INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.4 NO.2 ISSN 2165-8277 (Print) ISSN 2165-8285 (Online) http://www.researchpub.org/journal/jac/jac.html APRIL 2015 Artificial Neural Networks for Power Transformers Fault Diagnosis Based on IEC Code Using Dissolved Gas Analysis Sherif S. M. Ghoneim1, 2 and Ibrahim B. Taha1, 3 The most five criteria that are commonly used for dissolved gas analysis are the International Electrotechnical Commission standard (IEC) Code, the Central Electric Generating Board (CEGB) Code based on Rogers four ratios, Rogers’ method, Dornenburg method and Duval triangle according to the Institute of Electrical and Electronics Engineers standard (IEEE-C57) [3]. The above criteria do not involve any mathematical formulation and their interpretations are based on heuristic methods that may vary based on experience of the analyst, results in unreliable analysis [4]. To overcome the drawbacks come from these criteria, various computational models using Artificial Intelligence (AI) have been used to analysis the incipient fault in power transformer. Application of AI in transformer incipient fault diagnosis requires real DGA data. During the period of 1987-2012, there were over 400 research published on IEEE (26 EPSs, 72 ANNs, 58 FL and ANN-FL, 20 ANN-EPS; 248 DGA and related ones) [5]. Several AI methods have been developed for more accurate diagnosis. These methods are mostly suitable for transformers with a single fault or a dominant fault. These AI methods are: Artificial Neural Network (ANN) [6,7], Fuzzy Logic [8, 9], Neuro–Fuzzy [10, 11], Genetic [12, 13], Hidden Markov Model (HMM) [14], Support Vector Machine (SVM) [15, 16], and Graphical Techniques [17, 18]. They were developed as a novel technique to interpret the faults in power transformers. In this paper, back propagation ANN model is constructed based on DGA of the IEC Standard rules method. A comparison between the results of the ANN and that obtained from the literatures is presented. The results refer to the reliability of the proposed ANN model as a diagnostic tool for incipient power transformer fault. Abstract—Transformer is the main important equipment in electrical power system. Early stage detection of the transformer faults has great economic significance because it considered expensive equipment and it helps to maintain the continuous operation of the electrical power system. Transformer oil is used for two main purposes, one for insulating liquid and the other for cooling. Some physicalchemical tests are carried out to determine the physical and chemical properties of the oil. Dissolved Gas Analysis (DGA) is now considered a common practice method for detection of the transformer incipient fault. This paper focuses on the employment of the Artificial Neural Network techniques (ANN) to diagnose dissolved gas in transformers, in order to determine the fault causes based on the IEC standard method. The ANN on IEC Code results meets the similar results of the other techniques that use to diagnose the transformer fault. Therefore, this method is very reliable to use as a diagnostic tool for transformer fault detection. Keywords—Transformer faults, Dissolved gas analysis, Neural Networks. I. INTRODUCTION Power transformer is considered as one of the most vital, important and expensive components in electric power systems. Any fault in power transformer may result in power outages and black-outs of the electrical power system. Therefore, the early detection of the power transformer incipient faults lead to an improvement in power system reliability and operation. Moreover, the replacement of a power transformer is very costly and time consuming; hence it is very important to diagnose incipient faults as soon as possible to prevent an increase of the transformer faults Dissolved Gas Analysis (DGA) in the transformer oil is a wide spread method that is used to identify the incipient faults in oil-filled power transformers. There are different stresses affect on the insulating transformer oil, which are electrical and thermal stresses due to arcing, corona discharges, sparking, or overheating fault. As a result of these stresses, insulating materials may be damaged and several gases are released. The main dissolved gases in the transformer oil are: hydrogen (H2), methane (CH4), ethane (C2H6), ethylene (C2H4), acetylene (C2H2), carbon monoxide (CO) and carbon dioxide (CO2). The detection methods based on dissolved gas analysis are used to diagnose the incipient fault in power transformer before deteriorating to a severe state [1-2]. II. DISSOLVED GAS ANALYSIS (DGA): IEC STANDARD CODE The IEC three-ratio method is widely used as a guideline and a standard in diagnosis stage as it is being one of the effective and convenient guidelines and available standards [4]. Table 1 shows the relations between the three-ratios and the method codes while Table 2 tabulates the IEC standard fault types in power transformer. It consists of three key-gas ratios corresponding to the suggested fault diagnosis. 1 College of Engineering Taif University, Saudi Arabia Kingdom Faculty of Industrial Education, Suez University, Suez, Egypt, ghoneim_sherif2003@yahoo.com, 3Faculty of Engineering, Tanta University, Tanta, Egypt. ibm_taha_2013@yahoo.com 2 18 INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.4 NO.2 ISSN 2165-8277 (Print) ISSN 2165-8285 (Online) http://www.researchpub.org/journal/jac/jac.html working with the back-propagation learning algorithm [21, 22]. Table 1 IEC Code [1] Gas Ratio R1=C2H2/C2H4 R2=CH4/H2 R3=C2H4/C2H6 Value Code R1<0.1 0 0.1≤R1≤3 1 R1>3 2 R2<0.1 1 0.1≤R2≤1 0 R2>1 2 R3<1 0 1≤R3≤3 1 x1 y1 b1 x2 y2 b2 Inputs Outputs xn yn bn R3>3 2 Table 2 Fault diagnosis using IEC Code Input Layer Hidden Layers Output Layer Fig. 1: MLP neural network training The output from the sigmoid function lies between 0 and 1. The mean square error is proposed to a level of 0.0001, where a satisfactory agreement is found between the training set results and the network result. In this study 74 samples of DGA were provided by the electrical utility and 125 samples were taken from DGA results published in the literatures [23, 30]. All 199 samples are used for validating the neural network model. Code No. APRIL 2015 Fault Type R1 R2 R3 1 No fault 0 0 0 3 Partial discharge with low energy density 0 1 0 4 Partial discharge with high energy density 1 1 0 5 Arcing discharge with low energy 1or 2 0 1 6 Arcing discharge with high energy 1 0 2 7 Thermal fault with temperature less than 150 oC 0 0 1 This diagnosis criterion uses basically Rogers input vector as follows: 8 Thermal fault with temperature between 150 to 300 oC 0 2 0 [πΌπππ’π‘] = [π 1 , π 2 , π 3 ]π 9 Thermal fault with temperature between 300 to 700 oC 0 2 1 The output vector is build up with ten elements according to Table 2. Ten neurons are utilized in the output layer. 10 Thermal fault with temperature greater than 700 oC 0 2 2 IV. VALIDATION OF THE PROPOSED SMART DIAGNOSTIC DECISION SYSTEM 2 Undetermined fault (fail to determine the fault type) The input and output patterns are required for Neural network validity. Input patterns are considered the dissolved gas ratios codes according to each fault state. For each input pattern, there exists an output pattern that describes the fault type. Both input and output patterns constitute ANN training set. Input and output patterns are defined as follows: (1) The validation of the proposed model is achieved by comparing its results with the results in literatures. Some samples are collected from some researches and laboratory analysis then compare them with the results in literatures. Table 3 illustrates the agreement between the ANN results and the results in literatures. It is agreement percentage between the results from ANN and that in Literatures as shown in Table 3 is more than 90%. It appears that a conflict among the results comes from the No fault identification as well as normal operation state with the thermal state in literatures. The results refer to the reliability of the proposed ANN model as a diagnostic tool for incipient fault detection. For above codes not obtained III. APPLICATION OF ARTIFICIAL NEURAL NETWORK (ANN) FOR TRANSFORMER FAULT DETECTION ANN model is constructed using MATLAB software for IEC Standard code interpretation method. Figure 1 shows the multilayer feed forward back-propagation is chosen as the network architecture because it considers the most popular ANN Architecture [19] and its ability for pattern recognition [20]. The ANN architecture model consists of four layer networks (one input layer, two hidden layer and one output layer). V. CONCLUSION An artificial neural network (ANN) model is constructed for IEC Standard code method that based on dissolved gas analysis. To test the NN model based on IEC rules, 102 samples are used. The agreement of NN model with A two layer perception has been utilized because of two reasons. These are; the highly nonlinearity between the input and due to a good performance of ANN when 19 INTERNATIONAL JOURNAL OF CONTROL, AUTOMATION AND SYSTEMS VOL.4 NO.2 ISSN 2165-8277 (Print) ISSN 2165-8285 (Online) http://www.researchpub.org/journal/jac/jac.html the literatures is more than 90% of the tested cases. The problem is experienced, the difference between the results from the proposed model and the results from literatures come from No fault and No fault identification states with the thermal fault for the literatures results. ACKNOWLEDGMENT The authors thank Prof. Dr. Ayman A. Aly for his valuable Discussion in construction ANN model. REFERENCES Table 3 Comparison between the results from ANN based on IEC Standard interpretation method and the results from literatures and lab analysis H2 CH4 C2H6 C2H4 C2H2 CO IEC state Ref Ref. state 269 1081 347 1725 25 360 HTH [23] HTH 10 10 8 1 0.01 334 NF [23] LTH 30 22 14 4.1 0.1 400 NF [24] NF 2.9 2 1.5 0.3 0.1 200 UD [24] NF 4 99 82 4.2 0.1 200 LTH [24] TH 21 34 5 47 62 390 UD [24] HAD 50 100 51 305 9 400 HTH [24] TH 120 17 32 4 23 350 UD [24] NF 980 73 58 12 0.01 243 PD [24] PD 30.8 149 47.9 146 0.1 350 HTH [24] TH 27 136 46.9 131 0.1 360 MTH [24] TH 1607 615 80 916 1294 380 HAD [24] HAD 14.7 3.7 10.5 2.7 0.2 1046 NF [25] NF 181 262 41 28 0.01 415 LTH [25] TH 173 334 172 812.5 37.7 404 HTH [25] TH 127 107 11 154 224 478 HAD [25] HAD 60 40 6.9 110 70 678 HAD [25] HAD 27 90 42 63 0.2 470 MTH [25] TH 980 73 58 12 0.01 243 PD [25] PD 86 187 136 363 0.01 26 MTH [26] HTH 10 24 372 24 0.01 343 LTH [26] MTH 30.4 117 44.2 138 0.1 380 HTH [27] TH 260 3 18 2 0.01 350 PD [28] PD 586 19 77 6 0.01 370 PD [28] PD 200 700 250 740 1 415 MTH [29] TH 33 26 6 53 0.2 678 UD 34.45 21.3 3.19 45 19.62 211 HAD 180.85 0.5 0.234 0.18 0.0001 252 PD 12 8 40 5 0.01 436 NF 16 25 19 39 0.01 383 MTH 22 40 36 6 1 422 UD 1770 3630 1070 8480 78 350 HTH 86 30 10 59.3 41 239 27.5 469 147 35 29 1014 HAD 9.9 111 70 224 HAD 5.5 25.5 85 317 LAD 12.5 265 520 211 HAD 56 5.5 92 34.5 27.5 436 PD 14 237 92 470 0.01 365 HTH 157 127 34 96 0.01 422 LTH [29] [29] [29] [29] [29] [29] [29] [29] [30] [30] [30] [30] [30] [30] APRIL 2015 [1] IEC Publication 599, “Interpretation of the analysis of gases in transformers and other oil-filled electrical equipment in service”, First Edition 1978. 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Sharma, Sushil Chauhan, and Satyabrata Saho, "Transformer Diagnostics under Gas Analysis Using Support Vector Machine", International conference on Power, Energy and Control (ICPEC), pp. 181-186, 2013. APRIL 2015 Appendix ARC: discharge arcing UD: undetermined fault or no fault identification TH: thermal fault PD: partial discharge NF: no fault (normal operation) HAD: high discharge energy arcing LAD: low discharge energy arcing HTH: high temperature thermal fault LTH: low temperature thermal fault MTH: medium temperature Author' profile: Sherif S. M. Ghoneim Received B.Sc. and M.Sc. degrees from the Faculty of Engineering at Shoubra, Zagazig University, Egypt, in 1994 and 2000, respectively. Starting from 1996 he was a teaching staff at the Faculty of Industrial Education, Suez Canal University, Egypt. Since end of 2005 to end of 2007, he is a guest researcher at the Institute of Energy Transport and Storage (ETS) of the University of DuisburgEssen-Germany. In 2008, he got Ph.D Degree in Electrical power and machines, Faculty of Engineering-Cairo University (2008). He joins now the Taif University as an assistant professor in the Electrical Engineering Department, Faculty of Engineering. His research focuses in the area of Grounding systems, Dissolved gases analysis, Breakdown in SF6 gas and artificial intelligent technique applications. Ibrahim B. Taha Received B.Sc. degree from the Faculty of Engineering at Tanta, Tanta University, Egypt, in 1995. He received M.Sc. degree from the Faculty of Engineering at Mansoura, Mansoura University, Egypt, in 1999. Starting from 1996 he was a teaching staff at the Faculty of Engineering, Tanta University, Egypt. In 2007, he got Ph.D Degree in Electrical power and machines, Faculty of Engineering-Tanta University (2007). He joins now the Taif University as an assistant professor in the Electrical Engineering Department, Faculty of Engineering. His research focuses in the area of steady state and transient stability of HVDC systems, FACTS, Multi Level Inverters, Dissolved gases analysis, and artificial intelligent technique applications. 21