Previous Year Question

Correct Answer

A — Armature current with excitation (field) current

Concept and Reasoning

A synchronous-machine V-curve plots armature current against field current at constant mechanical load and terminal voltage. As excitation changes from under- to over-excited, armature current falls to a minimum near unity power factor and rises again, giving the V shape. Hence option A.

Calculation / Key Relation

V-curve: Ia versus If at constant load

Exam Takeaway

V-curve minimum approximately corresponds to unity power factor.

Common Mistake

Do not confuse a V-curve with an inverted V-curve, which plots power factor versus field current.