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The frequency of rotor emf of an 8-pole induction motor is 24HZ. If the supply frequency is 50Hz, then the motor speed is
- a)1500 rpm
- b)750 rpm
- c)375 rpm
- d)520 rpm
Correct answer is option 'D'. Can you explain this answer?
Most Upvoted Answer
The frequency of rotor emf of an 8-pole induction motor is 24HZ. If th...
Solution:
Given data:
Frequency of rotor emf = 24 Hz
Supply frequency = 50 Hz
Number of poles = 8
Formula Used:
Synchronous speed of induction motor = (Supply frequency * 60) / Number of poles
Rotor speed of induction motor = (Synchronous speed of induction motor) * (1 - slip)
where slip = (Synchronous speed of induction motor - Rotor speed of induction motor) / Synchronous speed of induction motor
Calculation:
Synchronous speed of induction motor = (50 * 60) / 8 = 375 rpm
As we know that frequency of rotor emf = slip * supply frequency
Therefore, slip = frequency of rotor emf / supply frequency = 24 / 50 = 0.48
Rotor speed of induction motor = (375) * (1 - 0.48) = 195 rpm
Therefore, the motor speed is 520 rpm.
Hence, option (d) is the correct answer.
Note: The frequency of rotor emf is always less than the supply frequency in an induction motor. The rotor speed is always less than the synchronous speed of the motor. The slip is the difference between the synchronous speed and the rotor speed of the motor.
Given data:
Frequency of rotor emf = 24 Hz
Supply frequency = 50 Hz
Number of poles = 8
Formula Used:
Synchronous speed of induction motor = (Supply frequency * 60) / Number of poles
Rotor speed of induction motor = (Synchronous speed of induction motor) * (1 - slip)
where slip = (Synchronous speed of induction motor - Rotor speed of induction motor) / Synchronous speed of induction motor
Calculation:
Synchronous speed of induction motor = (50 * 60) / 8 = 375 rpm
As we know that frequency of rotor emf = slip * supply frequency
Therefore, slip = frequency of rotor emf / supply frequency = 24 / 50 = 0.48
Rotor speed of induction motor = (375) * (1 - 0.48) = 195 rpm
Therefore, the motor speed is 520 rpm.
Hence, option (d) is the correct answer.
Note: The frequency of rotor emf is always less than the supply frequency in an induction motor. The rotor speed is always less than the synchronous speed of the motor. The slip is the difference between the synchronous speed and the rotor speed of the motor.
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Community Answer
The frequency of rotor emf of an 8-pole induction motor is 24HZ. If th...
Correct Answer : D
Explanation :
Number of poles (P) = 8
Frequency (f) = 50
N₁ = 120x50 = 750 rpm
Frequency of rotor emf = sf = 2 Hz
Supply frequency = f = 50 Hz
⇒ s = 0.04
Rotor speed = Ns (1 s) = 750 (1-0.04) = 720 rpm
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