Dissolved Gas Analysis
Bryan Harbuck
May 2017
DGA: WHAT and WHY
• DGA is the study of the dissolved gases in
transformer oil generated by normal operation and
fault conditions. As the equipment operates it will
create gases within the oil that can be analyzed to
determine the “Health” of the equipment.
• Involves the use of a syringe and bottle.
• It is used as a predictive maintenance tool and as a
monitoring point.
• DGA gives us a picture of what is going on inside the
equipment without having to actually go inside or
de-energize it.
• Careful analysis combined with trending of data can
predict at what stage of life your equipment is at.
Gases We Are looking For:
• Not all gases that are created are used in the analysis.
• What we are concerned with are the seven “Heating” Gases.
• These are the gases created by an overheating or fault condition.
• Each gas has its own signature temperature and tells a story.
• Gases we are concerned with: Hydrogen, Carbon Monoxide, Carbon Dioxide, Methane, Ethane,
Ethylene, and Acetylene.
• Let have a look at these and see what they are caused by.
Heating Gas Characteristics
GAS
Temp Formed At:
Solubility in Oil
(How fast it
dissipates)
Primary Causes
Hydrogen (H2)
> 110 C
7.0 % Quickly
Partial Discharge
(Corona)
Carbon Monoxide
(CO)
> 300 C
9.0 % Quickly
Overheated Cellulose
Methane (CH4)
> 110 C
30.0 % Moderate
Overheated Oil
Carbon Dioxide (CO2)
> 400 C
120.0 % Slowly
Overheated Cellulose
Ethane (C2H6)
> 150 C
280.0 % Very Slowly
Overheated Oil
Ethylene (C2H4)
> 300 C
280.0 % Very Slowly
Overheated Oil
(Hotspot) (Sparking)
Acetylene (C2H2)
> 700 C
400.0 % Extremely
Slowly
Arcing/Burning
Contacts
Oil Quality Tests
• Dielectric Test: Determines the breakdown point of the oil. Commonly used are ASTM D 1816 and
D 877 Test.
Color, Acidity, and Moisture
• Color: Indication of the oxidation of the oil. As oil ages and oxides it will get darker in color.
New oil should be a 0.5 and will get darker with age.
• Acidity : Another indication of the oxidation of the oil. Will start with a very
low number (.01 for new oil and rise as oil degrades)
Moisture: Karl Fischer Test is used. Moisture can come from 2 sources:
Leaking gaskets/Atmosphere and overheated Cellulose. Moisture in oil can be
Shown as Free Water and Dissolved Water.
• Interfacial Tension: Determines the cohesive strength of the oil. As oil breaks
down, its ability to resist moisture absorption reduces.
Data Collection, Analysis and Trending
• Very Important to keep good records. Location, temperature, equipment size and type, serial
numbers, and other pertinent info.
• With DGA, the first year (sample cycle) is the most difficult to diagnose because you do not have
any previous data. You will still be able to see some problems, due to spikes in gas levels and
ratios being off.
• As you start to trend data over the years (sample cycles), you will be able to notice when the oil is
beginning to degrade due to an issue or when you may need to maintenance the equipment.
• Sometimes you may get data back that is much different from what you have seen in years past or
is much different from other similar pieces of equipment. Usually the best option is to take
another sample before making any decisions about the equipment.
What We Have Found With DGA
Burnt/Damaged Contacts
Leaking/Damaged Gaskets Allowing
Moisture In
Making a DGA Kit
You will need fittings to
use on the main drain
valve. Do not use the
sample valve.
Try to use only Tygon
tubing, vinyl tubing can
be used if Tygon is not
available
Complete your kit with
Teflon pipe compound,
waste containers, and a
thermometer.
Taking a Sample
SUBHEAD HERE
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After draining about 1
pint (on a 1” valve) fill
your bottle about
halfway, swirl around,
dump, and refill. Leave
about 1” in neck for
expansion.
Fill syringe using down
pressure from oil. Fill
once, then push out into
waste, then fill again. Fill
to the 50mm level.
Mark bottle with the
same number as on the
syringe. Pack syringe in
supplied box and make
sure to include all
paperwork.
Any Questions?
Bryan Harbuck
[email protected]
830-868-4795
04/19/2017