Correct AnswerB. Damper winding reactance
Quick Explanation
Immediately after a sudden symmetrical fault, damper-winding currents produce the strongest opposing transient flux and therefore the smallest subtransient reactance. The effect associated with the damper winding decays first as those induced currents die out rapidly.
Detailed Explanation
Concept & Reasoning
A synchronous generator fault current passes through subtransient, transient and steady-state stages. Damper circuits dominate the very early subtransient interval; field-winding transients persist longer. As damper current decays, the effective reactance rises from Xd'' to Xd' and finally Xd.
How to Solve It in the Exam
First few cycles → damper winding → subtransient reactance.
Important Exam PointLink time sequence: damper dies first, field transient next.
Related Revision Path
This question sits in the revision path Power System → Fault Analysis → Synchronous Generator Reactances .
