Stray gassing (SG) of oil has been defined by CIGRE [1] as “the formation of gases in electrical insulating oils heated at relatively low temperatures of 90 to 200 °C”. SG is due to the chemical instability of oil molecules after they have been submitted to refining procedures, such as for example hydrogen treatment to remove impurities and undesirable chemical structures in mineral oils. Such treatments may oversaturate the hydrocarbon chains of mineral oil with hydrogen, which is then released as H₂gas, together with some C₂H₆and CH₄, when the oil is heated at various SG temperatures, or is in contact with oxygen [2].

1. CIGRE D1-01/A2.11.Recent Developments in DGA Interpretation; CIGRE Technical Brochure # 296; Convenor, M. Duval; CIGRE: Paris, France, June 2006.
2. CIGRE D1/A2.47.Advances in DGA Interpretation; CIGRE Technical Brochure # 771; Convenor M. Duval; CIGRE: Paris, France, July 2019.

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