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

实现液氮制冷的超导电机一直是人们关注的问题。然而，高温超导(HTS)带材中产生的大量交流损耗和带材表面取向磁场引起的带材临界电流退化一直是高温超导带材实现的严重障碍。前者来自于整个细丝充当粗单细丝，传输电流局部地在外细丝中流动的电磁现象。从理论上分析了Bi2223带材的电流分布与交流损耗之间的关系，并讨论了降低损耗的有效方法。由于以往的损耗测量方法不能满足本研究的目的，因此研制了一种新的测量系统，用于测量实际应用条件下的带材损耗，即传输电流和外加横向磁场的同时扫描。我们称这一系统为“坡印亭向量法”。并以短而直的Bi2223带材为例，验证了该方法的有效性和实用性。然后对它进行了改进，使其能够测量缠绕有高温超导带材的单层螺线管线圈的损耗。文中还详细测量了用Bi2223带材缠绕的双盘饼型线圈在液氮中产生的交流损耗。结果表明，高温超导带材在较宽的实际工作频率范围内具有较好的电磁性能。此外，本文还从理论和实验上研究了一种性能优良的新型绕组方法，为实现液氮冷却超导电机奠定了基础。

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.