System considerations for airborne, high power superconducting generators

The design of rotating superconducting field windings in high power generators is greatly influenced by system considerations. Experience with two superconducting generators designed to produce 5 and 20 Megawatts has resulted in a number of design restrictions. The design restrictions imposed by system considerations have not prevented low weight and high voltage power generation capability. The application of multifilament Nb3Sn has permitted a large thermal margin to be designed into the rotating field winding. This margin permits the field winding to remain superconducting under severe system operational requirements. System considerations include: fast rotational start-up, fast ramped magnetic fields, load induced transient fields and airborne cryogen logistics. Preliminary selection of a multifilament Nb3Sn cable has resulted from these considerations. The cable will carry 864 amperes at 8.5K and 6.8 Tesla.