How does the magnitude of field flux behave in a 3-phase synchronous motor?
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Answer: D. remains constant at all loads
Explanation
In a synchronous motor, the main field flux is produced by the DC excitation source. Since the DC excitation voltage remains constant, the resulting magnetic flux remains constant. Changes in mechanical load do not alter the magnitude of the main rotor magnetic flux. Rotor field flux is generated independently of the alternating current stator supply voltages. Direct current flows steadily through the rotor field winding to maintain constant magnetic strength. Armature reaction creates additional magnetic effects, but the main field flux remains steady.
Industrial operators rely on constant main field flux to maintain predictable motor performance characteristics. Stable rotor flux ensures consistent back electromotive force generation during normal operation. Power system engineers utilize constant excitation flux when modeling synchronous motor behavior. Field flux does not vary with power factor because excitation is set externally by the operator. Speed is completely fixed by supply frequency, meaning flux cannot vary with rotational speed. Stating flux varies with load confuses main rotor flux with armature current and torque angle changes.
- Subject
- Engineering
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- Electrical Engineering
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- —
- Difficulty
- medium
Related questions
Q1. Operating a synchronous motor with under-excitation results in what type of power factor_____________?
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Answer: C. lagging
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Q2. If the generated back e.m.f. in a no-load synchronous motor equals the applied voltage, then
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Answer: D. the excitation is said to be hundred per cent
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Q3. The spatial separation between the rotating stator flux and rotor poles is termed the _________ angle.
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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...
Q4. How does the armature current behave in a synchronous motor
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Answer: C. has large values for low and high excitation
The armature current in a synchronous motor is high under both very low and very high excitation. Low excitation forces the motor to draw high lagging reactive current to sustain the magnetic field. High excitation force...
Q5. At what coupling angle is maximum power achieved in a synchronous motor____________?
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Answer: C. 90°
The power transfer equation for a synchronous motor depends on the sine of the load angle. The mathematical sine function reaches its maximum value of one at ninety degrees. Therefore, maximum power and torque are achiev...
Q6. The back e.m.f. of a synchronous motor is a function of______________?
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Answer: C. load angle
The back electromotive force vector phase position depends directly on the load angle. As mechanical load shifts the rotor backward, the back emf vector shifts by the same angle. This angular displacement between applied...