Attached is a shot of a transformer. One of the windings is above 130C. The transformer is quite noisy, and under the windings was what appeared to be melted insulation. Sounds like a a slam dunk to replace the transformer.
My question is this:

Are there any online tests we can perform to get more information about the condition of these windings? We can take voltage drops and loads, but these are quite variable, and hardly definitive..
I plan on doing a Megger, and an All-test off-line inductance and impedance test, but I wanted to see how much progress I could make on-line.

TH710124.SIT (364 Kb, 159 downloads)

Is this an oil cooled transformer?Do you carry out oil analysis on these transformers? You can get some good knowledge from your oil resultsas to the condition of the transformer internals.

Hope this helps!

Hooch

Partial discharge testing is a method of measuring potential to ground while transformer is on line. Oil testing can tell you of arcing which creates soot and also acetelyne gas!! I believe that Pdma corporation in florida maybe able to help you with additional recommend testing.

Dave:

Partial discharge testing will detect the delamination of insulation from the conductors between conductors and conductors to ground. It also requires a baseline or comparison reading.

Please note that there is an IEEE standard on PD testing which has been updated and is presently being re-issued.

There are also additional standards, including IEEE 388 and IEEE 389 which cover transformer testing.

You may also want to look into less expensive and more direct equipment, such as TTR (Turn-To-Turn Ratio), Motor Circuit and Electrical Signature Analysis (voltage signature, in particular) and Doble Testing. These are the standard industry test methods.

Sincerely,
Howard