What factors determine the magnitude of the stator back e.m.f. in a synchronous motor_______________?
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Answer: A. d.c. excitation only
Explanation
Stator back emf is generated by the rotating magnetic flux cutting across the stator armature coils. This rotor flux magnitude is determined exclusively by the direct current supplied to the field winding. Therefore, DC field excitation is the sole factor controlling the magnitude of the back emf. Back emf represents the counter voltage induced in the motor armature during operation. The speed of a synchronous motor is strictly constant and tied to the constant grid frequency. Because speed and pole count are fixed, rotor flux strength dictates the back emf level.
Engineers adjust DC excitation to control reactive power exchange between the motor and the power grid. Understanding back emf generation helps technicians calculate phasor diagrams for synchronous machines. Proper excitation control ensures stable motor operation across various industrial load conditions. Speed remains constant at synchronous speed and does not vary to change the back emf. Load on the motor affects the torque angle rather than the fundamental magnitude of back emf. Speed and rotor flux are not both variable because synchronous speed is strictly constant.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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