Interpretation of DGA Results
Interpretation of DGA Results
(OP)
We have a transformer equiped with a HYDRAN Dissolved Gas Analyser, the unit displays the total of all dissolved gases in the oil in ppm. This level has been steadily rising. We have been sending regular oil samples for lab analysis. The results have been inconclusive. The results show a steady increase in Hydrogen and Carbon Dioxide with a steady decrease in oxygen. The so called nasty gases Acetylene, Ethylene and Methane have showed only fractional change (measurement error). Any thoughts as to possible causes?
Many Thanks, Sean
Many Thanks, Sean






RE: Interpretation of DGA Results
CO2 indicates solid insulation overheating. Worse when accompanied by CO.
H2 can come from a variety of things. Normally if low-temperature hot metal it would be accompanied by Methane (then ethylene at higher temperatures). That seems to rule out metal. I think that partial discharge (without arcing) can produce hydrogen alone.
I'm sure there are many more possibilities. Maybe ratio method would cover this case?
RE: Interpretation of DGA Results
Things to take into account - Tx age, oil/paper ratio, free breathing/nitrogen bags etc. Furan and DP test if its an old Tx can determine electrical age of paper if worried.
I'll go along with Electricpete on the suggested causes, and also add that H2 can be produced by coatings and reactions of the oil with stainless steel.
RE: Interpretation of DGA Results
We have some similar problems in new 83.33MVA autotransformers, que maker claims its a gas evolving problem of the oil, but no paper backs it.
Our opinion and is backed by other external opinions is that may be a design problem. As only H2 and CO2 is present, low furan content, the only thing it could be is a "hot area" of bad refrigeration (intra-winding or not).
Is the Tx old, and this "began" to happen now ?
The more the questions and answers, the better the diagnostic process.
RE: Interpretation of DGA Results
http://www.doble.com/
http://www.usbr.gov/power/data/fist/fist3~30/3~30_4~4.htm
RE: Interpretation of DGA Results
Maybe a stupid question, but here goes.... Have you checked the moisture levels?
(high moisture levels can be a contributor to insulation decomposition even at normal temperatures and a contributor to partial discharge).
RE: Interpretation of DGA Results
H2 increase usualy indicate a partial dicharge but try see the hidrocarbons load dependence. View the transformer condition (tgott link (3) table 4 and 5, I know it and is a good documentation)
Look this folowin link (I don't trust it very much but you can try)
http://www.nttworldwide.com/diag.htm