corona problems on a 8 MW leroy sommer generator 1

[mottt]

hi, i must do a cleaning on a 8 MW leroy sommer generator, and the guys send me a report of a thermographic of the generator, showing some hot spot in the head of the windings, they said that is a corona effect problem.... how do you see, does corona effect causing this hot spots?
on other way, maybe i need to use a new stress grading tape for the head of the windings? how would you start this work? they want to clean the machine... and the machine is open design, and is in cement factory, and maybe the winding are full of cement.
thanks for your always helply opinion

 

[electricpete]

In theory, tracking can produce very small amounts of radiation in the infrared wavelengths and also associated processes can cause localized heating which causes nearby surfaces to emit increased infrared radiation. What strikes me is that the amount of heating/radiation will be very small in comparision to the many other sources of heating/cooling in the generator that will create thermal gradients much larger than would be caused by corona (I would certainly like to see an image if it is available). For example, a location on the endwinding which is sheltered from cooling airflow could appear as a hotspot.

So this seems like a challenging application for infrared thermography imo. But never say never.

For detection of tracking on insulators in the T&D world, the device which tremendously outperforms infrared thermography is ultraviolet scanning. Detecting corona by ultraviolet creates a much higher signal to noise ratio since there are not many other things going on (besides corona, tracking, partial discharge) that create much energy in the higher frequency range of uv.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

To the question of do you need new stress grading - I would say in part it depends on where the tracking is alleged.

If it is tracking between phases in the endwindings well beyond the grading (where it should be at full phase voltage), then changing grading would do nothing to help.

Only if it appears as tracking back toward the slot section would improved grading have a chance at reducing the alleged tracking.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[mottt]

i´ll put the report of the thermographic, maybe you are mere experted than me about it...i thought from my ignorance that the heat produced by tracking or corona effect is too low in comparation with the heat of the windings.....
thanks for your nice help..... i sorry but report is on english but you could see pics

 

[mottt]

in the report, this people says that in the pics you could see excursions of current between phases and the core, but i see pics and don´t know or see nothing, maybe cause i´m not familiar with this tools.

 

[electricpete]

I don't think the link is working. I get to the download page but that can't get any file (can anyone else get it to work, or is it just me?)

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[Skogsgurra]

Can't see it either :-(

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[mottt]

sorry i try again... in anyway thanks for your atention

 

[mottt]

i don´t know what´s the problem but i couldn´t open the folder??

 

[mottt]

i try with only the pics...

 

[mottt]

this works....you could download the pics

 

[Zogzog]

There is no way you can determine there is a corona problem from that image, there are way too many variables there.

What about doing a corona scan if you are concerned?

What is the voltage?

 

[mottt]

yeah, i think that, i have no way to confirm that there´s a corona problem from that image...but i´m not a specialist... could you help me saying something about the variables there? the voltage is 6000 V.

What´s a corona scan? how this work?

 

[edison123]

If you see ash coloured coating on the coils at the slot exits or in end windings, it is an indication of serious corona.

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[Zogzog]

You can get Corona at 6000V, just wanted to be sure this was MV equipment.

Corona scanning is a new technology used mostly by utilities but is starting to become very popular in industrial plants.

A special camera is used that makes the light in the UV spectrum. We do these daily and have been very successful in industrial plants on MV equipment.

I have attached a couple of images from a scan we did last month.