Lightning response of transmission lines and impulse behavior of concentrated grounds

ACKNOWLEDGEMENTS First and foremost, I would like to express my sincere appreciation and utmost gratitude to my supervisor, Professor A C Liew, for his invaluable advice, guidance and assistance Thanks him for offering me his insight whenever I needed it and giving me the opportunity to learn from him I would also like to thank my fellow lab-mates for their encouragement and friendship Sincere thanks and gratitude are also due to Mr Seow Hung Cheng of Power Systems Laboratory for providing various supports for my research Finally, I thank my husband and parents for their understanding and encouragement during my candidature period i TABLE OF LIST ACKNOWLEDGEMENTS I TABLE OF LIST .II LIST OF PAPERS ARISING FROM WORK IN THIS THESIS IV LIST OF FIGURES V LIST OF TABLES VIII SUMMARY IX CHAPTER INTRODUCTION .1 1.1 BACKGROUND 1.1.1 Overview on Lightning 1.1.2 Review of previous work on calculating the lightning performance of distribution lines 1.1.3 Review of Liew’s work on dynamic model of impulse characteristics of concentrated earths 1.2 OBJECTIVE 1.3 ORGANIZATION OF THIS THESIS 11 CHAPTER MULTIPLE FLASHOVERS ACROSS THE SAME PHASE IN DIFFERENT TOWERS 13 2.1 INTRODUCTION OF LIGHTNING STROKES AND THEIR INFLUENCE TO POWER SYSTEMS 13 2.2 OVERVOLTAGE PROTECTIVE DEVICES 15 2.2.1 Insulators 16 2.2.2 Surge arresters 17 2.3 MULTIPLE FLASHOVERS ACROSS THE SAME PHASE IN DIFFERENT TOWERS 19 CHAPTER PROGRAM MFASP 22 3.1 DEVELOPMENT OF MFASP PROGRAM 22 3.2 FEATURES OF MFASP PROGRAM 23 3.3 FORMULATION OF PROGRAM MFASP 24 3.4 PROGRAM DESCRIPTION 30 CHAPTER CASE STUDY 33 ii 4.1 CASE A—LINE WITH ALL FLASHOVERS SUPPRESSED 35 4.2 CASE B—LINE WITH FLASHOVERS ACROSS THE INSULATORS CONSIDERED 38 4.3 CASE C— LINE WITH FLASHOVERS ACROSS THE INSULATORS AND SURGE ARRESTER CONSIDERED 46 4.4 DISCUSSION AND CONCLUSION 53 CHAPTER DEVELOPMENT OF DYNAMIC MODEL OF IMPULSE BEHAVIOR OF CONCENTRATED GROUNDS 55 5.1 INTRODUCTION 56 5.2 PHYSICAL MECHANISM OF BREAKDOWN 57 5.3 INTRODUCTION OF LIEW’S EXPERIMENT 58 5.3.1 Experiment Equipment and Preliminary Tests [26] 58 5.3.2 Experimental results on soil C—wet loamy sand 62 5.4 INTRODUCTION OF LIEW’S DYNAMIC MODEL [26] 65 5.4.1 Basic Assumptions 65 5.4.2 Liew’s dynamic model 67 5.5 INTRODUCTION OF EXPERIMENT IN CALIFORNIA AND ALABAMA 70 CHAPTER DYNAMIC MODEL OF IMPULSE BEHAVIOR OF CONCENTRATED GROUNDS AT HIGH CURRENTS 72 6.1 INTRODUCTION 72 6.1.1 Breakdown Process 74 6.1.2 Impulse Resistance 77 6.2 PROGRAM 79 6.3 VERIFICATION OF THE NEW MODEL 82 6.3.1 Use of proposed dynamic model to reproduce the triggered-lightning experimental results 82 6.3.2 Use of Proposed Model to Reproduce Liew’s Experimental Results on wet loamy sand (Soil C) 86 6.3.3 6.4 Reproduction of Liew’s oscillogram No 4910 89 DISCUSSION AND CONCLUSION 92 CHAPTER CONCLUSIONS 94 APPENDIX 97 APPENDIX A- TOWER CONFIGURATION 97 REFERENCES 98 iii LIST OF PAPERS ARISING FROM WORK IN THIS THESIS Wang Junping and A.C Liew, “Multiple flashovers across same phase in different towers”, manuscript submitted for publication in IEEE Power Engineering Society Transactions on Power Delivery, IEEE, USA Wang Junping, A.C Liew and M Darveniza, “Extension of Dynamic Model of Impulse Behavior of Concentrated Grounds at High Currents”, accepted for publication in IEEE Power Engineering Society Transactions on Power Delivery, IEEE, USA iv LIST OF FIGURES Fig 1.1 Diagram showing lightning mechanism and ground current [12] Fig 2.1 Voltage-current characteristics of an ideal overvoltage protection device [15] 15 Fig 2.2 Characteristics of insulators and gaps, all values are based on 11/2×40 positive waves and corrected to standard atmospheric conditions [12] 17 Fig 2.3 Thevenin equivalent circuit to calculate the surge arrester current [13] 18 Fig 2.4 Typical voltage and current waveshapes of the surge arrester during a surge discharge operation [13] 18 Fig 3.1 Voltage waves at a grounded pole node before flashover 25 Fig 3.2 Voltage waves at a grounded pole node after flashover across the insulators 28 Fig 3.3 Flowchart of program MFASP 32 Fig 4.1 220 kV transmission line model 33 Fig 4.2 Waveshape of the injected lightning surge 35 Fig 4.3 Overall voltages on towers and for case A—Line with all flashovers suppressed 37 Fig 4.4 Voltages on nodes involved in the flashovers for case B— Line with flashovers across the insulators considered 40 Fig 4.5 Voltages on nodes of tower for case B— Line with flashovers across the insulators considered 41 Fig 4.6 Voltages on nodes of tower for case B— Line with flashovers across the insulators considered 42 Fig 4.7 Current waveform for case B— Line with flashovers across the insulators considered 43 Fig 4.8 Voltages on all nodes of interest for case C— Line with flashovers across the insulators and surge arrester considered 48 v Fig 4.9 Voltages on nodes of tower for case C— Line with flashovers across the insulators and surge arrester considered 49 Fig 4.10 Voltages on nodes of tower for case C— Line with flashovers across the insulators and surge arrester considered 50 Fig 4.11 Currents waveforms for case C— Line with flashovers across the insulators and surge arrester considered 51 Fig 5.1 Equivalent Circuit of Surge Current Tests 58 Fig 5.2 Measurement of Earth Resistance 61 Fig 5.3 Oscillogram and corresponding photograph of surface sparkovers caused by a sparking connection on wet loamy sand (soil C) in the presence of rain sprays [26] 63 Fig 5.4 Oscillogram and corresponding photograph of surface sparkovers from the top of a driven rod when impulsed in wet loamy sand (soil C) in the presence of rain sprays [26] 64 Fig 5.5 Resistivity profiles in Liew’s dynamic-impulse resistance model 66 Fig 5.6 Hemispherical model for direct sparking connection in Liew’s model [26] 68 Fig 5.7 Percentages of return strokes producing detectable filamentary arcing from the base of the strike point as a function of peak stroke current [21] 70 Fig 6.1 Hemispherical model for direct sparking connection in the new model 73 Fig 6.2 Profiles of α as current rises and decays 76 Fig 6.3 Flowchart of the program to compute the earth resistivity 81 Fig 6.4 Sparking radius and the percentage of return strokes producing optically detectable surface arcing versus current peak Numbers above each histogram column indicate the number of strokes producing optically detectable arcing (numerator) and the total number of strokes in that return stroke current range (denominator) [22] 84 Fig 6.5 Coefficient α with current peak ranging from 1kA to 30kA 86 Fig 6.6 Comparison of experimental and calculated voltage and current against time for a sparking connection on wet loamy sand 87 vi Fig 6.7 Comparison of experimental and calculated resistance against current for a sparking connection on wet loamy sand 88 Fig 6.8 Comparison of experimental and calculated voltage and current against time for a driven rod connection on wet loamy sand 90 Fig 6.9 Comparison of experimental and calculated resistance against current for a driven rod connection on wet loamy sand 91 Fig A.1 220kV transmission line, tower top configuration……………………………………… 97 vii LIST OF TABLES Table 4.1 Flashovers in Case B Line with flashovers across the insulators considered 44 Table 4.2 Flashovers in case C— Line with flashovers across the insulators and surge arrester considered 52 Table 5.1 Parameters of surge-current generator 58 Table 5.2 Resistivity of soils tested 59 Table 6.1 Input Data for Triggered-Lightning Experiments Simulation 83 Table 6.2 Sparking Radius at Different Current Peaks 85 Table 6.3 Comparison of calculated and experimental results for a sparking connection on wet loamy sand 88 Table 6.4 Comparison of calculated and experimental results for a driven rod connection on wet loamy sand 91 Table 6.5 Input data for calculations to reproduce Liew’s experimental results on soil C 92 viii SUMMARY Lightning poses serious hazards to people, buildings, electrical power systems, telecommunication systems and radar stations etc Each year, the devastating effects of lightning cause considerable damage to human beings and properties The understanding of lightning phenomenon and its subsequent impacts are therefore of great importance In order to minimize the losses, two particular issues associated with the lightning phenomenon have been studied and presented in detail in this thesis: (1) multiple flashovers in multiphase systems including flashovers across the insulation of the same phase in different towers and (2) the dynamic model of impulse behavior of concentrated grounds at high currents First of all, the phenomenon of multiple flashovers in the multi-circuit and multi-phase line following a lightning strike to it is investigated This leads to the identification of the possible effect of multiple flashovers across the same phase in different towers In previous research, it is commonly thought that a flashover across insulators or through a lightning arrester on a tower can not lead to flashovers across the insulation of the same phase on adjacent towers or that it is of little consequence After the flashover, the earthwire, tower crossarm and the flashed-over phase conductor are connected together with the same voltage Hence, the flashed-over phase conductor comes in parallel with the earthwire Consequently, the voltages of the flashed-over phase conductor and the earthwire remain the same and therefore no voltage difference exists between them This is, however, true only until the waves arrive at the adjacent tower When the waves arrive ix at the adjacent tower, the voltage of the earthwire decreases as a large portion of lightning surge flows along the tower body down to the ground As a result, great voltage differences appear across the insulator strings on adjacent towers, which may lead to more flashovers In this project, a simulation program has been developed to demonstrate this effect of multiple flashovers across the same phase in different towers The simulation program may help to gain a deep understanding of this phenomenon The results obtained are important to the lightning protection of power systems Second, a dynamic model which describes the impulse behavior of concentrated grounds at high currents is presented in this thesis This model is an extension of previous models which can successfully account for the surge behavior of concentrated grounds over a much wider range of current densities It is able to describe the well-known effect of ionization of soil as well as the observed effect of discrete breakdowns and filamentary arc paths at much higher currents This model has been verified against the results from experiments on wet loamy sand [26] and also the triggered-lightning experiments in Florida and Alabama [21] The calculated and experimental results are in good agreement It is hence concluded that the newly developed model can be successfully applied to describe the impulse behavior of concentrated grounds at high currents x Chapter Dynamic model of impulse behavior of concentrated grounds at high currents is 136 kV The resistance at current peak is 7.03Ω The voltage peak is 227kV (see Table 6.3) The above oscillogram result is reproduced by the new dynamic model The input data are shown in Table 6.5 The comparisons of experimental and calculated voltage and current against time, and resistance against current for a sparking connection on wet loamy sand are shown in Fig 6.6 and Fig 6.7 respectively Fig 6.6 Comparison of experimental and calculated voltage and current against time for a sparking connection on wet loamy sand 87 Chapter Dynamic model of impulse behavior of concentrated grounds at high currents Fig 6.7 Comparison of experimental and calculated resistance against current for a sparking connection on wet loamy sand The comparison of calculated and experimental results is shown in Table 6.3 Table 6.3 Comparison of calculated and experimental results for a sparking connection on wet loamy sand Calculated Experimental Voltage peak Current peak (kV) 234.6 227 (kA) 19.33 19.35 Voltage at current peak (kV) 125 136 Resistance at current peak (Ω) 6.48 7.03 88 Chapter Dynamic model of impulse behavior of concentrated grounds at high currents 6.3.3 Reproduction of Liew’s oscillogram No 4910 Fig 5.4 shows the oscillogram and corresponding photograph of surface sparkovers from the top of a driven rod when impulsed in wet sand (soil C) in the presence of rain sprays [26] According to Liew’s record, the current peak is 17.16kA, and the voltage at current peak is 146.7 kV The resistance at current peak is 8.55Ω The voltage peak is 253.3kV (see Table 6.4) The above oscillogram result is also reproduced by the new model The input data are also shown in Table 6.5 The comparisons of experimental and calculated voltage and current against time, and resistance against current for a driven rod connection on wet loamy sand are shown in Fig 6.8 and Fig 6.9 respectively 89 Chapter Dynamic model of impulse behavior of concentrated grounds at high currents Fig 6.8 Comparison of experimental and calculated voltage and current against time for a driven rod connection on wet loamy sand 90 Chapter Dynamic model of impulse behavior of concentrated grounds at high currents Fig 6.9 Comparison of experimental and calculated resistance against current for a driven rod connection on wet loamy sand The comparison of calculated and experimental results is shown in Table 6.4 Table 6.4 Comparison of calculated and experimental results for a driven rod connection on wet loamy sand Voltage peak Current peak Calculated Experimental (kV) 256.7 253.3 (kA) 16.61 17.16 Voltage at current peak (kV) 133.2 146.7 Resistance at current peak (Ω) 8.02 8.55 91 Chapter Dynamic model of impulse behavior of concentrated grounds at high currents Table 6.5 Input data for calculations to reproduce Liew’s experimental results on soil C V0, charging voltage, kV Ls, series inductance, µH C, capacitance, µF Input for 4908 300 34 0.48 Input for 4910 300 34 0.48 ρ0, resistivity, Ωcm τ1, ionization time constant, µs τ2, deionization time constant, µs gc, BD gradient, kV/m 27000 0.5 19 27000 1.5 24 r0, radius of rod, mm ℓ, depth buried, m - 6.35 0.61 α0, coefficient α λ β1 β3 70 0.00017 0.8 70 0.00017 0.8 Using the improved dynamic model of impulse behavior of concentrated grounds at high currents, the agreement between the calculated voltage and current with Liew’s oscillogram results is very good Therefore, it is concluded that the proposed model can successfully describe the surge behavior of concentrated grounds subjected to high lightning currents which leads to discrete breakdown paths 6.4 Discussion and conclusion A dynamic model of impulse behavior of concentrated grounds has been developed It is an improvement over previous models for description of the surge behavior of 92 Chapter Dynamic model of impulse behavior of concentrated grounds at high currents concentrated grounds This model is capable of satisfactorily describing the nonlinear and time-variant behavior of earth resistance subjected to high lightning currents which lead to breakdown along discrete paths, instead of only a diffused growth of increasing ionization It also yields satisfactory agreement with experimental results in which discrete breakdown and filamentary arc paths were observed This proposed model provides a better description of the surge behavior of concentrated grounds and can be used to improve lightning-performance calculations In reproducing the experimental results, one set of variables/constants was selected for each soil and configuration type It is recognized that the set of these values selected is not unique However, each of these parameters is fairly independent of each other as they serve to shape a particular region/activity Notwithstanding, the challenge remains to tie in the expressions used with the theories of the physical processes of tracking and breakdown 93 Chapter Conclusions CHAPTER CONCLUSIONS Lightning has severe destructive effects on human life, buildings and public utility services such as power systems, communication systems, sensitive computers etc Every year, the devastating effects caused by lightning lead to millions of dollars worth of damage to power systems alone Hence, studies of the lightning response of power systems are of great importance Two aspects of lightning response of power systems have been studied in this thesis The first is multiple flashovers in multicircuit and multiphase lines including flashovers across the same phase in different towers, described in Chapters to 4, and the second is the development of a dynamic model of impulse behavior of concentrated grounds at high currents which is presented in Chapters and Firstly, the phenomenon of multiple flashovers in multicircuit and multiphase lines was studied This led to the identification of the phenomenon of multiple flashovers across the same phase in different towers, which was studied and simulated in this thesis The results demonstrated that a flashover across a surge arrester on a tower can lead to multiple 94 Chapter Conclusions flashovers across the insulation of the same phase on adjacent towers, contrary to the present expectation and thinking Following a lightning strike to a transmission line tower, flashover can and may occur across the insulator strings or through the surge arrester mounted on that tower Following the flashover, lightning surge is diverted to the flashedover phase conductor, leading to high voltage on it The voltage on the overhead earthwire and this flashed-over phase conductor remains substantially the same until the surge arrives at the adjacent tower Here, the voltage of the earthwire decreases as a large portion of the lightning surge flows along the tower body down to the ground As a result, great voltage differences appear across the insulator strings on adjacent towers, which can lead to more flashovers This result is of special significance in situation where surge arresters are mounted on towers on hill tops only The presence of the surge arrester on the stricken hill top tower cannot be relied upon to prevent flashovers on adjacent towers-even on the same flashed-over phases Secondly, a dynamic model of impulse behavior of concentrated grounds at high currents was described in this thesis This model is an extension of previous models for description of the surge behavior of concentrated grounds It satisfactorily describes the non-linear and time-iterative behavior of earth resistance subjected to high lightning currents which lead to discrete breakdowns and filamentary arc paths This model was verified against the results from Liew’s experiments on wet loamy sand and also the triggered-lightning experiments Very close correlation is obtained between simulation and experimental results Therefore, it can be concluded that the new model can successfully account for the impulse behavior of concentrated grounds at high current 95 Chapter Conclusions In conclusion, this thesis has two contributions First, the phenomenon of multiple flashovers across the same phase in different towers is identified and simulated Second, a new dynamic model is developed to describe the impulse behavior of concentrated grounds at high currents which lead to discrete breakdowns and filamentary arc paths Both results are of vital importance to the lightning protection of power systems The following recommendations are made for future research on multiple flashovers across the same phase in different towers Equations and the software simulations can be developed to include the corona effect on surge impedance and wavefront distortion Also, the software simulation can be applied to a large system for any stroke incident Research can also be carried out for in-depth physical explanation of dynamic model of impulse behavior of concentrated grounds at high currents which was developed in this thesis 96 Appendix APPENDIX Appendix A- Tower configuration The tower configuration is shown in Fig A.1 [13] Fig A.1 220kV transmission line, tower top configuration Average span length: 366m (1200ft) Insulators: 15 discs, 254×146mm Critical flashover voltage of insulators: 1350kV Critical sparkover voltage of the surge arrester: 515kV 97 References REFERENCES [1] A C Liew and M Darveniza, “Calculation of the Response of Unshielded Distribution Lines to Direct Lightning Strikes, Part I Multiconductor Traveling Wave Analysis,” Electric Power Systems Research, vol 22, 1991, pp 91-96 [2] A C Liew and M Darveniza, “Calculation of the Response of Unshielded Distribution Lines to Direct Lightning Strikes, Part II Validation and Studies,” Electric Power Systems Research, vol 22, 1991, pp 97-103 [3] Uman, M.A., “The Lightning Discharge”, Academic Press, Inc., 1987 [4] Uman, M.A and E.P Krider, “A Review of Natural Lightning: Experimental Data and Modeling”, IEEE Trans EMC, Vol EMC-24, No.2, pp 79-112, 1982 [5] Golde, R.H., “Lightning, Vol.1: Physics of Lightning, Vol.2: Lightning Protection”, London, U.K., Academic Press, Inc., 1977 [6] J M Clayton and A R Hileman, “A method of estimating lightning performance of distribution lines”, Trans AIEE, Part 3-B, 73 (1954) 933-945 [7] A C Liew and M Darveniza, “Lightning performance of unshielded transmission lines”, IEEE Trans., PAS-101 (1982) 1478-1486 98 References [8] A C Liew and M Darveniza, “Calculation of the lightning performance of unshielded transmission lines”, IEEE Trans., PAS-101 (1982) 1471-1477 [9] R J Frowd, “Calculation of the lightning response of distribution lines”, M.E Thesis, Univ Florida, 1980 [10] P C Thum and A C Liew, “Computer Analysis of Transmission Line Insulation for Lightning Performance,” IEE International Conference on Advances in Power System Control, Operation and Management, Hong Kong, 1991 [11] L V Bewley, Traveling Waves on Transmission Systems, New York, 1951, pp 186208 [12] Central Station Engineers of the Westinghouse Electric Corporation, Transmission and Distribution Reference Book, East Pittsburgh, Pennsylvania, 1964, pp 579-630 [13] W Diesendorf, Insulation Co-ordination in High-voltage Electric Power Systems, London, 1974, pp 99-126 [14] T K Saha and T Dinh, “Return Voltage Measurements on Metal Oxide Surge Arresters,” High Voltage Engineering Symposium, IEE, 1999 [15] A.P.Sakis Meliopoulos, Power System Grounding and Transients, Marcel Dekker, Inc 1988, pp 421-425 [16] A C Liew and M Darveniza, "Dynamic model of impulse characteristics of concentrated earths," in Proc IEE, Vol 121, No.2, pp 123-135, 1974 99 References [17] M.E Almedia, “Modeling the hysteresis behavior of the transmission tower footing”, 9th ISH in Graz., Australia, 1995 [18] F Popolansky, “Determination of Impulse Characteristics of Concentrated Earth Electrodes”, CIGRE SC33-86 (WG 01) IWD 22, Munich, August 1986 [19] William A Chisholm (M), Wasyl Janischewskyj (F), “Lightning Surge Response of Ground Electrodes”, IEEE Transactions on Power Delivery, Vol 4, No 2, April 1989 [20] Korsuncev, A.V., “Application on the Theory of Similarity of Calculation of Impulse Characteristics of Concentrated Electrodes”, Elektrichestvo, No 5, pp 31-35, 1958 [21] Richard J Fisher and George H Schnetzer, "1993 Triggered Lightning Test Program: Environments Within 20 Meters of the Lightning Channel and Small Area Temporary Protection Concepts," SAND94-0311, pp 3, 48-63, 1994 [22] V A Rakov, M A Uman, K J Rambo, M I Fernandez, R J Fisher, G H Schnetzer, R Thottappillil, A Eybert-Berard, J P Berlandis, P Lalande, A Bonamy, P Laroche and A Bondiou-Clergerie, " New insights into lightning processes gained from triggered-lightning experiments in Florida and Alabama," Journal of Geophysical Research, Vol 103, No D12, pp 14,117-14.130, 1998 [23] Zeqing Song, M R Raghuveer and Jingliang He, "Influence of the Nature of Impulse Current Propagation in Soils on Transient Impedance Characteristics," 2000 Conference on Electrical Insulation and Dielectric Phenomena, pp 739-742, 2000 100 References [24] Zeqing Song, He Jingliang and M R Raghuveer, "Experimental study on lightning breakdown channels in the soils," in High Voltage Engineering Symposium, Conference Publication No 467, IEE, pp 2.426-2.429, 1999 [25] Abdul M Mousa, "The soil ionization gradient associated with discharge of high currents into concentrated electrodes," in IEEE Transactions on Power Delivery, Vol 9, No 3, pp 1669-1677, 1994 [26] A C Liew, "Calculation of the lightning performance of transmission lines," Ph.D thesis, University of Queensland, 1972 [27] Martin A Uman, “Lightning”, McGraw-Hill Book Company, 1969 [28] T.A.Short, C.A.Warren, J.J.Burke, C.W.Burns, J.R.Godlewski, F.Graydon Jr and H.Morosini, “Application of Surge Arresters to a 115-kV Circuit”, pp 276-282, 1996 IEEE [29] Atsuyuki Inoue, Sei-ichi Kanao, “Observation and Analysis of Multiple-Phase Grounding Faults Caused by Lightning”, IEEE Transactions on Power Delivery, Vol 11, No 1, January 1996 101 [...]... model of the impulse behavior of concentrated grounds at high currents is developed in Chapter 6 The computer program to simulate the impulse behavior of concentrated grounds at high currents is also developed and introduced in this chapter Using the new dynamic model and the computer program, results from Liew’s experiment on wet loamy sand and triggered -lightning experiments in Florida and Alabama... dynamic model of impulse characteristics of concentrated earths In 1974, Liew and Darveniza developed a dynamic model of impulse characteristics of concentrated earths [16] This model successfully describes the nonlinear and timeiterative behavior of earths with resistivities ranging from 5000Ωcm to 31000Ωcm on a time-to-time basis A series of experiments were conducted at the University of Queensland High-Voltage... order to understand the lightning performance of transmission lines Liew [7]-[8] developed a comprehensive Monte Carlo/dynamic traveling wave program called WPTL This program is used to calculate the lightning performance of unshielded wood pole transmission lines, and it includes the effect of weak links and non-linearities such as corona, wavefront distortion and the voltage-time behavior of the insulation... Thus, to develop a new model is necessary and important to the understanding of the behavior of concentrated grounds subjected to high currents, such as lightning currents 10 Chapter 1 Introduction The new model was developed on the basis of Liew’s dynamic model [16] Results from experiments on wet loamy sand [26] and triggered -lightning experiments in California and Alabama [21]-[22] are used to verify... lightning protection of power systems The purpose of the second aspect of this thesis is to develop a new dynamic model to describe the impulse behavior of concentrated grounds at high currents which lead to discrete breakdowns and filamentary arc paths This kind of discrete breakdowns and resulting filamentary arc paths have been reported in several experiments [21-23] [26] However, a suitable concentrated. .. progress in understanding lightning until the late nineteenth century when photography and spectroscopy became available as diagnostic tools in lightning research The early history of lightning spectroscopy was reviewed by Uman [3] The invention of the double-lens streak camera by Boys in 1900 in England made possible the major advances in our understanding of lightning The first lightning current measurements... systems become more susceptible to the damage caused by lightning Therefore, an understanding of the lightning response of power systems is of vital importance 1.1 Background The characteristics of a lightning stroke are beginning to be understood by people after continuing analyses, research, field-intensive measurements and experiments The first study of lightning which could be termed scientific was carried... possibility of multiple flashovers across the same phase in different towers has not been discussed Therefore, a detailed analysis is very helpful and necessary to the understanding of the lightning response of transmission lines In addition, some problems, such as the use of surge arresters on hill tops to prevent flashovers on adjacent towers, are brought out and discussed They are very important to the lightning. .. by lightning in the final case The simulation results of these case studies are explained in detail in this chapter 11 Chapter 1 Introduction Chapter 5 reviews Liew’ experiment on wet loamy sand (soil C) and his dynamic model of impulse characteristics of concentrated earths Also, triggered -lightning experiments in California and Alabama are briefly introduced in this chapter A new dynamic model of. .. a dynamic model of impulse behavior of concentrated grounds at high currents The purpose of the first aspect is to study and simulate multiple flashovers across the insulation of all phases including the same phase in different towers Through computer 9 Chapter 1 Introduction simulations, multiple flashovers across the insulation of the same phase in different towers are identified and demonstrated ... new dynamic model of the impulse behavior of concentrated grounds at high currents is developed in Chapter The computer program to simulate the impulse behavior of concentrated grounds at high... the insulation of the same phase in different towers (ii) Development and analysis of a dynamic model of impulse behavior of concentrated grounds at high currents The purpose of the first aspect... different towers and (2) the dynamic model of impulse behavior of concentrated grounds at high currents First of all, the phenomenon of multiple flashovers in the multi-circuit and multi-phase