On the role of shield wires in mitigating lightning-induced overvoltages in overhead lines. Part I: a critical review and a new analysis

The ability of shield wires installed in overhead lines to mitigate lightning-induced overvoltages has been extensively investigated. Unfortunately, these studies came to different results, sometimes contradicting each other: some authors found that shield wires produce a significant overvoltage reduction, while others found the reduction negligible; conflicting results also pertain to the role played by the various parameters involved, such as the relative height of the shield wires compared to the phase conductors. This paper aims to clarify this topic. The paper is organized in two parts: Part I, which starts from the analysis of the theory behind the mitigation effect, is devoted to establishing a more solid base to the topic. Two fundamental improvements are proposed: the first one is the distinction between internal and external of the parameters involved: current literature makes an indiscriminate grouping of all of them; the second one is concerned with the point along the line where the mitigation effect needs to be assessed. Thanks to this new approach, we show that this effect can be precisely quantified. The analysis in this Part I is limited to the basic case of a single grounding point of the shield wire, which represents an unrealistic case. Part II is devoted to completing the study, by applying the proposed approach to more realistic and practical cases

Simulation and Analysis of High Voltage Engineering in Power Systems

This book address important issues regarding the modelling and simulation tools and techniques that are applied in high-voltage engineering in modern power systems. The presented conceptual, constructive, empirical, experimental, and theoretical results are obtained in the area of high-voltage engineering. Special attention is given to protection methods against direct lightning strikes, partial discharge tests, discharges’ influence on different structures, cable screening, and induced voltages, among others

On the role of shield wires in mitigating lightning-induced overvoltages in overhead lines. Part II: Simulation results for practical configurations

In the companion Part I, the theory relevant to the role of shield wires in mitigating lightning-induced overvoltages in overhead lines has been analyzed and clarified. A more consistent meaning has been assigned to the concept of Shielding Factor by introducing two innovations compared to the current literature: the first one concerning the distinction between internal and external parameters, and the other one concerning the point along the line where to assess the mitigation effect. Thanks to this new approach, uncertainties seen in the literature have been sorted out, and the Shielding Factor has been shown to be a parameter which can be precisely quantified. However, our new contribution was applied to a schematic (unrealistic) configuration: a line with a shield wire grounded at only one point. This Part II is precisely devoted to confirming the results obtained in Part I, by applying the proposed approach to more realistic and practical line configurations, namely a line with multi-grounded shield wire, and a line equipped with laterals too

Lightning Induced Overvoltages Caused by Non-Vertical Lightning and Earth Current Behavior

RÉSUMÉ Les surtensions induites par la foudre deviennent un sujet important dans le domaine des réseaux de distribution. Une évaluation précise des tensions induites est très essentielle pour la protection contre la foudre. Un problème des évaluations existantes est qu'un canal de foudre vertical et une terre parfaitement conductrice, qui ne sont pas réalistes, sont supposés dans la plupart des cas. Ces hypothèses nécessitent des recherches plus approfondies pour une évaluation précise de la tension induite. L'objectif principal de cette thèse est de révéler et résumer (1) les influences de la foudre non verticale sur les surtensions induites par la foudre dans les réseaux de distribution et (2) le comportement du courant de foudre dans une terre avec pertes, pour une évaluation précise des tensions induites. Pour (1), les circuits du modèle FDTD pour représenter la foudre non verticale sont construits et les influences de la foudre non verticale sur les tensions induites sont étudiées avec diverses conditions telles que la forme d'onde du courant de foudre, la géométrie du canal de foudre, l'état de la terre et la distribution ligne, etc. De plus, le mécanisme des changements est discuté en comparaison avec une formule analytique. Il est clair que l'inclinaison de la foudre vers la ligne augmente considérablement les tensions induites. Les tensions atteignent plus de deux fois plus que celles du boîtier vertical. L'inclinaison le long de la ligne ne montre que des différences mineures sur la tension de crête alors qu'elle rend le profil de tension le long de la ligne asymétrique. Des tendances similaires sont observées même lorsque l'on suppose une ligne triphasée réaliste avec mises à la terre et parafoudres. Les connaissances acquises dans cette thèse indiquent clairement que les influences de la foudre non verticale doivent être prises en compte pour une évaluation précise des surtensions induites par la foudre. Pour (2), les circuits du modèle FDTD sont validés par rapport aux résultats expérimentaux dans des articles publiés, et les influences de la distance de la foudre, de la position de la foudre sur la ligne, de la structure de mise à la terre, de la position du fil neutre, etc. sont étudiées par la FDTD. Il est confirmé que le couplage électromagnétique foudre-terre influence le courant de surface de la terre et l'augmentation du potentiel de terre (GPR) qui en résulte pendant une période transitoire, et donc l'inclinaison de la foudre rend le courant et le GPR différents du cas vertical.----------ABSTRACT Lightning induced overvoltages are becoming one of the most important topics in the field of distribution networks. An accurate evaluation of the induced voltages is essential for the design of lightning protection. One problem of existing evaluations is that a vertical lightning channel and a perfectly conducting earth, which are not realistic, are assumed in most cases. These assumptions require further careful investigations for an accurate induced-voltage evaluation. The main objective of this thesis is to reveal and summarize (1) the influences of non-vertical lightning on the lightning induced overvoltages in the distribution systems and (2) lightning current behavior in a lossy earth, for an accurate evaluation of the induced voltages. For (1), FDTD model circuits to represent the non-vertical lightning are built and influences of the non-vertical lightning on the induced voltages are investigated with various conditions such as lightning current waveform, lightning-channel geometry, earth condition, and distribution-line configuration etc. In addition, the mechanism of the changes is discussed in comparison with an analytical formula. It is made clear that lightning inclination toward the line significantly increases the induced voltages. The voltages reach values that are more than two times larger than those of the vertical case. The inclination along the line shows only minor differences on the peak voltage while it makes the voltage profile along the line asymmetric. Similar trends are observed even when a realistic three-phase line with groundings and arresters is assumed. The knowledge obtained in this thesis clearly indicates that the influences of non-vertical lightning should be considered for an accurate evaluation of lightning induced overvoltages. For (2), FDTD model circuits are validated in comparison with experimental results in published papers, and influences of lightning distance, lightning-struck position to the line, grounding structure, neutral wire position etc. are investigated by FDTD. It is confirmed that lightning-to-earth electromagnetic coupling influences the earth surface current and resulting ground potential rise (GPR) in a transient period, and thus the lightning inclination makes the current and GPR different from the vertical case. The coupling effect should be considered for accurate earth current and GPR studies. When there is a distribution line nearby, a large portion of lightning current flows into the nearby line via its groundings. Although the current itself does not make a large difference to the induced voltage, it would cause lightning surge problems in the line

Lightning Modeling and Its Effects on Electric Infrastructures

When it comes to dealing with high voltages or issues of high electric currents, infrastructure security and people’s safety are of paramount importance. These kinds of phenomena have dangerous consequences, therefore studies concerning the effects of lightning are crucial. The normal operation of transmission and distribution systems is greatly affected by lightning, which is one of the major causes of power interruptions: direct or nearby indirect strikes can cause flashovers in overhead transmission and distribution lines, resulting in over voltages on the line conductors. Contributions to this Special Issue have mainly focused on modelling lightning activity, investigating physical causes, and discussing and testing mathematical models for the electromagnetic fields associated with lighting phenomena. In this framework, two main topics have emerged: 1) the interaction between lightning phenomena and electrical infrastructures, such as wind turbines and overhead lines; and 2) the computation of lightning electromagnetic fields in the case of particular configuration, considering a negatively charged artificial thunderstorm or considering a complex terrain with arbitrary topograph

Modeling and experimental investigation of lightning arcs and overvoltages for medium voltage distribution lines

In this dissertation, lightning overvoltages in Medium Voltage (MV) lines are thoroughly investigated. The other goal is to propose new protection schemes for the designs. The lines consist of overhead lines, underground cables and covered conductors. These overvoltage problems range from direct and indirect strokes to lightning arcs. All the models and simulations are developed using the Electromagnetic Transient Program (EMTP) and Finite Element Method (FEM), while MATLAB is used for post-processing the results and identification of the model parameters. Improvement in the surge protection of MV overhead lines is demonstrated with a combination of surge arresters and a shield wire. Using the IEEE 34-node feeder injected with multiple lightning strokes, the feeder is simulated using EMTP. The response of the line is modeled both with and without the surge protection devices. The simulation study extends to the performance of a MV underground cable due to a nearby lightning discharge using FEM. The use of shield wire for limiting the overvoltage stress in the cables is proposed. A numerical analysis and simulations are performed to determine the outage rate of MV covered conductors due to lightning strokes of different characteristics. The optimum distance for surge protective devices on the conductors is also assessed. An enhancement in the surge analysis of distribution lines with the shielding effect of trees is proposed. An experimental study shows that a tree can intercept a lightning stroke in the vicinity of a distribution line. This study also analyzes experimental results of the shielding effectiveness of a tree and the induced voltages existing between the tree and the distribution line. The study is extended to evaluate the induced voltage on a distribution line for larger clearances using a Rusck model. This work investigates the lightning arc between an overhead line and a nearby tree under artificial rainfall. A full-scale laboratory experiment confirms that a direct stroke to a tree can cause severe damage to nearby power lines by initiating an arc channel through air to the conductors. A complete model of this phenomenon is developed by combining the existing static and dynamic arc equations. The model is accomplished by the bilateral interaction between the EMTP and Transient Analysis Control System (TACS) field. The experimental results have been reproduced by the computer simulations. The performance of the arc phenomenon is examined using a typical Finnish distribution network design. Using the modified arc model, the lightning arc performance of the MV/ LV network under the influence of nearby trees and the network characteristics is evaluated

Comparative study of 220 kV overhead transmission lines models subjected to lightning strike simulation by using electromagnetic and alternative transients program

Introduction. In high voltage networks intended for the transport of electrical energy, lightning can strike an electric line striking either a phase conductor, a pylon or a ground wire, causing significant overvoltage on the transmission lines classified as stresses the most dangerous for transformer stations and electro-energy systems in general. Modeling transmission lines becomes more complicated, if the frequency dependence of resistance and serial inductance due to the effect of lightning strike in the conductors and in the earth is considered. The difficulty increases the fact that the parameters of the line can be defined and calculated only in the frequency domain, while the simulation of transients is wanted to be in the time domain. Problem. Several models (J.R. Marti, Bergeron, nominal PI, Semlyen and Noda) exist for the modeling of transmission lines, the Electromagnetic Transients Program/Alternative Transient Program software (EMTP/ATPDraw) gives the possibility to choose between these models which is delicate due to the fact that we do not have experimental results to validate and justify the choice among the models available in the software. In this context, practical value: the overhead transport line OAT-El Hassi (220 kV) of the city of Sétif located in the north east of Algeria is used for the modeling of lightning strike by using the EMTP/ATPDraw software. Originality. A comparative study of the investigation of a lightning strike on an existing high voltage transmission line by different models of existing lines in the EMTP/ATPDraw software library of this software. Results. It was concluded that the choice of the model of the line is very important given the accuracy and quality of the curves of the voltage presented at the different calculation points. Вступ. У високовольтних мережах, призначених для передачі електроенергії, блискавка може вдарити по лінії електропередач, уразивши або фазний провід, опору, або заземлюючий провід, викликаючи значні перенапруги на лініях електропередач, визначені як загрози, найбільш небезпечні для трансформаторних підстанцій та електроенергетичних систем загалом. Моделювання ліній електропередач ускладнюється, якщо враховувати частотну залежність опору та послідовної індуктивності внаслідок дії удару блискавки у провідниках та землі. Складність підвищується тим, що параметри лінії можуть бути визначені і розраховані тільки в частотній області, в той час як моделювання перехідних процесів бажано проводити в часовій області. Проблема. Існує кілька моделей (J.R. Marti, Bergeron, номінальна П-подібна схема заміщення, Semlyen і Noda) для моделювання ліній електропередач, комп‘ютерна  програма електромагнітних перехідних процесів/альтернативна програма перехідних процесів EMTP/ATPDraw дає можливість вибирати між цими моделями, що є «тонким питанням» через те, що ми не маємо експериментальних результатів для перевірки та обґрунтування вибору серед моделей, доступних у програмному забезпеченні. У цьому контексті, практична цінність: для моделювання удару блискавки за допомогою програмного забезпечення EMTP/ATPDraw використана повітряна лінія електропередачі ОАТ-Ель-Хассі (220 кВ) міста Сетіф, розташованого на північному сході Алжиру. Оригінальність. Порівняльне дослідження вивчення удару блискавки на існуючій високовольтній лінії електропередач за різними моделями існуючих ліній у бібліотеці програм  EMTP/ATPDraw цього програмного забезпечення. Результати. Зроблено висновок, що вибір моделі лінії дуже важливий з урахуванням точності та якості кривих напруг, представлених у різних розрахункових точках.

Attenuation of Lightning-Induced Effects on Overhead Distribution Systems in Urban Areas

Overhead distribution systems can be strongly affected and damaged by indirect lightning. The induced voltages are usually computed neglecting the surrounding geometry and the presence of buildings in urban areas. Buildings can strongly change the behavior of the measured lighting-induced electromagnetic (EM) fields in the proximity of the point of impact. As a consequence, induced voltages can deviate from what would be measured in the absence of buildings. This work proposes an analysis of the main variables, which affect the deviation of the EM fields and of the consequent induced voltages along an overhead distribution line due to the presence of a building. Different distances between the line and the building and different building heights are considered