Answer / istiak

in measuring polarities of a transformer we use a very small
battery or dc supply voltage source.in that case,if we use
alternating current replace of D.C then we couldn't find
polarities because ac changes it's side within a few moment
and dc doesn't..................

Answer / k.prakashchandra

To create momentary magnetic field

ASTM D 3455 - Standard Test Methods for Compatibility of Construction Material with Electrical Insulating Oil of Petroleum Origin has been used for Testing Transformer Oils with a product placed in it. Aged Control Oil has a Power Factor of 0.032% at 100°C. Aged Oil with a Test component has a Power Factor of 0.093% at 100°. Is this increase acceptable? If not why? How much increase is acceptable?

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