Electrical Engineering ⇒ Topic : Introduction

INTRODUCTION:-

An induction motor is simply an electric transformer whose magnetic circuit is separated by an air gap into two relatively movable portion, one carrying the primary and the other the secondary winding.

The essential features which distinguish the induction machine from other type of electric motors is that the secondary currents are created solely by induction, as in a transformer instead of being supplied by a D.C. exciter or other external power source, as in synchronous and D.C. machines

A polyphase induction motor has stator and rotor. The stator is connected to a balanced three-phase supply and a constant amplitude rotating m.m.f. wave is produced in the air gap. Rotor receives energy from stator by means of transformer action. The rotor produces a m.m.f. wave in the air gap that rotates in the same direction of stator produced m.m.f. at a synchronous speed. A polyphase induction motor is a singly excited AC machine. Since the two m.m.f.s are stationary with respect to each other, electromagnetic torque is possible at a speed less than the synchronous speed. Therefore, this machine is also called asynchronous machine. The aim of this chapter is to explore the induction machine.