Stator Winding

A change in the environment local to the generator is where I would look first. From the photographs the "white deposit" doesn't look like it originated from inside the windings so something external would be the logical culprit.

Look for something that has been placed in the local of the cooling intake.

Baldor-Reliance published a white paper on the effects of localised pollution.

i agree that surroundings will have its effect.but then it should be on all bars and not few

Some guessing:

1. Its solidification of the white smoke that when it comes out of the appliance, the appliance (mainly electrical) does not work anymore
2. What material is the stator bar? Any coating? If so is there an oxide in existence that is white?
3. Are there any vermins?

Here is some info on problems with windings. The heavier deposits appear where the insulation has broken down. It may be the junction of where two different insulators were used. One on the winding where it passes though the slot may be deferent then whats on the rest of the winding.

http://www.irispower.com/pdf/techpapers/general%20testing/recent%20problems%20experienced%20with%20motor%20and%20generator%20windings%20-%20IEEE%20PPIC%20-%202009-06%20sep%202009.pdf

Good Answer!

I would also suggest analyzing the cooling gas (I am assuming hydrogen). If there is oil vaporizing in the cooling gas from the seals this could be deposits from it.

Drew K

Did some animal of some sort enter the enclosure, the white powder being its cremated remains?

Are those water cooled windings?

Drew K

I would take samples of that powder and have it analyzed to know exactly what it is. My guess is that it's mold, which could from a few sources. If the unit was out of service for an extended period without an inert gas blanket, the unit was left opened in a high humidity environment without any keep-warm heaters, or you have have a water leak in the cooling system.

To remedy the situation you need to first determine the nature of the contaminant, then track down the cause(s). If you want that machine to last another 34 years it needs extensive and complete testing to determine the level of insulation integrity since there is clear evidence of cracked, peeling, and questionable end turn insulation.

When it has been professionally inspected and evaluated, then you can decide if the needed work is economically justifiable.

The unit is air cooled.The air being cooled by water in surface air coolers.The black tape is the anti-corona taping.inside the anti corona taping is the mica and glass taping.The megger,Ductor results are normal

The more that gets added, the closer the solution. To speed things up next time, it is best to make sure all the relevant information is in the original posting as readers here have better things to do than play "20 Questions" games.

White powder in HV Electrical equipment could be caused by partial discharge.

Is it dusty, coarse, fine, thick, thin, loose, their by gravity, easy to remove by light brushing, or engrained needing a wire brush or sandpaper. And if brushed away what it the 'clean' surface like? pitted as if corrosion, or like new when wiped - Is it 'salty' ....etc, etc...?

Not that I could say what it was if you told me. But others might know.

Test the composition of the "powder" - It may be fungal / mould, or it may be corrosion on the metal parts above the windings dropping onto them.

External contamination may also be possible - trace the path of the deposits.

Let us know what you find.

As suggested by Mr. Ram, get the "powder" analyzed. It could be powder from end winding braidings. If the braids become loose, they may disintegrate into powder. Check the end winding clamping system for any looseness, looseness of the winding bars in stator slots, especially end wedges. Are there ripple springs below the slot wedges? What type of winding insulation is it? Glass Epoxy? In that case, loose winding bars may hammer the core slots due to bar vibrations and insulation may appear in the form of powder. Were the winding vibrations normal before the appearance of powder? Look into all these aspects and coma back.

I think the insulation layers have deteriorated at the line of stress grading (if there is) and the semicon layer. When it is not working properly, it overheats and produces PD's.

What was the reason? Did you tested the white dust?