The synchronous speed for an electric induction motor is determined by the power supply frequency and the number of poles in the motor winding and can be expressed as: n = f (2 / p) 60 (1) where n = shaft rotation speed (rev/min, rpm) f = frequency (Hz, cycles/sec, 1/s) p = number of poles

EXAMPLE – SPEED OF ELECTRIC MOTOR WITH TWO POLES

A motor with two poles is supplied with power with frequency 50 Hz (1/s). The rotation speed can be calculated as n = (50 1/s) (2 / 2) (60 s/min)  = 3000 rpm (1/min)