Clarification of electromagnetic properties of high temperature superconducting tapes used for superconducting power machines cooled by

液氮冷却超导发电机的实现一直受到关注。然而，大量的交流损耗产生的高温超导（HTS）磁带和退化的临界电流的磁带由于正面定向磁场施加到磁带已严重障碍的实现。前者来自于电磁现象，即整条暗条就像一根粗的单暗条，而传输电流在外部暗条中局部流动。从理论上分析了Bi-2223带材中电流分布与交流损耗的关系，并讨论了减小交流损耗的方法。由于以前的损耗测量方法不足以满足本研究的目的，提出了一种新的系统来测量磁带在真实的应用条件下的损耗，即，同时扫描的运输电流和外部横向磁场，开发。我们称这个系统为坡印廷矢量法。该方法的有效性和实用性在短直Bi-2223带材上得到了成功的验证。然后，它被改进，能够测量的单层，螺线管线圈缠绕的高温超导带材的损失。在液氮中详细测量了用Bi-2223带材绕制的双饼型线圈的交流损耗。其结果是，高温超导带材的电磁性能澄清了广泛的频率范围内的真实的条件下施加到磁带。此外，本文还从理论和实验上研究了一种新的线圈绕制方法，以获得良好的性能，这对实现液氮冷却的超导动力机是有益的。

Realization of superconducting power machines cooled with liquid nitrogen has been concerned. However, a large amount of ac losses produced in high temperature superconducting (HTS) tapes and degradation of critical currents of the tapes due to the face-on orientated magnetic field applied in to the tapes have been serious barrier to the realization. The former comes from the electromagnetic phenomena that whole filaments act as a thick mono-filament, and transport currents locally flow in the outer filament. The latter is the characteristic property of the Bi-2223 tape that is the most hopeful candidate as a real tape for power applications.Theoretical analyses were carried out on the relation between current distributions and ac losses in Bi-2223 tapes, and an adequate method to reduce the loss was discussed. Because the previous loss-measuring method is not adequate with purpose of this study, a new system to measure losses of the tape under the real application conditions, i.e., simultaneous sweep of transport currents and external transverse magnetic fields, was developed. We call this system the 'Poynting vector method.' The validity and usefulness of it were successfully demonstrated for the short and straight Bi-2223 tape. Then it was improved to be able to measure losses of the single-layered, solenoidal coil wound with HTS tapes. The ac loss produced in the double pan-cake type coil wound with Bi-2223 tapes was also measured in detail in liquid nitrogen. As the result, the electromagnetic properties of the HTS tapes were clarified for the wide range of frequencies of the real condition applied to the tape. Moreover, a new coil winding method to get excellent performances was studied theoretically and experimentally, and showed this is useful for realization of the superconducting power machines cooled with liquid nitrogen.