What is a major advantage of synchronous motors over wound-rotor induction motors?
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Answer: A. its power factor may be varied at will
Explanation
Synchronous motors feature independent DC field excitation controlled separately from the stator supply. This independent control allows operators to adjust the operating power factor to any desired value. Induction motors lack this feature and always consume lagging magnetizing current from the supply. Power factor control improves electrical efficiency and reduces reactive power losses in transmission lines. Wound-rotor induction motors permit external rotor resistance control for starting and speed regulation. Synchronous motors require a DC exciter source to supply current to their rotating field windings.
Large industrial facilities install synchronous motors to correct plant power factor and lower electricity bills. Operating at leading power factor helps offset inductive loads from nearby transformers and induction motors. This flexibility makes synchronous drives popular for heavy continuous industrial processing loads. Speed is strictly dependent on supply frequency and pole count, remaining constant during normal operation. Speed control is actually more complex for synchronous motors than for wound-rotor induction motors. Selecting none of the above is wrong because power factor variability is a major documented advantage.
- Subject
- Engineering
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- Electrical Engineering
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- Difficulty
- medium
Related questions
Q1. What components are included in a three-phase synchronous motor_____________?
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Answer: C. two slip-rings
The rotating field winding of a synchronous motor requires a continuous direct current supply. Connecting this external DC source to a rotating shaft requires exactly two electrical slip-rings. One slip-ring connects to...
Q2. When does a synchronous motor function as a synchronous capacitor____________?
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Answer: D. over-excited
When a synchronous motor is over-excited, it generates reactive power and acts as a capacitor. Excess field excitation forces the machine to supply leading reactive current to the AC power grid. An over-excited synchrono...
Q3. How can the constant operational speed of a synchronous motor be shifted to a new fixed value?
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Answer: A. By changing the supply frequency
The synchronous speed of the motor is mathematically tied to the alternating current supply frequency. Altering the electrical supply frequency changes the speed of the rotating magnetic stator field. Since the rotor loc...
Q4. What modification allows a synchronous motor to start independently?
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Answer: D. none of the above
Damper windings are placed on the rotor pole faces, not the stator, to enable starting as an induction motor.
Q5. What type of equipment serves as exciters for synchronous generators______________?
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Answer: B. d.c. shunt machines
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Q6. Which statement regarding single-phase induction motors is true?
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Answer: D. It is not self-starting
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