Energy loss study for AC excited superconducting coils

本课题为交流励磁超导线圈的能量损耗研究。超导带绕成线圈的使用是高温超导最有效应用的共同特点。然而，这些磁带对垂直于磁带横截面宽度的时变磁场产生的交流损耗高度敏感。这就对交流线圈的设计施加了一些限制，特别是电机的定子绕组。在实际应用中，我们有交流和直流磁场的组合作用在线圈上，而线圈又有直流或交流传输电流。此外，磁场不是均匀的，甚至不是正弦的，电流也是如此。磁场和输运电流在大背景场或电流存在下的小叠加纹波效应是高温超导电机和发电机非常关注的问题，但尚未得到详细研究。我们强调在特定系统中研究线圈在实际磁场和电流配置下的重要性。在这种情况下，实验测量可能比建模更可靠。我们将使用液氮蒸发和电子技术对高温超导线圈进行实验研究，这些结果将用于验证描述线圈的数值模型。我们相信这种方法的结合将为实际用户系统提供可靠的线圈性能表征系统。作为这项工作的输出，我们将有：(i)磁带的相关参数和整体线圈属性之间的互连的工作知识；（ii）确定线圈能量损失的可靠实验技术；（iii）验证线圈模型作为设计和建造大型电机的数据源。

The project is for energy loss study for AC excited superconducting coils.The use of superconducting tape wound into coils is a common feature of the most effective applications of HTS. However, these tapes are highly sensitive to AC losses produced by time-varying magnetic field perpendicular to the cross-sectional width of the tape. This imposes some constraints upon the design of ac coils particularly for stator windings in electrical machines. In real applications, we have a combination of AC and DC magnetic fields acting on a coil that, in turn, has DC or AC transport current. Moreover, magnetic fields are not uniform and not even sinusoidal and the same is true for currents. This effect of small superimposed ripples of magnetic field and transport current in the presence of large background field or current is a great concern for HTS motors and generators and it has not been studied in detail. We stress the importance of studying coils in real configurations of magnetic fields and currents for particular systems. In this case, experimental measurements are likely to be more reliable than modelling.We will study HTS coils experimentally using both liquid nitrogen boil-off and electrical techniques and these results will be used to validate numerical models describing coils. We believe this combination of methods will deliver a reliable system for characterising the performance of coils for practical user systems.As the output of this work, we will have: (i) a working knowledge of the interconnection between relevant parameters of the tape and the overall coil properties; (ii) a reliable experimental technique for determining the energy loss in coils; (iii) validated coil models as a data source for the design and construction of large-scale electrical machines.