Practical Application of DGA to Envirotemp™ FR3™
Fluid-Filled Transformers
Gene DelFiacco, John Luksich, Kevin Rapp
Cargill, Incorporated – Envirotemp™ Dielectric Fluids
Version 1.0 │ June 2013
W1000
Cargill Industrial Oils &
Lubricants
9320 Excelsior Blvd
Hopkins, MN 55343-3444
www.cargill.com
P: 800-842-3631
Envirotemp™ and FR3™ are valuable trademarks of Cargill, Incorporated.
©2012 Cargill, Incorporated. All Rights Reserved.
IEEE Standard C57.104™ and IEEE Standard C57.147™ are trademarks of the Institute of Electrical and
Electronics Engineers, Inc.IEC® is a registered trademark of the International Electrotechnical Commission
PRACTICAL APPLICATION OF DGA
TO ENVIROTEMP™ FR3™ FLUID FILLED TRANSFORMERS
Dissolved Gas Analysis (DGA) is a diagnostic tool
used in the maintenance of (power class)
transformers. The analysis methods interpret
specific dissolved gas levels (patterns of
concentrations) in the dielectric fluid to help
understand the health of a transformer. Since all
(normally operating and faulted) transformers
produce gases, the keys to understanding the health
of your transformer are:
a) understanding which gases are generated
under specific conditions, and
b) determining the rate at which these gases
are being generated by your transformer.
IEEE C57.104 Guide for the interpretation of gases
generated in (mineral) oil-immersed transformers
details specific patterns of gas concentrations
associated with specific events, and provides
methods of interpreting these gases. Rate of gas
generation indicates if the event is on-going or a
one-time occurrence. Thus with two or more sets of
dissolved gas data, a rate of gas generation can be
calculated. With the IEEE C57.104 guide in hand,
the operating condition of the transformer in
question is more easily determined.
Because of the prevalence of DGA use in our
industry, many believe the art of interpreting
dissolved gases has evolved into a science. In fact,
many trend the dissolved gas results to classify and
rank which transformers are in trouble (or likely to
become problematic) and should be serviced versus
those that are relatively healthy and can be left
alone for a certain time period.
Can DGA be used to diagnose Envirotemp
TM
FR3 fluid filled transformers?
TM
Given the many positive attributes of Envirotemp
FR3 fluid, there is an increasing use in power class
transformers. Many asset managers ask if DGA can
be used to diagnose the health of an Envirotemp
FR3 fluid filled transformer. The short answer is
YES.
Envirotemp FR3 fluid-filled power transformers have
been in service since 2001, and Envirotemp FR3
fluid is being applied in increasingly higher voltage
classes. Customers on two continents have
Envirotemp FR3 fluid-filled generator step-up
transformers, substation transformers, and reactors
operating at 230 kV. Dissolved gas data collected
from these units indicate that DGA is as applicable
for esters as it is for mineral oil. However,
interpretation of Envirotemp FR3 fluid dissolved gas
data has not yet evolved into a science; IEEE is
working on the creation of the guide for the
interpretation of gases generated in natural ester
fluid immersed transformers.
What should I expect when I see an Envirotemp
FR3 fluid DGA report?
Like mineral oil, there is much to understand about
Envirotemp FR3 fluid DGA reports. First, most
normally operating Envirotemp FR3 fluid filled
transformers have ethane concentrations higher
than those seen in mineral oil; this is to be expected
and appears to be nothing more than stray gassing.
Unless accompanied by other combustible gases
that occur when a fault is present, the significance of
this reading may be reduced.
Second, water content is typically higher than in
mineral oil. Since Envirotemp FR3 fluid has a higher
affinity for water, at room temperature, Envirotemp
FR3 fluid saturates at approximately 1000 ppm
water content while mineral oil saturates at
approximately 70 ppm.
As a practical example, at room temperature, water
concentrations of 100 ppm in mineral oil would result
in free water and dielectric failure. For Envirotemp
FR3 fluid, this is approximately 10% relative
saturation and should not be regarded as a major
concern. IEEE C57.147 Guide for the acceptance
and maintenance of natural ester fluids in
transformers indicates initial water concentrations of
100 ppm are acceptable in new Envirotemp FR3
fluid filled transformers.
As the transformer ages, additional water generated
by degradation of cellulose will be driven off from the
paper and absorbed in the fluid. C57.147
recommends that maintenance action be considered
when water approaches 400ppm (40% relative
saturation) in Envirotemp FR3 fluid.
Third, while every laboratory report should be
referencing IEEE C57.147, many do not. As a
result, there may be values reported that could be
misinterpreted.
What methods are used to interpret
Envirotemp™ FR3™ fluid DGA reports?
Most of the mineral oil diagnostic methods outlined
in IEEE C57.104 work well with Envirotemp FR3
fluid since, generally speaking, the gases generated
in mineral oil filled transformers (both normally
operating and faulted) are the same as gases
generated in Envirotemp FR3 fluid filled
transformers.
Like mineral oil, the keys to diagnosing the health of
Envirotemp FR3 fluid-filled transformers are to
establish which gases are present and the rate at
which those gases are being generated. In order to
calculate the rate of generation of gases, at least
two DGA reports are required.
Then, applying IEEE C57.104 or IEC 60567 to the
data, one can determine fault condition using:
o
o
o
o
the Key Gases method
the IEC Duval triangle (Michel Duval has
recently published an Envirotemp FR3 fluid
triangle)
the Doernenburg ratio (when it applies),
the Rogers ratio (which sometimes gives a
false indication of partial discharge)
These analyses combined with the rate of gas
generation should help in determining the next
course of action.
What should I remember about DGA?
Many believe that the condition method outlined in
C57.104 applies to all transformers all of the time.
The guide specifically states that this method is used
to make ‘an original assessment’ of large power
class transformers, and is applicable when no other
dissolved gas data exists for the transformer.
However, once a second DGA sample is received,
the original assessment should be discarded. The
second DGA sample along with other methods of
interpreting dissolved gases (key gas or ratios
methods, etc) should be undertaken to better
calculate the rate of rise of gases.
Typically, using IEEE C57.104 methods of analysis
is best suited for diagnosing larger power class
transformers than distribution class transformers, as
distribution class transformers have much less
dielectric fluid. Concentrations of gases increase
proportionally as quantity of fluid goes down; small
transformers can give a false positive indication of
problems if the analysis is solely based on the gas
presence/concentrations. For example, a bayonet
fuse or a load break switch operations will inject the
same types of gases as will a minor transformer
fault. The gases typically do not cause or indicate
any major operational problems. With experience
and adjustments to IEEE C57.104, the methods may
be used to diagnose distribution class equipment.
As with any emerging technology, there are many
questions yet to be answered. However,
Envirotemp FR3 fluid has extensively been tested in
the application of transformers, and users are
validating many of its laboratory and field findings.
Until IEEE issues its dissolved gas guide for natural
ester fluids, please see Envirotemp FR3 Fluid
Dissolved Gas Guide (R900-20-19) for additional
information.
Finally, many events happen over the course of
time. DGA may highlight an active, developing, or
past fault condition, but it cannot predict the future.
Many previously identified healthy transformers fail
without notice, while many transformers identified as
potentially in trouble continue to operate without
incident.
The reality we must acknowledge is that every
transformer is unique, and an event can end a
transformer’s life without notice. DGA is useful for
establishing snap shot conditions of transformers
and given the information available, identifying fault
conditions (arcing, partial discharge, hot metal faults,
severe overloading) if they exist within the time
frame of the snap shot. While DGA is a useful tool,
it cannot predict the next transformer failure.