Introduction

The objective of this section is an understanding of induction motors from first principles. The analysis developed here results in the equivalent circuit models discussed in section 4.1, along with more complex models which give a fuller explanation of some of the loss mechanisms in induction machines.

The analysis starts with a circuit theoretical point of view of wound-rotor induction machines, which is used to explain the basics of induction machine operation. Following that, a model for squirrel-cage machines is developed. Finally, analysis of solid-rotor machines and mixed solid rotor plus squirrel-cage machines is developed.

The view taken in this chapter is relentlessly classical. All of the elements used here are calculated from first principles, with only limited use of numerical or empirical methods. While this may seem to be seriously limiting, it serves the basic objective, which is to achieve an understanding of how these machines work. Once that understanding exists, it is possible to employ further sophisticated methods of analysis to achieve more results for those elements of the machines which do not lend themselves to simple analysis.

An elementary picture of the induction machine is shown in Fig. 4.14. The rotor and stator are coaxial. The stator has a polyphase winding in slots. The rotor has either a winding or a cage, also in slots. Generally, this analysis is carried out assuming three phases. As with many systems, this generalizes to different numbers of phases with little difficulty.