Abstract
Recently, a tri-axial cable composed of three concentric phases has been intensively developed, because it has advantages such as reduced high-temperature superconducting (HTS) tape, small leakage field and small heat loss as compared with three single-phase cables. However, there is an inherent imbalance in the three-phase currents in tri-axial cables due to the differences in the radii of the three-phase current layers. The imbalance of the currents causes additional loss and a large leakage field in the cable, and deteriorates the electric power quality. We have already showed that it is possible to obtain a balanced three-phase currents by adjusting all of the twist pitches. To verify the theory, we have fabricated a 1-m-long tri-axial HTS cable and tested it. The balanced three-phase voltages of the cable were measured by imposing an AC transport current with a frequency in the range of 50-500 Hz at 77 K. From this test, we demonstrated that the balanced three-phase currents can be realized by adjusting all of the twist pitches.
