Under which of the following condition the squirrel cage induction motor is preferred over the wound rotor induction motor?
Right Answer is:
When the cost is the major consideration
When the cost is the major consideration the squirrel cage induction motor is preferred over the wound rotor induction motor.
In the squirrel cage motor, the bar at both ends is a permanently short circuit by the end rings. Hence the resistance of the squirrel-cage induction motor cannot be varied as compared to the slip ring induction motor.
In the squirrel-cage induction motor, the rotor has very low fixed resistance, therefore, the starting torque is low due to low power factor and high reactance. The starting torque could be increased by increasing starting resistance but due to high current in the rotor during starting will increase the copper loss which will decrease the motor efficiency.
Advantages of Squirrel cage induction motor
- Cheaper cost
- Ruggedness of conduction
- No moving contacts.
- Slightly higher efficiency than wound motor
- By using a double cage rotor, it; possible t obtain the higher starting torque
- Trouble-free performance. Minimum maintenance.
- Looses are relatively less
Disadvantages of Squirrel cage induction motor
- Low starting torque.
- It cannot be used in cases where it requires considerable load torque.
- Starting current is about 6 to 3 times full-load current.
- Speed control is not possible.
- Because of the high starting current, it requires a starting device like an auto-transformer or star-delta starter.