At what speed does the rotor of an induction motor operate__________?
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Answer: B. below synchronous speed
Explanation
Induction motor operation requires relative motion between the stator field and the rotor conductors. If the rotor reached synchronous speed, relative motion would drop to zero and induce no current. Therefore, the rotor must always operate at a speed slightly below synchronous speed to produce torque. Synchronous speed is determined by the electrical supply frequency and the stator pole count. The speed difference between synchronous speed and rotor speed is known as motor slip. Torque generation depends entirely on this continuous cutting of magnetic flux lines by rotor bars.
Industrial drives rely on this slight speed lag to maintain stable electromechanical energy conversion. Monitoring rotor speed helps maintenance personnel ensure motors are not overloaded during operation. Electric motor nameplates clearly list full-load speeds that are always slightly below synchronous speeds. Operating at synchronous speed would eliminate rotor current and cause the motor torque to drop to zero. Operating above synchronous speed turns the induction motor into an induction generator. Option D is incorrect because the rotor speed is strictly constrained to be below synchronous speed.
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- Engineering
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- Electrical Engineering
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- medium
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