6.685 Electric Machines, Course Notes 12: Single Phase Induction Motors, Modeling of Inductances and Resistances

This short note is a description of the analysis of single phase induction motors. It is intended to be read along with a description of the analysis of polyphase motors1.This will be called the ’reference document’. The style of analysis used here is described in more detail in that note and many of the elements of this analysis appear only in that other note. The single phase machine contemplated here actually has two windings, usually referred to as the ”main” or ”run” winding and the ”auxiliary” or ”start” winding. We assume here that the two windings are geometrically in quadrature but they need not have the same number of turns or the same distribution. A cartoon view of an axial section of such a machine is shown in Figure 1. We assume the direction of rotation is counter-clockwise (in the θ direction). The two windings are labeled as A (run) and B(start). The usual strategy for making one of these motors start is to arrange the impedances of the two windings so that current flows in the start winding with a phase advance with respect to the current in the run winding.