No. | Gases Detected in Oil Sample | Fault Interpretations |
1 | Nitrogen plus 5% or less oxygen | Normal operation |
2 | Nitrogen, carbon monoxide, and carbon dioxide | Transformer winding insulation overheated; Key gas is carbon monoxide CO |
3 | Nitrogen, ethylene, and methane―some hydrogen and ethane | Transformer oil is overheated; minor fault causing oil breakdown. Key gas is ethylene C2H4 |
4 | Nitrogen, hydrogen, small quantities of ethane and ethylene | Corona discharge in oil; key gas is hydrogen H2 |
5 | Same as 4 with carbon dioxide and carbon monoxide | Corona involving paper insulation; key gas is hydrogen H2 |
6 | Nitrogen, high hydrogen and acetylene; minor quantities of methane and ethylene | High-energy arcing; key gas is acetylene C2H2 |
7 | Same as 6 with carbon dioxide and carbon monoxide | High-energy arcing involves paper insulation of winding; key gas is acetylene C2H2 |