Stator construction of Induction motor is already discussed in my article Stator of Induction Motor and in my current article I'll discuss construction of Rotor for three phase induction motor.
RotorThe building construction of rotor are somewhere similar with that of stator. It is also made up of thin laminated silicon steel sheets of low losses and high permeability. There are two types of rotor commonly used for Induction motor. These are :
- Squirrel Cage Rotor
- Slip Ring Rotor
Squirrel Cage RotorThis is also termed as Cage rotor. It consists of a cylinder shape rotor made up of laminated thin sheets of silicon steel. In such rotor slots to place winding are cut nearly parallel to the shaft but with an angle of inclination.
Slip Ring RotorSlip ring rotor is a bit different from Squirrel cage rotor. In slip ring type rotor, rotor conductors are not short circuited at the end with the help of end rings but are taken out with the help of slip rings.
Comparison of Cage and Slip Ring RotorsWe have seen both type of rotors of Induction motors. These are Squirrel cage rotor and Slip ring rotor. Now its time to compare both these rotors, which one is better lets see.
Advantages of Squirrel Cage Rotor
- It has simple construction so easy to construct/manufacture.
- It is cheap as compare to slip ring rotor.
- It require less maintenance as no fraction is there.
- Frictionless rotor results in higher efficiency.
- It has no contacts so low chances of sparking
Advantages of Slip Ring Rotor
- High starting torque may be obtained by adding resistance.
- High starting resistance means low starting current.
- Speed control with change of rotor resistance is possible.