A generalized circle diagram for a four-terminal network and its application to the capacitor single-phase motor

THE MAIN PURPOSE of this paper is to present an operating circle diagram for the capacitor motor, showing that the input-current vector follows a circular envelope, as the mechanical shaft power is varied. A secondary aim is to review the theory of the generalized four-terminal network, thereby developing circle-diagram equations which can be applied to any linear network which delivers its output power into a variable impedance of constant power factor. This generalized method of approach can be applied quite readily to the three-phase induction motor, obtaining the same results which now are available in practically all textbooks on a-c machinery. The same point of view can be extended to single-phase motors, the capacitor motor being a good example. Considerable work still remains to be done in order to make the single-phase circle diagram as useful as the one commonly used for three-phase motors,¹ but the author believes that the generalized treatment offered in this paper may be a step in the right direction.