Squirrel Cage Induction Motor

A 3 phase induction motor is an electromechanical device that converts electrical energy into mechanical energy that works based on the Electromagnetic induction principle.

A 3 phase induction motor has two main parts, Stator and Rotor. The rotor is separated from the stator by a small air gap which ranges from 0.4 to 4mm, depending on the power of the motor.

Stator:

Stationary part of the machine is called stator.

Stator frame:

• Stator frame is the outer protecting part of the motor, made up of Cast iron or cast steel.
• Main function of the stator frame is support the stator core and provides protection and mechanical strength of all inner part of the machines.

Stator Core and Winding:

• It is an outer, stationary, hollow cylindrical structure made up of thin laminations of silicon steel having slots on the inner periphery.
• Laminated silicon steel used to reduce hysteresis and eddy current loss.
• The insulated copper conductors placed in the stator slots and are suitably connected either in star or delta depending upon which type of starting method we use.
• 3phas stator winding is wound for a definite number of poles as per the requirement of speed.
• 3 phase ac supply is applied to the 3 phase winding, produce a  rotating magnetic field running at synchronous speed.

Rotor:

Rotating part of the motor, made up of laminated silicon steel mounted on the shaft. It is a hollow core having slots on its outer periphery. Copper or aluminium windings placed in these slots.

Squirrel cage rotor:

• Most used type of induction motor, because of simple and rugged construction.
• It consists of laminated cylindrical core having slots on its outer periphery, slots are not parallel to the shaft axis they are skewed at a certain angle. A thick copper or aluminium bars are placed in each slots.
• All these bars are permanently joined together at both ends by metal rings called end rings.
• The rotor bars and end rings together resembles the cage of a squirrel and hence the name.
• Rotor is not electrically connected to the supply but has current induced in it by transformer action from the stator.
• These type rotor motor have low starting torque, because of no addition any external resistance to the rotor circuit.