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The number of poles required to achieve a speed of 1800 RPM, when operated on 400V, 60 Hz frequency is:
1. 2
2. 4
3. 6
4. 8

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Correct Answer - Option 2 : 4

Synchronous Speed (Ns):

The synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. It is the speed at which the electromotive force is produced by the alternating machine.

The Synchronous Speed (Ns) is given by,

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

Where,
f is the frequency in Hz and P is the number of poles

Given,

Ns = 1800 RPM

f = 60 Hz

From the above formula,

\(P=\frac{120f}{N_s}=\frac{120 \times 60}{1800}=4\)

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