Slotless-disc alternator with AC-side excitation

The paper examines a version of the double-disc alternator with AC-side excitation that uses a slotless stator. It is an interesting form of slotless machine because Gramme ring windings can be wound automatically on the strip-wound circular core and produce a mechanically secure unit. A basis for the design of this form of machine is described, and the main considerations which influence the choice of a suitable geometry are discussed. Experimental results demonstrate that the performance of the machine is satisfactory. Predictions of direct- and quadrature-axis reactances and full-load field current by standard synchronous machine methods are also adequate. A particular feature of the machine, the absence of stray loss in the solid rotor due to stator-slot permeance variations, is seen to be particularly beneficial. Eddy-current losses in the stator windings exposed to the main airgap field are examined and are shown to be relatively small but measurable. Methods of predicting these losses for round and rectangular conductors in both sinusoidal and uniform airgap fields are presented.