FAULT
KEY GAS
RESULTS
Arcing
Acetylene
Large amounts of acetylene and
hydrogen or minor quantities of methane
and ethylene can be produced.
Corona
Hydrogen
Low energy discharges generate
hydrogen and methane as well as minor
quantities of ethane and ethylene.
Overheated
Oil
Ethylene
and
Methane
Overheating will produce ethylene and
methane (300 degrees F) or hydrogen
and methane (1,112 degrees F). Traces
of acetylene may be formed if the fault is
severe or involves electrical contacts.
Overheated
Cellulose
Carbon
Monoxide
If cellulose is overheated, carbon
monoxide is generated.
It is important to differentiate between normal and excessive
gassing rates. These will vary based on the transformer design,
insulation material and loading. It is recommended that laboratories use key gas analysis (KGA) supplemented by the
Dornenburg and Rogers ratios in analyzing dissolved gas analysis
(DGA) results. DGA measures the oil for methane, acetylene,
ethylene, hydrogen, ethane and carbon monoxide. It can also
provide an indication of arcing, corona, overheating oil and overheating cellulose.
Other tests that can be
performed measure inorganic
chlorides and sulfates (ASTM
D878) and specific gravity
(ASTM D1298). Some of these
tests will be conducted by the
blender or supplier. These tests
will establish a baseline for
comparison in future analysis.
Keep in mind that it is not
uncommon for transformer oils
to be in use for 30 years or more,
so a little expense on the front
end can lead to huge returns in
the future.
From page 36
About the Author
Loren Green is a technical consultant with Noria Corporation,
focusing on machinery lubrication and maintenance in support of
Noria's Lubrication Program Development (LPD). He is a mechanical
engineer who holds a Machine Lubrication Technician (MLT) Level I
certification and a Machine Lubricant Analyst (MLA) Level I certification
through the International Council for Machinery Lubrication (ICML).
Contact Loren at lgreen@noria.com.
www.machinerylubrication.com
| May - June 2013 | 17
