Development and test of an HTS induction generator

A superconducting induction generator (SIG) with two rotors is presented. The two rotors are called inner rotor and outer rotor, respectively. The inner rotor is located inside of the outer rotor and free to rotate. The inner rotor consists of an HTS winding and iron yoke. The outer rotor is made of a copper shell. It is driven by a mechanical power source. The outer rotor rotates at higher angular velocity than that of the rotating magnetic field generated by the stator current while the inner rotor rotates at the same angular velocity with the field made by the stator current. The HTS winding produces enough magnetic field to compensate the reactive armature current, which improves the power factor of the generator close to unity. A 1.5 kVA SIG was manufactured and tested to realize the concepts of the HTS free inner rotor. Good electrical characteristics were shown by experiment. Due to the simplified structure of the inner rotor cooled with LN₂, the SIG presented in this paper can be realized as a medium-sized generator, as well as a large one and used as a supplemental power source connected to a conventional power system