Three phase Inducion Motor

Principle

Three phase induction motor works under the principle of electromagnetic induction.

Working

When a three phase supply is given to the three phase stator winding, a Rotating Magnetic Field of constant magnitude is produced. This rotating magnetic field produces an effect of rotating poles around a rotor. Let us assume that the direction of rotating magnetic field is in clockwise direction. Clearly, the rotating magnetic field from the stationary stator cuts the rotor, so that emf is induced in the rotor conductor called rotor induced emf. The electromotive force induced in the rotor condutor is by the principle of electromagnetic induction. By Lens law, the rotor try to catch the synchronous speed, so that the relative motion between RMF(Ns) and rotor(N) is reduced to zero to stop the emf inducing in rotor. But practical it is impossible for the rotor to hold its speed to synchronous speed i.e) as the rotor attain the synchronous speed, there will be no rotor induced emf, due to inertia the rotor will not attain zero speed. When the rotor speed is reduced below synchronous speed again there will be the rotor induced emf, then the rotor tries to catch the synchronous speed by len's law. This process is repeated as long as the supply is given to the stator of three phase induction motor.

Advantages of three phase Induction Motor

• Three phase Induction motors are self starting.
• Three phase Induction motors have higher power factor.
• Three phase Induction motors are good is speed regulation.
• Robust construction.

Applications of three phase Induction Motor

• Three phase Induction motors are widely used in lift, hoist, cranes, elevators etc.
• Lathes, drilling machine, fans, blowers are also make use of three phase Induction motors.

Note:

The speed of the rotating magnetic field is synchronous speed, Ns rpm.