At full load, a transformer can have zero voltage regulation
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Answer & Explanation
Correct AnswerC. at leading power factor load
Quick Explanation
Approximate transformer regulation is proportional to R_eq cosφ + X_eq sinφ for lagging load, while the reactance term changes sign for a leading load. At a suitable leading power factor, the negative reactive drop cancels the resistive drop, giving zero regulation. Therefore option C.
Formula / Key Relation
VR≈Req cosφ − Xeq sinφ for leading load; zero when tanφ=Req/Xeq
Detailed Explanation
Correct Answer
C — at leading power factor load
Concept and Reasoning
Approximate transformer regulation is proportional to Req cosφ + Xeq sinφ for lagging load, while the reactance term changes sign for a leading load. At a suitable leading power factor, the negative reactive drop cancels the resistive drop, giving zero regulation. Therefore option C.
Calculation / Key Relation
VR≈Req cosφ − Xeq sinφ for leading load
zero when tanφ=Req/Xeq
Exam Takeaway
Zero regulation requires a particular leading power factor.
Common Mistake
Do not expect zero regulation at unity or lagging power factor when winding resistance is nonzero.
Quick Trick
Zero regulation requires a particular leading power factor.
Common Mistake
Do not expect zero regulation at unity or lagging power factor when winding resistance is nonzero.
Exam Tip
Zero regulation requires a particular leading power factor.
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