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A 6 pole, 50 Hz, induction motor is running at a speed of 600 rpm. What is the slip speed of the machine?
1. 200 rpm
2. 300 rpm
3. 400 rpm
4. 600 rpm

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Correct Answer - Option 3 : 400 rpm

Concept of slip:

  • The speed of the rotor structure with respect to stator structure is Nr
  • With the rotor running at Nr, the relative speed of the stator rotating magnetic field with respect to the rotor conductors is Ns - Nr in the direction of Ns 
  • This relative speed is referred to as slip speed.


Where Ns is the synchronous speed of the machine

\(N_s =\frac{120f}{p}\)

Where,

f is the frequency of the machine

p is the number of poles of the machine

Slip speed = Ns - Nr

\(slip,s = \frac{(N_s - N_r)}{N_s}\)

Calculation:

Given that, poles (P) = 6

Frequency (f) = 50 Hz

Speed (Nr) = 600 rpm

Synchronous speed Ns = 120f / P = 120 × 50 / 6 = 1000 rpm

Slip speed = Ns - Nr = 1000 - 600 = 400 rpm

Note: In the official paper frequency is not mentioned, but we considered frequency as 50 Hz, other for different frequencies different answers are possible,

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