三相同一軸超電導ケーブルの平衡分布特性実験

抄録

High Temperature Superconducting (HTS) cables have been studied because of low loss and compactness, compared with conventional copper cables. Three-phase cables are usually composed of three single-phase coaxial cables. Recently, a tri-axial cable, composed of three concentric phases, has been intensively developed, because it has advantages such as reduced amount of HTS tapes, small leakage fields and small heat loss in leak, compared with the three single-phase cables. However, there is an inherent imbalance in the three-phase currents in the tri-axial cable due to the differences in radii of the three-phase current layers. The imbalance of the currents causes additional loss and large leakage field in the cable, and deteriorates the electric power quality. Therefore, we propose a new model which is a tri-axial cable composed of two longitudinal sections with different twist pitches to obtain the solutions of the balanced three-phase currents and homogeneous current distribution in each phase of the tri-axial cable. We derive general equation satisfying both the balanced three-phase currents and homogeneous current distribution, as functions of winding pitches, and finally apply it to the simplest cable. We fabricated and tested a 1m long HTS cable in order to verify the proposed theory that satisfies the balanced distribution. The results demonstrate the theory is right. We also investigate the current distributions along the long tri-axial cable considering the capacitances between the layers in the tri-axial cable.