Michiharu Ichikawa

Magnetic characteristics of a high-T/sub c/ superconducting cylinder for magnetic shielding type superconducting fault current limiter

The superconducting fault current limiter (SCFCL) is expected to be the first application of high-T/sub C/ superconductors (HTSs) in power systems. To develop a magnetic shielding type superconducting fault current limiter, we have carried out some fundamental experiments concerning the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into a Bi(2223) cylinder are shown. AC magnetic field is applied to the sample by a primary winding (copper coil) excited by AC triangular- and sinusoidal-waveform currents in the frequency range of 0.1 Hz to 100 Hz. We also developed a finite element method (FEM) computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage-current (E-J) characteristic are compared with experiments.

Superconducting Sr0.875Nd0.125CuO2-δ thin films

Single‐phase Sr0.875Nd0.125CuO2−δ (SNCO) thin films of the ‘‘infinite‐layer’’ structure were fabricated by a pulsed‐laser deposition technique. The films directly grown on SrTiO3 (100) substrates had superconductivity onset temperatures around 20 K, but zero resistances were not observed down to 4.2 K. The a‐axis length of the film samples did not exceed the values reported for bulk SNCO samples. It was demonstrated that, when deposited onto a Pr2CuO4 buffer layer formed on a SrTiO3 substrate, the a‐axis length of the thin film SNCO increased up to 0.395 nm which was comparable to that for bulk SNCO. The film sample exhibited a zero resistance state below 7 K. Thermoelectric‐power measurements indicated that the carrier density for the film deposited on a Pr2CuO4 buffer layer was higher than that for the film fabricated without a buffer layer.

Microstructure of the infinite-layer structural Sr1−xCuO2−δ thin films

Abstract The microstructure of Sr1−xCuO2−δ thin films with x=0.00 and 0.10 was investigated by X-ray diffraction and transmission electron microscopy. Both films were single phase of the “infinite-layer” structure. However, in both films certain defects were observed, being extended along the ac-plane. The defect was found to be intergrown Sr2CuO3 crystallites between the infinite-layer structure Sr1−xCuO2−δ crystals. It was suspected that one of the reasons why superconductivity was not observed in these films was that Sr-deficient ab-planes were not observed in these film samples.

Growth of Sr1−xNdxCuOy thin films by RF-magnetron sputtering and their crystallographic properties

Abstract Sr 1- x Nd x CuO y thin films are grown by a RF-magnetron sputtering technique. The film with x =0 has an “infinite-layer ” structure whose lattice constants are: a =0.390 nm and c =0.347 nm . The resistivity of this film shows a semiconductive behavior. The infinite-layer structure does not form when x exceeds 0.05. For compositions with x less than 0.08, the films contain a multiple number of phases. When x is larger than 0.1, the films have a phase of the Sr 14 Cu 24 O 41 structure. The b -axis of the (Sr, Nd) 14 Cu 24 O 41 crystalline is perpendicular to the substrate surface and the a - and c -axes are aligned in plane with the crystal axes parallel to those of the (1 0 0) SrTiO 3 substrate.

Inductive type fault current limiter with Bi-2223 thick film on a MgO cylinder

Fault current limiters for electric power systems have been researched. We have studied a inductive type superconducting fault current limiter. The limiter has superconducting cylinder as active element. We developed a high Jc Bi-2223 thick film on a MgO cylinder. Jc was over 5800 A/cm/sup 2/ at 77 K. We made a inductive type superconducting fault current limiter with the Bi-2223 thick film cylinder and investigated limiting performances.

Inductive type fault current limiter using Bi-2223 thick film on MgO cylinder with Bi-2212 buffer Layer

We have been developing an inductive type superconducting fault current limiter with a superconducting cylinder. For practical use, a high critical current density (Jc) is needed in a large diameter. To achieve these items, we have developed a Bi-2223 thick film on a MgO substrate, with a Bi-2212 buffer layer. This cylinder was 450 mm in diameter and 120 mm in length. We describe the superconductive characteristics of this cylinder, and the limiting properties of the fault current limiter using these cylinders.

Dielectric properties of 500 m long HTS power cable

The 500-m high temperature superconducting (HTS) cable has been constructed in the Yokosuka area, CRIEPI, by CRIEPI, The Furukawa Electric Co. and Super-GM. Its design voltage is 77 kV and the thickness of the electrical insulation layer should be 8 mm made of semi-synthetic paper (polypropylene laminated paper). During cooling, the capacitance and dielectric loss tangent were measured periodically. After cooling, which means that the HTS cable was fully filled with liquid nitrogen (LN/sub 2/), the initial voltage withstand test was carried out. This paper describes the design method of the electrical insulation layer including determination of the testing voltage and the result of the initial voltage withstand test, and the permittivity calculated from the capacitance, and dielectric loss tangent.

Thermomechanical characteristics of 500-m HTS power cable

A 500-m single-core high temperature superconducting (HTS) cable system has been constructed and tested in Yokosuka area, CRIEPI, by CRIEPI, The Furukawa Electric and Super-GM. In the actual power grid, the HTS cable distance extends sometimes several km. And has to be cooled down from about room temperature to liquid nitrogen temperature. As, the HTS cable is contracted and suffers mechanical stress. In the case of the long distance HTS cable, it remains a major development issue. The HTS cable constructed in this test system has an offset section for absorbing the thermal contraction. In this paper, we describe the validity of that offset section and the thermomechanical characteristics on the cooldown and warm-up test. The offset functioned successfully as designed.

Demonstration and verification tests of 500 m long HTS power cable

A high-temperature superconducting (HTS) power transmission cable is considered as one of the next-generation power transmission technologies. The introduction of HTS cables into the actual power grid requires a long-distance cooling tube, due to the location of the cooling stations at intervals of several kilometers along the cable length. Therefore, it is essential to understand the flow property of the liquid nitrogen as a coolant for the HTS cable, the current flow properties, electrical insulation characteristics, thermal insulation properties and mechanical behavior for the HTS cable taking into account its long length. This paper provides a brief summary of the HTS cable test system with a length of 500 m constructed in the Yokosuka area of CRIEPI.

Detection of deformation and displacement of transformer winding by frequency response analysis

Frequency response analysis (FRA) is a diagnosis method to detect troubles of a transformer, which are deformation and displacement of winging and so, by detecting change of a transfer function compared with that measured when the transformer is normal. However, identification of the troubles detected by FRA is not clear. In this paper, firstly, identification method of the troubles is investigated using a model transformer. Secondly, the proposed identification method is applied to identify a trouble of a real transformer caused by short-circuit tests.