Friday, 22 July 2016

Difference between Squirrel Cage and Slip Ring Induction Motor


Please have a look at the below figures of Squirrel Cage Induction and Wound Rotor / Slip Ring Induction Motor.

Squirrel Cage Induction Motor:



Slip Ring / Wound Rotor Induction Motor:



Sr. No.
Squirrel Cage Induction Motor
Slip Ring / Wound Rotor Induction Motor
1)     
1.    In Squirrel cage induction motors the rotor is simplest and most rugged in construction.
In slip ring induction motors the rotor is wound type. In the motor the slip rings, brushes are provided. Compared to squirrel cage rotor the rotor construction is not simple.
2)     
Cylindrical laminated core rotor with heavy bars or copper or Aluminum or alloys are used for conductors.
Cylindrical laminated core rotor is wound like winding on the stator.
3)     
Rotor conductors or rotor bars are short circuited with end rings.
At starting the 3 phase windings are connected to a star connected rheostat and during running condition, the windings are short circuited at the slip rings.
4)     
Rotor bars are permanently short circuited and hence it is not possible to connect external resistance in the circuit in series with the rotor conductors.
It is possible to insert additional resistance in the rotor circuit. Therefore it is possible to increase the torque; the additional series resistance is used for starting purposes.
5)     
Cheaper cost.
Cost is slightly higher.
6)     
No moving contacts in the rotor.
Carbon brushes, slip rings etc are provided in the rotor circuit.
7)     
Higher efficiency.
Comparatively less efficiency.
8)     
Low starting torque. It has 1.5 time full load torque.
High starting torque. It can be obtained by adding external resistance in the rotor circuit.
9)     
Speed control by rotor resistance is not possible.
Speed control by rotor resistance is possible.
10)  
Starting current is 5 to 7 times the full load current.
Less starting current compared to squirrel cage Induction Motor.

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