Most suitable power-factor test voltage for 13.8kV?

Certification Forum NETA Level 3 Exam
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1

I came across this question going through the NETA 3 testguy exam.

What would be the most suitable insulation power-factor test voltage for a 13.8kV dry-type transformer winding?
|a.|2kV|
|b.|8kV|
|c.|10kV|
|d.|A and B|
|e.|A and C|

Why does it say the correct answer is D? Wouldn’t you power factor it at 10kV?

2

You are performing Power Factor test on a dry-type transformer >5kV which requires tip-up testing which is conventionally performed at 2kV. Also, it states 13.8kV transformer which means the test voltage must be kept within the phase to ground voltage rating, so they limit you to 8kV.
Doble documentation states you are allowed to test at 10kV, but per IEEE standards this is not acceptable.

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THANKS! This has been bugging me for awhile.

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