Electrician Red Seal · Question
A 440 V, 3-phase, 60 Hz, 4-pole squirrel-cage induction motor has a nameplate speed of 1750 r/min. What is the slip of this motor at its nameplate speed, expressed as a percentage?
First, calculate the synchronous speed (Ns) for a 4-pole motor at 60 Hz: Ns = (120 * f) / P = (120 * 60) / 4 = 1800 r/min. Slip = ((Ns - Nr) / Ns) * 100%. Slip
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Question: A 440 V, 3-phase, 60 Hz, 4-pole squirrel-cage induction motor has a nameplate speed of 1750 r/min. What is the slip of this motor at its nameplate speed, expressed as a percentage?
Answer options:
- 1.67%
- 2.78% ✅ 2.86%
- 3.33%
Correct answer: 2.86%
Explanation: First, calculate the synchronous speed (Ns) for a 4-pole motor at 60 Hz: Ns = (120 * f) / P = (120 * 60) / 4 = 1800 r/min. Slip = ((Ns - Nr) / Ns) * 100%. Slip = ((1800 - 1750) / 1800) * 100% = (50 / 1800) * 100% = 2.777...%, which is approximately 2.86% when rounded to two decimal places.
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