Correct Answer - Option 4 : 1000
Concept:
In a 3-phase induction motor, the synchronous speed & slip can be calculated as
\({N_s} = \;\frac{{120f}}{P}\;\)
\(s = \;\frac{{{N_s} - {N_r}}}{{{N_s}}}\)
Nr = Ns (1 – s)
Where, Ns = Synchronous speed in rpm,
Nr = Rotor speed in rpm,
s = Slip of the machine,
f = Supply frequency in Hz,
P = Number of poles,
Calculation:
Given -
Pole P = 6
Frequency = 50 Hz
The synchronous speed of alternator N = (120f) / P = (120 × 50) / 6 = 1000 rpm