Experimental study on AC loss reduction of HTS coils by use of ferromagnetic disks

Manufacturing techniques suitable for fabricating low AC loss high-temperature superconductor (HTS) coils are necessary to realize high-efficiency power equipment. Usually, the AC magnetization loss of HTS tape conductors is anisotropically dependent on the magnetic field, with a magnetic field perpendicular to the tape surface degrading HTS coil performance. Therefore, decreasing the magnetic field perpendicular to the tape surface is an efficient method of reducing the total AC loss of HTS coils. In a previous study, the possibility of AC loss reduction through the use of ferromagnetic materials was shown numerically, and the total AC loss of HTS coils with and without attached ferromagnetic disks was measured. However, no obvious differences in AC loss were observed because the total AC loss was dominated by mechanical loss. In this study, a low mechanical loss, 30 A, 90 mH HTS coil is fabricated by winding with stainless-steel tape and employing epoxy impregnation. A clear reduction in AC loss is then observed by attaching the ferromagnetic disks.