INTRODUCTION

The induction motor is the most rugged and widely used machine in industry. Both stator winding and rotor winding carry alternating current. The alternating current is supplied to the stator winding directly and to the rotor winding by induction hence the name induction machine.

The induction machine can operate both as a motor and as a generator. However, it is seldom used as a generator. The performance characteristics as a generator are not satisfactory for most applications.

The three-phase induction motor is used in various sizes. Large motors are used in pumps, fans, compressors, and paper mills.

EQUIVALENT CIRCUIT

The stator winding can be represented as shown in Fig. 5.1. Note that there is no difference in form between the stator equivalent circuit and that of the transformer primary winding. The only difference lies in the magnitude of the parameters. For example, the excitation is considerably larger in the induction motor because of the air gap. The rotor winding can be represented as shown in Fig. 5.2.

Figure 5.1: Stator equivalent circuit.

Figure 5.2: Rotor equivalent circuit.

The equivalent circuit of the induction motor is obtained by combining the stator and rotor equivalent circuit (Fig. 5.3). Note that the form of the equivalent circuit is identical to that of a two-winding transformer.