Transformer Dissolved Gas Problem ??

[fb599]

I have a 60MVA Transformer which has had a DGA carried out as I am switching it out for routine checks in a months time. The analysis looks normal apart from one result. The Ethane content, instead of being around 10 ppm is 42ppm. Should I be worried so early into the life of this 1 year old transformer ?? Any practical guidance welcomed...:-(

 

[wbd]

Is this the first DGA performed or has the C2H6 been trending upward? Can you post the results of the other gases and TCG? That would help in looking at the overall picture but offhan it looks like some local overheating.
Whats the voltages and any faults seen by this txf? Maybe a lead connection inside has loosened.

wbd

 

[bru]

wbd is correct, you should consider the ratio of gasses rather than one gas alone. There is a tried and true method called Rogers Ratio which is a simplified math model to indicate what the problems may be. Arcing from tap changer or lead is more likely with acetylene.
Bru

 

[gmazumder]

single test results increase is many a times misleading and as suggested by other members trending and comparision of the ratios is the correct analysis methods. recently about an year back the ratios have been modified by the CIGRE group 15 and the new ratios are more accurate in their interpretation. if you have atlest two or more the better then send me the same to the following email. i will complete the analysis and send you the details
my email is gmazumder@yahoo.com

regards

gautam mazumder

 

[fb599]

Thanks all for your help. Here is the summary of the test which is the first test in the transformers one year life:
Oxygen 26601.6ppm
Nitrogen 105310.0 ppm
Hydrogen 10.9 ppm
Carbon Monoxide 38.0 ppm
Carbon Dioxide 986.6 ppm
Methane 7.0 ppm
Ethlyene 3.6 ppm
Ethane 3.6 ppm
Acetylene 0.0 ppm
Moisture content 9 ppm

Total Gas in Oil 13.83% CO2/CO 25.09

Thanks to all.

 

[hy]

Dear sirs:

The gas content seams to be normal.
DGA needs to analysis 3 items.
1- the gas content, there are two limits, one minimun for being considered and the upper limits.
2- the gas ratios, using diferent criterias such as Rogers, IEC, Dornemburg, Duval.
3- the trending of the 2 items.

It is not recommended to use only one gas or ratio.

The IEC 60599 is very complete for doing diagnosys.
Also you can use the U.S.B.R. papers.

sincerely
HY

 

[wbd]

The DGA seems to be normal. I don't see where the numbers came from in your original post. You might also want to do a dielectric oil test, moisture content, Karl Fischer, Oxidation inhibitor, power factor and if you have pumps for forced oil cooing a metals in oil test on the transformer oil. This would give a good picture of the txf oil after a year of operation.

wbd

 

[fb599]

Thanks wbd, neither do I !!!

The Ethane value should have been : 41.9 ppm
All others are correct.

Thanks for the info

fb599

 

[TonyMcG]

After some useful discussion - the need for trends, fault history etc, a number of questions still remain...

Why do you think the ethane should be ~10?
How many DGA results do you have for this unit, and were they all analysed at one lab?
What is the load history on this unit - full 60 MVA or part load?
Have you any similar units, and what are they doing?
Have you resampled since the worrying result?

DGA is about getting a feel for a transformer's life blood - the oil. But DGA needs to be used carefully - there are risks of both false positives and false negatives. Use as many standard interpretations of levels and ratios as possible to help see what the picture is.

 

[fb599]

Hi Tony McG

We have a similar unit again one year old that has a 9.4 ppm reading. From what I've learnt in supporting literature below 10-15 is normal. These tests were carried out at the same lab and they are the first tests too for the unit. Loading has been cyclic and not always fully loaded. I'm not sure if I'm worried.....maybe just concerned at the reading and looking for reassurance. Since talking to colleagues on the same network in a different island their readings are up to 200 ppm Ethane for a simiolar units so we are now working together on this one. Thanks fb599

 

[TonyMcG]

If these were my units, I'd be looking to resample both of them - if it can be done safely. Then you can see what the latest values are, what variation there is in each gas, and beging to see if one of them has a naturally high ethane level. It may be naturally high, or there may be early indications of an overheating problem.

 

[cshro]

Your transforme can have a local overheating. Try to view the generation rate (some new transformers can have some hidrocarbon gases from manufacturing but usualy not ethan). Resample and view the genration rate.

 

[rboz]

Information provided by a testing lab we use from some testing and analysis we had done on a transformer earlier this year:

Ethane content usually indicates some overheating at some point; this is something that needs to be trended to get any useful information. A single data point is pretty meaningless.

If you had acetylene, you'd be looking at arcing - much more serious.

 

[wbd]

Was there a heat run test performed on this transformer as part of a factory acceptance test? If so, was a DGA performed afterwards for a baseline prior to leaving the factory?

 

[jbartos]

Suggestion: Since the Ethane higher ppm is linked to overheating at some location(s), any enhanced temperature sensing and recording could help at a time when the next test results are available. Why to wait?