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Synchronous speed in RPM of 6 pole, 50 Hz, 3-phase induction motor will be:
1. 1500
2. 3000
3. 1800
4. 1000

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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,

N= 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 

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