Introduction

A motor is probably the most utilized invention of mankind after the ignition of fire. We always wanted to increase the energy of a motor. Electricity is the most trusted source of energy in science and technology. Electrical energy can be efficiently applied to run a motor. We have seen in chapter 8 how a DC voltage source can operate a DC motor. In the era of AC generation, use of DC motors became quite obsolete. We know an AC generation is generally essentially of three phase. A motor which can be operated by three phase power can make the coordination between power and motor useful. We have also seen that a three phase current can induce a rotating magnetic field. This phenomenon was first discovered by French physicist Francois Arago in 1824. This Arago's rotation helped the engineers to design a rotating machine which takes power from a three-phase AC power supply. The most used motor in technology of these days is the three phase induction motor. The induction motor operates on the principle of transformer emf induced in rotor three phase circuit due to three phase power supplied in stator winding. In this chapter we shall solely concentrate on three phase induction motor.

To understand the working principal of three phase induction motor, let us consider a magnetic strip of alternating poles situated sequentially. Let us consider another bar magnet is placed above the magnetic strip without any physical contact. The strip and the bar are magnetically coupled. This is depicted in Fig. 10.1.