Physical conceptions of induction motor operation
Journal of the American Institute of Electrical Engineers
C ONFRONTED by the particular behavior of the single-phase induction motor, it is but natural that in order to familiarize ourselves with it, we should substitute for the direct, the indirect des cription, and explain the single-phase motor by means of the better known polyphase performance. This indirect method originated by E. Arnold and F. Eichberg and recently modified by B. G. Lamme, looks upon the single-phase induction motor as a special case of the polyphase motor and considers it as a
... considers it as a revolving field machine. Yet in the same manner as it has been found advis able to abandon today the indirect method of describing heat phenomena by means of Black's heat substance, for the direct description through the more general prin ciples of modern energetics, it may be preferable to abandon the explanation of the single-phase motor per formance by the polyphase for a more direct method. Of the direct methods, the Qne originated by Potier FIG. 1 and G rges and further developed by V. Fynn, McAl lister and others, carefully studies the action of the secondary rotating member in the production of a field at right angles in space and time phase' to the transformer field. Since the right angle field is generally called the speed field or cross flux, we can refer to the direct method as the ' 'cross-flux theory" and to the indirect method as the "revolving-field theory." It is known that the circular current locus or circle diagram determines the performance of the induction motor with an accuracy well within the limits of the practical engineer's needs. The circle diagram is determined when the following three characteristic points are given: The no-load or synchronous speed current, the locked or short-circuit current and the infinite speed current points. Based on either the revolving-field theory or the cross-flux theory analy tical expressions for the three characteristic current values can be obtained. It has been shown by E. Arnold that the characteristic current values are the same when calculated from the formula obtained by either method.