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Speed of 4 and 6 pole alternators for 50 Hz

Short answer

Synchronous speed N_s = 120f/P. For 4-pole, N_s = (120×50)/4 = 1500 rpm. For 6-pole, N_s = (120×50)/6 = 1000 rpm.

What should be the rpm of a 4 pole and 6 pole alternators to produce a frequency of 50 Hz.

The frequency of an alternator is related to speed and poles by

f=PNs120⇒Ns=120fPf = \frac{PN_s}{120} \quad\Rightarrow\quad N_s = \frac{120f}{P}

For f=50f = 50 Hz:

  • 4-pole: Ns=120×504=1500N_s = \frac{120\times50}{4} = 1500 rpm
  • 6-pole: Ns=120×506=1000N_s = \frac{120\times50}{6} = 1000 rpm

Answer: 1500 rpm for the 4-pole alternator and 1000 rpm for the 6-pole alternator.

✓ Answer checked by Claude Opus 5.5 (high effort)

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