Electrical Interview Questions | Which Motor Is Best, Squirrel Cage Or Slip Ring Induction Motor

Hello guys, welcome back to my blog. In this article, I will discuss which motor is best to use, the squirrel cage motor is best or slip ring induction motor is best. I will also discuss the advantages and disadvantages of squirrel cage and slip ring induction motor, and conclusion.

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Which motor is the best squirrel cage or slip ring induction motor?

Electrical Interview Questions | Which Motor Is Best, Squirrel Cage Or Slip Ring Induction Motor



Introduction: 

The difference of squirrel cage and slip ring induction motor is mainly on torque, speed, slip, resistance and reactance.



Present scope or objectives:

Squirrel cage induction motor - Squirrel cage induction motors are usually used in various industrial applications. They are particularly suited for applications where the motor must maintain a constant speed, be self-starting, or there is a desire for low maintenance.

Applications of Squirrel Cage Induction Motor:

These motors are commonly used in, Centrifugal pumps, Industrial drives (e.g. to run conveyor belts), Large blowers and fan machine tools lathes and other turning equipment

Slip ring induction motor - Slip ring motors are most suitable for rolling mill, kiln. centrifugal fans, blowers because all these high inertia equipment demands high starting torque.

Squirrel cage induction motor:


Electrical Interview Questions | Which Motor Is Best, Squirrel Cage Or Slip Ring Induction Motor


1. In Squirrel cage induction motor, the rotor is most rugged and simplest in construction.
2. Cylindrical laminated core rotor with heavy bars of copper or Aluminum is used for conductors.

3. Rotor conductors or bars are short-circuited with end rings.
4. Rotor bars are permanently short-circuited and hence it is impossible to connect an external resistance in the circuit in series with the rotor conductors.
5. It has a low cost.
6. There are no moving contacts in the rotor.
7. Higher efficiency.
8. Low starting torque. It has a 1.5-time full load torque.
9. Speed control is not possible by rotor resistance.
10. The starting current is 5 to 7 times of full load current.

The advantages of skewing are as follows:

a. There is a production of uniform torque. Due to this noise during operation reduces.
b. The magnetic locking tendency of the rotor reduces. During the locking process, the stator and rotor teeth attract each other due to magnetic action. This locking process is called as Cogging. To overcome magnetic locking due to cogging, that's why conductors are skewed.

Note: Number of Poles and phases develop automatically in a cage rotor and equal to the number of Poles and phases as in stator. This means that the rotor responds automatically to the change in stator poles.

Advantages of Squirrel cage Induction Motor:



1. Higher efficiency
2. Higher power factor
3. Robust construction
4. Less cost
5. The absence of brushes reduces the risk of sparking.
6. Lesser maintenance
7. It has a good running performance.

Disadvantages of Squirrel cage Induction Motor:

1. Low starting torque
2. Rotor impedance at the time of starting is less. So starting current is high. Hence, it needs extra starting equipment.
3. It has poor starting performance.

Slip ring induction motor:


Electrical Interview Questions | Which Motor Is Best, Squirrel Cage Or Slip Ring Induction Motor


1. In slip ring induction motors the rotor is wound type. In the slip ring induction motor the slip rings, brushes are provided. Compared to the squirrel cage rotor, the rotor construction is not simple
2. Cylindrical laminated core rotor is wound like winding on the stator
3. At starting the 3 phase windings are connected to a star connected rheostat and during the running condition, the windings are short-circuited at the slip rings.
4. It is possible to insert additional resistance in the rotor circuit. Therefore it is possible to develop the torque; the extra series resistance is used for starting purposes. 
5. The cost is slightly higher.
6. Carbon brushes, slip rings, etc. are provided in the rotor circuit.
7. It has comparatively less efficiency
8. High starting torque. It can be achieved by adding external resistance in the rotor circuit.
9. Speed control by rotor resistance is possible.
10. Less starting current is there related to squirrel cage Induction Motor.


Note:

1. The purpose of using phase resistance in the rotor circuit is to decrease the supply starting current and increase the starting
torque. Secondly, it is used for controlling the speed of the motor
2. Rotor winding must be star connected.
3. Like a stator, rotor windings must be distributed and short-pitched.

Advantages of Slip ring Induction Motor:

1. High starting torque
2. Low starting current
3. External resistance can be connected to the rotor circuit to control the motor speed

Disadvantages of Slip ring Induction Motor:

1. Cost is high (3 times compare to squirrel cage)
2. Large Size
3. Space requirement increases
4. There are wear and tear.
5. There is sparking
6. Maintenance is large

Conclusion: hence, by the above information we can conclude that which is the best suitable motor for our application purpose.

I hope this article may help you all a lot. Thank you for reading.
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