Doble Tests of Power Transformer

[CuriousElectron]

Hi All,
Are Doble tests effective in evaluating health of GSU transformer windings? Does a transformer need to have its oil drained prior to performing a test(Doble or Megger) to focus on winding insulation, since oil would act as an insulator?
Thank you for your thoughts.
EE

 

[bacon4life]

No. The typically tests are done on will the transformer filled with oil. Oil is an integral part of the insulation system you are attempting to test.

The one exception I can think of is a sweep frequency analysis (SFRA) test to detect any damage that may have occurred when shipping the transformer from the manufacturer to the site. The shipping related SFRA is done with the transformer configured for shipping, which typically includes removing bushings and radiators.