The application of superconductivity to rotating electrical machines

After a brief review of the general properties of superconductors, the difficulties encountered in employing superconducting wires in solenoids are described together with the measures it has been found necessary to take in order to construct coils with satisfactory performance. A comprehensive review of the attempts and proposals in the literature to employ superconductors in rotating energy converters and appraisal of each, is then given. The possibilities of utilizing superconducting winding in conventional types of rotating machines are then examined, and it is shown that probably only the d.c. homopolar machine, the synchronous machine and a toroidal reciprocating generator proposed by Harrowell are suitable for development with superconducting ·windings. The present state of development of superconducting d ,c , homopolar machines is described, and the economic and market prospects for such machines assessed on the basis of the limited data available supplemented by reasonable assumptions. Design procedures for the Harrowell machine are propose, and from these some conclusions are drawn regarding its characteristics. The prospects for superconducting synchronous generators are examined for use in large power systems and shown to be promising, but for aircraft applications it is shown there is no case for mmachines with ratings below 1 MVA at 400 Hz. The inadequacies of existing theories of synchronous machines to cover superconducting types are examined and proposals are put forward to modify the conventional two-axis theory for the superconducting case including parameter evaluation. The experimental work reported covers the design, construction and testing of a.400 Hz rotating armature synchronous generator, with a rating of 50 kVA initially, but capable of being extended to 100 kVA subsequently