USCG Exam PracticeElectrical fundamentals — DC/AC, motors, distribution
A three-phase squirrel-cage induction motor is running at full load. Its rotor speed compared to the stator's synchronous field speed is best described as:
- A. Exactly equal to synchronous speed because the rotor is dragged along by the field
- ✓ Slightly less than synchronous speed due to slipCorrect
- C. Slightly greater than synchronous speed to maintain induced rotor current
- D. Exactly half of synchronous speed at full load
Why B is correct
The rotor can never reach synchronous speed because at synchronism there would be no relative motion, no induced current, and no torque. The difference between synchronous speed and rotor speed is slip, typically 2–5% at full load. (NEETS Mod. 5 §4-1)
Cited:NEETS Mod. 5 §4-1