Low-inertia reluctance machines

Two forms of reluctance machine with rotors of low inertia, believed to be novel, are described. In the first, the salient poles are detached from the inactive portion of a normal rotor to give what may be regarded as the reluctance equivalent of the drag-cup induction machine. Inertias as low as one fifth of those of conventional machines appear to be attainable, with correspondingly high values of the torque/inertia ratio and the power ratio. The second form of machine is based upon the use of peripheral segments rather than poles. While not permitting the use of values of inertia as low as the first form, it can give higher pull-out torque, power factor and impedance. The construction of experimental versions of both machines is described. Test results for all aspects of their synchronous performance are given, and they are found to be in very satisfactory agreement with computed values, based on previous analytical work by the authors3 and certain simple extensions of it. Test results relating to pull-in performance, and theoretical results relating to standstill torque, are also given. It is shown that there is a need for a better understanding of losses caused by harmonic fluxes in the air gap, and of the effects of saturation. The latter leads to nonsinusoidal space variations of reactance and could be of importance in connection with all types of salient-pole synchronous machines.