Difference between Squirrel cage and Wound rotor Induction Motor

Squirrel cage motor and slip ring (wound rotor) motor are the two types of induction motor↗. Slip ring induction motor is also known as wound rotor induction motor. Both these types of induction motor operates on the principle of faraday law of electromagnetic induction. The basic difference between squirrel cage↗ and wound rotor induction motor↗ is as follows;

Slip ring Induction Motor :

Slip ring motor is complicated in construction due to the presence of slip rings.

These type of motors are expensive.

Regular maintenance is required due to the presence of slip rings and brushes.

Rotor is wound for the same number of poles as that of stator.

3- phase windings are present in wound rotor motor, the ends of which are permanently connected to the slip rings.(can be seen in below fig)

Slip ring induction motor

Starting current of these type of motor is low.

External resistance can be added in slip ring induction motors.

Slip rings and brushes are present to add external resistance in the rotor circuit.

Current induced in the rotor windings can be controlled by using external resistance.

Slip ring induction motor provides high starting torque. With the help of external resistance, we can also increase the starting torque of slip ring induction motors.

We can control the speed of slip ring induction motor by rotor resistance method. Hence it is variable speed motor.

Rotor copper losses are high in slip ring induction motors and they have less efficiency.

Due to high cost and complicated construction of slip ring induction motor, only 5-10% of the industry uses slip ring induction motor.

Squirrel Cage Induction Motor:

Construction of squirrel cage motor is simple and robust.

Squirrel cage induction motor cost is very low.

Less maintenance is required due to the simple construction.

Rotor itself automatically adjusts to the number of poles as that of stator.

Squirrel cage motor consists of cylindrical rotor having skewed slots in  which aluminum bars are placed. No windings are present in squirrel cage rotor.

Squirrel cage Rotor

Squirrel cage induction motor has high starting current.

External resistance cannot be added since the rotor bars of squirrel cage induction motor are short circuited by end rings.

Slip rings and brushes are not present.

Current induced in the rotor conductors depends on the motor slip↗ and we cannot control it.

Starting torque is very low in squirrel cage motor. Moreover, we cannot add external resistance in order to increase the starting torque.

It is constant speed motor since speed control is not possible in squirrel cage induction motors.

Rotor copper losses are less and they have high efficiency.

Due to simple construction and low cost, 90-95% industries uses squirrel cage induction motor.

That’s all. Hope this will helps you.

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