Dissolved Gas Analysis (DGA) Test for Transformer Health Monitoring

ABSTRACT
Transformers have been a necessary and vital component in electrical and
electronic circuits since 1830s. Even though novice electronic equipments reduce the
usage of transformers, they still play their major part in the power distribution system.
There is a necessity of the transformers which should be maintained annually and it
should be regularly monitored. There are several tests for analysis and in this particular
module we had explained regarding the Dissolved Gas Analysis (DGA) test and the
decision had to be made by this analysis test whether a transformer should function or
not. An asset manager plays a major role in this contribution.

SNO TITLE PAGENO
1. INTRODUCTION 3
2. DISSOLVED GAS ANALYSIS (DGA) 3
3. ESTIMATED DGA OUTCOME 5
4. INTERPRETATION OF DGA TEST 6
5. ASSET MANAGER DECISION MAKING 8
6. CONCLUSION 9
REFERENCES 10

INTRODUCTION:
Transformers are the most important component in the field of electrical engineering which
could have a long life and said to be a cost intensive component. These transformers constitute
an electrical supply networks. A transformer works on the principle of electromagnetism to
modify an AC voltage to another. The oil sample analysis is said to be a maintenance method
which is carried out to monitor the transformer health. There are various types of analysis test
such as standard oil test, Dissolved Gas Analysis (DGA) and furan analysis through which
detailed information regarding the operation of the transformer is collected. Normally the
Dissolved Gas Analysis (DGA) test is carried out to find the electrical (Hjartason, 2006)
abnormalities. Through this method we can able to determine the electrical fault as well as the
thermal faults. Each fault can be categorized into three different division based on the
international standard IEC 60599. Though there are different techniques, the Dissolved Gas
Analysis became most accepted technique in the last decade. In this paper, the discussion is done
regarding the DGA and also brief information is given about the decision making of an asset
manager with the data received from the analysis.
Dissolved Gas Analysis (DGA):
Performance which is carried out by DGA (Hjartason& Otal, 2006) in the insulating oil
with the oil sampling analysis test is used as an evaluation of the transformer health. Any
malfunction that happens inside a transformer and its required equipment could generate some
gases inside it. Therefore, the identification of these gases and the information obtained from that
could be very useful for some maintenance and prevention. There are many methods to estimate
these gases but the Dissolved Gas Analysis (DGA) is said to be the most efficient. In order to
measure the concentration of the dissolved gases, there are two process carried out: 1) Sampling
the oil obtained 2) Testing the samples. This DGA analysis should be carried out at least a year
and the details should be compared with the previous analysis data. There are several standards
such as ASTM D3613, ASTM D3612, and ANSI/IEEE C57.104(Rowland & Bahadoorsingh,
2008), respectively to evaluate the result.

The main causes of the formation of the gases are due to the electrical strife and thermal
putrefaction. At some point, each and every transformer could produce gases in usual working
temperature. The transformer insulation process is done through several mineral oils which is
said to be the composition of several hydrocarbons. The decomposition process in these
hydrocarbons is said to be tedious due to the thermal and the electrical fault (Abu-Elanien &
Salama, 2009). The basic reaction occurs due to the breakage of C-H bonds and C-C bonds.
Hence we could get the fragments of hydrocarbon and some hydrogen atoms. This leftover
mingle with each other and leads to the formation of gases such as hydrogen (H2), methane
(CH4), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6). Moreover, due to the cellulose
insulation, thermal decomposition or electrical problem generates methane (CH4), hydrogen (H2),
carbon monoxide (CO), and carbon dioxide (CO2). These gases are considered to be the key
gases and their property is said to be combustible (here the exceptional gas is CO2 which is non-
combustible).
This key gas depends highly on their temperature (John, 2006) which is based on their
volume of material at that circumstantial temperature. The small volume at high temperature
could produce the same quantity of gases as produced by the huge volume at restrained
temperature. This is mainly caused due to the effect on volume. For this reason, the gases which
are formed due to the transformer’s insulating oil is used for the evaluation process by
comparing with the past history of these transformers (Ridwan, Talib & Ghazali, 2014) in order
to find out any faults that could happen potentially or thermally.
Later the appropriate samples is examined and evaluated, the foremost step of the DGA analysis
is to find the concentration levels of each and every key gases samples. This could be expressed
in parts per million (ppm). It is endorsed that the concentration of the key gases change in time
and therefore the rate of change of the concentration is calculated (Jongen, Gulski, Morshuis,
Smith, Janseen, 2007). Fundamentally, the probable fault in the transformer could be indicated
by the sharp rise in the value of key gas concentration. Therefore it could be said that the result
of the DGA analysis gives a sharp rise in the value of the concentration level of the gases. If the
normal value limit is surmounted, then supplementary analysis of the sample should be taken and
once again we have to confirm where the key gas concentration level is accumulating. When the
level reach the action level point then the transformer (Ledwich and Islam, 2000) should be