Transformer oil usually contains oxygen in addition to other gases. A significant portion of the Oxygen is from atmosphere entering through the defects. Apart from this, are there other reasons for presence of Oxygen that can indicate other abnormalities in the transformer?
You are right; oxygen & air enter an oil system due to defect suction lines, but also when there is insufficient de-aeration "using dry air" after set-up of transformer and when there is inadequate tank design. In transformers, gas also results from degradation of cellulose in paper insulation.
As you know, this is a serious problem & I think that the most efficient & inexpensive way to remove oxygen, air or gases is by using vacuum filters.
A less rapid, but more serious characteristic deterioration in the Transformer Oil is the formation of acids and sludge, which is caused by oxidation.
leaky gaskets constitute a real hazard, causing both oxidation and moisture contamination.
Oxygen ingression is of particular concern as it will greatly increase the oxidation of the oil and the ageing of the insulation.
The following Reference give a clear idea of ingress of Oxyge in Transfarmer oil,its ill effects and methods to overcome damage doe to oxygen.
1. http://www.wtc.com.au/Services/services_oxygen.aspx
Ageing of transformers is directly linked to the ageing rate of the cellulose insulation, which is affected by operating temperature, water and oxygen content and contaminants.
Oxygen ingression is of particular concern as it will greatly increase the oxidation of the oil and the ageing of the insulation.
It has been proven that the presence of high levels of oxygen in oil halves the life of paper insulation and that ideally oxygen levels should not exceed 3,000 PPM. A normal free-breathing transformer has an oxygen level of approximately 25,000 PPM.
A conservator Oil Preservation System (COPS) effectively controls the oxygen content and thus greatly slows down the ageing phenomena.
2. http://cdn2.hubspot.net/hub/272197/file-250899189-pdf/white_papers/afi-wp-transoil2.pdf
Deterioration of Transformer Oil :The Effect of Oxygen Moisture contamination is one of the most obvious causes of deterioration in the insulating quality of transformer oil.This contamination can be eliminated by purification. A less rapid, but more serious characteristic deterioration is the formation of acids and sludge, which is caused by oxidation. Thus the exclusion of oxygen is of prime importance. In open-breather transformers, the oxygen supply is almost unlimited and oxidative deterioration is much faster than in sealed transformers. Atmospheric oxygen is not the only source of oxygen available for the oxidation of insulating oil; water also serves as a carrier of oxygen and leaky gaskets constitute a real hazard, causing both oxidation and moisture contamination. The rate of oxidation also depends on the temperature of the oil; the higher the temperature, and the faster the oxidative breakdown.
This points to the importance of avoiding overloading of transformers, especially in summer time. Oxidation results in the formation of acids in the insulating oil which in turn, contributes to the formation of sludge.
P.S.
Thanks for your reply. Much appreciated. I am studying the effects of non-hc gases and particles in transformer oil. I also have a suspicion that oxygen in oil/tank can be a by product of arcing. I am just writing this based on my assumption and I need to confirm this. I am also of the opinion that increased particles can also be in some ways influenced by oxygen content-again, need to study this. Thanks for your reply.
Apart from ingressed air, oxygen could also be aroused from the moisture liberated from cellulose insulants.
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