Difference between squirrel cage and slip ring induction motor

The squirrel cage induction motor is the most popular and widely used AC motor because it is very cheap, efficient, robust and reliable. The slip ring motors are rarely used in industries because it has several disadvantages like frequent maintenance, high copper loss. 

Main difference : 

The slip ring motor has an external resistance circuit for controlling the speed of the motor whereas the squirrel cage motor not possible to add any external circuit because, at the end of the ring, the bar of the motor is permanently slotted. 

Difference :

• A slip ring is a motor whose rotor is wound type whereas the squirrel cage motor has a squirrel cage type rotor. 
• The rotor of the slip ring motor has a parallel slot cylindrical core and each slot consists of each bar while the slot is not parallel in case of the squirrel cage motor.
• The slip ring motor is also called a phase wound rotor and the name of the squirrel cage motor is cage motor. 
• The slip ring motor consists of a slip ring and brushes which is complicated whereas the construction of the squirrel cage motor is simple. 
• At the start, the slip ring motor the rotor resistance the starter is used, while the slip ring motor doesn't require any starter. 
• The phase wound motor consists of external resistance circuit, on the other hand, whereas no internal resistance circuit can be added in the squirrel cage motor due to the permanent slotting of their rotor bars.
• The starting torque of the slip ring motor is very high and low in case of squirrel cage motor. 
• Compared to the squirrel cage motor, the maintenance cost of the slip ring motor is high because the slip ring motor consists of brushes and rings.
• Compared to the squirrel cage motor, the copper loss is more in the slip ring engine.
• Compared to the squirrel cage motor, the slip ring motor has a low power factor.
• The motor of the slip ring has brushes to transfer power while the motor of the squirrel cage is brushless.
• The efficiency of the slip ring motor is low and high in the squirrel cage motor.
• The resistance circuit is used to control the speed of the slip ring motor whereas impossible to control the speed of the squirrel cage motor. 
• The wound rotor phase price is high because it is made up of brushes and the squirrel cage motor is cheap.
• The starting current of the slip ring motor is small because it is regulated by the resistance circuit while it is high in the squirrel cage motor. 
• The slip ring motor is mostly used in places where high starting torque is required like a hoist, cranes and the squirrel cage motor is used in a drilling and lathe machine.
• Compared to squirrel cage motor, overloading capacity is high in the slip ring motor and is smoothly running under heavy loads.