Correct AnswerA. Both stator and rotor windings carry current
Quick Explanation
In a conventional doubly excited rotating machine, electromagnetic torque results from interaction between stator and rotor magnetic fields; hence both windings must be excited and carry current for this torque-production mechanism.
Formula / Key Relation
Electromagnetic torque (conceptually):
Te ∝ Φs Φr sinδ
Energy method:
Te = ∂W'_{fld}/∂θ |_{currents constant}
Detailed Explanation
Concept & ReasoningElectromagnetic torque is produced when two magnetic fields have a tendency to align. In a conventional machine with both stator and rotor windings, stator current produces one field and rotor current produces the other. Their interaction creates tangential force and torque. The broader energy-conversion principle also includes reluctance torque, where a wound rotor current may not be required, but the question is framed around the standard doubly excited machine model represented by the given options.How to Solve It in the ExamTorque needs interacting fields, not merely a uniform air gap.Important Exam PointIdentify whether the question refers to doubly…
Concept & Reasoning
Electromagnetic torque is produced when two magnetic fields have a tendency to align. In a conventional machine with both stator and rotor windings, stator current produces one field and rotor current produces the other. Their interaction creates tangential force and torque. The broader energy-conversion principle also includes reluctance torque, where a wound rotor current may not be required, but the question is framed around the standard doubly excited machine model represented by the given options.
How to Solve It in the Exam
Torque needs interacting fields, not merely a uniform air gap.
Important Exam Point
Identify whether the question refers to doubly excited torque or reluctance torque.
Related Revision Path
This question sits in the revision path Electrical Machines → Electromechanical Energy Conversion → Torque Production .
Quick Trick
Torque needs interacting fields, not merely a uniform air gap.
Common Mistake
Overgeneralizing the statement to every machine type can cause confusion; switched-reluctance machines are a special case.
Exam Tip
Identify whether the question refers to doubly excited torque or reluctance torque.
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