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