An Experience of DGA Monitoring on Power Transformers.
PF-40
AN EXPERIENCE OF DGA MONITORING ON POWER TRANSFORMERS
W. G. Ariastina1*, I N. Setiawan1, I. A. D. Giriantari1, R. P. Sari2 and I. K. Solin3
1
Department of Electrical Engineering, Udayana University, Bali-80362, Indonesia
2
PT PLN (Persero) Surabaya Maintenance Service Area, Sidoarjo-61257, Indonesia
3
PT PLN (Persero) Head Office, Jakarta-12160, Indonesia
*Email: w.ariastina@unud.ac.id
Abstract: This paper presents DGA test results of three similar types of power
transformers with different operation commencing dates. The first transformer is
comparatively new transformer with five years servicing the network. This apparatus has
a high vibration and noise. The second transformer has been operated for about ten
years, while the third represents a seventeen year in service equipment. A series of DGA
tests for the transformers have been carried out over five year period. Results from
several DGA interpretation techniques then are compared to look possible fault existence.
It has been shown that in addition to analysis of an individual gas concentration, the
trends of gas concentration and gas proportion over time, have been very useful in
assisting researchers and engineers in monitoring condition of the power transformers.
1
technique. DGA interpretation techniques with
artificial intelligent tools have also been introduced
recently [4-6].
INTRODUCTION
DGA has been well known since decades and
currently is the most extensively used test for
transformer condition monitoring. For a DGA test, a
small amount of transformer oil is taken from
transformer tank. The oil sample must be
completely sealed to prevent gas escaping from
the sample vessel or further moisture ingress into
the oil. Hydrocarbon gases dissolved in the oil are
then extracted and analysed by means of a gas
chromatograph.
In addition to the absolute value and ratios of
dissolved gases, it is important to consider the
increase rate of a particular gas over time.
Continuous tests that provide trends of the
dissolved gas quantity will be very useful in
providing an accurate interpretation of the DGA
results. A sudden increase in distinctive gas
content may specify a fault occurrence [4,7].
This paper presents a field experience of DGA
monitoring of three 150/20kV power transformers.
The first transformer is a five year in service
equipment with high vibration and noise. The
second has been operated for about ten years,
while the third represents a seventeen years in
service transformer. Results from several DGA
interpretation techniques then are compared to
look possible fault existence. Figure 1 illustrates
one of the investigated power transformer
(Transformer 1).
The presence and the quantity of the gases
determine the quality of the insulating liquid and
the existence of failures within the transformer
tank. There are several gases that can be used as
indicators, which include carbon monoxide (CO),
carbon dioxide (CO2), hydrogen (H2), methane
(CH4), ethane (C2H6), ethylene (C2H4), and
acetylene (C2H2). A corresponding oil quality test is
usually carried out to identify the insulation integrity
level of the oil. The later basically covers
examination of physical characteristics, which
include breakdown test, viscosity, flash point, water
content and acidity level.
Since it was firstly developed, research into DGA
interpretation has been extensively carried out. A
large number of technical papers have been
published accordingly. A number of well known
DGA interpretation techniques have also been
developed. Among the available techniques are
the key gas interpretation, IEC methods, Roger’s
ratio, Doernenburg’s ratio, and Duval’s triangle
fault indicator [1-7].
Many other techniques have also been developed
to increase the interpretation accuracy. Several
approaches applied modified single method and
the other applied a combined interpretation
Figure 1: Transformer 1 (150/20kV, 60MVA)
2136
PF-40
2
The maximum transformer loading during first year
of operation was slightly above 15MW. It has been
100% increased of load since the time. Figure 2
shows typical daily load pattern of the transformer.
The transformer is currently operated with a low
loading scheme, mostly below 50% of its maximum
capacity. During day time, the load is
comparatively steady of about 21MW. Beginning
about 5pm, the load increases to meet night peak
demand. The maximum transformer loading is
about 32MW and lasts for a few hours before
decreases because of less power demand later at
night. The recorded maximum oil temperature is
about 65°C.
DGA MONITORING
As part of asset management strategy, the state
electricity company of the Republic of Indonesia,
has implemented DGA as a standard method for
condition monitoring of HV transformers. The time
interval of the DGA monitoring is determined based
on the condition of the equipment. The DGA has
been applied as a standard method, since it is
efficient to determine and classify the thermal and
electrical faults.
In addition to the DGA monitoring, condition
monitoring of transformer using electrical,
mechanical and thermal methods have also been
applied. The later include Partial Discharge (PD),
Frequency Response Analysis (FRA), Acoustic
Emission (AE), vibration analysis and infrared
thermography techniques.
35
30
25
Load (M W )
DGA test results of three different transformers of
similar type and capacity are discussed in this
paper. The first transformer has been operated for
five years with high vibration and noise. The
second has operated for about ten years with
thermal fault indication, while the third represents a
seventeen years in service transformer.
20
15
10
5
0
8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00
The DGA tests have been carried out for five years
in series. The time interval between measurements
is approximately a year. Interpretation techniques
of the DGA test results presented here are of key
gas method, Doernenburg’s ratio, IEC ratio and
Duval’s triangle. In addition to the diagnosis using
these interpretation methods, the trends of
individual concentration and composition of the
hydrocarbon gases are also presented. The trend
of gas quantity may provide a useful fault indication
within the transformer.
Time
Figure 2: Typical load pattern of Transformer 1
Individual gas concentration in oil for Transformer
1 over the time period is illustrated in Figure 3.
There was an increase in concentration of carbon
dioxide, carbon monoxide, hydrogen, methane,
and ethane during first year operation of the
transformer. The concentrations of these gases
were comparably high, with carbon dioxide of
2714.29 ppm, carbon monoxide of 755.93 ppm,
hydrogen of 281.45 ppm and the ethane of 192.48
ppm. Over the following three years however, the
concentrations of the hydrocarbon gases have
decreased gradually.
The sample for DGA tests was of bottom oil of the
main tank. The oil was taken from bottom drain
valve of the transformer (see yellow arrow sign in
Figure 1). The oil sample was obtained during
normal operation of the transformers, with an
approximate temperature of 60°C.
RESULTS AND DISCUSSION
G as C o n cen tratio n (p p m )
3
3,000
3.1 Transformer 1 (5 years in service)
The power transformer was manufactured in 2007,
and commenced to operate in early 2008. It is an
ONAN/ONAF type with a capacity of 60MVA. The
equipment is installed within a network substation,
with an operating voltage of 150/20kV. The cooling
fan is set to operate at an oil temperature of 60°C
and above. Previous measurement showed that
the transformer produced a vibration acceleration
2
of 311.27m/s , the highest among other tested
power transformers in the region [8]. As a result of
the high vibration, the transformer also produces a
high audible noise.
2,500
2,000
1,500
1,000
500
0
2008
2009
2010
2011
2012
Year
CO2
CO
H2
CH4
C2H6
C2H4
C2H2
Figure 3: Trend of individual gas concentration of
Transformer 1
2137
PF-40
The key gas chart in Figure 4 shows that the
proportion of carbon monoxide and hydrogen has
decreased over time period. In contrast, the
proportion of methane and ethane was constantly
increased. This indicates that during early
operation of the transformer, there is a possibility
of occurrence of low energy discharges that
produces hydrogen, and slightly methane, ethane
and ethylene. This approach has also indicated an
occurrence of cellulose decomposition for the
following years. However; after five years in
service the key gas interpretation suggested no
fault and the transformer has been classified into
normal operation (see Table 1).
not only as a result of faults within the equipment
but also because of rusting process or other
chemical reactions involving steel, uncoated
surfaces or protective paints [7]. The amount of the
produced gasses is very dependent on the
characteristics of the oil, cellulose materials and
other metallic components within the transformer.
This condition is signified by the reduction in
hydrocarbon gas concentrations for the following
years, which may indicate that the chemical
reaction is reaching a new equilibrium point. The
increase of methane and ethane proportion
between year 2011 and 2012 however, has been a
concern for further investigation. The transformer is
currently continued in normal service.
G as C om position (% )
100
3.2 Transformer 2 (10 years in service)
80
The second transformer has a similar type of
Transformer 1. This apparatus has been in service
for about ten years. The maximum transformer
loading is about 14 MW. No failure was previously
occurred during operation of the transformer. Oil
degassing process or reclamation has also never
been carried out.
60
40
20
Individual gas concentration in oil for the last five
years of Transformer 2 is presented in Figure 5. It
can be seen that there was a consistence increase
in concentration of carbon dioxide, methane,
ethane and ethylene for the last four years. In
2008, a high concentration of ethane was
recorded. The gas concentration suddenly
decreased on the following year, before beginning
to gradually increase again. In 2009, there was an
abrupt increase in methane concentration and
occurred only in single year.
0
CO
H2
CH4
2008
2009
C2H6
2010
2011
C2H4
C2H2
2012
Figure 4: Trend of hydrocarbon gas composition of
Transformer 1
DGA interpretation using Doernenburg’s ratio has
shown different results from year to year. There
was an indication of low energy discharge in 2008
and thermal fault in 2011. In contrast, no fault
indication was given by IEC ratio for five years in
service. Similarly, Duval’s triangle approach
provided no results. This is due to a low monthly
increase rate of the hydrocarbon gases. Details of
the DGA interpretations are shown in Table 1.
G as C o ncen tratio n (p p m )
1,200
Table 1: DGA interpretations of Transformer 1
Year
Technique
2008
2009
2010
Low
Cellulose Cellulose
Key Gas
energy
decom- decomDischarge position position
Low
High
Doernenburg
energy
energy
N/A
Ratio
Discharge discharge
IEC Ratio
Normal
Normal Normal
Duval’s
Triangle
N/A
N/A
N/A
2011
2012
Cellulose
decom- Normal
position
Thermal
fault
N/A
Normal
Normal
N/A
N/A
1,000
800
600
400
200
0
2008
2009
2010
2011
2012
Year
CO2
CO
H2
CH4
C2H6
C2H4
C2H2
Figure 5: Trend of individual gas concentration of
Transformer 2
The key gas analysis shows that the proportion of
hydrogen was gradually decreased over the five
year period, as illustrated in Figure 6. In contrary,
ethane was present at a very high proportion in
year 2008. A high increase in methane was also
noticeable in year 2009. A relatively small increase
The formation of comparably high carbon oxides
and hydrogen during first year of transformer
operation may relate to an early stage oxidation of
the transformer oil. These gases may be generated
2138
PF-40
in acetylene proportion was noticed in 2010. For
the last three years, the proportion of the key
gases was dominated by carbon monoxide. Note
also that in year 2012, the proportion of ethylene
was increased significantly from the previous year.
The summary of DGA interpretation using key gas
and other techniques over the last five years is
presented in Table 2.
maintenance. Currently, the transformer is still in
service with a low loading scheme and further
monitoring has been planned accordingly.
3.3 Transformer 3 (17 years in service)
The third transformer has a similar type to those of
Transformer 1 and 2. The transformer has the
longest period of service among the three. It has
been in service for about seventeen years. The
maximum daily transformer loading is about
40MW. No short circuit or other failure occurred
during operation of the transformer. Oil degassing
has not previously been carried out.
G as C o m p o sitio n (% )
100
80
60
Figure 7 shows individual gas concentration in oil
over the last five years for Transformer 3.
Relatively high concentration of carbon dioxide is
clearly observed. Although the concentration of the
carbon dioxide gas decreased significantly in 2009
however, the gas concentration has been
increased with a high rate during the last three
years. The concentration of carbon monoxide was
slightly increased during period of 2008 to 2011,
before decreased significantly in year 2012. A
comparatively small amount of other dissolved
gasses was produced during this period.
40
20
0
CO
H2
CH4
2008
2009
C2H6
2010
2011
C2H4
C2H2
2012
Figure 6: Trend of hydrocarbon gas composition of
Transformer 2
Interpretation using Doernenburg’s ratio for the last
four years indicated fault occurrence involving high
energy discharge and thermal fault. Particularly in
year 2012, similar diagnosis was also indicated by
IEC ratio and Duval’s triangle approaches. Quite
similar interpretation results were also observed in
year 2009, however with a PD indication by
Duval’s triangle technique. In other years of
observation, results of the DGA interpretation
techniques varied, thus it is difficult to provide a
conclusive interpretation.
The key gas approach shows a variation of the
dissolved gas proportion from year to year. The
hydrocarbon gas compositions were dominated by
carbon monoxide, with a proportion well above
70%. A noticeable increase in hydrogen and
acetylene was observed in 2012. The trend of
hydrocarbon gas composition of Transformer 3 can
be seen in Figure 8.
5,000
G as C on cen tration (pp m )
4,500
Table 2: DGA interpretations of Transformer 2
Approach
Key Gas
Doernenburg
Ratio
IEC Ratio
Duval’s
Triangle
Year
2008
2009
Normal Normal
2010
Normal
2011
2012
Cellulose
decom- Normal
position
PD
N/A
N/A
3,500
3,000
2,500
2,000
1,500
1,000
500
High
Thermal Thermal
N/A
energy
fault
fault
discharge
Thermal
Thermal
Normal
Normal Normal
Fault
fault
0
Thermal
fault
N/A
4,000
2008
2009
2010
2011
2012
Year
CO2
CO
H2
CH4
C2H6
C2H4
C2H2
Figure 7: Trend of individual gas concentration of
Transformer 3
T3
Although the increase in acetylene was clearly
observed in 2012, the interpretation using key gas
technique however, showed a normal operation of
the transformer. In contrary, interpretations of the
DGA test results for four years earlier indicated an
occurrence of low energy discharge and a
possibility of cellulose decomposition as shown in
Table 3.
Regular increase in carbon monoxide and other
hydrocarbon gasses for the last four years have
been a concern for the continuity of the transformer
service. DGA interpretations results indicated a
possibility of fault occurrence involving high
temperature. It has not been decided yet however,
whether the transformer will be put into
2139
PF-40
DGA interpretation using several techniques
showed variation in diagnosis results. This may
lead to a difficulty in deriving comprehensive
interpretation of DGA test results. Condition
examination using combination of DGA with
several other monitoring techniques, such as PD
technique, furanic compound analysis, and FRA
has been planned for future investigations.
G as C om position (% )
100
80
60
40
5
20
The authors greatly appreciate PT PLN (Persero)
Transmission and Load Dispatch Centre for
providing access to the investigated power
transformers. The authors would also like to extend
their appreciation to Udayana University for
providing partial funding for the study.
0
CO
H2
CH4
2008
2009
C2H6
2010
2011
C2H4
C2H2
2012
Figure 8: Trend of hydrocarbon gas composition of
Transformer 3
DGA interpretation using Doernenburg’s ratio
technique showed a consistent indication of the
occurrence of high energy discharge for the last
four years, which was started by an occurrence of
low energy discharge in year 2008. In contrary,
normal operation was indicated by IEC ratio
interpretation technique. Similarly, Duval’s triangle
fault indicator has shown no particular results for
the five years period.
6
[2] S. Besner, J. Jalbert and B. Noirhomme,
“Unusual Ethylene Production of In-Service
Transformer Oil at Low Temperature”, IEEE
Trans. DEI, Vol. 19, No. 6, pp. 1901-1907, Dec
2012.
Year
[3] I. Höhlein-Atanasova, R. Frotscher, “Carbon
Oxides in the Interpretation of Dissolved Gas
Analysis in Transformers and Tap Changers”,
IEEE EI Magazine, Vol. 26, No. 6, pp. 22-26,
Nov/Dec 2010.
2008
2009
2010
2011
2012
Cellulose Cellulose Cellulose
Low
Normal
decom- decom- decomKey Gas
energy
discharge position position position
Low
High
High
High
High
Doernenburg
energy
energy
energy
energy
energy
Ratio
discharge discharge discharge discharge discharge
IEC Ratio
Normal
Normal
Normal
Normal
Normal
Duval’s
Triangle
N/A
N/A
N/A
N/A
[4] M. Duval, “Calculation of DGA Limit Values
and Sampling Intervals in Transformers in
Service”, IEEE EI Magazine, Vol. 24, No. 5, pp.
7-13, Sep/Oct 2008.
N/A
[5] M. Arshad and S. M. Islam, “Significance of
Cellulose Power Transformer Condition
Assessment”, IEEE Trans. DEI, Vol. 18, No. 5,
pp. 1591-1598, Oct 2011.
Although the concentration and the increase rate of
the hydrocarbon gasses are within their suggested
limits, constant increase in carbon dioxide over the
past four years has been focused for further
investigation. This may be an indication of fault
occurrence involving cellulose materials [7]. The
equipment is currently kept servicing the network.
4
REFERENCES
[1] S. Singh and M. N. Bandyopadhyay,
“Dissolved Gas Analysis Technique for
Incipient
Fault
Diagnosis
in
Power
Transformers: A Bibliographic Survey”, IEEE EI
Magazine, Vol. 26, No. 6, pp. 41-46, Nov/Dec
2010.
Table 3: DGA interpretations of Transformer 3
Approach
ACKNOWLEDGMENTS
[6] A. Akbari, A. Setayeshmehr, H. Borsi, and E.
Gockenbach, I. Fofana, “Intelligent AgentBased System Using Dissolved Gas Analysis
to Detect Incipient Faults in Power
Transformers”, IEEE EI Magazine, Vol. 26, No.
6, pp. 27-40, Nov/Dec 2010.
CONCLUSIONS
[7] IEC
Publication
60599,
“Mineral
OilImpregnated Electrical Equipment in Service –
Guide to the Interpretation of Dissolved and
Free Gases Analysis”, Mar 1999.
Investigation of DGA test results on power
transformers has been carried out. Different test
results from three transformers with different case
and duration of service have been presented. In
addition to the analysis of an individual gas
concentration, the trends of dissolved gas
concentration and proportion over time have been
very useful in assisting researchers and engineers
in monitoring condition of the power transformers.
[8] W. G. Ariastina, I. A. D. Giriantari, I. K. Solin
and O. Yolanda, “Condition Monitoring of
Power Transformer: A Field Experience”, Proc.
th
of the 9 ICPADM, Harbin, Vol. 3, pp. 10511054, Jul 2009.
2140
AN EXPERIENCE OF DGA MONITORING ON POWER TRANSFORMERS
W. G. Ariastina1*, I N. Setiawan1, I. A. D. Giriantari1, R. P. Sari2 and I. K. Solin3
1
Department of Electrical Engineering, Udayana University, Bali-80362, Indonesia
2
PT PLN (Persero) Surabaya Maintenance Service Area, Sidoarjo-61257, Indonesia
3
PT PLN (Persero) Head Office, Jakarta-12160, Indonesia
*Email: w.ariastina@unud.ac.id
Abstract: This paper presents DGA test results of three similar types of power
transformers with different operation commencing dates. The first transformer is
comparatively new transformer with five years servicing the network. This apparatus has
a high vibration and noise. The second transformer has been operated for about ten
years, while the third represents a seventeen year in service equipment. A series of DGA
tests for the transformers have been carried out over five year period. Results from
several DGA interpretation techniques then are compared to look possible fault existence.
It has been shown that in addition to analysis of an individual gas concentration, the
trends of gas concentration and gas proportion over time, have been very useful in
assisting researchers and engineers in monitoring condition of the power transformers.
1
technique. DGA interpretation techniques with
artificial intelligent tools have also been introduced
recently [4-6].
INTRODUCTION
DGA has been well known since decades and
currently is the most extensively used test for
transformer condition monitoring. For a DGA test, a
small amount of transformer oil is taken from
transformer tank. The oil sample must be
completely sealed to prevent gas escaping from
the sample vessel or further moisture ingress into
the oil. Hydrocarbon gases dissolved in the oil are
then extracted and analysed by means of a gas
chromatograph.
In addition to the absolute value and ratios of
dissolved gases, it is important to consider the
increase rate of a particular gas over time.
Continuous tests that provide trends of the
dissolved gas quantity will be very useful in
providing an accurate interpretation of the DGA
results. A sudden increase in distinctive gas
content may specify a fault occurrence [4,7].
This paper presents a field experience of DGA
monitoring of three 150/20kV power transformers.
The first transformer is a five year in service
equipment with high vibration and noise. The
second has been operated for about ten years,
while the third represents a seventeen years in
service transformer. Results from several DGA
interpretation techniques then are compared to
look possible fault existence. Figure 1 illustrates
one of the investigated power transformer
(Transformer 1).
The presence and the quantity of the gases
determine the quality of the insulating liquid and
the existence of failures within the transformer
tank. There are several gases that can be used as
indicators, which include carbon monoxide (CO),
carbon dioxide (CO2), hydrogen (H2), methane
(CH4), ethane (C2H6), ethylene (C2H4), and
acetylene (C2H2). A corresponding oil quality test is
usually carried out to identify the insulation integrity
level of the oil. The later basically covers
examination of physical characteristics, which
include breakdown test, viscosity, flash point, water
content and acidity level.
Since it was firstly developed, research into DGA
interpretation has been extensively carried out. A
large number of technical papers have been
published accordingly. A number of well known
DGA interpretation techniques have also been
developed. Among the available techniques are
the key gas interpretation, IEC methods, Roger’s
ratio, Doernenburg’s ratio, and Duval’s triangle
fault indicator [1-7].
Many other techniques have also been developed
to increase the interpretation accuracy. Several
approaches applied modified single method and
the other applied a combined interpretation
Figure 1: Transformer 1 (150/20kV, 60MVA)
2136
PF-40
2
The maximum transformer loading during first year
of operation was slightly above 15MW. It has been
100% increased of load since the time. Figure 2
shows typical daily load pattern of the transformer.
The transformer is currently operated with a low
loading scheme, mostly below 50% of its maximum
capacity. During day time, the load is
comparatively steady of about 21MW. Beginning
about 5pm, the load increases to meet night peak
demand. The maximum transformer loading is
about 32MW and lasts for a few hours before
decreases because of less power demand later at
night. The recorded maximum oil temperature is
about 65°C.
DGA MONITORING
As part of asset management strategy, the state
electricity company of the Republic of Indonesia,
has implemented DGA as a standard method for
condition monitoring of HV transformers. The time
interval of the DGA monitoring is determined based
on the condition of the equipment. The DGA has
been applied as a standard method, since it is
efficient to determine and classify the thermal and
electrical faults.
In addition to the DGA monitoring, condition
monitoring of transformer using electrical,
mechanical and thermal methods have also been
applied. The later include Partial Discharge (PD),
Frequency Response Analysis (FRA), Acoustic
Emission (AE), vibration analysis and infrared
thermography techniques.
35
30
25
Load (M W )
DGA test results of three different transformers of
similar type and capacity are discussed in this
paper. The first transformer has been operated for
five years with high vibration and noise. The
second has operated for about ten years with
thermal fault indication, while the third represents a
seventeen years in service transformer.
20
15
10
5
0
8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00
The DGA tests have been carried out for five years
in series. The time interval between measurements
is approximately a year. Interpretation techniques
of the DGA test results presented here are of key
gas method, Doernenburg’s ratio, IEC ratio and
Duval’s triangle. In addition to the diagnosis using
these interpretation methods, the trends of
individual concentration and composition of the
hydrocarbon gases are also presented. The trend
of gas quantity may provide a useful fault indication
within the transformer.
Time
Figure 2: Typical load pattern of Transformer 1
Individual gas concentration in oil for Transformer
1 over the time period is illustrated in Figure 3.
There was an increase in concentration of carbon
dioxide, carbon monoxide, hydrogen, methane,
and ethane during first year operation of the
transformer. The concentrations of these gases
were comparably high, with carbon dioxide of
2714.29 ppm, carbon monoxide of 755.93 ppm,
hydrogen of 281.45 ppm and the ethane of 192.48
ppm. Over the following three years however, the
concentrations of the hydrocarbon gases have
decreased gradually.
The sample for DGA tests was of bottom oil of the
main tank. The oil was taken from bottom drain
valve of the transformer (see yellow arrow sign in
Figure 1). The oil sample was obtained during
normal operation of the transformers, with an
approximate temperature of 60°C.
RESULTS AND DISCUSSION
G as C o n cen tratio n (p p m )
3
3,000
3.1 Transformer 1 (5 years in service)
The power transformer was manufactured in 2007,
and commenced to operate in early 2008. It is an
ONAN/ONAF type with a capacity of 60MVA. The
equipment is installed within a network substation,
with an operating voltage of 150/20kV. The cooling
fan is set to operate at an oil temperature of 60°C
and above. Previous measurement showed that
the transformer produced a vibration acceleration
2
of 311.27m/s , the highest among other tested
power transformers in the region [8]. As a result of
the high vibration, the transformer also produces a
high audible noise.
2,500
2,000
1,500
1,000
500
0
2008
2009
2010
2011
2012
Year
CO2
CO
H2
CH4
C2H6
C2H4
C2H2
Figure 3: Trend of individual gas concentration of
Transformer 1
2137
PF-40
The key gas chart in Figure 4 shows that the
proportion of carbon monoxide and hydrogen has
decreased over time period. In contrast, the
proportion of methane and ethane was constantly
increased. This indicates that during early
operation of the transformer, there is a possibility
of occurrence of low energy discharges that
produces hydrogen, and slightly methane, ethane
and ethylene. This approach has also indicated an
occurrence of cellulose decomposition for the
following years. However; after five years in
service the key gas interpretation suggested no
fault and the transformer has been classified into
normal operation (see Table 1).
not only as a result of faults within the equipment
but also because of rusting process or other
chemical reactions involving steel, uncoated
surfaces or protective paints [7]. The amount of the
produced gasses is very dependent on the
characteristics of the oil, cellulose materials and
other metallic components within the transformer.
This condition is signified by the reduction in
hydrocarbon gas concentrations for the following
years, which may indicate that the chemical
reaction is reaching a new equilibrium point. The
increase of methane and ethane proportion
between year 2011 and 2012 however, has been a
concern for further investigation. The transformer is
currently continued in normal service.
G as C om position (% )
100
3.2 Transformer 2 (10 years in service)
80
The second transformer has a similar type of
Transformer 1. This apparatus has been in service
for about ten years. The maximum transformer
loading is about 14 MW. No failure was previously
occurred during operation of the transformer. Oil
degassing process or reclamation has also never
been carried out.
60
40
20
Individual gas concentration in oil for the last five
years of Transformer 2 is presented in Figure 5. It
can be seen that there was a consistence increase
in concentration of carbon dioxide, methane,
ethane and ethylene for the last four years. In
2008, a high concentration of ethane was
recorded. The gas concentration suddenly
decreased on the following year, before beginning
to gradually increase again. In 2009, there was an
abrupt increase in methane concentration and
occurred only in single year.
0
CO
H2
CH4
2008
2009
C2H6
2010
2011
C2H4
C2H2
2012
Figure 4: Trend of hydrocarbon gas composition of
Transformer 1
DGA interpretation using Doernenburg’s ratio has
shown different results from year to year. There
was an indication of low energy discharge in 2008
and thermal fault in 2011. In contrast, no fault
indication was given by IEC ratio for five years in
service. Similarly, Duval’s triangle approach
provided no results. This is due to a low monthly
increase rate of the hydrocarbon gases. Details of
the DGA interpretations are shown in Table 1.
G as C o ncen tratio n (p p m )
1,200
Table 1: DGA interpretations of Transformer 1
Year
Technique
2008
2009
2010
Low
Cellulose Cellulose
Key Gas
energy
decom- decomDischarge position position
Low
High
Doernenburg
energy
energy
N/A
Ratio
Discharge discharge
IEC Ratio
Normal
Normal Normal
Duval’s
Triangle
N/A
N/A
N/A
2011
2012
Cellulose
decom- Normal
position
Thermal
fault
N/A
Normal
Normal
N/A
N/A
1,000
800
600
400
200
0
2008
2009
2010
2011
2012
Year
CO2
CO
H2
CH4
C2H6
C2H4
C2H2
Figure 5: Trend of individual gas concentration of
Transformer 2
The key gas analysis shows that the proportion of
hydrogen was gradually decreased over the five
year period, as illustrated in Figure 6. In contrary,
ethane was present at a very high proportion in
year 2008. A high increase in methane was also
noticeable in year 2009. A relatively small increase
The formation of comparably high carbon oxides
and hydrogen during first year of transformer
operation may relate to an early stage oxidation of
the transformer oil. These gases may be generated
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PF-40
in acetylene proportion was noticed in 2010. For
the last three years, the proportion of the key
gases was dominated by carbon monoxide. Note
also that in year 2012, the proportion of ethylene
was increased significantly from the previous year.
The summary of DGA interpretation using key gas
and other techniques over the last five years is
presented in Table 2.
maintenance. Currently, the transformer is still in
service with a low loading scheme and further
monitoring has been planned accordingly.
3.3 Transformer 3 (17 years in service)
The third transformer has a similar type to those of
Transformer 1 and 2. The transformer has the
longest period of service among the three. It has
been in service for about seventeen years. The
maximum daily transformer loading is about
40MW. No short circuit or other failure occurred
during operation of the transformer. Oil degassing
has not previously been carried out.
G as C o m p o sitio n (% )
100
80
60
Figure 7 shows individual gas concentration in oil
over the last five years for Transformer 3.
Relatively high concentration of carbon dioxide is
clearly observed. Although the concentration of the
carbon dioxide gas decreased significantly in 2009
however, the gas concentration has been
increased with a high rate during the last three
years. The concentration of carbon monoxide was
slightly increased during period of 2008 to 2011,
before decreased significantly in year 2012. A
comparatively small amount of other dissolved
gasses was produced during this period.
40
20
0
CO
H2
CH4
2008
2009
C2H6
2010
2011
C2H4
C2H2
2012
Figure 6: Trend of hydrocarbon gas composition of
Transformer 2
Interpretation using Doernenburg’s ratio for the last
four years indicated fault occurrence involving high
energy discharge and thermal fault. Particularly in
year 2012, similar diagnosis was also indicated by
IEC ratio and Duval’s triangle approaches. Quite
similar interpretation results were also observed in
year 2009, however with a PD indication by
Duval’s triangle technique. In other years of
observation, results of the DGA interpretation
techniques varied, thus it is difficult to provide a
conclusive interpretation.
The key gas approach shows a variation of the
dissolved gas proportion from year to year. The
hydrocarbon gas compositions were dominated by
carbon monoxide, with a proportion well above
70%. A noticeable increase in hydrogen and
acetylene was observed in 2012. The trend of
hydrocarbon gas composition of Transformer 3 can
be seen in Figure 8.
5,000
G as C on cen tration (pp m )
4,500
Table 2: DGA interpretations of Transformer 2
Approach
Key Gas
Doernenburg
Ratio
IEC Ratio
Duval’s
Triangle
Year
2008
2009
Normal Normal
2010
Normal
2011
2012
Cellulose
decom- Normal
position
PD
N/A
N/A
3,500
3,000
2,500
2,000
1,500
1,000
500
High
Thermal Thermal
N/A
energy
fault
fault
discharge
Thermal
Thermal
Normal
Normal Normal
Fault
fault
0
Thermal
fault
N/A
4,000
2008
2009
2010
2011
2012
Year
CO2
CO
H2
CH4
C2H6
C2H4
C2H2
Figure 7: Trend of individual gas concentration of
Transformer 3
T3
Although the increase in acetylene was clearly
observed in 2012, the interpretation using key gas
technique however, showed a normal operation of
the transformer. In contrary, interpretations of the
DGA test results for four years earlier indicated an
occurrence of low energy discharge and a
possibility of cellulose decomposition as shown in
Table 3.
Regular increase in carbon monoxide and other
hydrocarbon gasses for the last four years have
been a concern for the continuity of the transformer
service. DGA interpretations results indicated a
possibility of fault occurrence involving high
temperature. It has not been decided yet however,
whether the transformer will be put into
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PF-40
DGA interpretation using several techniques
showed variation in diagnosis results. This may
lead to a difficulty in deriving comprehensive
interpretation of DGA test results. Condition
examination using combination of DGA with
several other monitoring techniques, such as PD
technique, furanic compound analysis, and FRA
has been planned for future investigations.
G as C om position (% )
100
80
60
40
5
20
The authors greatly appreciate PT PLN (Persero)
Transmission and Load Dispatch Centre for
providing access to the investigated power
transformers. The authors would also like to extend
their appreciation to Udayana University for
providing partial funding for the study.
0
CO
H2
CH4
2008
2009
C2H6
2010
2011
C2H4
C2H2
2012
Figure 8: Trend of hydrocarbon gas composition of
Transformer 3
DGA interpretation using Doernenburg’s ratio
technique showed a consistent indication of the
occurrence of high energy discharge for the last
four years, which was started by an occurrence of
low energy discharge in year 2008. In contrary,
normal operation was indicated by IEC ratio
interpretation technique. Similarly, Duval’s triangle
fault indicator has shown no particular results for
the five years period.
6
[2] S. Besner, J. Jalbert and B. Noirhomme,
“Unusual Ethylene Production of In-Service
Transformer Oil at Low Temperature”, IEEE
Trans. DEI, Vol. 19, No. 6, pp. 1901-1907, Dec
2012.
Year
[3] I. Höhlein-Atanasova, R. Frotscher, “Carbon
Oxides in the Interpretation of Dissolved Gas
Analysis in Transformers and Tap Changers”,
IEEE EI Magazine, Vol. 26, No. 6, pp. 22-26,
Nov/Dec 2010.
2008
2009
2010
2011
2012
Cellulose Cellulose Cellulose
Low
Normal
decom- decom- decomKey Gas
energy
discharge position position position
Low
High
High
High
High
Doernenburg
energy
energy
energy
energy
energy
Ratio
discharge discharge discharge discharge discharge
IEC Ratio
Normal
Normal
Normal
Normal
Normal
Duval’s
Triangle
N/A
N/A
N/A
N/A
[4] M. Duval, “Calculation of DGA Limit Values
and Sampling Intervals in Transformers in
Service”, IEEE EI Magazine, Vol. 24, No. 5, pp.
7-13, Sep/Oct 2008.
N/A
[5] M. Arshad and S. M. Islam, “Significance of
Cellulose Power Transformer Condition
Assessment”, IEEE Trans. DEI, Vol. 18, No. 5,
pp. 1591-1598, Oct 2011.
Although the concentration and the increase rate of
the hydrocarbon gasses are within their suggested
limits, constant increase in carbon dioxide over the
past four years has been focused for further
investigation. This may be an indication of fault
occurrence involving cellulose materials [7]. The
equipment is currently kept servicing the network.
4
REFERENCES
[1] S. Singh and M. N. Bandyopadhyay,
“Dissolved Gas Analysis Technique for
Incipient
Fault
Diagnosis
in
Power
Transformers: A Bibliographic Survey”, IEEE EI
Magazine, Vol. 26, No. 6, pp. 41-46, Nov/Dec
2010.
Table 3: DGA interpretations of Transformer 3
Approach
ACKNOWLEDGMENTS
[6] A. Akbari, A. Setayeshmehr, H. Borsi, and E.
Gockenbach, I. Fofana, “Intelligent AgentBased System Using Dissolved Gas Analysis
to Detect Incipient Faults in Power
Transformers”, IEEE EI Magazine, Vol. 26, No.
6, pp. 27-40, Nov/Dec 2010.
CONCLUSIONS
[7] IEC
Publication
60599,
“Mineral
OilImpregnated Electrical Equipment in Service –
Guide to the Interpretation of Dissolved and
Free Gases Analysis”, Mar 1999.
Investigation of DGA test results on power
transformers has been carried out. Different test
results from three transformers with different case
and duration of service have been presented. In
addition to the analysis of an individual gas
concentration, the trends of dissolved gas
concentration and proportion over time have been
very useful in assisting researchers and engineers
in monitoring condition of the power transformers.
[8] W. G. Ariastina, I. A. D. Giriantari, I. K. Solin
and O. Yolanda, “Condition Monitoring of
Power Transformer: A Field Experience”, Proc.
th
of the 9 ICPADM, Harbin, Vol. 3, pp. 10511054, Jul 2009.
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