Doble Testing on Dry Type Transformers
Doble Testing on Dry Type Transformers
(OP)
Hello:
We recently specified Doble testing (tip-up) on a 750/1000kVA dry-type transformer (20+ years old) as part of a comprehensive test regimen. Our NETA certified test company said that they would do it, but would not be able to get any useful information because the transformer is a dry-type.
Any comments, folks?
Thank you,
hidalgoe
We recently specified Doble testing (tip-up) on a 750/1000kVA dry-type transformer (20+ years old) as part of a comprehensive test regimen. Our NETA certified test company said that they would do it, but would not be able to get any useful information because the transformer is a dry-type.
Any comments, folks?
Thank you,
hidalgoe






RE: Doble Testing on Dry Type Transformers
In the absence of this data, interpretation of a single test is more difficult because dry transformers employ several different construction methods giving varying dielectric constants within the transformer. What is an acceptable reading for one make and model is not acceptable for another.
A power factor tip-up test might be useful in detecting voltage-related issues. Also, testing a "good" transformer today will provide data for comparison with future tests for better evaluation.
Some transformer users do not bother to test transformers in this size range.
old field guy
RE: Doble Testing on Dry Type Transformers
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If we learn from our mistakes I'm getting a great education!
RE: Doble Testing on Dry Type Transformers
One of the problems with the dry type transformer is the surface of the transformer (typically an expoxy or resin) becomes partially conductive which skews readings all over the place.
The most consistent test I have seen for dry type transformers is Polarisation index where we look for readings above 2 (10 minute result/1 minute result) The test voltage should be below the operating voltage of the transformer (L-G)
RE: Doble Testing on Dry Type Transformers
RE: Doble Testing on Dry Type Transformers