If a 60 Hz, 4‑pole motor operates with a slip of 3%, what is the rotor speed?

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Multiple Choice

If a 60 Hz, 4‑pole motor operates with a slip of 3%, what is the rotor speed?

Explanation:
Rotor speed of an induction motor depends on the synchronous speed and the slip. For a 60 Hz supply with four poles, the synchronous speed is Ns = 120 f / P = 120 × 60 / 4 = 1800 rpm. The given slip is 3%, so the rotor runs 3% slower than synchronous: Nr = Ns × (1 − s) = 1800 × 0.97 = 1746 rpm. Equivalently, 3% of 1800 is 54 rpm, so 1800 − 54 = 1746 rpm. Thus the rotor speed is 1746 rpm.

Rotor speed of an induction motor depends on the synchronous speed and the slip. For a 60 Hz supply with four poles, the synchronous speed is Ns = 120 f / P = 120 × 60 / 4 = 1800 rpm. The given slip is 3%, so the rotor runs 3% slower than synchronous: Nr = Ns × (1 − s) = 1800 × 0.97 = 1746 rpm. Equivalently, 3% of 1800 is 54 rpm, so 1800 − 54 = 1746 rpm. Thus the rotor speed is 1746 rpm.

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