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Description
The superconducting synchronous generator is one of the breakthrough elements for direct-drive wind turbine because it is light and small. Normally the superconducting one has copper armature windings in the stator and superconducting field windings on the rotor. The electrical frequency of the output voltage of the direct-drive generator is very low, so the total length of the armature windings should be long for the rated line voltage. The high resistance of the armature can make large copper losses, comparing with the conventional generators with a gear box.
One of the solutions for the large copper losses could be the fully superconducting generators. But the high magnetic fields from the superconducting field windings on the rotor also make high perpendicular magnetic fields on the superconducting tapes in the armature windings. We have proposed a fully superconducting synchronous generator with dual field windings. It could immensely decrease the circumferential component of the magnetic field from the field windings at the armature windings.
In this paper, we conceptually designed 4 types of superconducting synchronous generators. The first one is normal superconducting one with only superconducting field windings. The second one is the fully superconducting one with conventional structure, which has superconducting armature windings in the stator and superconducting field windings on the rotor. The third one is the one with dual superconducting field windings and superconducting armature windings between them. The last one is the same as the third one except the structure of the armature. If the concentrated armature windings are superconducting ones with cryostats, then they cannot be installed within the span of 2 poles. So, we adopted 3 phases windings within 4 poles system. It makes more AC losses but can be manufactured really. We compared the AC losses of the 4 superconducting generators and analyzed their electrical characteristics.
