RPM (revolutions per minute) depends on electrical frequency and number of poles. The kVA rating determines generator/motor capacity class.
RPM = 120 × f ÷ P. f = frequency (Hz), P = number of poles.
The magnetic field rotation speed — actual rotor speed is slightly less (slip).
Generator sizing, motor speed selection, VFD programming.
50 Hz in most countries, 60 Hz in USA/Canada. This affects RPM directly.
Synchronous speed from frequency and poles.
120 is a constant. Common pole counts: 2, 4, 6, 8. More poles = lower RPM.
3 steps to find motor/generator speed.
50 Hz (Europe/Asia) or 60 Hz (Americas). Check your grid standard.
Check the nameplate: 2-pole (high speed), 4-pole (standard), 6/8-pole (low speed).
RPM = 120 × frequency ÷ poles. A 4-pole motor at 50 Hz = 1500 RPM.
Synchronous RPM for common pole/frequency combinations.
| Poles | 50 Hz | 60 Hz |
|---|---|---|
| 2 | 3,000 | 3,600 |
| 4 | 1,500 | 1,800 |
| 6 | 1,000 | 1,200 |
| 8 | 750 | 900 |
| 10 | 600 | 720 |
| 12 | 500 | 600 |
Common motor and generator speeds.
500 kVA generator:
120 × 50 ÷ 4 = 1,500 RPM
100 kVA motor:
120 × 60 ÷ 2 = 3,600 RPM
75 kVA pump motor:
120 × 50 ÷ 6 = 1,000 RPM
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Common questions about kVA and RPM.
No. RPM depends on frequency and poles. kVA indicates capacity, not speed.
The speed of the rotating magnetic field: RPM = 120 × f ÷ P. Actual rotor speed is slightly less due to slip.
To produce the correct frequency (50/60 Hz). A 4-pole generator must spin at 1500 RPM for 50 Hz output.
Slip is the difference between synchronous speed and actual rotor speed, typically 2–5% at full load.
Yes, using a Variable Frequency Drive (VFD) to change the supply frequency, or by using a motor with different pole count.