A four pole, 60 Hz, three-phase synchronous...

Question 1 of 270705eccefa4bacbc34ba4d48226

A four pole, 60 Hz, three-phase synchronous motor comes up to 1760 RPM when started as an induction motor. What is the percent slip after the rotor field is energized?

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Question 1 of 27070

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A four pole, 60 Hz, three-phase synchronous motor comes up to 1760 RPM when started as an induction motor. What is the percent slip after the rotor field is energized?

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🔍 Key Concepts

• Synchronous speed formula for AC motors • Definition of slip in an induction motor • What happens to slip when a motor is operating as a synchronous motor (rotor field energized)

💭 Think About

• First, calculate the synchronous speed of a 60 Hz, 4‑pole motor and compare it to 1760 RPM. • Think about whether the rotor of a synchronous motor, once its DC field is energized and it locks in, runs at synchronous speed or slightly below it. • Use the standard slip formula and ask yourself: after the rotor field is energized and the machine is truly synchronous, is there still a speed difference between rotor and stator fields?

✅ Before You Answer

• Confirm the synchronous speed using the pole count and frequency, in RPM. • Write the slip formula $s(\%) = \frac{N_s - N_r}{N_s} \times 100$ , and identify which rotor speed you should use after the rotor field is energized. • Decide if a synchronous motor in steady operation has nonzero slip or zero slip between rotor field and rotating stator field.