Squirrel Cage Induction Motor:
- 3 phase squirrel cage induction motor is a type of 3-ϕ induction motor based on the principle of electromagnetism.
- It is called a ‘squirrel cage’ motor because the rotor inside of it looks like a squirrel cage and is known as a squirrel cage rotor.
- This rotor is a cylinder of steel laminations, with highly conductive metal (typically aluminum or copper) embedded into its surface.
- It is also known as short-circuited rotor type motor.
- It doesn't need a slip ring and brush assembly.
- Airgap between the stator and rotor is uniform.
- External resistance cannot be introduced in the rotor circuit.
These motors are commonly used in:
- Centrifugal pumps
- Industrial drives (e.g. to run conveyor belts)
- Large blowers and fans
- Machine tools
- Lathes and other turning equipment
The moment rotor catches the rotating magnetic field the rotor current drops to zero as there is no more relative motion between the rotating magnetic field and rotor. Hence, at that moment the rotor experiences zero tangential force hence the rotor decelerates for the moment.
DIFFERENCE BETWEEN SLIP RING AND SQUIRREL INDUCTION MOTOR
Slip ring induction motor | Squirrel cage induction motor |
It has a slip ring type rotor | It has a squirrel cage type rotor |
Cylindrical laminated core with parallel slots and each slot consist one bar | The slots of the rotor are not parallel but are skewed |
Construction is complicated | Construction is simple |
We can add external resistance to the rotor | The rotor bar is permanently shorted at the end of the ring; thus, it is not possible to add any external resistance |
The rotor resistance starter can be used | Rotor resistance starter cannot be used |
Starting torque is high | Starting torque is low |
Brushes are present | Brushes are absent |
| The air gap between the stator and rotor is non-uniform. | The air gap between the stator and rotor is uniform. |
Frequent maintenance is required | Less maintenance required |
The power factor is low | Power factor is high |
Speed control is possible | Speed control is not possible= |
