Kazutomi Miyoshi

Uniform current distribution conductor of HTS power cable with variable tape-winding pitches

In the multilayer conductor, the inner layers have higher impedance than the outer layers. As a result, the current concentrates in the outer layers. Our early study showed that its AC losses were reduced to one-tenth by making the current of each layer uniform. From such a point of view, a trial to realize the uniform current distribution was made by adjusting the winding pitches of high-temperature superconducting (HTS) tapes layer by layer. A 1 m long conductor was fabricated, where the inner layer had longer winding pitch than the outer layer. Experimental results showed that the currents flowing in individual layers were almost the same and that this conductor had lower AC losses than the nonuniform current distribution conductor.

50-m long HTS conductor for power cable

The long conductor fabrication is one of key technologies to realize the High-T/sub c/ superconducting power cable. A 50-m long conductor was fabricated by helically winding the High-T/sub c/ superconducting tape onto a former with a winding machine. The conductor consisted of ten layers of Ag-sheathed Bi-2223 tape which had a high critical current density of 10,000 A/cm/sup 2/ (at 77 K). AC losses and layer-by-layer current distribution were measured, feeding AC current of 100 to 2,000 Arms to the conductor cooled by LN2. The results showed that most of the current flowed in the outer layers where the impedance was low, and that AC losses were remarkably reduced by making the current distribution uniform.

Enhancement of Critical Current Densities by the Prebending Strain at Room Temperature for Nb3Sn Wires

The influence of a repeated bending strain at room temperature on the critical current densitiy of bronze route Nb3Sn wires was investigated. We found that the critical current Ic is significantly increased by applying a repeated bending load (pre-bending treatment) at room temperature. The maximum enhancement of Ic was approximately twice at 16 T for CuNb-reinforced Nb3Sn wires by a 0.5% prebending strain and the critical current density Jc became about 528 A/mm2 at 4.2 K and 16 T. A comparison of the stress dependent Ic values obtained before and after applying prebending treatments for CuNb/Nb3Sn wires indicates that not only the stress dependence of Ic but also the maximum Ic at the axial strain-free state are improved. The improvement of the stress dependent Ic is in agreement with the prediction made based on the calculation using the uniaxial stress/strain distribution model. Moreover, the increase in the maximum Ic may be related to the release of stress/strain states along the radial direction through prebending treatments.

Development of high-strength Nb/sub 3/Sn conductor

Nb/sub 3/Sn superconducting wires reinforced with Cu-Ni/Nb-Ti composite have been developed. Nb/sub 3/Sn wires reinforced with Cu-Ni/Nb-Ti showed good mechanical and electrical properties. In this study, 1.2 mm-diameter (Nb, Ti)/sub 3/Sn superconducting wire of 13 km in length reinforced with Cu-Ni/Nb-Ti was successfully fabricated. Moreover, the effect of copper fraction to the strength of the wire was studied.

66 kV-2 kA peak load test of high-Tc superconducting model cable

Abstract The superconducting power transmission cable is one of the most feasible applications for oxide superconductors. One case of introducing superconducting cables into power cable systems is as a replacement type in cable ducts, so that it is necessary to develop a compact superconducting cable which can be installed in existing ducts of diameter 150 mm. For this purpose, long-length Bi-2223 phase multifilamentary silver-sheathed wires with high critical current densities, such as over 7000 A cm −2 , have been developed and the effects of mechanical strain were investigated. As the next step, we have designed a 66 kV-2 kA superconducting cable of outer diameter 124 mm and developed a 5 m long model cable having a flexible conductor assembled by winding the foregoing wires in layers around a former. Furthermore, two different types of termination have been developed for a simultaneous current and voltage withstand test. As a result, we have been able to successfully perform a 66 kV-2 kA withstand test on an oxide superconducting power cable. The AC loss of the cable measured by the four-probe method was about 35 W m −1 . Moreover, generation of partial discharge in the cable was not observed at the test voltage.

Large T/sub c/, B/sub c2/ and I/sub c/ enhancement effect due to the prebending treatment for bronze route Nb/sub 3/Sn wires

In order to develop a react-and-wind (R&W) processed Nb/sub 3/Sn superconducting magnet, we investigated the influence on the superconducting properties due to the prebending treatment. Since a reacted Nb/sub 3/Sn superconducting wire reveals a very sensitive response from stress and strain, we focus on the prebending treatment which is repeatedly applied to the Nb/sub 3/Sn wire through several pulleys in the R&W coil winding process. We found that the prebending treatment doubles the I/sub c/ value at 20 T and 4.2 K for bronze route Nb/sub 3/Sn wires. This I/sub c/ enhancement effect comes from the T/sub c/ and B/sub c2/ enhancement. It turned out that T/sub c/ increases from 17.4 to 17.9 K and as a result B/sub c2/ also increases from 23.7 to 25.2 T at 4.5 K for bronze route multifilamentary Nb/sub 3/Sn wires prebent at bending strain of 1.0% and at 5 repeated times.

Design and production of high-Tc superconducting power transmission cable

The design and production of high temperature superconducting (HTS) power transmission cables was studied. In the production of HTS cable, difficulties are mainly caused by the poor mechanical properties of HTS tapes, because critical currents of the HTS tapes deteriorate due to the strains applied during cable production and usage. Therefore, two basic characteristics of HTS cables were experimentally analyzed to improve HTS cable design and production: (1) the mechanical-electrical properties of the HTS cable; and (2) the properties of electrical insulation. The analysis results indicate that the most important technology is the control of the strains applied to the tape in the cable. Based on the results, the design of the HTS cable was then improved, and the machines at Furukawa Electric fabricated a three-phase prototype HTS cable of 30 m in length. The results of the performance test of the cable demonstrated the proposed design and the production method are appropriate.

Winding techniques for conduction cooled LTS pulse coils for 100 kJ class UPS-SMES as a protection from momentary voltage drops

In order to develop the 100 kJ class UPS-SMES as a protection from momentary voltage drops, design of the conduction cooled LTS pulse coil was carried out and special winding machine has been developed. Such coil is required to simultaneously attain low AC loss and high stability and the distributions of temperature in the coil are sensitively controlled. For this purpose, an aluminum stabilized conductor with circular cross-section composed of a Cu stabilized NbTi Rutherford cable was used as the winding conductor, and in the winding process the twist angle of the conductor around its axis was controlled to adjust the direction of edge-on orientation to the Rutherford cable to direction of local transverse magnetic fields applied to the conductor in winding area of the coil. The developed winding machine is used for this winding method. As a result, conduction cooled LTS pulse coil can be expected to operate stably in adequate temperature margin.

The Nitrogen Boil-Off Method for Measuring AC Losses in HTS Coils

We have developed a novel apparatus for applying a nitrogen boil-off method as a mean of making calorimetric measurements and allowing for simple measuring and evaluating of AC losses in HTS coils at liquid nitrogen temperature. With the ability to measure AC loss generated in superconductors directly, this method produces more reliable data than that obtained by general, electro-magnetic measurements. A sensitivity of about 0.1 W was achieved by improving sensitivity in measuring gas evaporation via the following three steps: (1) use of nonmetallic vessel, heat-insulated housing in which the sample is located; (2) optimization for sample vessel thickness and tube size; and (3) stabilization of evaporating gas emitted by the heater. It is widely expected that the proposed apparatus may be used for individual measurement of the magnetization loss and the transport current loss in HTS coils, as well as their total losses, in addition to the AC loss in irregularly shaped samples

Development of an Immunochromatographic Assay Kit Using Fluorescent Silica Nanoparticles for Rapid Diagnosis of Acanthamoeba Keratitis

ABSTRACT We developed an immunochromatographic assay kit that uses fluorescent silica nanoparticles bound to anti-Acanthamoeba antibodies (fluorescent immunochromatographic assay [FICGA]) and evaluated its efficacy for the detection of Acanthamoeba and diagnosis of Acanthamoeba keratitis (AK). The sensitivity of the FICGA kit was evaluated using samples of Acanthamoeba trophozoites and cysts diluted to various concentrations. A conventional immunochromatographic assay kit with latex labels (LICGA) was also evaluated to determine its sensitivity in detecting Acanthamoeba trophozoites. To check for cross-reactivity, the FICGA was performed by using samples of other common causative pathogens of infectious keratitis, such as Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, and Candida albicans. Corneal scrapings from patients with suspected AK were tested with the FICGA kit to detect the presence of Acanthamoeba, and the results were compared with those of real-time PCR. The FICGA kit detected organisms at concentrations as low as 5 trophozoites or 40 cysts per sample. There were no cross-reactivities with other pathogens. The FICGA was approximately 20 times more sensitive than the LICGA for the detection of Acanthamoeba trophozoites. The FICGA kit yielded positive results for all 10 patients, which corresponded well with the real-time PCR results. The FICGA kit demonstrated high sensitivity for the detection of Acanthamoeba and may be useful for the diagnosis of AK.