducting fault current limiter (SFCL) has two drawbacks-relatively higher impedance and longer recovery time than the requirement of the electric power system. A parallel-connected bypass reactor (BPR) can be a solution to both problems. As a stage of proof-of-concept, an SFCL comprised of an YBCO S/N switch and a Bi2223-BPR had been presented in the former paper. Although the previous one has shorter recovery time, the generated impedance after a fault was too low to satisfy the requirement of the power system. To apply the SFCL into the power system, the SFCL has proper impedance during the fault. Therefore, we proposed bypass reactors to achieve higher impedance than the previous one in this paper. The SFCLs with a bypass reactor were fabricated and short-circuit test with the SFCLs were conducted. The test results were compared in point of current limiting characteristics and recovery. This research would be applied to a conceptual design of BPR.