Effects of AC disturbance on cowinding HTS coils according to the inserted materials

Alternating field causes energy loss due to induced back electromotive force (EMF) to high-temperature superconducting (HTS) coils in the superconducting electric machines. Therefore, a method of reducing the effects of the alternating fields on the HTS coils in superconducting machines according to the winding insulation conditions has been investigated. In addition, the HTS coils cowound with turn-to-turn inserted materials to control the time constant has been proposed. The charge-discharge delay can be determined with the time constant, also the time constant is related to the radial directional resistance of the no-insulation coil. The variation of the radial resistance would affect the reduction effect of ac disturbance on the no-insulation coil. Therefore, trade-off between the reduction effect of the alternating disturbance and charge-discharge delay could be considered. In this paper, we evaluated the effects of alternating magnetic fields on the HTS coils according to the varying radial resistance caused by cowinding method with metal tapes in liquid nitrogen. Four types of the HTS coils are: 1) no-insulation coil, 2) cowound coil with copper tape, 3) cowound coil with stainless steel tape and 4) insulation coil which have different radial resistance respectively. The experimental result shows that the co-winding method can be applicable in the superconducting electric machines.