Key Gas Method

The key gas method was initially investigated at Doble laboratories and proposed in 1974 [Pugh73, Pugh74]. Initial comparisons were made to other methods especially that of the Rogers Ratio Method where the application of these methods were investigated [Rick78]. The Key Gas Method was mainly developed using sealed or blanketed transformers. Thus the application of this method must be carefully assessed especially for free breathing conservator-type transformers [Griffin88]. 

The Key Gas method focuses on the levels of the individual gases generated as a result of the breakdown of insulating material after a fault [IEEE C57.104, IEC 60567]. Prevalence of a certain gas infers a corresponding fault diagnosis. Conventional key gases are composed of hydrogen (H₂), hydrocarbons (CH₄, C₂H₂, C₂H₄, and C₂H₆) and carbon oxides (CO and CO₂).

This method associates high levels of the key gas hydrogen with that of partial discharges or corona in oil. 

Methane and Ethane are associated with low temperature overheating of oil. 

Hydrogen (H2) and Acetylene (C2H2) with arcing.

Ethylene (C2H4) is associated with high temperature overheating of oil, Carbon Monoxide (CO) and Carbon Dioxide (CO2) with overheating of cellulose.

The challenge with this method is that most oil sample profiles do not usually fit into the key gas profiles and this method is not able to distinguish between more than one fault mechanisms happening at the same time.  

References

[Pugh73]	D.R. Pugh, “Combustible Gas Analysis”, Minutes of Fortieth International Conference of Doble Clients, 1973, Section 10-401
[Pugh74]	D.R. Pugh, “Advances in Fault Diagnosis by Combustible Gas Analysis”, Minutes of Forty-First International Conference of Doble Clients, 1974, Section 10-1201
[Rick78]	A.L. Rickley, A.E. Baker, G.W. Armstrong, Jr., “Analytical Techniques for Fault-Gas Analysis”, Minutes of Forty-Fifth International Conference of Doble Clients, 1978, Section 10-401
[Griffin88]	P.J. Griffin, “Criteria for the Interpretation of Data for Dissolved Gases in Oil from Transformers (A Review)”, Electrical Insulating Oils, STP 998, H.G. Erdman edited, American Society for Testing and Materials, Philadelphia, 1988, pp.89-106
[C57.104]	ANSI/IEEE, C57.104-2008, Guide for the Interpretation of Gases Generated in Oil Immersed Transformers, Institute of Electrical and Electronic Engineers, Inc., New York, NY, 2008
IEC 60587	Guide for the sampling of gases and of oil-filled electrical equipment and for the analysis of free and dissolved gases. IEC Standard 60567, 2005.