Operating a synchronous motor with under-excitation results in what type of power factor_____________?
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Answer: C. lagging
Explanation
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 meet the internal voltage requirements, absorbing inductive reactive current. Under-excitation means the DC field current supplied to the rotor is set below normal operating levels. Lagging power factor means the current waveform lags behind the voltage waveform in phase. Inductive loads in power systems naturally cause lagging power factors that require compensation.
Operating synchronous motors under-excited is rarely desired because it worsens grid power factor. Electrical systems must account for under-excited motor loads when calculating total facility reactive power. Proper excitation control prevents undesirable lagging power factor conditions on distribution transformers. Zero power factor implies pure reactive power exchange without active work, which does not occur here. Unity power factor occurs only at normal excitation levels where armature current is minimized. Leading power factor is produced by over-excitation rather than under-excitation conditions.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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