When a normally excited synchronous motor experiences a load increase, its armature current rises because
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Answer: D. Er (net resultant voltage) in armature is increased
Explanation
When a mechanical load is applied, the rotor momentarily lags behind the rotating stator field. This mechanical lag increases the load angle between the rotor and stator magnetic fields. The larger load angle directly increases the net resultant voltage in the armature, raising current. Armature current in a synchronous motor depends on the phasor difference between applied voltage and back emf. The load angle is the spatial displacement angle between the rotor poles and rotating stator flux. Vector addition of applied voltage and inverted back emf determines the net resultant voltage.
Load changes occur frequently in industrial manufacturing plants driven by large synchronous motors. Understanding armature current response helps engineers protect motor windings from thermal overload conditions. Electrical protection systems rely on monitoring these current variations during normal operation. The motor speed remains strictly constant at synchronous speed despite changes in the mechanical load. The power factor changes as a consequence of load increases rather than being the primary root cause. The back emf magnitude remains largely constant because field excitation is not altered during the load change.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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