White dust inside generator 1

[irishal]

Hi,

We recently opened up our generator (150MW, air cooled) to inspect for oil leaks and a general look. This is the first time I have been involved in this inspection but I noticed a thin film of white dust lying on the tops of strengthening bars and other surfaces. I am pretty sure it is not just general dust or dirt getting inside the machine. The machine has been in service for just 18 months.

Has any one heard of any similar occurrences and what the problem could be?

Thanks,
Irish Al

 

[metengr]

If the source of the dust is not coming from your Plant, it is possible the source of the dust could have been from the source (manufacturer), during shipment and/or storage of the generator prior to installation because nobody bothered to look for or note the dust. I have seen white dust accumulation in plants that have fluidized bed boilers, but this dust is typically everywhere.

 

[rmw]

On the stator end windings look between the legs of the coils of adjacent phases. If you see the white dust there, especially on the long flat sides of the coils, between the coils, you may have corona.

If so, your generator requires a look by a qualified service person and may require some cleaning and/or varnishing.

rmw

 

[unclesyd]

I have to agree with rmw in that the times I've seen white dust fried varnish has been found.
My experience has been that the problem occurred on generators that had been online for longer periods than yours.
I would definitely get a service rep involved and make sure his findings are recorded.

If you have a problem not is the time to catch it.

 

[tmoritz]

Our hydro units have end ties which restrain the motion of the end windings. When these ties break down they can produce a white powder. I have only seen this result due to age. Ozone, heat, and vibration will accelerate the breakdown of the ties. Take a sample of the white powder and have it analyzed. That'll give you a clue on where to look for the damage.

Good luck,


Tom Moritz
Mechanical Engineer
US Bureau of Reclamation

 

[ScottyUK]

RMW is very probably on the right track. Other possibility: are you on a coastal location? Any possibility of airborne salt making its way into the machine? How localised is the deposition?


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I don't suffer from insanity. I enjoy it...

 

[irishal]

In reply to your comments, from the limited access I can see that the dust is fairly widespread through the unit (covers end stay bars, end windings, etc.) Our site is coastal but not too exposed - I don't think there's much airborne salt. The air in the generator is cooled with a tube heat exchanger as it is recirculated so the number of air changes is small in comparison to once through air cooled generators. I'll get a sample of the powder analysed and have the OEM involved. If I get any answers I'll post them here to let you know the findings.

Thanks for your help.
Irish Al