Synchronous Speed of Electrical Motors

Engineering ToolBox > 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

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
Frequency - f - (Hz)	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

Motors designed for 50 Hz are common outside U.S
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.

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

Variable Frequency Drive

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