BP 145 RP, Biskra, Algeria

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1 International Symposium on Computational and Experimental Investigations on Fluid and Structure Dynamics CEFSD 2015, March 16-18, 2015, Hammamet, TUNISIA Experimental Study of the various pollution and simulation of potential and electric field distribution using FEMM at a high voltage insulator under alternative current Hani Benguesmia 1,2, Nassima M ziou 1, Abdelmadjid Chouchou 2, Leboukh Rachdi 2 1 L I3CUB University of Biskra, Algeria, BP 145 RP, Biskra, Algeria 2 Department of Electrical Engineering, Faculty of Technology, Mohamed Boudiaf University, M sila, Algeria, Abstract: This paper presents a work devoted to the impact study of the pollution severity on the energy level dissipated on high voltage insulator. Pollution of high voltage insulators is a factor of prime importance in the quality and reliability of power transmission. It causes the circumvention of high voltage insulators. However, when it is wet, it causes the dissolution of salts and the formation of an electrolyte layer on the surface of insulators, thus reducing dielectric strength. Pollution generally poses few problems. However, when it is humid, it causes the dissolution of salts and the formation of an electrolytic layer on the insulator surfaces; as a result, it reduces their dielectric rigidity. The aim of this paper is the experimental study of the flashover process and the distributions of the potential and the electric field carried out under 50 Hz applied voltage on a real model simulating the 175CTV outdoor insulator largely used by the Algerian company of electricity and gas (SONELGAZ). This real model is under different surface conductivity and different level of uniform discontinues pollution. The computer simulations are carried out by using the FEMM(Finite Element Magnetism Method) 4.2 software. This program uses the finite element method to solve the partial differential equations that describe the field. Original experimental results made in the laboratory are presented and compared with a real insulator, and simulations presented in this paper are originals. Key words: insulator, flashover, superficial conductivity, high voltage, electric potential, electric field. * Corresponding author: Hani Benguesmia hanibenguesmia@yahoo.fr 1

Introduction In power system, line insulators often work outdoors, which are affected by adverse environmental and atmospheric factors, such as dust, fog, dew, rain, snow and other industrial

2 Hani et al. / CEFSD 2015, March 16-18, 2015 Use: isolation of lines 20 and 30 kv. Assembly: by accommodation (housing) of kneecap and kneecap. Materials: Dielectric: wrong glass Cap: metal alloy Pin: galvanized steel Graphical abstract 1. Introduction In power system, line insulators often work outdoors, which are affected by adverse environmental and atmospheric factors, such as dust, fog, dew, rain, snow and other industrial pollution. When the air humidity is lower, the existence of these contaminations will not affect the normal work of the insulator. But when the air humidity is higher, the contamination layers on the surface of the insulators will be wet, and the soluble salt of the contaminations will be dissolved in water. The conductive water film is formed which leads to the higher conductance of the insulator surface. And then the leakage current increases sharply, and the flashover voltage of the insulators reduces greatly. Because of this, the flashover can occur in the operating voltage. The security and stability of power system are affected. [1 4] The flashover voltage mechanism was investigated by many researchers.[5-9] In particular, the final stages of the complex mechanism [10 12] that occur when an intermediate pollution band forms on the insulating surface. The non-homogeneity is due to the presence of different polluting agents in the same region, and the non-uniformity of the distribution on the insulator surfaces is because of the insulator profile, wind direction, and the position of the insulator chains in relation to the ground (vertical, horizontal, inclined). The insulator position in the chain, the degree of the site s pollution where the upper or lower 2

3 Research on An International Marketing Strategy for Japanese Rice 3 insulator surface is found and the unknown effect of humidity on the pollution. [3,13-14] The electric field distribution on the surface and within insulators string is a function of numerous parameters including applied voltage, insulator design, tower configuration, corona ring, hardware design, phase spacing. To approach the ideal conditions obtained for a linear potential distribution along an insulators string, corona rings are required. Unfortunately, there exist no specific standards for the design and placement of corona rings. Each manufacturer makes independent recommendations for the use of their corona rings. [15] In the present work, experimental results, electric field and potential distribution under normal operating conditions are simulated by a two dimensional finite element model using the FEMM 4.2 software. P N D Fig.1 Real model of the insulator CTV 175 The tension of test is measured using a capacitive tension divider C m connected to the secondary of a transformer of test 140kV (fig. 2). 2. Experimental techniques The real insulator CTV175 consists of an insulating block carrying to its upper part a cap sealed out of malleable pig iron and inside a steel stem, with grooves and whose conical head is also sealed in glass. The lower end of this stem is round and has dimensions wanted to penetrate in the cap of the following element and to be maintained by a pin there. The assembly consists in carrying out a sealing of the cap and the dielectric one by cement, then that of the stem and the dielectric one fig. 1. Dimensions concerning the insulator CTV175 are mentioned in Table I. I.T : Isolating transformer R.T : Regulating transformer H.T: High voltage transformer T.O: Test object (insulator 175CTV) V.C: Video, Camera Fig.2 Schematic diagram of the experimental setup Designation D (mm) P(mm) N(mm) Length of leakage distance (mm) The tests carried out for an element of an insulator, we measured the three tensions which represent the stages of skirting and to see the influence of pollution on the behavior of insulator CTV175, for the following cases: breaking load Weight (kg) CTV CTV Dryness: at the clean state of the insulator.

4 Research on An International Marketing Strategy for Japanese Rice Polluted insulator: for the two so wet cases used the water distilled only and polluted

to simplify the calculation of the electric field which satisfies these conditions, FEMM uses the derivative of the potential (V) which is defined by the relation

case the insulator was carried out. A digital video setup was used to monitor the glass surface discharge activity.

4 Fig.3 Real insulator in the laboratory; (a)clean insulator, (b)wet (distilled water), (c)polluted (distilled water and sand). The software (FEMM 4.

Gauss, which indicates that the total flow of the outgoing electric field of a closed surface is equal to the sum of the interior loads: = (1) ρ: the density of

4 4 Research on An International Marketing Strategy for Japanese Rice Polluted insulator: for the two so wet cases used the water distilled only and polluted (distilled water sand) on the surface of the insulator and inside the insulator.fig.3. to simplify the calculation of the electric field which satisfies these conditions, FEMM uses the derivative of the potential (V) which is defined by the relation field-potential: = (4) (a) (c) (b) It is the equation which FEMM solves for the potential V on a field programmed by the user and one defines also the source and the boundary conditions. 2.1 Flashover development process In this section, the flashover development process under 50 Hz alternative current voltage was examined with non-uniform pollution distribution. The influence of the pollution on the surface of insulation on the electric discharges behavior were investigated, thus simulation by using the FEMM for the clean case the insulator was carried out. A digital video setup was used to monitor the glass surface discharge activity. Careful analysis of these video recordings has allowed visual examination of the electric discharge development with increasing the applied voltage magnitude. Fig.4 Fig.3 Real insulator in the laboratory; (a)clean insulator, (b)wet (distilled water), (c)polluted (distilled water and sand). The software (FEMM 4.2) determines the potential by solving the electrostatic equation in addition to the conduction equation: The first relation is the application of the theorem of Gauss, which indicates that the total flow of the outgoing electric field of a closed surface is equal to the sum of the interior loads: = (1) ρ: the density of load equalizes 0 in our case. The second is the application of the theorem of Ampere: =0 (2) The density of the electric flux and the intensity of the electric field are also bound by the following relation: D =εe (3) ε: the electric permittivity; (a) (b) (c) Fig.4 The process of flashover, (a) Initiation of arcs; (b) Evolution of arcs, (c) Flashover total For all the states of the real insulator clean, wet and polluted, the activity of discharge follows same three stages. In the case polluted and wet the insulator becomes less rigid, and with the concentration of pollution I push give the observations following:

Research on An International Marketing Strategy for Japanese Rice 5 Appearance of a large number of partial arcs which are characterized by a low intensity.

Weak discharges located at the ground electrode side were also seen and these are thought to be due to the high field (high tension applied) at the interface between the electrode and the glass

5 Research on An International Marketing Strategy for Japanese Rice 5 Appearance of a large number of partial arcs which are characterized by a low intensity. It was also noted that the discharges disappear and reappear quickly along the clean strip in a continuous way. fig.4(a). - Intensifications and increase of the number of arcs through the clean strip. Weak discharges located at the ground electrode side were also seen and these are thought to be due to the high field (high tension applied) at the interface between the electrode and the glass surface. fig.4(b). - Following the increase in the tension applied, shortly after the connection, the final jump will begin, and an electric partial arc is formed between the two electrodes. (Total flashover). fig.4(c). 3. Experimental and simulation results In this part we present the three tensions which thus represent the stages of flashover, and the simulation using the FEMM of real insulator CTV Influence of the pollution The objective of this test is to determine the tension of skirting of insulator CTV175 of severity of pollution, (clean (dry), wet and polluted), to carry out this objective we must applied a tension and to make with measurement augment until obtaining it from a flashover of the insulator. With the first place we must determine the tension of flashover in a clean state (dry) and for the continuation introduce pollution. During the experiment we mentioned the evolution of the tension of skirting as follows: -Appearance of the effect crowns in the surroundings of 4-17 kv. For the three clean cases (dry), wet and polluted. - Appearance of the electric arcs which represents the second stages of flashover, then the stages finale if the total flashover of the insulator. fig.5. We notice that the tension of flashover decreases in an almost linear way according to severity of pollution. Then we can say the equivalent impedance of the insulator decreased and the insulator becomes more conducting. fig.5. Sparks voltage (kv) Flashover voltage (kv) Arcs voltage (kv) 3: Polluted (water distilled+sand), 2: Wet (water distilled), 1: Dryness. 3.1 Simulation of the real model We calculated the electric field and the electric potential; we used the software FEMM. This last is a continuation of the programs making it possible to give the distribution of the electric field in two dimensions. For that, we introduced, in this software, our model with all its specifications (forms and nature of the electrodes and the various mediums, tension applied, boundary conditions, ). The configuration of our model gives a relatively difficult representation for that uses of them the FEMM (Finite Element Magnetism Method) then one makes the call of the model, we fixed the tension applied to the electrode activates with 10kV.fig.6. Fig.5 Influence state of surface on the tension of sparks, arcs and flashover.

6 Research on An International Marketing Strategy for Japanese Rice Cap (ground electrode) Line of leakage distance Pin (high voltage electrode) Fig.8 Distribution (echograms) of the potential Fig.

The mesh density is higher in the critical regions of the insulators where higher accuracy is required. The number of meshes for insulator string is 5244 nodes. Fig.7 Fig.

2 Distribution of the potential and electric field on the real model We were interested in the determination of the distribution of the potential and the electric field on the insulators CTV175.

6 6 Research on An International Marketing Strategy for Japanese Rice Cap (ground electrode) Line of leakage distance Pin (high voltage electrode) Fig.8 Distribution (echograms) of the potential Fig.6 Presentation of the real insulator in the FEMM The profile of the insulator is introduced in the software. The mesh density is higher in the critical regions of the insulators where higher accuracy is required. The number of meshes for insulator string is 5244 nodes. Fig.7 Fig.9 Distribution of the electric field Fig.7 Discretization in finite elements and determination of mush elements of the insulator CTV Distribution of the potential and electric field on the real model We were interested in the determination of the distribution of the potential and the electric field on the insulators CTV175. The tension was maintained constant and equal to 10 kv. This allows simulating the behavior of insulators of line 30 kv. The figure8 illustrate the variation of the distribution of the potential of the insulators. The potential is very important on the level of the electrode of high voltage then decreases as one move away from the electrode credit. In a dry state, the potential takes the maximum value 10 kv on the active level of the electrode then decrease in a linear way as one move away from this

7 Research on An International Marketing Strategy for Japanese Rice 7 electrode until the attack of the electrode of mass where the potential is cancelled. In the case of the clean plate, the electric field is intense meadows of the active electrode. It decreases as one move towards the ground electrode along the leakage distance. In addition, the lines of the field are divergent (outgoing of the electrode of high voltage). It comes out from these characteristics the following remarks: fig.9 The electric field is intense at the end of the electrode of high voltage. The field will not vanish in the glass but gives a very low value. The electric field is practically null inside the two electrodes, because the two electrodes are conductive. 4. Conclusions Based on the above analysis, we have presented the results of different tests on the laboratory s model high voltage insulator, the experimental results obtained from tests performed on a real model were analyzed in order to understand then correlation between pollution severity and partial arcs activity, as well as the real one and simulation of electric field and potential distribution under normal operating conditions in 30kV AC transmission lines has been carried out using a two dimensional finite element model. According to the results: The flashover reduces with the conductivity of the polluted environment. Otherwise the insulator is more rigid when the conductivity of the surface increases as well as its width. Simulation results show that potential distribution is not linear, and electric field is not uniform along the string for the clean condition. For the dry state, the potential takes the maximum value 10 kv on the active level of the electrode then decrease in an almost linear way as one move away from this electrode until the attack of the electrode of mass where the potential is cancelled. We also saw that the potential decreases as one move away from the active electrode. The maximum value of the electric field is obtained on the level of the clean layers of lower width. Field calculations help in improving the design and identification of vulnerable areas. References [1] Guan Zhicheng, Liu Yingyan, Zhou Yuanxiang, et al. Insulator And outdoor Insulation of Power Transmission And Transformation Equipment[M]. Beijing: Tsinghua university press, [2] Liang Xidong, Chen Changyu, Zhou Yuanxiang.High Voltage Engineering[M]. Beijing: Tsinghua university press, [3] Gao Bo, Wang Qingliang, Zhou Jianbo, et al. Effect of Dry Band on Electric Field Distribution of Polluted Insulator[J]. High Voltage Engineering, 2009,35(10): [4] Huo Feng, Chen Yong, Cai Wei, et al. Surface Electrical Field Distribution Simulation and Insulation Characteristics Test of Polluted Insulators[J]. High Voltage Engineering, 2008, 34(12): [5] B.F. Hampton, Flashover mechanism of polluted insulation, Proc. IEE, Vol. 111, No. 5, pp , [6] Y. Liu, S. Gao, D. Huang, T. Yao, X. Wu, Y. Hu, and W. Cai, Icing flashover characteristics and discharge process of 500 kv AC transmission line suspension insulator strings, IEEE Trans. Dielectr. Electr. Insul., Vol. 17, No. 2, pp , [7] S. Venkataraman and R. S. Gorur, Prediction of flashover voltage of nonceramic insulators under contaminated conditions, IEEE Trans. Dielectr. Electr. Insul., Vol. 13, No. 4, pp , [8] X. Jiang, J. Yuan, Z. Zhang, J. Hu, and L. Shu, Study on pollution flashover performance of short samples of composite insulators intended for ±800 kv UHV DC, IEEE Trans. Dielectr. Electr. Insul., Vol. 14, No. 5, pp , [9] Z. Zhang, X. Jiang, Y. Chao, C. Sun and J. Hu, Influence of low atmospheric pressure on AC pollution flashover performance of various types of insulators, IEEE Trans. Dielectr. Electr. Insul., Vol. 17, No. 2, pp , 2010

8 8 Research on An International Marketing Strategy for Japanese Rice [10] C. Texier and B. Kouadri, Model of the formation of dry band on NaCl polluted insulation, IEE Proc. A, Vol. 133, No. 5, pp , [11] M.T. Gencoglu and M. Cebeci, The pollution flashover on high voltage insulators, Electr. Power Syst. Res., Vol. 78, No. 11, pp , [12] X. Jiang, J. Yuan, Z. Zhang, Q. Hu, and A. Cheng, Study on AC pollution flashover performance of composite insulators at high altitude sites of m, IEEE Trans. Dielectr. Electr. Insul., 16, No. 1, pp , [13] L.E Zaffanella, H.M Scheinder, Dunlap J.H, "Perfermances des isolateurs polluées pour lignes ccht", 1986, CIGRE, rapport [14] N. Dhahbi-Meghriche, A. Beroual, "Flashover dynamic model of polluted insulators under ac voltage", 2000 IEEE Transactions on Dielectrics and Electrical Insulation, 7(2), pp [15] B. M'hamdi,M. Teguar and A. Mekhaldi, Potential and Electric Field Distributions on HV Insulators String Used in The 400 kv Novel Transmission Line in Algeria IEEE International Conference on Solid Dielectrics, Bologna,Italy,June 30 July 4, 2013:

Modeling Electric Field and Potential Distribution of an Model of Insulator in Two Dimensions by the Finite Element Method

International Journal of Energetica (IJECA) https://www.ijeca.info ISSN: 2543-3717 Volume 3. Issue 1. 218 Page 1-5 Modeling Electric Field and Potential Distribution of an Model of Insulator in Two Dimensions