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Synchronous Speed of Electrical Motors

The speed at which an induction motor will operate depends on the input power frequency and the number of electrical magnetic poles in the motor

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The synchronous speed of an induction motor is based on the supply frequency and the number of poles in the motor winding and can be expressed as:

ω = 2 60 f / n         (1)

where

ω = pump shaft rotational speed (rev/min, rpm)

f = frequency (Hz, cycles/sec)

n = number of poles

The rotational speed at different frequencies and number of poles can be listed as:

Pump shaft rotational speed - ω - (rev/min, rpm)
Frequency - f -
(Hz)		 Number of poles - n
2 4 6 8 10 12
10 600 300 200 150 120 100
20 1200 600 400 300 240 200
30 1800 900 600 450 360 300
40 2400 1200 800 600 480 400
501) 3000 1500 1000 750 600 500
602) 3600 1800 1200 900 720 600
70 4200 2100 1400 1050 840 700
80 4800 2400 1600 1200 960 800
90 5400 2700 1800 1350 1080 900
100 6000 3000 2000 1500 1200 1000
  1. Motors designed for 50 Hz are common outside U.S
  2. Motors designed for 60 Hz are common in U.S

Variable Frequency Drive

With a variable frequency drive its possible to modulate the speed of the motor by changing the frequency supplied to the synchronous motor. The relation between motor speed, frequency and number of poles in the motor can be found in the table above.

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Related Topics

  • Electrical - Amps and electrical wiring, AWG - wire gauge, electrical formulas, motors and units

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