Dissolved Gas Analysis Method

FINAL YEAR PROJECT 1 PROGRESS REPORT 1 AUTHOR’S NAME:Ruban s/o Paramasivam STUDENT ID:EP083765 REPORTING PERIOD:18TH JUNE 2012 – 15TH JULY 2012 SUPERVISOR’S:Mr. John Steven NAME PROJECT TITLE:Dissolved Gas Analysis in determining Transformer Faults SUBMISSION DATE:16TH JULY 2012 1. 0 Background of Studies Oil sampling analysis is a useful, predictive, maintenance tool for determining transformer health. DGA is identified as one of the sufficient method of oil sampling in evaluating transformer health. The breakdown of electrical insulating material inside the transformer generates gases within the transformer.

The identity of gases being generated is useful in any preventive method maintenance program. DGA method involves oil sampling method and testing the sample to measure the concentration of the dissolved gases. The two typical principal cause of gas formation within an operating transformer are electrical disturbance and thermal decomposition. All transformers generate gasses to some extent at normal operating temperature. Insulating mineral oils for transformer are mixtures of many different hydrocarbons and the decomposition process for these hydrocarbons are complex.

During this process, active hydrogen atoms and hydrocarbons fragments are formed. These fragments can combine with each other to form gasses such as Hydrogen (H2), Methane (CH4), Acetylene (C2H2), Ethylene (C2H4), Ethane (C2H6) and many more. The gasses listed are considered combustible. The rate at which each gas are produced depends on the temperature. Therefore, the concentration of the individual dissolved gasses found in transformer insulating oil may be used directly to evaluate the transformer and suggest any faults within the transformer.

After samples have been taken and analysed, the first step in evaluating DGA result is to consider the concentration level of each gasses. Basically, any sharp increase of the key gasses stated above indicates potential problem within the transformer. The type of faults which the key gasses can produce will be further discussed in the study. Literature Review 2. 0 Dissolved Gas Analysis Power Transformers are filled with oil which acts as a dielectric medium and also as a heat transfer agent besides being an insulator to the transformer. The insulated oil is made up of saturated hydrocarbons.

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These molecules are connected together to form a chain liked manner by carbon and hydrogen. [1] Table 1: Chemical structure of insulating oil and fault gases During normal use, there is a slow degradation of mineral oil which produces gases that dissolve in the oil, but when there is a electrical fault, the oil starts to degrade and temperature rises. Different patterns of gases are generated due to different intensities of energy dissipated according to the type of faults. This happens because of the broken chain of the chemical structure of the insulating oil.

Therefore, the broken chain will form its own chemical structure which is known as hydrocarbon gases or also known as fault gases. It can be divided into 3 categories which is Thermal heating, Corona and Arching, The most severe intensity of energy dissipation occurs with arching, followed by thermal heating and the least severe is Corona. Figure 1 illustrates the process of breaking chain within the insulating oil chemical structure of the fault arcing, thermal heating, and corona. Figure 1: Breaking chain process of fault arcing, corona, thermal heating and pyrolysis of cellulose

Gases which are produced by the degradation of oil because of the increase of temperature may be caused by several factors: [2] * severe overloading * lighting * switching transients * mechanical flaws * chemical decomposition of oil or insulation * overheated areas of the windings * bad connections which have a high contact resistance The type of gases present in an oil sample makes it possible to find the type of fault that occurs in the transformer. This is done by evaluating the concentration of gases present in the oil during maintenance.

The type of fault and its characteristics are as below [3]: * Arcing Arcing is the most severe of all fault processes. Large amount of hydrogen and acetylene are produced, with minor quantities of methane and ethylene. Arcing occurs in high current and high temperature conditions. Carbon dioxide and carbon monoxide may also be formed if the fault involved cellulose. In some instances, the oil may become carbonized. * Thermal heating Decomposition products include ethylene and methane, together with smaller quantities of hydrogen and ethane.

Traces of acetylene may be formed if the fault is severe or involves electrical contacts. * Corona Corona is a low-energy electrical fault. Low-energy electrical discharges produce hydrogen and methane, with small quantities of ethane and ethylene. Comparable amounts of carbon monoxide and dioxide may result from discharge in cellulose. 2. 1 How DGA Works DGA method includes sampling of oil inside the transformer at different locations. Chromatographic analysis will be done on the oil sample to find the concentration of dissolved gas.

The gases are then separated, identified and quantitatively determined such that the DGA method can then be applied in order to obtain reliable diagnosis [6]. The extracted gases meant for analysis purpose are Hydrogen (H2), Methane (CH4), Ethane (CH6), Ethylene (C2H4), Acetylene (C2H2), Carbon Monoxide (CO), Carbon Dioxide (CO2), Nitrogen (N2) and Oxygen (O2). These fault gases can be classified into 3 groups which are shown in Table 2. Group| Hydrocarbons & Hydrogen| Carbon Oxides| Non-fault gases| Gases| CH4,H2,CH6, C2H4,C2H2| CO, CO2| N2, O2| Table 2 :Fault Gases Group

Depending on the concentration of the dissolved gases, condition of the transformer can be evaluated. This is achievable because each type of fault burns the oil in a different way where it generates different type of gases. Therefore, it is easy to examine the fault base on the gas released and its concentration level. Table 3 : Relation between Fault type and Fault gases 2. 2 DGA Diagnostic Methods Insulating oil breakdowns to small quantity of gases due to over electrical or thermal stress. Thus, the composition of these gases plays a role in determining type of fault.

Through DGA diagnostic methods, it is possible to find faults as discussed earlier. There are many methods in DGA and 5 methods will be studied in this literature review part. 2. 2. 1 Rogers Ratio Method The Roger’s method utilizes four gases ratios: CH4/H2, C2H6/CH4, C2H4/C2H6 and C2H2/C2H6. Diagnosis if faults are accomplished via a simple coding scheme based on ranges of the ratio as shown in tables below [4]. Table 4: Gas Ratio Codes [4] Table 5: Roger’s Ratio Code [4] The combination of the coding gives 12 different types of transformer faults. The type of faults based on the code is shown in table 6 below: [4]

Table 6 : Classification based on Roger’s Ratio Codes 2. 2. 2 IEC Ratio Method This method originated from the Roger’s Ratio method, except that the ratio C2H6 /CH4 was dropped since it only indicated a limited temperature range of decomposition [3]. Here, the remaining three gas ratios have different ranges of code as compared to the Roger’s ratio method and they are shown in table 7. The faults are divided into nine different types as listed in table 8. [4] Table 7: IEC Ratio Codes [4] Table 8: Classification based on IEC Ratio Codes 2. 2. 3 Doenenbury Ratio Method

This method utilizes the gas concentration from ratio of CH4/H2, C2H2/CH4, C2H4/C2H6 and C2H2/ C2H4. The value of the gases at first must exceed the concentration L1 to as certain whether there is really a problem with the unit and then whether there is sufficient generation of each gas for the ratio analysis to be applicable [5]. Table 9 shows the key gases and their concentration L1 [5], and table 10 shows fault type of specific ratios. Table 9: Concentration of L1 for Doernenburg Ratio Table 10: Fault diagnosis for Doernenburg Ratio Method 2. 2. 4 Duval Triangle Method M.

Duval developed this method in the 1960s. To determine whether a problem exists at least one of the hydrocarbon gases or hydrogen must be at L1 level or above and the gas generation rate is at least at G2. [6] The L1 level and the gas generation rate for this method are shown in table 11. Table 11: L1 limits and gas generation rate for Duval Triangle Methode Once a problem has been determined to exist, to obtain diagnosis, calculate the total accumulated amount of the three Duval Triangle gases (CH4, C2H2, C2H4) and divide each gas by the total to find the percentage of each gas of the total.

Plot the percentages of the total on the triangle (Figure2) to arrive at the diagnosis [6] Figure 2: Duval Triangle Transformer Fault Diagnosis 2. 2. 5 Key Gas Method Figure 3 : Key Gases Diagnosis The principle of the Key Gas method is based on the quantity of fault gases released from the insulating oil when a fault occurs which in turn increase the temperature in the power transformer. The presence of the fault gases depends on the temperature or energy that will break the link or relation of the insulating oil chemical structure.

This method uses the individual gas rather than the calculation of gas ratios for detecting fault. The significant and proportion of the gases are called “key gases”. Figure 3 indicate these “key gases” and relative proportions for the four general fault types [5]. 3. 0 Scheduled Work Task| Start Date| Duration (days)| Remarks| Progress| Project Title Selection| 28. 05. 2012| 12| Proposed own project title and submitted it on 4th June 2012| Completed| Research for Project Proposal| 08. 06. 2012| 10| Journals and articles were browsed through in IEEE, Science Direct, Scopus| Completed| Project Proposal| 14. 6. 2012| 3| Project Proposal was done based on the journals and articles found. | Completed | Research for Literature Review| 19. 06. 2012| unknown| Journals and articles were searched for the literature review| Ongoing| Progress Report 1| 01. 07. 2012| 15| Each progress towards the completion of Final Year Project 1| Completed| Research / Oral Presentation Preparation| 17. 07. 2012| 24| Complete the literature review and getting prepared for the oral presentation while doing research for the project| Incomplete| Oral Presentation| 10. 08. 2012 / 29. 08. 012| -| Presentation of all the findings and research and logbook to be submitted| Incomplete| Progress Report 2| 10. 08. 2012| 3| Each progress towards the completion of Final Year Project 1| Incomplete| 4. 0 Conclusion In the end of this study, I’ll be able to determine the pros and cons of all the different types of DGA diagnostics methods and be able to determine transformer faults out of the diagnostic methods which are very essential to prevent transformer damage. Suggestions and recommendations will be given to further improve the efficiency of those available diagnostic methods . 0 Reference 1. Church, J. O. , Haupert, T. J. and Jakob, Fredi (1987). “Analyze Incipient Faults with Dissolved-gas Nomograph. ” Elecrical World. Oct. Pgs. 40-44. 2. DiGiorgio, Joseph B. (1997). “Dissolved Gas Analysis of Mineral Oil Insulating Fluids. ” California: Northern Technology & Testing 3. Domun, M. K. (1996). “Condition Monitoring of Power Transformers by Oil Analysis Techniques. ” Proc. of the 11th Conference on Electric Power Supply Industry (CEPSI). Kuala Lumpur, Malaysia 4. Siva Sarma, D. V. S. S. and G. N. S.

Kalyani, ANN Approach for Condition Monitoring of Power Transformers using DGA. 2004 IEEE Region 10 Conference, TENCON 2004. , 2004. C: p. 444-447. 5. C57. 104. 1991, I. , IEEE Guide for Interpretation of Gases Generated in Oil-Immersed Transformer, I. The Institute of Electrical and Electronic Engineers, Editor. 1992, The Institute of Electrical and Electronic Engineers, Inc p. 27 6. FIST3-31, Facilities Instructions, Standards and Techniques Volume 3-31 Transformer Diagnostics. 2003, Bureu of Reclamation Hydroelectric Research and Technical Services Group Denver. p. 5-13.

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