Correct AnswerB. Internal or partial discharge test
Quick Explanation
Internal/partial-discharge testing is specifically aimed at detecting deterioration, void activity and localized insulation discharge inside a bushing before it develops into complete breakdown.
Detailed Explanation
Concept & Reasoning
A bushing experiences high electric stress across solid/liquid insulation interfaces. Voids, delamination or contamination can initiate partial discharges that erode insulation progressively. Measuring PD magnitude and inception/extinction behavior is therefore a sensitive diagnostic for internal insulation condition.
How to Solve It in the Exam
Internal deterioration/voids → partial-discharge test.
Important Exam PointPower-factor/tanδ tests assess bulk dielectric condition; PD is more localized-discharge focused.
Related Revision Path
This question sits in the revision path Power System → High Voltage Engineering → Bushings .
