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In a three-phase induction motor, the slip is generally:
1. 15% to 25%
2. 2% to 5%
3. 0
4. More than 45%

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Correct Answer - Option 2 : 2% to 5%


Synchronous speed in rpm of a three-phase induction motor is given by,

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

Where f is the frequency in Hz

P is the number of poles

A rotor of a three-phase induction motor rotates at a speed close to the synchronous speed but not equal to the synchronous speed.

The difference between the synchronous speed and the rotor speed is known as slip speed.

It is given by Slip speed = Ns - Nr

Slip is defined as the ratio of slip speed to the rotor speed.

Mathematically, Percentage slip, \(\% \;s = \left[ {\frac{{{N_s}\;-\;N}}{{{N_s}}}} \right] \times 100\)

Or fractional slip, \(s = \frac{{{N_s}\;-\;N}}{{{N_s}}}\) 


s is the slip

f is the supply frequency

In a three-phase induction motor, the slip is generally 2% to 5%.

  • Range of slip motoring mode is 0 < s < 1
  • Range of slip for generating mode is 1 < s < 2 

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