Significance of CO2 when CO/CO2 ratio is low
Significance of CO2 when CO/CO2 ratio is low
(OP)
Let’s say we have a conservator type GSU with steady state levels on the order of
500ppm CO
18,000ppm CO2
The CO exceeds the IEEE threshhold by a small amount.
The CO2 exceeds the IEEE threshhold by a large amount.
My understanding is the CO and CO2 are both byproducts of thermal aging of cellusoe
insulation, but that ratio of CO/CO2 increases as the aging occurs at higher temperature.
CO/CO2<(1/7) is a good thing per IEEE standard.
If I looked at CO only, I would say we are only slighly above the limit.
If I look at CO2, it says way above the limit.
However the low CO/CO2 suggests lower temperature
QUESTION: Does adding CO2 to the picture cause any higher of concern compared to looking at CO only?
[yes, I realize there are many aspects of evaluating aging such as complete oil history and.. furanic compounds... the question is about the significance of CO2 in the above case... if we add it into the picture does it make the picture any worse than if CO2 was not monitored]
500ppm CO
18,000ppm CO2
The CO exceeds the IEEE threshhold by a small amount.
The CO2 exceeds the IEEE threshhold by a large amount.
My understanding is the CO and CO2 are both byproducts of thermal aging of cellusoe
insulation, but that ratio of CO/CO2 increases as the aging occurs at higher temperature.
CO/CO2<(1/7) is a good thing per IEEE standard.
If I looked at CO only, I would say we are only slighly above the limit.
If I look at CO2, it says way above the limit.
However the low CO/CO2 suggests lower temperature
QUESTION: Does adding CO2 to the picture cause any higher of concern compared to looking at CO only?
[yes, I realize there are many aspects of evaluating aging such as complete oil history and.. furanic compounds... the question is about the significance of CO2 in the above case... if we add it into the picture does it make the picture any worse than if CO2 was not monitored]
=====================================
(2B)+(2B)' ?






RE: Significance of CO2 when CO/CO2 ratio is low
RE: Significance of CO2 when CO/CO2 ratio is low
Are you familiar with the Rogers Ratios for hydrocarbons? How do they look? What is the furan trend doing?
RE: Significance of CO2 when CO/CO2 ratio is low
Let me enlarge my question to say I am trying to understand the significance we should attach to the two parameters CO and CO2, individually and in combination.
I think the interpretation of CO2 may be a source of some disagreement within the industry.
IEEE includes a limit on CO2... our insurance does not (they only have a limit on CO).
My quote above was based on IEEE which seems to suggests CO2/CO > 7 is good. (I added the comments about temperature but may have been offbase...I'll see if I can track down a refernce.)
But I get a different slant from Bureau of Reclamation CO2/CO>3 is good. CO2/CO<7 is good. Outside these bounds a problem
Let me list some quotes:
=====================================
(2B)+(2B)' ?
RE: Significance of CO2 when CO/CO2 ratio is low
I did review Duval’s “Review of Faults Detectable by Gas in Oil Analysis in Transformers”. It gives a number of laboratory studies and case studies which seem to support the conclusion that the ratio CO2/CO produced goes down as the temperature of the thermal aging reaction increases.
=====================================
(2B)+(2B)' ?
RE: Significance of CO2 when CO/CO2 ratio is low
IEEE C57.104:
"CO2/CO Ratio of <3 Excessive
CO2/CO Ratio of >7 - <10 Normal
CO2/CO Ratio of >10 Excessive
*These ratios are only valid when levels exceed minimums: CO>500ppm and CO2>5,000pmm"
CIGRE SC15 "New Guidelines for Interpretation of Dissolved Gas Analysis in Oil-Filled Transformers, (Electra NO.186 October 1999):
"Key Gas Ratio #4, CO2/CO, >10 Indicates overheating of Cellulose"
In response to your question "Does adding CO2 to the picture cause any higher of concern compared to looking at CO only?" No the CO2 doesn't add much to the picture. The elevated CO already tells you that there is overheated cellulose, what would be of more use is the H2 level. If the H2 is elevated you have a thermal fault, if the H2 is not elevated you just have cellulose aging. With just the CO and CO2 you don't know if it is excessive aging or a thermal fault.
RE: Significance of CO2 when CO/CO2 ratio is low
Interesting. That seems to mirror the Bureau of Reclamation document (available on-line free). I don't se that in IEEE Std C57.104-2008.... all I see is the part I quoted above which has a different spin. I wonder if it was in an old version or I'm just missing it.
By the way, I noticed in front of the guide Steven Alexanderson. Could that be our own stevenal?
=====================================
(2B)+(2B)' ?
RE: Significance of CO2 when CO/CO2 ratio is low
RE: Significance of CO2 when CO/CO2 ratio is low
RE: Significance of CO2 when CO/CO2 ratio is low
"CO and CO2 formation increases not only with temperature but also with the oxygen content of oil and the
moisture content of paper." "Air-breathing equipment, for example, saturated with approximately 10 % of dissolved air, may
contain up to 300 μl/l of CO2 coming from the air" "If necessary subtract last values from present ones before calculating ratios, particularly in the case of CO, CO2"
There are also cases when abnormal values can be due to other reasons. In India in some 420 kV reactors co/co2 values of 1247/17,705 and 784/18,459 ppm were reported with in a year.Other thermal gases were insignificant.Finally it was found out that these values were from synthetic rubber(with inadequate vulcanisation) and resin impregnated wood used in reactor. Lab tests conducted on these materials(ASTM 3455-02 80C at 164 hrs)with oil showed high content of CO/Co2 under DGA.When these materials were replaced with good quality material CO/co2 became normal.
In a traction transformer where oil content is low, showed Co/CO2 of 292/1237 ppm with thermal gases Ch4 = 509,C2H2 =8,C2H4=799,C2H6=150 ppm after a few months of service.Inside, charring of wood was noticed at one place where a hot metal was touching wood.Almost similar results got in another unit where there was no involvment of any cellulose or wood but only a heated joint in a lead connection.
Hence it seems CO2/Co may be misleading during analysis.It can be affected by stray gases,passivators added in oil,certain paints ,gaskets,wood etc.