| Co-Investigator(Kenkyū-buntansha) |
FUKUNAGA Tetsuya Gifu National College of Technology, Department of Electronic Control Engineering, Associate Professor, 電子制御工学科, 助教授 (50249794)
INADA Ryoji Toyohashi University of Technology, Department of Electrical and Electronic Engineering, Research Associate, 工学部, 助手 (30345954)
NAKAMURA Yuichi Toyohashi University of Technology, Department of Electrical and Electronic Engineering, Associate Professor, 工学部, 助教授 (40259940)
|
|---|
| Research Abstract |
1. Reduction in AC transport losses for Ag-sheathed Bi2223 tapes by introduction of resistive barriers
We succeeded in reducing AC transport losses in self-Held at 77 K for the Ag-sheathed Bi2223 tapes, fabricated by a four-roller machine to make a rectangular deformation and also by the introduction of Bi2201 sheets as resistive barriers in an arrangement parallel to the wide surface of tapes. Although the main contribution to the losses comes from the hysteresis loss of the superconductor, the loss value for the tape is reduced by approximately 70% compared with the value for the multifilamentary tapes prepared by a standard powder-in-process without the resistive barriers. However, the critical current densities (J_c) are much lower than that for the standard tape without the resistive barriers because of the some reaction of Bi2201 sheets with Bi2223 filaments during the heat treatments. To solve this problem, we introduced the mixture of Ca_2CuO_3 and 30 wt.% Bi2212 powders as resi
… More
stive barriers. The Ca_2CuO_3 powder is has little side effect on the J_c values of the Bi2223 tapes. The experimental results indicate that the transport losses were reduced by introduction of the resistive barrier in an arrangement parallel to the wide surface of tapes, while the J_c value was almost not deteriorated compared with the tape without barriers.
2. Reduction in AC transport losses for Ag-sheathed Bi2223 tapes by changing the filament arrangements
Significant reduction in AC transport losses in self-field at 77 K has been achieved to Ag-sheathed Bi2223 multifilamentary tapes, which were fabricated by a rectangular deformation process using a two-axial rolling (TAR). This achievement is not made by the introduction of resistive barriers but the improvements of filament arrangements in the tapes. Despite the main contribution to the losses comes from the hysteresis loss of the superconductor, the transport losses for the tape samples are decreased by 50-70% particularly in high current range near the critical current (I_c) compared with the value for the Bi2223 multifilamentary tapes prepared by standard PIT process. Numerical calculations suggest that the reduction of transport losses mainly ascribed to the division of field-free core with neither currents nor electromagnetic field in the sectioned filament groups near the tape edge under AC current transmission.
3. Evaluation of AC transport losses for cable conductors composed of superconductor tape strands
We investigated the AC transport losses in self-field on cable conductor composed of Ag-sheathed Bi2223 tape strands with different cross sectional geometry. The loss values of the conductors strongly depend on the filament arrangements in the tape strands and the arrangement of tape strands in the conductors. This can be explained the calculation result of current distributions and loss density distributions, varying with the geometrical factor of conductors. We also calculated the inter-layer magnetic flux under the condition of I_o=I_c for the magnetic field distributions in multi-layer cables as a parameter of spiral length. Although the value of inter-layer flux becomes zero in an adjusted spiral length, the flux between tape center and edges shows non-zero values, indicating that the transport losses for the cables with adjusted spiral length are mainly generated in the edge part of tape strands. Therefore, there is much room for further improvement in actual magnetic field structure to suppress the loss generation in the cables. Less
|
