Correct Answer - Option 4 : 1,500 rpm
Concept:
In an alternator, synchronous speed is
\({N_s} = \frac{{120f}}{P}\)
Where Ns = Synchronous Speed in rpm
f = supply frequency in Hz
P = number of poles
Rotor speed, Nr = Ns (1 – s)
Calculation:
Number of poles (P) = 4
Frequency (f) = 50
The synchronous speed of the induction motor is,
\({N_s} = \frac{{120 \times 50}}{4} = 1500\;rpm\)