Chapter 4 Induction Machines

4.1. Introduction

“Induction machines” are energy converters characterized by the fact that the rotation speed of their rotor is different from the synchronous speed, defined by:

where ω is the angular frequency of the stator currents, and p is the number of pole pairs. These machines are called “induction machines” because their rotor currents are generally induced by the currents running through the stator coils.

These machines are rustic, robust and cheap. Formerly their use was restricted to simple and low performance applications when they were connected to constant frequency and constant voltage networks.

Now, induction machines have spread in every domain of industrial motorization, including high-tech applications, since the recent progress in power electronics and in digital control have made it possible to control them with good dynamic performance.

4.2. General considerations

4.2.1. Structures

4.2.1.1. Stator

The stator of induction machines is a 3-phase field spool with 2p non-salient poles identical to the stator of synchronous machines (Figure 4.1). It is connected, either with a 3-phase network, or with a static converter, and a 3-phase current system is produced.

Figure 4.1. Induction machine stator before winding, 45 kW, 440 V, 590 rpm (ECA EN document)