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Sunday, September 11, 2011

Winding Resistance Testing for Power Transformer

Measurement of winding resistanceThe purpose of testing the winding resistance is to detect and confirm faults in the transformer winding.  The standard criteria being used before is that the standard deviation of three readings must not exceed 0.5. However, the new IEEE standard C57.12.90, there is no specific requirements for the resistance but will serve as reference for future testing.

2.1 Instrument
Transformer Resistance Test Equipment (Resistance Bridge)

Note: Please click the photos for larger images.

Engineers while conducting winding resistance test

2.2 Testing Schematic

2.3 Testing procedure
a. According to the diagram, via the resistance bridge we can get the resistance value of the windings. Common winding, series winding and tertiary will be measure. The windings with tap winding will be measured tap by tap.
b. At the same time, we will measure the top and bottom oil temperature. The mean value of the two will be taken as the winding temperature of the winding. Before this test the transformer has to be standing still without oil flow for at least 3 hours.

2.4 Checking point
According to IEEE STD. C57.12.90, there is no specific requirements for the resistance; it is just for the reference.


  1. Rob is this a hi-pot test?

  2. This is not hi-pot sir. the objective of this test is to confirm faults on transformer windings. The DC hi-pot determines the insulation condition of transformer parts (usually tested are the transformer bushings)


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