USCG Exam PracticeElectrical fundamentals — DC/AC, motors, distribution
A three-phase squirrel-cage induction motor is running at full load. Which statement best describes the rotor speed relative to synchronous speed?
- A. The rotor runs at exactly synchronous speed because the stator field locks it in.
- ✓ The rotor runs slightly below synchronous speed due to slip, typically 2–5% at full load.Correct
- C. The rotor runs slightly above synchronous speed to maintain induced rotor currents.
- D. The rotor speed equals synchronous speed only when the motor is lightly loaded.
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. Slip is typically 2–5% at full load. NEETS Mod. 5 §4-1.
Cited:NEETS Mod. 5 §4-1