Finite element analysis of power transformer

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Failure in power transformer can be catastrophic to electric systems, since transformers play a vital role in the power sector. Metallic particles in transformer oil lead to Partial discharge which can result in serious conditions.

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 03, March 2019, pp. 1384–1391, Article ID: IJMET_10_03_139 Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed FINITE ELEMENT ANALYSIS OF POWER TRANSFORMER Dr. N. Vasantha Gowri and Zainab Akthar Chaitanya Bharathi Institute of Technology, Hyderabad, India ABSTRACT Failure in power transformer can be catastrophic to electric systems, since transformers play a vital role in the power sector. Metallic particles in transformer oil lead to Partial discharge which can result in serious conditions. The existence of conducting particle in the winding of a transformer accumulates electrical stress. Simulations are carried out for the electrical analysis of power transformer. The impact of this electrical stress on particle at different position has been analyzed in this paper. Key words: Partial Discharge, Power Transformer, finite element method. Cite this Article: Dr. N. Vasantha Gowri and Zainab Akthar, Finite Element Analysis of Power Transformer, International Journal of Mechanical Engineering and Technology 10(3), 2019, pp. 1384–1391. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3 1. INTRODUCTION Power Transformer being a vital element in the electrical network, is anatomized such as to protect it from any catastrophic failure. The transformer collapse can be perilous. To avoid transformer from being damaged, its testing and analysis is necessity. Studies divulge that over 85% of failure in HV equipment is due to Partial Discharge (PD).The integrity of insulation HV equipment is needed to be confirmed with PD analysis in each stage of manufacturing, commissioning for the reliability of HV winding of transformer. Analysis of PD is performed for quality assessment of the insulation. The PD analysis detects the incapacitated points in the insulation. As a part of investigation on PD, analysis of PD due to particle movement is transformer is studied using CFD [1]. Fluid flow was carried out to find the setting point of different particles. Mar Lar Myint [2] analyses the transformer through FEA for determining the electric stress. The current density for low and high voltage winding is chosen and verified through finite element indicating low voltage winding has higher current density than high voltage winding. DU Zhi-ye [3] presents the method of calculating parameter required for propagation characteristic of PD pulses in electric equipment. 2D FEM model is structured using ANSYS considering winding and transformer core made of iron. The simulation shows that maximum voltage winding decreases along the winding. Carlos M. FONTE [4] uses CFD analysis to analyse the flow distribution and heat removal in the core of a power transformer. Monte-Carlo simulation [5] is used for determining the random movement of metallic particle in HV transformer. Here, strike of particle is observed conveying that in forced oil cooled transformer indicating whether particle is touching winding which is determined by velocity of http://www.iaeme.com/IJMET/index.asp 1384 editor@iaeme.com
Dr. N. Vasantha Gowri and Zainab Akthar oil and random solid angle at any instant of time. Linsou Zeng [6] analyses the maximum electric field intensity and distribution of electric field at HV lead of SFP-400000/500 transformer. The result obtained from it is a reference value to insulation design of ultrahigh power transformer. This paper represents a conceptual modelling of conducting metallic copper particle of different size and position present on the HV winding in power transformer is implemented through Electric module in ANSYS. 2. SIMULATION The Power Transformer considered for analysis is 100MVA, 220KV with interleaved disc winding. The turns in a disc winding are wounded radially outward with winding moving from one disc to another, connecting at their ends to form a complete winding. Figure 1 shows the configuration of interleaved configuration of transformer, which is used in transformer for ensure the robust construction and greater mechanical strength. Discs are distanced from one another with vertical strips attached with the pressboard. Figure 1. Interleaved disc winding of transformer IEC 60270 defines Partial Discharge as localized dielectric discharges in a partial area of a solid or liquid electrical dielectric insulation system under high-voltage stress. PD activity is influenced by the availability of conducting particle in transformer. This paper deals with electrical analysis of transformer winding with the availability of particle at low, medium and highest voltage disc. Electrical stress on the particle is measured by using finite element method (FEM) and presented in this paper. HV winding of this transformer comprises of two parts with one part containing 58 discs which is identical with the other. As only high voltage side of the transformer is prone to PD, analysis is done for the HV side only. The height of 58 discs is 975.3mm. The gap between cylinder and disc is 8mm. The width of a given transformer is 61mm and height of each disc is 12.85 mm respectively. The outer and inner diameter of coil is 1408mm and 1286mm respectively. The spacing between discs is 4mm.The geometrical designing is done in Computer Aided Three-dimensional Interactive Application (Catia V5 R20). Figure 2 illustrates the cross-section of HV winding of a power transformer. http://www.iaeme.com/IJMET/index.asp 1385 editor@iaeme.com
Finite Element Analysis of Power Transformer Figure 2. HV winding of a transformer Each disc of HV winding is energized with voltages. Highest voltage in this transformer is 127.12KV and the disc with least voltage is 77.09KV. Discs are numbered from top to bottom.The physical properties of solid and liquid insulation transformer material are taken into consideration for simulation. The typical values are shown in Table 1. Table 1 Material Properties S.No. Material Properties Values Density (Kg/m3) 890 Specific heat (J/kg-k) 2000 1. Oil Thermal Conductivity (W/m-k) 0.109 Viscosity (kg/m-s) 0.02403 Density 900 2. Paper Specific heat 1500 Thermal Conductivity 0.5 Density 1066 3. Pressboard Specific heat 1260 Thermal Conductivity 0.151 A spherical particle of copper material is made available near the highest, low and medium voltage disc. For the simulation, following discs with voltages are considered for the electrical impact. High voltage at Disc 1: 127.12 KV Medium voltage at Disc 52: 82.34 KV Low voltage at Disc 58: 77.09 KV 3. RESULT Electrical analysis helps in peruse about electrical voltage, current, electrical field intensity and current density of a model.The particle is made available at the places as discussed above. It also includes analysis by altering the size of metallic particle by changing the diameter. Three points of impacts are considered in this investigation at one of the higher, medium and lower voltage discs. Points of impacts are derived from REF [1]. 3.1. Electrical analysis of at disc no. 52 The copper spherical particle of diameter 1mm is considered to be present on the disc 52 with medium voltage of 82.34 kV. Cross-section of energized HV winding is shown in figure 3. http://www.iaeme.com/IJMET/index.asp 1386 editor@iaeme.com
Dr. N. Vasantha Gowri and Zainab Akthar Figure 3 Cross section of energized HV winding Electric field intensity on the particle when particle strikes on disc 52 is given in Figure 4. The Electric field intensity elucidates the strength of electric field at a point, due to the presence of electric voltage. On particle, it is 1.2986e-9 KV/cm. Figure 4. Electric Field Intensity on the particle Figure 5 represents Directional current density which allows viewing individual vector component as contours. Its value is 2.2695e-006 mA/µm2 in x-direction. Figure 5 Directional Current Density http://www.iaeme.com/IJMET/index.asp 1387 editor@iaeme.com
Finite Element Analysis of Power Transformer Figure 6 shows the simulation result for total current density due to the presence of electric voltage, the amount of current flowing through per unit area which is 8.6061 mA/µm2. Figure 6. Total Current Density 3.2. Electric analysis of dia. 2mm on disc 52 Here, analysis result is observed with increased diameter. Figure 7 shows the conducting particle of diameter 2mm is present on disc no. 52.The electric field intensity is analysed. Figure 7 Electric Field Intensity Figure 8 shows the EFI due to the presence of electric voltage with increased diameter of size 2mm is 5.9762e-7KV/cm on the particle. Figure 8 Electric Field Intensity on conducting particle Figure 9 shows the directional field at the palce of particle and measured as 3.5999e-003 mA/ µm2. It gives electric field intensity on the particle in x-direction. http://www.iaeme.com/IJMET/index.asp 1388 editor@iaeme.com
Dr. N. Vasantha Gowri and Zainab Akthar Figure 9 DFI on particle Figure 10 shows the Current density on the particle which is measured by tool as 1.11e-3 mA/ µm2. Figure 10 Current density on 2 mm sphericle particle Similar analysis was considered by changing the size of particle of diameter 1mm, 2mm, 4mm and placing it in different positions with disc no. 52, 58 and 1. The analysis of the above discussed is presented in Table 2. Table 2 Electrical Result Electric Field Current Density Size of particle Intensity(KV/cm) (mA/ µm2) Position of (on disc) particle With Without With Without particle particle particle particle 1mm 52 1.2986e-6 8.6061e-6 1.0913e-10 6.0849e-8 2mm 52 5.9762e-7 1.11e-3 1mm 58 1.2227e-6 2.3104e-3 1.1017e-10 5.9764e-8 2mm 58 4.4862e -7 3.8785e -3 1mm 1 1.204e-9 1.7795e-10 8.2302e-6 9.7287e-8 http://www.iaeme.com/IJMET/index.asp 1389 editor@iaeme.com
Finite Element Analysis of Power Transformer 2mm 1 9.9398e-10 5.2903e-6 4mm 1 2.9837e-10 1.8763e-6 4. CONCLUSIONS Relative study of PD analysis is done on the disc without and with the presence of conducting copper particle in different positions. The analysis is performed for the electrical stress on the particle due to voltage of the disc of the HV winding of transformer. From the above analysis it can be concluded that the electric field intensity and current density is comparatively negligible with the absence of particle. When the conducting metallic particle is present, electric field intensity is found to be increased. The stress on the smaller particle is found slightly higher than that on bigger size due to the fact that the stress will be more on sharp corners and edges. Current Density on the particle is increasing with the increase in diameter. REFERENCES [1] N. Vasantha Gowri, M. Ramalinga Raju, B.P.Singh, “Analysis of Partial Discharge due to Movement of Spherical Particle in Power Transformer Using Computational Fluid Dynamics” International Journal of Engineering & Technology. [2] Mar Lar Myint, Yan Aung Oo, “Analysis of Distribution Transformer Design Using FEA”International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882, Volume 3, Issue 4, July 2014 [3] DU Zhi-ye, ZHAO Chun,RUAN Jiang-Jun,YU Shi-Feng YUN Wen-Bing, “Calculation Of Distribution Parameters For Researchon Propagation Characteristic Of Pdin Transformer Winding”. [4] Carlos M. Fonte Jose Carlos B. Lopes Madalena M. Diasrenato G. Sousa Hugo M. Campelo R. Castro Lopes, “CFD Analysis Of Core Type Power Transformers” 21st International Conference On Electricity Distribution Frankfurt, 6-9 June 2011Paper 0361Paper No 0361 [5] N. Vasantha Gowri, M Ramlinga Raju, B. P Singh, “Monte - Carlo Simulation of Particle Movementin an Un-Energized Transformer” 2014 Annual Report Conference on Electrical Insulation and Dielectric Phenomena. [6] Linsuo Zeng, Peng Xiao, Shan Bai, Yan Wu, and Yuanhai Xia, “Analysis of Electric Field of HV Lead inUltrahigh Voltage Power Transformer”. [7] Shi Chen and Tadeusz Czaszejko, “Partial discharge test circuit as a spark gaptransmitter”IEEE Electrical Insulation Magazine May/June 2011- Vol. 27, No. 3pp.36- 44. [8] Yuan Li, Qiaogen Zhang, Yi Zhao, Tonglei Wang, Guangqi Liu, Ke Wang, “The Influence of Temperature on Partial Discharges and Wormhole Effect of Oil-paper Insulation under DC Voltage” 2017 Electrical Insulation Conference (EIC), Baltimore, MD, USA, 11 - 14 June 2017. [9] Kamran DAWOOD, Bora ALBOYACI, Mehmet Aytac CINAR, Olus SONMEZ, “Modelling and Analysis of Transformer using Numerical and Analytical Methods”. [10] Preethy V. Warrier, Preetha P.K., “Electromagnetic Analysis of Transformer Using Solidworks” 2015 IEEE International Conference on Technological Advancements in Power & Energy. [11] N. A. M. Amin, M. T. Ishak, M.H.A. Hamid, M. S. Abd Rahman, “Partial Discharge Investigation on Palm Oil Using Needle-Plane Electrode Configuration and Electric Field http://www.iaeme.com/IJMET/index.asp 1390 editor@iaeme.com
Dr. N. Vasantha Gowri and Zainab Akthar Distribution Using ANSYS Maxwell” 2017 International Conference on High Voltage Engineering and Power System, October 2-5, 2017, Bali, Indonesia. [12] Chao Tang, Song Zhang, Qian Wang and Jian Hao, “Thermal Stability of Modified Insulation Paper Cellulose Based on Molecular Dynamics Simulation”. [13] C. Thirumurugan, G.B. Kumbhar, “Effect of Electrode Configurations and Gap Spacings on Partial Discharge Characteristics of Oil-Pressboard Insulation System” 2015 IEEE 11th International Conference on the Properties and Applications of Dielectric Materials(ICPADM). [14] Sandeep Patel, “Mathematical Modelling of Disc Type Winding Of Transformer” International Journal of Engineering Research & Technology(IJERT) ISSN: 2278-0181 Vol.2 Issue 9, September – 2013. [15] Nor Azizah Mohd Yusoff, Kasrul Abdul Karim, Sharin Ab Ghani, Tole Sutikno, Auzani Jidin, “Multiphase Transformer Modelling using Finite Element Method” International Journal of Power Electronics and Drive System(IJPEDS) Vol. 6, No. 1, March 2015, pp. 56-64 ISSN: 2088-8694. http://www.iaeme.com/IJMET/index.asp 1391 editor@iaeme.com