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Calculate Rotational Speed of an Induction Motor

FAQ No. FAQ02018

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We are using an Inverter for speed control. How can we calculate the rotational speed of an induction motor?


Generally, the speed (N) of an induction motor is expressed by the following formula:

N = (120f/P) × (1 - S) (rpm)

f: Primary frequency

P: Number of motor poles

S: Slip


Where f = 60 Hz, P = 4 poles, and S = 3%,

N = ( (120 × 60) ⁄ 4) × (1 − 0.03) = 1,746 (rpm