One of the most common electrical motorused in most applications which is known as induction motor. This motor is also called as asynchronous motor because it runs at a speed less than synchronous speed. In this, we need to define what is synchronous speed. Synchronous speed is the speed of rotation of the magnetic fieldin a rotary machine and it depends upon the frequency and number poles of the machine. An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux electric current in the rotor with flux electric current in the stator, the rotor will never reach to its rotatingmagnetic field speed i.e. the synchronous speed. There are basically two types of induction motor that depend upon the input supply - single phase induction motor and three phase induction motor. Single phase induction motor is not a self starting motor and three phase induction motor is a self-starting motor. Now in general we need to give two supply i.e. double excitation to make a machine to rotate. For example if we consider a DC motor, we will give one supply to the stator and another to the rotor through brush arrangement.