Calculation on Current Distributions among Transposed Three- and Six-parallel Conductors in Superconducting Armature Coils for Superconducting Synchronous Motors

The armature coil of the superconducting synchronous motor for electric aircraft requires a current of 1,000 A or more. However, a single superconducting tape at liquid nitrogen temperatures is insufficient for this operating current. Therefore, the armature coil should be composed of multi-strand parallel conductors. If the coil is constructed from parallel conductors, the inductance balance between the parallel conductors will be collapsed, so the current distributions will be non-uniform. As a solution for this issue, the uniform current distribution can be achieved by the transposition technique that changes the order in which tapes are stacked. Our previous research has developed the transposition method for the 2n-strand parallel conductors (n = 1, 2, 3, and so on). However, some of the superconducting synchronous motors are actually designed using a number of parallel conductors other than 2n. This study focused on the three- and the six-strand parallel conductors. We analytically clarified the unique transposition configuration for the three-strand parallel conductors that achieves uniform current distribution, and the transposition configuration for the six-strand parallel conductors by combining the transposition configuration for the three- and two-strand parallel conductors. As a result, the current distribution ratio became less than ±5% when the number of turns of the double pancake coil was a multiple of six by applying the transposition.