Circle diagram of polyphase induction motors

In submitting this article the writer wishes to disclaim any intention of making a contribution to the theory of a subject so thoroughly studied as the circle diagram of polyphase induction motors. But while the theory of the circle diagram may be considered as a closed chapter, its practical application, as a method of determining the characteristics of motors from test data, has not kept pace with the theory; at least, all constructions known to the writer are either not simple enough for practical use, or are based on assumptions which hold good only within rather vaguely defined limits, in particular, there is no simple and accurate method applicable to small and fractional horse power motors for which the approximate diagram is entirely inadequate. The method given in the article is applicable to all cases, but has been primarily developed and used in connection with small motors, its characteristic feature being that the smaller the motor, the easier the construction of the diagram. It is thought that in view of the enormous development of the small motor industry this feature may be of sufficient interest to justify an addition to the literature of the circle diagram.