Development of direct current heteropolar machines with superconducting field windings

摘要

A practical and theoretical study of direct current heteropolarudmachines with superconducting field windings was conducted with the aimudof proving their technical feasibility and to indicate their advantagesudand disadvantages over machines of more conventional design. These studiesudwere conducted in conjunction with extensive tests on small superconductingudD.C. machines of various formats. udThree stages of machine development occurred. In the first stageudmachine the superconducting field winding was shielded from armatureudreaction fluxes with the aid of iron and compensating windings. udIn the second stage machine the superconducting field winding wasudsubjected to the full effects of the armature reaction fluxes. udTests conducted with these machines indicated that the operation ofudthe superconducting field winding was not influenced by the flow of armatureudcurrents. A third, four pole superconducting D.C. machine which exhibitsudall the advantages gained by using superconductors in the field windingsudhas been constructed. This machine has most of the construction featuresudof a full size prototype machine for future industrial applications. Asuda result of difficulties encountered in inducing the superconducting stateudinto the field windings operational tests on this machine could not beudconducted. Possible reasons for the difficulties are discussed with theudresult that some of the reasons are rejected and measures that couldudovercome the difficulties are forwarded. udThe project began with no experience in cryogenics, cryostat designudand construction nor superconductivity. Consequently details of practicaludtechniques utilised during the project are included. udContinued development of superconducting heteropolar D.C. machinesudshould prove that the design and operation of a prototype machine withuda rating in excess of 10 MW is possible. This is essential if this typeudof machine is to make any impact in the future. Providing the expectationudthat voltage per commutator bar limits can be substantially increasedudis realised, machine ratings that are limited only by armature coolingudshould be possible.