Sparking on slip rings of generator

[ansmehmood]

Hello,

We have 150MW turbo generator of SIEMENS. There are total 12 carbon brushes on each pole. Sparking is related to only positive pole. And same thing that if we push one carbon brush sparking stops on all. We have cleaned the slip rings as well with coordination of OEM. But after 24-48 hours sparking again appears.

Can anyone tell me what is going on?

I think the problem is with slip rings surface. But if anyone of you have encountered the same problem please let me know the solution for this?

 

[Sahib]

Brush spring defective?

 

[ansmehmood]

Brush spring defective?

No. Everything is checked and there is no abnormality that is visible. My point is there will be a problem with slip rings surface. but I want overviews from different professionals so that it is easy to make any decision.

Sparking is only on positive slip ring and from 12 o'clock to 5 o'clock angle. But if we press one carbon with insulated stick sparking on all other carbon brushes stops.

 

[Sahib]

Everything is checked .

What are the checks carried out?

 

[ansmehmood]

What are the checks carried out?

Following checks are done:

Current is measured on each carbon brush
temperature monitored
carbon brush replacement with new ones
carbon brush holder replaced with new ones
carbon brush movement inside the holder
cleaning of slip rings
carbon brush carrier adjustments

 

[Sahib]

Following checks are done:

carbon brush replacement with new ones

When the sparking started? Only recently with replacement of worn out brushes with new ones of different composition?

 

[ansmehmood]

When the sparking started? Only recently with replacement of worn out brushes with new ones of different composition?

No. machine was on base load. Everything was running normal and then the sparking starts.

There was no recent replacement of brushes. Carbon brushes were changed after the sparking initiated.
Have you experienced this fault in your career. Please guide if you have encountered this?

 

[Sahib]

No. machine was on base load. Everything was running normal and then the sparking starts.

Have you experienced this fault in your career. Please guide if you have encountered this?

No. I have not experienced this fault. I am in charge of much smaller alternators in telephone exchanges and I just try to help you locate the problem area. Now coming back to your problem, have you checked with the OEM for the possible remedies?

 

[Tony S]

Is there a difference in colour of the patina on the two rings?

Airborne contaminants can cause glazing on individual rings and brush faces depending on polarity. Applying extra pressure to one brush is possibly breaking through the glaze. Some brush manufactures make brushes with an abrasive insert to clear glazing. You only use one per ring, the other bushes remain as normal. The only company I know of for specialist carbon brushes is Morganite here in the UK, they will have agents in other countries.

http://www.morganelectricalmaterials.com/en-gb/products/carbon-brushes/

 

[zbang]

If a new set starts out fine and then later starts sparking (and after the other maintenance)....

Atmosphere? what kind of plant is this? we know that some places, like waste-water treatment, can have more hydrogen sulfide gas, which eats up some metals.

Could be a bad batch of brushes.

If they're interchangeable, have you tried swapping all of the positive and negative brushes?

Is there some airflow condition that's blowing at one set but not the other?

 

[Smart $]

...
Airborne contaminants...

...
Atmosphere?...

+1

 

[Tony S]

One contaminate carbon brushes don’t like is the fumes from silicon sealant as it dries out. How many times do we seal electrical containment with silicon?


A good site for information on brushgear is Reliance Electrical but it’s mainly DC motors / generators. Morganite’s site also has some good information.

 

[Sahib]

The most sensible course of action OP may take is as I already suggested: Consult with the OEM of the machine for possible remedies.

 

[gadfly56]

The most sensible course of action OP may take is as I already suggested: Consult with the OEM of the machine for possible remedies.

If you paid attention to the original post, you would notice that he had already done so.

 

[Sahib]

If you paid attention to the original post, you would notice that he had already done so.

Yes. I did. But it seems OP engaged the OEM just for cleaning the slip rings only. He better ask a report from the OEM for the remedial course of action to be taken.

 

[Smart $]

Yes. I did. But it seems OP engaged the OEM just for cleaning the slip rings only. He better ask a report from the OEM for the remedial course of action to be taken.

If it can be determined whether the sparks are a result of an airborne contaminant, is one possible remedial action is to use contaminant-free pressurized air to purge the enclosure?

 

[Sahib]

If it can be determined whether the sparks are a result of an airborne contaminant, is one possible remedial action is to use contaminant-free pressurized air to purge the enclosure?

It may be already if the OP turbo generator is provided with hydrogen cooling.

 

[ansmehmood]

Thanks all for all your comments and suggestions. Everything is already been done and checked.

I only want to have some suggestion from a person who had encountered this problem in his career. Thanks again.

 

[wbdvt]

My experience with sparking brushes is usually they are not seated onto the ring. This can be the contour of the brush faces does not match the ring, something causing the brush to jump, weak brush spring/holder or out of round ring.

 

[drcampbell]

... I only want to have some suggestion from a person who had encountered this problem in his career. ...

I think you misunderstand the Internet.