USCG Exam PracticeMotors and generators
A three-phase squirrel-cage induction motor is running 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 due to rotor inertia
- D. The rotor speed equals synchronous speed only when the motor is lightly loaded
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%.
Cited:NEETS Mod. 5 §4-1