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European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
Available online: https://ejbss.org/ P a g e | 2018
Dissolved Gas Analysis Technique Based
Assessment of High Voltage Power Transformer
BHUVGANESWARI . P
M.Tech – Power System Engineering,
PRIST Deemed University, Madurai, Tamilnadu
Abstract - Dissolved Gas Analysis (DGA) is a widely used
technique to estimate the condition of oil-immersed
transformers. The experimental results of the level and the
change in concentration of different combustible gases in the
insulating oil is a trustworthy diagnostic tool which can be used
as indicator of undesirable events occurring inside the
transformer, such as hot spots, electrical arcing or partial
discharge. The objective of this paper is mainly to analyse
available data from DGA, and investigate data that may be
useful in quantitative modeling of the transformer’s reliability.
Dissolved Gas Analysis (DGA) of transformer oil is the best
indicator of a transformer’s overall condition. It will provide
useful information about the condition of oil and help to identify
the type of fault in the transformer. Depending upon the location
of a transformer, its rating and the nature of its usage, some
dissolved gas analysis is to be scheduled which will be
appropriate for that transformer. The more critical the unit is the
more frequently it should be sampled. Hence DGA is mainly
performed in Power transformers.
I.INTRODUCTION
Power transformers play an important role in both the
transmission and distribution of electrical power. Since a fault in
a transformer can have a huge repercussion when failures occur,
and as the number of old transformers and of those that are
difficult to operate in overload conditions is on the rise, it is
important to detect incipient faults in a transformer and forecast
and prevent failures [17]. In operation, transformers are subject
to electrical and thermal stresses, which can cause the
degradation of the insulating materials. Generally the
degradation products are gases, which will get dissolve in the oil
entirely or partially. In the oil these gases are easily detected at
the ppm level by dissolved gas analysis. Dissolved gas analysis
(DGA) is a widely used most powerful method to detect
incipient faults on oil filled electrical equipment [16]. The
electrical equipment may be a transformer, a load tap changer or
a cable. When the mineral oil is subjected to high thermal and
electrical stresses, it decomposes and, as a result, gases are
generated. Different types of faults will generate different gases,
and the chemical analysis of these gases, performed through a
procedure called DGA (Dissolved Gas
Analysis), will provide useful information about the condition of
the oil, and help to identify the type of fault in the transformer.
DGA is performed accordance with ASTM D3612 or IEC
60567. There are different types of faults which can be detected
by DGA. The details about the faults are explained below
Partial Discharge (PD):
The temperature plays a less important role in the chemical
reaction occurring in the PD since the vapour temperature in the
discharge zone is not higher than 60-150°C. Hydrocarbon
cracking in the partial discharges occurs as a result of excitation
of molecules and their subsequent dissociation by collision with
high energy electrons, atomic hydrogen, ions and also free
radicals. It often generates large amounts of hydrogen. Example:
Discharges of the cold plasma (corona) type in gas bubbles or
voids, with the possible formation of X-wax in paper.
Discharges of Low energy (D1):
Partial discharges of the sparking type, inducing pinholes,
carbonized small punctures in paper. Low energy arcing results
in surface tracking of paper or the formation of small amount of
carbon particles in oil.
Discharges of High energy (D2):
Discharges in paper or oil, with power follow-through, resulting
in extensive damage to paper or large formation of carbon
particles in oil, metal fusion, tripping of the equipment and gas
alarms.
Thermal fault (T1):
These types of faults occur below . These are evidenced by
paper turning brownish (> 200 °C) or carbonized (> 300 °C).
Thermal fault (T2): These types of faults occur in between to .
These are evidenced by carbonization of paper, formation of
carbon particles in oil.
Thermal fault (T3):
Page 2 of 7
European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
Available online: https://ejbss.org/ P a g e | 2019
The high temperature faults whose temperature is more than falls
in this kind of fault. These are evidenced by extensive formation
of carbon particles in oil, metal coloration (800 °C) or metal
fusion (>1000 °C).
Thermal & Electrical fault (DT): Sometime both thermal and
electrical fault occurs inside the transformer. These faults
accelerate the decomposition of dielectric fluid and solid
insulation
II.DETECTION TECHNIQUES OF DISSOLVED GASES
The DGA technique detects gas in parts per million
(ppm) dissolved oil by the use of gas extraction unit and a gas
chromatograph. The DGA analysis is performed in three steps:
1. Collection of Oil sample
2. Extraction of gases from the oil
3. Detection of gases
Collection of oil sample
The oil sample collection is carried out using different apparatus
and methods. The most appropriate container is a gas-tight glass
syringe of capacity 150 ml or 250 ml and fitted with three way
Teflon valves. The oil should retain and transport the sample of
transformer oil in the same condition as it is inside a transformer
with all fault gases dissolved in it. Attention to cleanliness is the
key to success. Oil samples shall be taken from the main oil
stream: points outside the main oil stream shall be disregarded.
This point should be located in a place where a live oil sample
can be collected rather than in an area where the oil is static. To
prevent oxidation the samples shall be shielded from direct light
by wrapping the container in aluminium foil or by storing in an
opaque enclosure.
Three samples have been collected. After doing the DGA
process of those oils, gas concentrations are found out. The
transformers from which oils have been collected are;
MSDS2/Transformer # 2 (132 kV/33 kV, 63 MVA)
CRM Transformer # 53 (33 kV/7.1 kV, 16 MVA)
Tandem mill rectifier transformer # 4 (33 kV/7.1 kV, 16
MVA)
III.DIAGNOSTIC METHODS OF DISSOLVED GASES
Different types of DGA methods have been
implemented in order to determine the fault in a transformer
which are analyzed as follows;
Key gas method
Ratios methods or Basic gas ratios method and
National Standard’s method
Duval Triangle method
Key gas method
Ratios methods or Basic gas ratios method
National Standard’s method
The Duval Triangle method
The Duval Triangle method, like any other DGA diagnostic
method, should be applied only when there is some suspicion of
a fault, based on an increase in combustible gas or some other
suspicious symptom. The diagnostic method itself is not a means
of fault detection. Because of the relative inaccuracy of gas-in- oil concentration measurements at low concentrations, DGA
diagnostic methods, including the Duval Triangle, should not be
Page 3 of 7
European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
Available online: https://ejbss.org/ P a g e | 2020
applied unless the gas concentrations are well above the
detection limit.
The faults which are detected by Duval triangle are expressed as
follows;
Partial Discharge (PD)
Discharges of Low energy (D1)
Discharges of High energy (D2)
Thermal fault, (T1)
Thermal fault, (T2)
Thermal fault, (T3)
Thermal & Electrical fault (DT)
IV.NOVEL METHODS FOR DETECTION OF DISSOLVED
GASES
Introduction
As discussed earlier the accurate knowledge of the
condition of transformers is essential for all electrical networks.
With the help of this information the maximized and expensive
failures can be avoided. As transformer is oil filled equipment
the DGA should give accurate, rapid and reliable results in the
field. So new technologies have been achieved to get extremely
high performance standards and genuine portability, giving
measurement of all the fault gases plus moisture. Infrared photo- acoustic spectroscopy (PAS) is such kind of the methods in
which the gases are extracted from the oil sample using highly
stable proprietary dynamic headspace equilibrium and then
measured.
Infrared Photo-Acoustic Spectroscopy for DGA
The conceptual design of a practical PAS measurement
module is shown in Figure. A simple hot wire source produces
broadband radiation across the IR range that is focused into the
measurement cell using a parabolic mirror. When a species
absorbs some of the incoming light, one of several mechanisms
of de-excitation is intermolecular colliding, which ultimately
leads to increases in translation energy of the gas particles —
that is, heating. According to the various gas laws, an increase in
the temperature of the gas leads to an increase in the pressure of
an isochoric (constant- volume) sample. The chopper wheel
rotates at a constant speed to give a modulated frequency light
signal from single to several thousand hertz
TRANSPORT X
The Kelman TRANSPORT X is a compact portable
Dissolved Gas Analysis (DGA) system which analyses oil
samples for all dissolved fault gases and moisture using infrared
photo-acoustic spectroscopy. If abnormal levels are detected, it
further provides a diagnostic using various IEEE/IEC approved
interpretation rules. The TRANSPORT X can also test direct gas
samples taken from transformer headspace or a Buchholz Relay.
The dynamic range of measurement and ability to have no
contamination between samples means it very suitable for
testing tap-changers and circuit breakers also
V.EXTENSION TO THE DUVAL TRIANGLE
The Duval triangle method previously discussed was
the classical Duval Triangle method for Transformers, Bushings
and cables filled with mineral oils. There are other triangles
analysed by Michael Duval, which are for Bio temperature oil,
FR#3 oil and silicon oil etc. For mineral oil he has also analysed
low temperature faults & faults in paper in mineral oils and
Thermal faults & faults in paper in mineral oils [16]. While the
previous method was giving the results with the value of the
concentration of methane, ethylene and acetylene; these analysis
give us more accurate information about the transformer taking
the concentration of other gases like hydrogen and ethane into
consideration.
It is an extension to the classical Duval triangle which gives
more specific information about the fault which is helpful for the
accurate analysis.
There are two such methods which are helpful to give more
details about the faults in a transformer, such as;
Duval Triangle for low temperature faults & faults in
paper in mineral oils
Duval Triangle for Thermal faults & faults in paper in
mineral oils
Duval Triangle for low temperature faults includes hydrogen,
methane and ethane for fault analysis while the Duval Triangle
for Thermal faults includes methane, ethylene and ethane for the
fault analysis.
Duval Triangle for low temperature faults & faults in paper in
mineral oils
This Duval triangle for low temperature faults in mineral oils
uses three gases for the analysis such as hydrogen, methane and
ethane. It is used to get more information about the faults
identified as low temperature faults i.e. PD, T1 and T2 as in
classical Duval Triangle. It should not be used for D1, D2 and
T3 as these are high temperature thermal faults but this triangle
is only helpful for low temperature faults.
There are five zones in this Duval triangle such as;
PD- Corona partial discharge
S- Stray gassing of mineral oil ( T < 200o C )
C- Hot-spots with carbonization of paper
O- Over-heating
N/D- Not determined
In zone C, the probability of having carbonization of paper is 80
%.
Software Implementation
In software implementation of Duval triangle it is first required
to find out the coordinates of each zone and then it is applied in
