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International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 Influence of Electrostatic Effects on Conductive Objects in the Vicinity of Overhead Transmission Line Mya Thida Tun, Aung Ze Ya Abstract— To transmit electricity, overhead transmission lines are sometimes passed through near the residential zones. These transmission lines have harmful environmental effects. Therefore, the electrostatic effects of overhead transmission lines on the vicinity of conductive objects are needed to consider preventing the person from hazards. This paper presents the electrostatic effects on conductive objects. The transmission line voltage of 132 kV and 230 kV are studied for electrostatic effects on automobile, building and fence. The results are solved by the help of Matlab Program. The induced voltage and shock current on automobile, building and fence are calculated. Index Terms— electrostatic, induced voltage, shock current and conductive objects. I. INTRODUCTION A time-varying electric fields are induced in the vicinity of AC power transmission systems. Due to increase in transmitted voltages and currents, possible problems associated with electrostatic coupling between the overhead AC transmission line and conductive objects increase. When a conductive object insulated from ground is in the vicinity of overhead lines, the conductive object picks up a electrostatically induced voltage that is proportional to the transmission line voltage. Electric fields from high voltage AC power lines can be hazard for personal and public that may be in contact or in proximity with a conductive object which is within the right-of-way of high voltage power lines. Most conductive objects in the vicinity of overhead transmission lines are fences of industries and buildings. So, conductive objects existing overhead transmission lines right-of-way (ROW) are studied in this paper. To mitigate the effects of electric field levels from high voltage lines on human beings living or working close to the lines, any building constructed along the high voltage lines should have right location along the corridor. The shock currents by induced voltage in objects due to electrostatic effects of overhead transmission lines should be less than “let-go” current. II. ELECTROSTATIC EFFECTS In this paper, the electrostatic effects are analysed based on the evaluation of electric field, shock current and induced voltage on conductive objects. A. Calculation of Electric Field The electric fields are calculated by the Gauss equation. The horizontal component of electric field is: Q Ex sin φ (1) 2πεx and the vertical component of electric field is: Q Ev cosφ (2) 2πεx Where Q = the charge on the conductor, C/m x = the radial distance, m φ = angle between the electric vector and its vertical components Ds = self-geometrical mean distance, m hi = height of conductor, m Dij = distance between conductor i and image conductor j, m dij = distance between conductor i and conductor j, m hj = height of the conductive object, m i hi j Dij Air Earth hi Image of conductor i Manuscript received May 18, 2014. Mya Thida Tun, Department of Electrical Power Engineering, Mandalay Technological University, (e-mail: [email protected]). Mandalay, Myanmar, +9595062788 Aung Ze Ya, Department of Electrical Power Engineering, Mandalay Technological University, Mandalay, Myanmar, +9595038549, (e-mail: [email protected]).. dij dij Image of conductor j Fig.1 Geometric layout of conductors and their images The charge Q on the conductors is determined through the voltage V and Maxwell potential coefficients P with matrix equation. 1 All Rights Reserved © 2012 IJSETR International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 Q P1V (3) The element of the shunt capacitance matrix is computed from the geometry of the tower configuration as shown in Fig.1.and from the conductor radii [3]. The capacitance is: 1 (4) C P Then, the diagonal element becomes: 2h 1 (5) Pii ln i 2πε0 Ds and the off- diagonal element is Dij 1 Pij ln (6) 2πε0 dij TABLE II TRANSMISSION LINE PARAMETER Specifications 230 kV line 132 kV line Length 26.162 km 34.1342 km Phase spacing, di 8m 6m Height of conductor ,hi Number of bundles, N 14 m 12.2 m 2 _ Bundle diameter, D 0.381 m _ The system is for 230 kV AC power transmission line is parallel with a conductive object as shown in Fig.2. B. Calculation of Shock current Shock current on object is occurred, when induced voltage is inserted in the object. object The amount of shock current on conductive objects is, I shock jωEv S (7) Where ω = angular frequency, rad/sec ε0 = permittivity of free space F/m S = charge collecting area of the object, m2 Ev = vertical components of electric field, V/m C = Capacitance of the object, F Fig .2. Object paralleled with power line phase conductors a,b,c C. Calculation of Induced voltage The electrostatically induced voltage on conductive object is mainly due to the effect of capacitive coupling between overhead transmission line and object [1]. The electrostatically induced voltage on conductive object, I (8) V shock jC In this paper, automobile, buildings and fence are studied as the conductive objects. The electrostatic effect on the building has been analysed at the three different types of building (type 1 is house insulated roof conductive building, type 2 is house conductive roof insulated building and type 3 is house and roof conductive building). Distance between middle conductor and conductive object, dj is 13.5 m. The calculations are for the distance between middle conductor and object, from 0 to 50 m, line-to-line voltage of 132 kV and 230 kV. IV. ANALYSIS RESULTS III. SYSTEM MODEL PARAMETERS The following is the list of parameters used in this study: A. Shock Current on Fence 14 TABLE I CONDUCTIVE OBJECTS 230 kV 132 kV 12 Specifications Fence Automobile Building Capacitance to ground, C Length 11.15 nF 1800 pF 6.22 nF 1.5 km 10.4 m 100 m Height 1.8m 2.4 m 33.5 m width - 2.8 m 50 m 4 Radius of fence wire, rf 2.032 mm _ _ 2 Height of roof _ _ 12.5 m Charge collecting area of the object, S 2268.1 m2 89.856 m2 System Separation distance: range from 0 to 50 m Shock current (mA/m) 10 8 6 0 0 5 10 m2 (type 1) 20167 (type 2) 17487 m2 (type 3) 24924 m2 15 20 25 30 distance dj (m) 35 40 45 50 Fig.3 Shock current on fence due to electrostatic effect Shock current on fence is occurred when induced voltage is inserted in the fence. Based on the electrostatically induced 2 All Rights Reserved © 2012 IJSETR International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 voltage on the fence as shown in Fig.6, the shock current on fence is calculated. The calculated results for shock current on fence due to electrostatically induced voltage are shown in Fig.3 for various distances between middle conductor and fence. As it is the shock current of electrostatically induced voltage, the capacitance of the fence is needed to consider calculating the current. The maximum shock current on fence is about 12.2324 mA/m at the distance 13.5 m between middle conductor and fence. The minimum shock current on fence is occurred at fence under middle conductor. The shock current is sharply increased the distance 7-13.5 m between middle conductor and fence. Beyond that distance, the shock currents are slightly decreased. The shock current due to 230 kV on transmission line is higher than others, and due to 132 kV on line is lower than others. B. Shock Current on Automobile Fig.4 shows the shock current on automobile due to 230 kV and 132 kV overhead transmission line for various distances between middle conductor and automobile. The maximum shock current on automobile is 0.4846 mA/m about at the distance 13.5 m from the middle conductor. When the automobile is under middle conductor, the shock current on automobile is minium. The shock current on automobile is slightly reduced by increasing the distance between middle conductor and automobile The maximum shock current on type 3 building is 134.4205 mA/m about at the distance 13.5 m between middle conductor and building. The minium shock current on type 2 building is occurred at building is under the middle conductor. The shock current due to type 3 building is higher than others, and due to type 2 building is lower than others. It can be regarded as the level of shock current on the buildings decrease with the increasing the separation distance between middle conductor and buildings. D. Induced voltage on Fence Fig.6 shows the induced voltage on fence due to 230 kV and 132 kV on overhead transmission line for various distances between middle conductor and fence. The voltage induced on the fence is of electrostatically induced voltage. It is due to the effect of capacitive coupling between overhead lines and fence. For the study, the maximum induced voltage on the fence is 3.4916 kV/m at the distance 13.5 m from the middle conductor. Beyond that distance, the coupling effect reduces slightly and for that reason, the induced voltage on fence is less, and the least at far distance. But when the fence is under middle conductor, the induced voltage on the fence is least. 3.5 3 0.5 230 kV 132 kV Induced voltage (kV/m) 0.45 0.4 Shock current (mA/m) 230 kV 132 kV 0.35 0.3 2.5 2 1.5 1 0.25 0.2 0.5 0.15 0 0 0.1 0.05 0 5 10 15 20 25 30 distance dj (m) 35 40 45 Shock current (mA/m) 20 25 30 distance dj (m) 35 40 45 50 0.9 (type 1 building) (type 2 building) (type 3 building) (type 1 building) (type 2 building) (type3 building) 230 kV 132 kV 0.8 0.7 Induced voltage (kV/m) 140 100 15 E. Induced voltage on Automobile C. Shock Current on Building The calculated results for shock current on buildings is shown in Fig.5 for various distance between middle conductor and buildings. 230 kV 230 kV 230 kV 132 kV 132 kV 132 kV 10 Fig.6. Electrostatically induced voltage on fence 50 Fig.4. Shock current on automobile due to electrostatic effect 120 5 0.6 0.5 0.4 0.3 0.2 80 0.1 60 0 0 5 40 10 15 20 25 30 distance dj (m) 35 40 45 50 Fig.7. Electrostatically induced voltage on automobile 20 0 0 5 10 15 20 25 30 distance dj (m) 35 40 45 50 Fig.5. Shock current on buildings due to electrostatic effect The induced voltage on the automobile is of electrostatic induced voltage. It is mainly due to capacitive coupling between overhead line and automobile. Fig.7 shows the 3 All Rights Reserved © 2012 IJSETR International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 induced voltage on automobile due to 230 kV and 132 kV overhead transmission line for various distances between middle conductor and automobile. Based on the electrostatically shock current on automobile as shown in Fig.4, the induced voltage on automobile is calculated. For this study, the maximum induced voltage on automobile is about 0.857 kV/m at the distance 13.5 m from the middle conductor and it decreases slightly with distance. When the automobile is under the middle conductor, induced voltage on automobile will be minium level. The induced voltage due to 230 kV on transmission line is higher than due to 132 kV on transmission line. F. Induced voltage on Building Fig.8 is the calculated results of induced voltage on building due to 230 kV and 132 kV over head transmission line for various distances between middle conductor and building. Based on the electrostatically shock current on building as shown in Fig.5, the induced voltage on building is calculated. The induced voltage on the building is highest at type 3 building and is lowest at type 2 building at the same distance from middle conductor. The peak induced voltage on the building for the study is 68.79 kV/m at the distance 13.5 m from the middle conductor. The induced voltage due to type 3 building is higher than others, and due to type 2 building is lower than others. maximum shock current on fence for the study is about 12.2324 mA/m. The maximum shock currents on building and fence are higher than the current magnitude of 5 mA maximum “let-go” current [2]. So to safe for a person in touching the conductive object, the conductive object should be grounded. VI. CONCLUSION Electrostatic effects caused by high voltage overhead power transmission lines on neighboring, parallel conductive objects have been analyzed. For the study, 132 kV and 230 kV AC transmission lines are used and automobile, building and fence are studied as conductive objects. Due to the electrostatic effect, high induced voltage on the conductive objects is occurred. For any conductive objects in the vicinity of overhead transmission lines should be grounded. ACKNOWLEDGMENT The author would like to express grateful thanks to her supervisor Dr. Aung Ze Ya, Associate Professor, Department of Electrical Power Engineering, and to all her teachers from childhood till now, especially Dr. Min Thu San, Associate Professor, Department of Myanmar Scientific and Technological Research, Yangon. The author’s special thanks are sent to her father, mother and aunt, for their guidance and support for all times. REFERENCES [1] Transmission Line Reference Book-345 kV and Above 2nd ed., Electrical Power Research Institute, Palo Alto, CA, 1982. [2] Electrostatic and Electromagnetic Effects of Overhead Transmission Lines, REA Bulletin 62-4, United States Department of Agriculture, May, 1978. [3] Electric Power Generation, Transmission and Distribution 2nd ed., Leonard L. Grigsby, 2007. [4] Electrostatic and Electromagnetic Effects of Ultrahigh-Voltage Transmission Lines, EL-802, Research Project 566-1, June 1978. [5] EPRI Transmission Line Reference Book-115-230 kV Compact Line Design,2007. [6] Transmission and Distribution of Electrical Power, Dr. Houssem Rafik El- Hana BOUCHEKARA, 2009/2010. 70 230 kV 230 kV 230 kV 132 kV 132 kV 132 kV Induced voltage (kV/m) 60 50 type 1 type 2 type 3 type1 type2 type3 40 30 20 10 0 0 5 10 15 20 25 30 distance dj (m) 35 40 45 First A. Author ― M s . M y a T h i d a T u n Place ― Room no: 2 47, Manthazin Hostel, MTU, Mandalay Date of birth ― 1.5.1980 50 Fig.8. Electrostatically induced voltage on buildings V. DISCUSSIONS The voltage induction effects of overhead transmission lines on conductive objects are governed by the amount of capacitive coupling, inductive coupling and resistive coupling. For the study, the effect of capacitive coupling is considered. Increasing the applied voltage will increase the induced voltage on the conductive objects due to the effect of capacitive coupling. The differences in induced voltages and shock currents are occurred when the lateral distance of conductive objects is increased. As the maximum shock current on the automobile for the study is about 0.4846 mA/m, it is less than the maximum “let-go” current magnitude of 5 mA. But the peak shock current on the type 3 building is 134.4205 mA/m and the Ms. Mya Thida Tun received her B.E. degree in Electrical Power Engineering from Technological University, Meikhtila, Mandalay Division, Myanmar, in February 2004. Afterwards, she received M.E. degree in Electrical Power Engineering from West Yangon Technological University (WYTU), Hlaingtheryar township, Myanmar, in October 2010. She worked as an assistat lecturer in the Department of Electrical Power Engineering at Technological Collage, Kyaukpadaung Township, Mandalay Division in Myanmar from April 2004 to Dec 2009. Currently, she is an lecturer in the Department of Electrical Power Engineering at Technological University, Pinlon, Shan State in Myanmar since Jan 2010. Ms. Tun is currently a Ph.D. candidate in the Department of Electrical Power Engineering at MTU, Myanmar. Her research interest is in the high-voltage transmission lines with a special emphasis on analysis and reducing the environmental effects of high-voltage AC transmission lines. 4 All Rights Reserved © 2012 IJSETR