Stray losses in synchronous electrical machinery

Abstract

The earlier part of the paper discusses the problem of eddy currents from the point of view of the effect of the physical arrangement of an alternator on the stray losses. The later Sections deal with the components of stray loss, and, since these can be classified conveniently in accordance with their position in the alternator, the stray losses which occur in the stator are considered first. It is shown how the arrangement of the end-windings influences the shape of the end leakage field and thus the intensity of loss in the adjacent metallic structures, and how the loss in the core end-plate or end-shield can be estimated. The effect of magnetic and non-magnetic shielding arrangements is discussed, together with details of their arrangement. Experiments in connection with eddy-current losses in the stator end connections are described. Consideration is given to the iron loss which occurs in the stator core under steady 3-phase short-circuit conditions owing to the flux waveshape, and the indications are that this provides at least a partial explanation why the stray losses can be so appreciably greater on short-circuit than on load.The stray losses in the rotor, generally grouped under the heading of rotor surface losses, are shown to be due to several effects, notably those due to the concentration of ampere-conductors in one slot and to the irregularities present in the stator m.m.f. wave. Consideration is also given to the surface or pole-face losses resulting from the tufting of flux under the stator teeth, which loss is experienced under conditions of no load and is normally measured with the stator iron loss. The factors affecting the surface losses are discussed, together with methods for reducing the losses to a minimum.An indication is given of the relationship between the stray losses at the ends and those located within the core length of an alternator, together with a description of the effect of load conditions on each of the components of stray loss.