スパイラルループ法による高温超電導テープ線材の交流通電損失測定の有効性の検証

抄録

High temperature superconducting (HTS) wires are expected to be applicable to electric power apparatuses such as transmission cables and transformers operating at liquid nitrogen temperature. Reduction of AC losses at power frequency is one of the most important and critical issues for these AC apparatuses to be feasible. The AC losses of the HTS wires are caused by the transport current and external magnetic fields. The former one, the AC losses from the current power supply to the wire, is usually called as the AC transport current losses. Many works have been done to measure the AC transport current losses of HTS tapes with no external field or with DC external field. Usually, the AC transport current losses of HTS tapes are measured by measuring voltage across the voltage taps attached on the tape. It has been pointed out that the voltage measurement loop should include the magnetic flux over a distance much larger than the tape width to correctly measure the AC losses of the tape. However, this wide voltage loop needs wide space and the linkage flux of the voltage leads loop may include loss components caused by other parts of the tapes than the part between the voltage taps when multiple tapes are assembled. In our previous work, we have proposed a new measurement method to properly measure AC transport current losses of HTS tapes which are subjected to external magnetic field generated by adjacent tapes in a conductor assembled from multiple tapes or generated by a winding of a coil. In our measurement arrangement, the leads from voltage taps on the tape are wound on a cylindrical surface enclosing the tape. This method can save space for voltage leads and avoid spurious loss component caused by the magnetic field of the other tape. The basic principle of our method has been presented and verified. In the paper, the previously presented results on the measurement method using the spiral voltage lead loop are summarized. The additional experimental and numerical data are completed to examine the problems of application to the practical loss measurement. The validity and effectiveness of the spiral lead loop arrangement are systematically demonstrated.