Induction Motor,Construction,working Principle of Induction motor,Types of Induction motor,Power factor of Induction motor,Advantages & disadvantages of Induction motor

Induction Motor
       Induction motor (asynchronous motor) is an AC motor in which the electrical current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.So their is no need of electrical connection to the rotor.
Working Principle
        In an induction motor the rotor does not receive power by conduction but by inductions is exactly the same way as the secondary of a two winding transformer receive its power from the primary.that is why such motor are known as induction motors.In other words we can say that an induction motor is a rotating transformer in which primary winding is stationary but the secondary is free to rotate. 
          If we consider supply voltage we have two types of induction motors. Single phase induction motor and three phase induction motor.Single phase induction motor is not self starting where as three phase induction motor is self starting . Self Starting means that the motor starts running automatically with out any external source applied to the motor.
          As we know that the A.C. supply is sinusoidal wave and it produce a pulsating magnetic field in the uniformly distributed stator winding since we can assume the pulsating magnetic field as two oppositely rotating magnetic fields there will be no resultant torque produced at the starting so the motor does not run.So, we need some external force to run the motor.So to solve this problem we split stator winding into two parts.One is main winding and other is auxiliary winding .One capacitor is connected in series with the auxiliary winding .This capacitor make a phase difference when current flows through both coils.Due to this phase difference the rotor will generate a starting torque,and it will start to rotate.
Construction of a A.C. Induction Motor
          following are the main parts of the induction motor.
  • Stator Core.
  • Stator Windings.
  • Rotor.
  • Enclosure.
  • Bearing and Fan.
Rotor Construction
          Rotor is the rotating part of the induction motor .Most common type of rotor used in a three phase induction motor is a Squirrel Cage Rotor. A squirrel cage rotor core is made by stacking thin steel lamination to form a cylinder.Rather than using coils of wire as conductors,Conductor bars are die case into the slots evenly spaced around the cylinder.Most squirrel cage rotors are made by die casting aluminum to form the conductor bars.After die casting rotor conductor bars are connected mechanically and electrically with end rings.
Types of Induction Motors
           The types of induction motors can be classified depending on whether they are a single phase or three phase induction motor.
Single Phase Induction Motor
           The types of single phase induction motors include.
  • Split Phase Induction motor.
  • Capacitor start Induction motor.
  • Capacitor start and capacitor run Induction motor.
  • Shaded pole Induction motor.
Three Phase Induction Motor
  • Squirrel Cage Induction Motor.
  • Slip Ring Induction Motor.
 Advantage of Induction Motor
  • These are very simple and rugged.
  • It is very high efficiency.Due to no brushes its frictional losses are reduced.
  • These are having very good power factor.
  • Its cost is very low.
  • Needs very low maintenance.
  • Its starting arrangement is very simple especially for squirrel cage type.
Disadvantages of Induction Motor 
  • Its speed cannot be varied with out reducing its efficiency.
  • When we increase the load its speed reduces.
  • Its starting torque is some what inferior to that of a D.C. shunt motor. 
Power Factor of Induction Motor
              The power factor of an induction motor varies with load at full load it is normally 0.85 or 0.90 and at no load it is 0.20.Power factor of an induction motor can be improved by connecting the capacitor.

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