Studies on current distributions and AC losses of High Tc Superconducting conductors used for electrical power machines and devices

为了阐明高温超导线圈的交流损耗特性，我们开发了一种新的测量系统，使我们能够定量地评估暴露于外部交流磁场下高温超导磁带中的电流分布。在我们的测量中，电流分布是通过位于胶带周围的一组拾取线圈测量的自场分布的结果间接发现的。为了提高外磁场作用下的测量精度，采用补偿线圈对拾取线圈信号中的外磁场分量进行抵消。我们使用测试导体验证了该测量系统的精度和灵敏度，发现我们的系统足够精确，可以测量HTS磁带的电流分布。利用该系统，我们详细地测量了在外加磁场作用下银合金多丝包覆的Bi-2223带中的电流分布特性。实测结果表明了该测量系统的实用性。此外，我们还开发了一种测量方法来评估螺线管线圈形状的电流分布。在这种方法中，我们通过在线圈表面周围使用拾取线圈来测量场分布。我们用一个测试线圈验证了该测量系统的精度和灵敏度，发现我们的方法足以测量高温超导线圈的电流分布。利用该方法，对Bi-2223螺线管线圈的电流分布进行了初步测量。测量结果表明，I-ITS线圈中的电流分布并不均匀。电流分布的幅值和频率依赖性较弱。

In order to elucidate the AC loss characteristics of HTS coils, we developed a new measurement system that enabled us to quantitatively evaluate the current distributions in HTS tapes exposed to an external AC magnetic field. In our measurement the current distributions are indirectly found from the results of the self-field distributions measured by an array of pickup coils located around the tape.For improved measurement accuracy under the external magnetic field, a compensation coil was used to cancel the coniponent of the external magnetic field from the signal of pickup coil.We confirmed the accuracy and the sensitivity of this measurement system by using a test conductor, and found that our system was accurate enough to measure the current distributions for the HTS tapes. Using this system, we minutely measured the characteristics of the current distributions in multifilamentary Ag alloy sheathed Bi-2223 tape exposed to an external magnetic field.Measured results showed the practicality of our measurement system.Further, we also developed a measurement method to evaluate the current distributions of a solenoidal coil shape.In this method, we measured the field distributions by using pickup coils located 'around the coil surface. We confirmed the accuracy and the sensitivity of this measurement system by using a test coil, and found that our method was accurate enough to measure the current distributions for the HTS coils. By using our method, the preliminary measurement of the current distributions of a Bi-2223 solenoidal coil was performed. Measured results showed that the current distributions in the I-ITS coil were not uniform.The amplitude and frequency dependencies of the current distributions were observed slightly.