Fabrication and test of a superconducting generator with ring windings

Application of superconductivity to electric machines can bring about wider alternatives to the fundamental configuration comparing with the conventional counterparts. As well known, multi-phase AC electric machines can be easily realized with ring-winding configuration. Because a multi-phase machine is effective to obtain smooth DC voltage with low ripples, it would be attractive as a generator for the exclusive use in HVDC power transmission systems. Besides, the ring-winding configuration is suitable for high-voltage design. Armature windings do not cross each other as in the conventional windings. In order to confirm the fundamental characteristics, a multi-phase generator with superconducting ring windings was manufactured and examined. The armature is composed of nine coils, i.e., the number of phases is nine. It has also a superconducting field winding. The machine does not have an iron core except for the outer magnetic shield made of laminated iron. Well-balanced nine phase output voltages with phase angle differences of 40 degree were obtained. When full-wave rectification circuits were connected to each armature winding directly, a smooth DC voltage and a current with sufficiently low ripple factor were obtained without any smoothing circuits and transformer banks.