DGA values of transformer oil
DGA values of transformer oil
(OP)
Is there any standard/reference that lists the dissolved gas values in transformer oil ?
We got a DGA test result as below in a 11 KV/150 V, 3 MVA rectifier transformer.
H2 - 2 ppm
Methane - 155 ppm
Ethane - 683 ppm
Ethylene - 1101 ppm
Acetylene - 1 ppm
CO2 - 480 ppm
Water content - 50 ppm
Are these values worrisome ?
We got a DGA test result as below in a 11 KV/150 V, 3 MVA rectifier transformer.
H2 - 2 ppm
Methane - 155 ppm
Ethane - 683 ppm
Ethylene - 1101 ppm
Acetylene - 1 ppm
CO2 - 480 ppm
Water content - 50 ppm
Are these values worrisome ?






RE: DGA values of transformer oil
Water - max 35ppm for oil; 100ppm for silicone
Hydrogen - 100ppm
Methane - 120ppm
Ethane - 35ppm
Ethylene - 30ppm
Acetyelene - 15ppm (though any acetylene indicates arcing under oil - not a good thing)
CO - 350ppm
CO2 - no limit
O2 - 50000ppm
Nitrogen - no limit
From your results, I would imagine you have some overheating issues, and possibly some water intrusion.
RE: DGA values of transformer oil
Yes, there has been some overheating issues with the two LV neutral terminals, which carry DC return current of over 6000 amps. I am planning on modifying these terminals from round to flat.
Is there any standard that specifies those DGA values ?
RE: DGA values of transformer oil
These standards may have been updated; I haven't checked recently.
RE: DGA values of transformer oil
Ethlyne and water content seems to be on the high side.
Please refer IEEE C57.104-IEEE Guide for the Interpretation of Gases in Oil Immersed Transformers.
You can come to a conclusion.
RE: DGA values of transformer oil
RE: DGA values of transformer oil
You might wish to investigate the Rogers Ratio criteria which, as you probably can guess, look at the ratio between different gasses rather than the absolute values. I think there is a guideline that the total hydrocarbons should be above 500ppm when applying the Rogers tests. I'm pretty sure there is some discussion in the J&P Transformer Book and this document is worth a read: http://
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If we learn from our mistakes I'm getting a great education!
RE: DGA values of transformer oil
RE: DGA values of transformer oil
mgtrp - any link to that CIGRE guide ? Thanks.
RE: DGA values of transformer oil
The likely reasons for the restrictions in the FIST manual are: Oil in a transformer which is out of service and cool doesn't have oil circulation due to convection, resulting in a sample which isn't representative of true conditions. A transformer which is newly returned to service needs time for the dissolved gases to reach equilibrium, and as before taking a sample too early will result in a sample which isn't representative of true conditions.
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If we learn from our mistakes I'm getting a great education!
RE: DGA values of transformer oil
RE: DGA values of transformer oil
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If we learn from our mistakes I'm getting a great education!
RE: DGA values of transformer oil
RE: DGA values of transformer oil
The typical allowable values as per IEC is acetylene-2-20ppm, H2- 50-150 ppm, Methane -30-130 Ethylene - 60-280 ppm, Ethane 20-90 ppm, CO-400-600ppm,CO2- 3800-14000 ppm
When oil is filtered,all dissoved gases are removed in the vaccum chamber of the filter.It will take some time for the gaeses to reach the saturation levels.
RE: DGA values of transformer oil
Thanks prc for those numbers and confirming that the DG's are removed in the vacuum chamber. Yes, we did find the problem of loose connections and fixed it. But the nos. I posted were after fixing the problem (at least as per my client) and hence my query.
I think the oil requires more filtration. I will be visiting the site this week-end and will post here my findings.
RE: DGA values of transformer oil