Identify The Problem and Discuss It, 15MW Generator

What are the ratings of the generator, how old is it, what type of environment is it in, and how long ago was it rewound? More pictures showing the area where this occurred would help.

A before and after picture would be a great help.

Right now the only thing I can identify as the problem is the OP cannot communicate the problem with a single image and no annotations. All of the white I see might be lighting highlight. It might also be dust or mold. The color of the insulation might be the natural color of the varnish. It might also be from overheating.

If you are referring to the white residue, does it wipe off?

Have you contacted the maker of the generator and asked their opinion?

How old is the generator? How long has the white stuff been there?

Does anyone in your organization have an opinion?

Looks like a wicker chair starting to mildew.....coronal discharge...probably

http://www.dtic.mil/dtic/tr/fulltext/u2/a212924.pdf

Identify The Problem? If you didn't notice a problem, how do expect me to? What did you identify it as? The only problem I see, is a lack of info to go on.

Solar Eagle gave you the correct diagnosis. That is Corona and page 13 of the link he gave says, "Stator - 22. Visual inspection should include observation of the end turns for evidence of corona attack from deposits that can be white, gray, or red or from erosion of the insulation, especially where adjacent turns are markedly different potentials."

The existence of corona is inevitable, especially where voltage stress is the highest, like where one phase ends and the nest phase begins. Corona is controlled by construction process, like minimizing voids in the insulation and tight fit to core iron, and use of conductive paint to get the surface currents away.

Basically, you need a generator specialist to inspect your entire machine and make recommendations on the whole system. Normally, we clean up the corona deposits and fix any obvious problems and figure how much life the stator windings have, based on all of the inspection results.

I think the problem is that the camera is too close to show the whole chair...

The question that OP should answer is "why does he think there is a problem?" Generator windings consist of many interleaved surfaces that are at different potentials relative to each other over a single cycle. This difference in potential may cause the surfaces to attract charged particles of dust, which build up over time.

Solving the "problem" may be as simple as determining if there even is one by using a high voltage insulation tester, then cleaning the surfaces with the proper solvent and replacing the cooling air filters more often.

The preventive maintenance interval is the key.

I suppose these are phase rings. If yes, then are you referingr to size variation (swelling of insulation)? Please give more information about voltage, class of insulation, age of the generator.