USCG Exam PracticeMotors and generators
A three-phase squirrel-cage induction motor is operating at full load. Which statement best describes the relationship between rotor speed and synchronous speed?
- A. The rotor turns at exactly synchronous speed to maintain maximum torque
- ✓ The rotor turns slightly below synchronous speed, with a typical slip of 2–5%Correct
- C. The rotor turns slightly above synchronous speed to sustain induced rotor currents
- D. The rotor speed equals synchronous speed only when the load is removed
Why B is correct
NEETS Mod. 5 §4-1 explains that the rotor of an induction motor can never reach synchronous speed because at synchronism there would be no relative motion, no induced current, and no torque. Slip at full load is typically 2–5%. The rotor always runs below synchronous speed.
Cited:NEETS Mod. 5 §4-1