An induction motor is essentially a transformer with a rotating, short-circuited secondary. The stator acts like the primary and the rotor like the secondary, with power crossing the air gap electromagnetically.
Formula / Key Relation
Rotor frequency:
f₂ = s f₁
Equivalent rotor resistance for power split:
R₂'/s = R₂' + R₂'(1-s)/s
Detailed Explanation
Concept & ReasoningBoth transformers and induction motors operate by mutual induction. The stator winding produces an alternating/rotating magnetic field that induces rotor emf and current, just as transformer primary flux induces secondary emf. At standstill the analogy is especially direct; during rotation, rotor frequency becomes sf rather than supply frequency and the mechanical output introduces the slip-dependent equivalent resistance R2'/s. This transformer analogy is the foundation of the induction-motor equivalent circuit.How to Solve It in the ExamInduction motor = rotating transformer.Important Exam PointUse the transformer equivalent circuit first, then introduce slip.Related Revision PathThis question sits in the revision path Electrical…
Concept & Reasoning
Both transformers and induction motors operate by mutual induction. The stator winding produces an alternating/rotating magnetic field that induces rotor emf and current, just as transformer primary flux induces secondary emf. At standstill the analogy is especially direct; during rotation, rotor frequency becomes sf rather than supply frequency and the mechanical output introduces the slip-dependent equivalent resistance R2'/s. This transformer analogy is the foundation of the induction-motor equivalent circuit.
How to Solve It in the Exam
Induction motor = rotating transformer.
Important Exam Point
Use the transformer equivalent circuit first, then introduce slip.
Related Revision Path
This question sits in the revision path Electrical Machines → Induction Motors → Equivalent Circuit .
Quick Trick
Induction motor = rotating transformer.
Common Mistake
Do not equate an induction motor to a synchronous motor; its torque requires slip.
Exam Tip
Use the transformer equivalent circuit first, then introduce slip.
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