International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 1, Issue 2, October 2012
ISSN 2319 - 4847
Dissolved Gas Analysis (DGA) of Mineral Oil
Used in Transformer
Rahul Pandey1, M.T.Deshpande2
1
IEEE Student Member & M.E. student (Power System) at SSCET Bhilai (C.G.) INDIA
2
IEEE Member & H.O.D Electrical Department at SSCET Bhilai (C.G.) INDIA
ABSTRACT
Transformer oil is one of the most common materials used for transformers. The oil has two important functions. The oil need
to provide cooling and electrical insulation for the transformer. Any deterioration in the oil can lead to the premature failure of
the transformer. When the mineral oil is subjected to high thermal and electrical stress, gases are generated from the
decomposition of the mineral oil. Different type of faults will generate different gases, and the analysis of these gases will
provide useful information about the condition of the oil and the identification of the type of fault in the transformer. The
chemical analysis of these gases is called dissolved gas analysis or DGA. The DGA will require the removal of an oil sample
from the transformer and this can be done without de-energization of the transformer. The oil sample is analysed in the
laboratory using gas chromatography technique.
Keywords: Transformer, Dissolved Gas Analysis (DGA), Fault types, Gas Chromatograph
1. INTRODUCTION
Power generation industry is most important in any country all over the world. By and large entire economy of the
country depends upon its capacity to generate power. During the last decade a lot of accidents took place in this
industry and causes of these accidents/explosions remained unexplained. Recently with the advent of latest technology
in the field of analysis, it has been possible to pin point the possible cause of explosion in the power stations.
In oil-filled equipment, such as power transformers, which is mainly a mixture of hydrocarbons, failures are inevitable
if proper care is not taken. With the use of transformer, the oil starts degrading due to various factors such as ageing of
the oil, overvoltage, environmental condition, overheat and numerous unknown factors. In the process of degradation
lot of lower hydrocarbons like methane, ethane, acetylene, ethylene etc. are produced along with some permanent gases
like CO, CO2 and H2. These mixtures in sealed environment can cause an explosion [3]. The gases depend upon the
condition of the oil and hence, it is extremely vital to monitor the concentration of these explosive gases in the running
transformer.
2. MECHANISM OF GAS GENERATION
The cause for the gas generation in the mineral oil is the breaking of the chemical bonds in the hydrocarbon molecules
of the mineral oil. Energy is needed for the breaking of the chemical bonds and this comes from the energy contained
in the fault of the transformer. The gases generated include hydrogen (H2), methane (CH4), ethane (C2H6), ethylene
(C2H4), acetylene (C2H2), carbon dioxide (CO2) and carbon monoxide (CO).
Figure1 Chemical Structure of Gases
Figure 2 Formations of Radicals
These generated gases will initially dissolve in the oil and cannot be seen by the naked eye. As the volume of generated
gases increases, more of these gases will dissolve into the oil. There will come a point when the oil will be totally
saturated with the dissolved gas, and any further increase in gases cannot be contained as dissolved gas in the oil. The
excess gases will come out as free gas.
Volume 1, Issue 2, October 2012
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 1, Issue 2, October 2012
ISSN 2319 - 4847
Table1: Recombination of Radicals
3. CLASSIFICATION OF FAULT
There are four basic types of faults [1], which can occur in the transformer:
 Arcing or high current break down
 Low energy sparking or partial discharges.
 Localized overheating or hot spots and general overheating due to inadequate cooling or sustained overloading
Each of the faults results in thermal degradation of the oil either alone or in combination with paper insulation. This
gives rise to the evaluation of various hydrocarbon gases, hydrogen and oxides of carbon, in quantities depending on
the type of fault [4].
 Heavy current arcing is characterized by the evolution of significant quantities of hydrogen and acetylene
(C2H2). If the arcing also involves paper insulation, the oxide of carbon will also be present.
 Partial discharge usually results in evolution of hydrogen and lower order hydrocarbons.
 Localized heating or hot spot gives rise to methane and ethane in appreciable amount.
 Prolonged overloading or impaired heat transfer can cause CO and CO2 to be generated due overheating paper
insulation.
IEC-599[7] is the guide to the interpretation of dissolved gas analysis in mineral oil. The faults are broadly divided into
thermal and electrical type.
Table 2: Types of Fault
Faults
Thermal
Electrical Type
Type
Thermal
Partial Discharge
Fault (T1)
Thermal
Discharge of Low
Fault (T2)
energy
Thermal
Discharge of High
Fault (T3)
energy
Fault of low energy will favour the breaking of C-H molecular bonds. More energy or higher temperature is needed to
break the C - C single bonds, C = C double bonds and C ≡ C triple bonds in ascending order of greater energy or higher
temperature. Acetylene gas will require very high temperature of at least 800 to 1200 degree Celsius to form because it
has a C ≡ C triple bond. Ethylene gas will form at a lower temperature of more than 500 degree Celsius because of the
C = C double bond. Ethane and methane will form at lower temperature because of the C - C single bond.
For thermal fault T1 of less than 300 degree Celsius, the paper insulation of the transformer will turn brownish. For
thermal fault T2 between 300 to 700 degree Celsius, the paper insulation will carbonize. For thermal fault T3 of more
than 700 degree Celsius, the oil will carbonize, metal will colorize of fuse.
For electrical fault of partial discharge is nature, wax may form in the oil. Electrical fault of low energy discharge and
high energy can be due to discharge through the oil, discharge through the paper insulation or discharge at the surface
of the paper insulation, or degradation of the surface of the paper insulation to form conducting paths or small arcs.
4. NORMAL VALUES OF DISSOLVED GAS
The mineral oil will contain normal values of dissolved gas which will indicate no incipient fault in the transformer.
Figure shows the normal values of dissolved gases in the oil. When the DGA results of all the 7 key gases are less than
the values of figure it can be concluded there was no incipient fault in the transformer.
Table 3: Normal Values of Dissolved Gas in Oil
Volume 1, Issue 2, October 2012
Gas
ppm
H2
CH4
C2H6
100
50
50
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Volume 1, Issue 2, October 2012
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C2H4
C2H2
CO2
CO
50
5
5000
200
5. STANDARD GAS
Figure 4 Standard Gas
Figure shows the standard gas cylinders are used for calibration of these gases. The cylinder contains approximately
100 ppm of hydrocarbons, 200 ppm of H2 and 5000 ppm of each CO and CO2.
Table 4: Concentration levels of Standard Gas
RT
Peak Area
Area
Heigh Heigh
(min) name (mV*sec) %
t (mV) t %
0.91
CO
625.914
34.41
80.6
53.463
1.28
CH4
163.738
9.003
23.408
15.527
4.04
CO2
439.803
24.18
23.193
15.384
5.45
C2H4
226.796
12.47
10.703
7.099
6.93
C2H6
202.329
11.12
7.939
5.266
10.6
C2H2
156.659
8.614
4.272
2.834
Figure5 Sample Gas
Table 5: Concentration levels of Sample Gas
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RT
(min)
Peak
name
Area
(mV*sec)
0.91
CO
307.637
1.29
CH4
4.18
Area
%
Height
(mV)
Height
%
22.66
31.393
36.612
144.512
10.64
16.83
19.628
CO2
383.266
28.23
17.896
20.871
5.71
C2H4
197.47
14.54
9.043
10.547
7.3
C2H6
180.775
13.31
6.723
7.841
11.1
C2H2
143.55
10.57
3.78
4.413
Figure 6 Corona or Partial Discharge
Figure shows large quantities of hydrogen can indicate heavy current arcing. Oxides of carbon may also be found if the
arcing involves paper insulation. Partial discharge usually results in evolution of hydrogen and lower order
hydrocarbons.
Table 6: Concentration levels of Gases
RT
(min)
Peak
name
Area
(mV*sec)
Area
%
Height
(mV)
Height
%
0.05
H2
120.894
71.78
13.413
71.85
0.4
H2
47.521
28.21
5.255
28.14
Figure 7 Overheating
Figure shows Localized heating or hot spot gives rise to methane and ethane in appreciable amount.
Table7: Concentartion levels of Gases
RT (min)
Peak name
Area (mV*sec)
Area %
Height (mV)
0.98
CO
14.305
7.915
1.094
12.362
1.3
CH4
5.297
2.931
0.548
6.194
4.01
CO2
143.223
79.24
6.48
73.202
5.42
C2H4
6.339
3.507
0.296
3.34
6.9
C2H6
2.183
1.208
0.126
1.427
10.3
C2H2
9.39
5.19
0.308
Volume 1, Issue 2, October 2012
Height
%
3.474
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International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org, editorijaiem@gmail.com
Volume 1, Issue 2, October 2012
ISSN 2319 - 4847
6. APPLICATION
In a new transformer, typical hydrocarbon gases concentration for good new oil after vacuum filtration would be within
5 p.p.m. DGA shall be repeated once a month after commissioning and then at increasing intervals as found necessary.
In an overhauled and repaired transformer, the transformer should be subjected to DGA a week after decommission and
again after about three months in service.
7. CONCLUSION
In interpretation of the results obtained for a particular transformer, due regard should be given to the following factors
before arriving at a specific conclusion:
 Date of commissioning of the transformer
 Loading cycle of the transformer
 Date on which the oil was last filtered
Early diagnosis and periodic monitoring of the condition of oil-filled electrical equipment used in generation and
distribution of power can improve reliability and availability of power. DGA is an unique condition monitoring tool and
has given significant benefits in the form of major reductions in unscheduled transformer failure, reduced maintenance,
and reduced cost of repairs.
Some inaccuracy is always associated with laboratory DGA measurements of transformer oil, which may affect the gas
ratios, concentration differences and other calculations upon which transformer condition assessment and fault
diagnosis by DGA are based.
REFERENCES
[1] J.J Kelly, “Transformer fault diagnosis by dissolved–gas analysis” IEEE Trans. On Industry Applications, vol. 16,
no.pp.777-782, Dec.1980.
[2] R.Rogers, “IEEE and IEC codes to interpret incipient faults in transformer, using gas in oil analysis,” IEEE
Trans. On Electr.Insul. vol.13, no.5, pp.349-354, October 1978.
[3] M. Duval, “Dissolved gas analysis: It can save your transformer,” IEEE Electrical Insulation Magazine, Vol 5,
No.6, pp. 22-27, 1989.
[4] IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers, IEEE Standard C57-1042008, Sep.2008.
[5] M.Duval, “New technologies for dissolved gas in oil analysis,” IEEE Electrical Insulation Mag., vol.19, no.2 pp.
6-15, 2003.
[6] R.R. Roger, “IEEE and IEC Codes to Interpret Incipient Faults in Transformers, Using Gas-In-Oil Analysis,”
IEEE Tran. Elect. Insul. Vol. EI-13, No. 5, pp. 348-354, 1978.
[7] IEC Publication 599, “Interpretation of the Analysis of the Gases in Transformers and Other Oil-Filled Electical
Equipment in Service,” 1978.
[8] Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers, IEEE Std C57. 104-1991, 1991.
[9] J. Singh, Y. R. Sood, and R. K. Jarial, “Condition monitoring of power transformers – bibliography survey,”
IEEE Electr. Insul. Mag., vol. 24, no. 3, pp. 11–24, 2008.
Rahul Pandey presently pursuing his M.E in power system engineering from Shri
Shankaracharya College of Engineering & Technology.
M.T Deshpande presently working as Head of Department (Electrical) in Shri Shankaracharya
College of Engineering & Technology, IEEE member.He is M.Tech in Power System, having 31
years of experience in steel industry and 9 years in teaching,
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