Correct Answer - Option 1 : 450
Concept:
In the induction motor rotor always rotates speed less than synchronous speed.
The difference between the rotor speed (N) and the rotating magnetic flux speed (Ns) is called slip.
The induction motor slip is usually expressed as a percentage of synchronous speed (NS) and is represented by symbol s.
Mathematically, Percentage slip, \(\% \;s = \left[ {\frac{{{N_s}\;-\;N}}{{{N_s}}}} \right] \times 100\)
Or fractional slip, \(s = \frac{{{N_s}\;-\;N}}{{{N_s}}}\)
Calculation:
Given,
Ns = 600 RPM
slip s = 0.25
∴ \(\;s = \left[ {\frac{{{N_s}\;-\;N}}{{{N_s}}}} \right]\)
0.25 = \([\frac{600-N}{600}]\)
N = 450 RPM