Which motor features stator and rotor fields rotating simultaneously?
Show answer Hide answer
Answer: D. Synchronous motor
Explanation
Synchronous motors feature stator and rotor fields rotating simultaneously at the exact same speed. The rotor magnetic field locks magnetically with the rotating stator magnetic field during operation. This simultaneous rotation ensures zero relative speed difference between the two main magnetic fields. Stator fields rotate at synchronous speed determined by supply frequency and pole count. Rotor fields are created by direct current excitation supplied through slip rings or brushless exciters. Magnetic locking allows the rotor to track the rotating stator flux without slipping.
Precision industrial drives utilize synchronous motors to maintain exact synchronization across multiple sections. Synchronous motors provide superior efficiency in large-scale industrial applications requiring constant speed. Understanding magnetic field rotation helps technicians troubleshoot synchronous motor synchronization issues. Direct current motors rely on mechanical commutation rather than simultaneously rotating stator and rotor fields. Reluctance motors operate on magnetic reluctance principles without DC rotor field windings. Induction motors operate with slip, meaning rotor and stator fields do not rotate at identical speeds.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. At what speed do synchronous motors always operate______________?
Show answer Hide answer
Answer: A. the synchronous speed
Synchronous motors operate at a strictly constant speed known as synchronous speed. Rotor speed is permanently locked to the frequency of the alternating current power supply. There is zero slip between the rotating stat...
Q2. When does hunting occur in a synchronous motor___________?
Show answer Hide answer
Answer: B. when load varies
When mechanical load varies abruptly, the rotor experiences a sudden transient torque angle shift. This sudden shift causes the rotor to oscillate back and forth around its new equilibrium position. These sustained mecha...
Q3. The breakdown torque of a synchronous motor is__________?
Show answer Hide answer
Answer: B. directly proportional to applied voltage
The maximum or breakdown torque of a synchronous motor is directly proportional to applied voltage. Peak torque capability depends on the product of terminal voltage and excitation voltage magnitudes. Higher applied term...
Q4. Operating a synchronous motor with under-excitation results in what type of power factor_____________?
Show answer Hide answer
Answer: C. lagging
Under-excitation of a synchronous motor causes it to draw lagging reactive power from the supply. Drawing lagging reactive power results in a lagging power factor at the motor terminals. Weak rotor excitation fails to me...
Q5. If the generated back e.m.f. in a no-load synchronous motor equals the applied voltage, then
Show answer Hide answer
Answer: D. the excitation is said to be hundred per cent
Standard electrical machine testing defines one hundred percent excitation as the condition where back emf equals voltage. At this specific excitation level under no-load with zero phase angle, internal voltages match te...
Q6. The spatial separation between the rotating stator flux and rotor poles is termed the _________ angle.
Show answer Hide answer
Answer: C. torque
The physical angular displacement between rotating stator and rotor poles is called the torque angle. This angle represents the mechanical lag of the rotor behind the rotating stator magnetic field. Torque angle increase...