Torque And Force Distribution in the Superconducting Alternator

Abstract

There is continuing world-wide interest in the superconducting machine; but many problems, both theoretical and practical, remain to be solved before a large superconducting alternator can be successfully designed. One of the major problem areas relates to the rotating screening system and it is now widely accepted that there will be two rotor screens to shield the superconducting field winding from armature-excited transient magnetic fields. The mechanical construction of these concentric rotating screens is complex and the knowledge of the types and magnitudes of the torques and forces which these shells have to withstand during the operation of the alternator under power-system conditions is essential at the design stage. In this paper torque and force distribution are examined for both fixed and free outer rotor configuration taking into consideration the mechanical stiffness between the turbine shaft and (i) the inner rotor and (ii), in the case of the former, the outer rotor. Detailed representation of the inertias and stiffnesses of the turbine shaft are not included. To see the effect of inertia and stiffness of the outer and the inner screens on the torques and forces, both these inertias and stiffnesses are varied over a reasonably wide range. Special attention is given to the peak torque experienced by the weaker member, the inner rotor screen. Damping and stability are studied with the help of a linearized model.