Wound Rotor vs Squirrel Cage Rotor

by | Jul 9, 2021

The wound rotor and squirrel cage rotor are the two categories of induction motor rotors. They both operated on the principle of the faraday law of electromagnetic induction. Here are the fundamental differences between the wound rotor and the squirrel cage rotor.

What is Wound Rotor Induction Motor

A wound-rotor motor is an induction motor in which the rotor windings are connected to external resistance through the slip rings. The resistance adjustment allows control of the speed-torque characteristic of the motor. You can start t Phase wound with a low current by putting high resistance into the rotor circuit. The resistance can be decreased as the motor accelerates.

What is Squirrel Cage Induction Motor

The name “squirrel cage” originated from the shape of their rotor, where the internal component is connected to the output shaft and looks like a cage. The squirrel-cage rotor is the rotating component of the squirrel-cage induction motor. It has a steel collar cylinder with copper or aluminum conductors implanted on its surface.

While running, an alternating current power source is connected to the non-rotating stator winding. Then a rotating magnetic field is produced by the alternating current. The squirrel cage rotor winding has an induced current in it by the stator field. Torque is produced on the rotor by the interaction of the magnetic fields of currents in the rotor and stator.

Differences between wound rotor and squirrel-cage rotor

The Wound rotor induction motor has three-phase windings with magnet wire present in the rotor in their Constructions. In comparison, the squirrel cage induction motor has no windings present but a cylindrical rotor that consists of aluminum bars inside the slots. Wound rotor is commonly used where and when high starting torque is needed. But squirrel cage rotor is used for general, tough, and rough applications.

The following are the basic differences between wound rotor and squirrel cage rotor.

Wound RotorSquirrel cage rotor
Useful in applications that require speed control for loads.cannot be considered for applications that require speed control for loads
requires high maintenance, and it is expensive to affordrequires low maintenance
low efficiencybetter efficiency
complicated construction featuressimple and robust constructional features
Higher starting torque when using a rotor resistance and a better running torque poor starting torques and good running torque
low starting currenthigh starting current
high power factor of about 0.8-0.9.moderate power factor of about 0.6-0.8
high rate of change in slip ringless rate of change in slip ring
 can add external External resistancecannot add External resistance to it due to the structure of the rotor bars
It has slip rings and brushes present to add an external resister to the rotorNo slip rings and brushes present in it
has a variable speed due to its speed control mechanismhas a constant speed due to the absence of speed control
has a starting current that is twice that of the full loadhigh starting current that is about 5 to 7 times that of the load
used for constant loads, such as drill machines and lathe machinesused variable load and speed applications, such as cranes, lifts, elevators, conveyor belts, etc.
Its rotor bars are jointly circuited with an aluminum end ring.Its rotor windings are lifted out and linked with the carbon slip rings
could regulate the induced current in the rotor windings by using external resistance.The induced current in the rotor conductors depends on the motor slip, and you cannot regulate it
5-10% of industries use this wound rotor due to its complicated structure and high maintenance cost90-95% of industries use this squirrel cage rotor due to its simple structure and low maintenance cost
Its rotor is wound for the exact number of poles as that of the statorIts rotor automatically adapts to the number of poles as that of the stator
high rotor copper loss, and it is less efficientlow doctor cooper loss and is highly efficient

Conclusion

The wound-rotor induction motor has a complex structure and a bit hard to control, this has limed its application. when its start-up, the running torque is larger, so the wound rotor is always used in heavy load.

Squirrel-cage motors are simple in structure, low in price, and relatively simple to control the operation of the motor, so they are widely used in the industrial.