Dissertations / Theses on the topic 'Lightning Surge'

Hydropower plants contains a lot of vital electrical power technology such as generators and transformers. To prevent damage to this equipment due to overvoltage, they are often protected by surge arrester and in some cases also by surge capacitors. The design and dimension of these components vary between different sites and regions and are often done using a template without considering the actual conditions of the site. In this thesis Simulink and Simscape Power System are used to study the case when a hydropower station is exposed to overvoltage. One of Fortum’s hydropower stations is simulated when being exposed to lightning and switching overvoltage to see how the existing overvoltage protection handles this stress. The results show that the surge arresters mounted in front of the generator managed to keep it safe for all overvoltage scenarios it is exposed to. They also shows that the surge capacitors mounted in front of the generator reduces the gradient of the overvoltage surge. However, as the surge arresters already keeps the overvoltage at safe levels, there is no need of reducing the overvoltage gradient and the surge capacitors becomes excessive in this particular hydropower plant.<br>Vattenkraftverk innehåller många vitala komponenter så som generatorer och transformatorer. För att skydda dessa oftast väldigt dyra komponenter mot överspänningar, används ventilavledare och ibland också överspänningskondensatorer. Utformning och dimensionering av skydden varierar mellan olika anläggningar och regioner. Dimensioneringen av skydden görs ofta schablonmässigt, utan någon väsentlig anpassning till de faktiska förhållandena. I detta examensarbete används simuleringsverktyget Simulink tillsammans med tillägget Simscape Power Systems för att simulera vad som händer när ett vattenkraftverk utsätts för olika överspänningar. Ett av Fortums vattenkraftverk studeras när det utsätts för blixt- och kopplingsöverspänningar för att se vad ventilavledarna samt överspänningskondensatorerna i denna anläggning fyller för funktion. Resultaten visar att ventilavledarna monterade framför generatorn klarar av att hantera alla överspänningar de utsätt för under simuleringarna. Resultaten visade också att överspänningskondensatorerna monterade framför generatorn sänker spänningsgradienten, men eftersom ventilavledarna redan håller spänningen på en säker nivå blir överspänningskondensatorerna överflödiga i denna station.

This thesis has proposed a simplified model of corona discharge from an overhead wire struck by lightning for surge computations using the FDTD method. In the corona model, the progression of corona streamers from the wire is represented as the radial expansion of cylindrical conducting region around the wire. The validity of this corona model has been tested against experimental data. Then, its applications to lightning electromagnetic pulse computations have been reviewed.<br>博士(工学)<br>Doctor of Philosophy in Engineering<br>同志社大学<br>Doshisha University

Thesis (MEng)--University of Stellenbosch, 2001.<br>ENGLISH ABSTRACT: Unshielded distribution lines has a poor performance during lightning activity. Lightning initiates flashovers between the phases and earth and causes line breakers to trip several times during a lightning storm. In addition equipment like fuses, surge arresters and transformers are damaged by lightning and cause in some cases long power interruptions to customers. The application of line surge arresters on distribution lines is a solution that is implemented worldwide to limit the lightning related problems. This thesis investigated using line surge arresters in conjunction with bushing-mount fuses to decrease nuisance fusing and transformer damage during lightning activity. Two new pieces of equipment (dropout surge arresters and transformer bushingmount fuses) were developed and strategically placed on 4 different distribution lines. Equipment failures decreased by 90 % while financially the project had an excellent return on investment.<br>AFRIKAANSE OPSOMMING: Distribusie lyne sonder skermdrade presteer swak gedurende weerlig aktiwiteit. Weerlig veroorsaak oorvonking tussen fases en aard geleiers wat lei tot breker klinke. Transformators, sekerings, stuwingsafleiers en ander toerusting word ook deur weerlig beskadig en veroorsaak in sommige gevalle lang toevoer onderbrekings. Installering van lyn stuwingsafleiers op distribusielyne is 'n metode wat wêreldwyd gebruik word om oorvonking en weerligskade te beperk. Hierdie tesis ondersoek die installering van lyn stuwingsafleiers en deurvoerder gemonteerde sekerings om transformator skade en onnodige blaas van sekerings te beperk tydens weerlig aktiwiteit. Nuwe toerusting (uitval stuwingsafleiers en transformator deurvoerder gemonteerde sekerings) was ontwikkel en strategies op 4 verskillende distribusie lyne geïnstalleer. 'n Negentig persent vermindering in toerusting beskadiging is behaal terwyl die projek finansiël 'n goeie opbrengs op belegging meegebring het.

A measurement method of small-capacitance using transient waveforms is proposed in this thesis. A pi-circuit is used to express the stray capacitors between terminals and those from each terminal to ground. Two measuring modes, differential and common modes, are required to obtain the parameters of the circuit. The parameters are determined by transient current waveforms of the modes with an applied voltage, i.e., the open circuited voltage at the end of the current injection cable. The parameters of the pi-type circuit are obtained from a slope of the transient current waveforms or a waveform fitting by a nonlinear method. These methods enable the derivation without a voltage measurement by a probe connecting across the small capacitance, since the parasitic capacitance of the voltage probe obscures the small capacitance.<br>博士(工学)<br>Doctor of Philosophy in Engineering<br>同志社大学<br>Doshisha University

<p>The present society is highly dependant on complex electronics systems, which have a low damage threshold level. Therefore, there is a high risk of partial or total loss of the system’s electronics when they are exposed to a thunderstorm environment. This calls for a deep understanding on the mechanism related to the interaction of lightning generated electromagnetic fields with various large distributed/scattered systems. To accurately represent the interaction of lightning electromagnetic fields with electrical networks, it is necessary to have return stroke models capable to reproduce the electromagnetic field signatures generated by a lightning flash. Several models have been developed in the recent past to study the field-to-wire coupling mechanism. The most popular, simple and accurate among the available models is the Agrawal et al. model. On the other hand, ATP-EMTP is a well-known transient simulation package widely used by power engineers. This package has various built-in line models like Semlyen, Marti and Noda setups. There is a difficulty in applying the Agrawal et al. model with the built-in line models of ATP-EMTP, as the voltage source due to the horizontal component of electric field in Agrawal et al. model is in series with the line impedance and not in between two transmission line segments. Furthermore, when the electromagnetic field is propagating over a finite conducting ground plane, the soil will selectively attenuate the high frequency content of the electromagnetic field; causing a change in the field wave shape. A finite conducting ground will also produce a horizontal field component at the ground level. Several approximations are available in the literature to obtain the horizontal electric field; namely the wave-tilt and the Cooray-Rubinstein approximation. Consequently, it is important to investigate the change on the induced voltage signature when the power line is located over a finitely conducting ground. Additionally, to provide protection from lightning induced transients it is necessary to use Surge Protective Devices (SPDs) capable of diverting the incoming transients and provide protection level necessary to avoid damage in the equipment. However, standard test procedures of the SPDs do not take into account sub-microsecond structure of the transients. Therefore, to provide the required protection level to sensitive equipments connected to the low voltage power network, it is essential to understand the response of SPDs subjected to high current derivative impulses. This thesis is aimed to investigate the research problems as addressed above. Special attention will be given to a new proposed return stroke model, a simple circuit approach for efficient implementation of Agrawal et al. model using ATP-EMTP, the effect of the soil conductivity on the lightning induced overvoltage signatures and the response of surge protective devices subjected to high current derivative impulses.</p>

Vattenfall Eldistribution AB distribuerar el till ca 900 000 kunder i Sverige. Det handlar om både privatkunder och företagskunder. Enheten Nätdrift vars driftcentral är placerad i Trollhättan har till uppgift att se till att elnätet är spänningssatt och att man skall minimera avbrottstiderna. Då dagens samhälle är allt mer beroende av störningsfri leverans av el är det viktigt att kartlägga faktorer som orsakar korta avbrott på nätet. Ett kort avbrott definieras som ett avbrott som varar allt från 100 millisekunder till 3 min. I myndigheternas föreskrifter finns inga krav angående hur frekvent korta avbrott får förekomma i elnätet, då dessa avbrott oftast är orsakade av åska och därmed omöjliga att förutse. Genom att åskan åstadkommer en nedbrytning av isolationshållfastheten i systemet kan en ljusbåge uppträda vilken drar med sig nätspänningen till jord. Ledningsskydden känner av förekommande felströmmar och löser ut. En konsekvens av detta är att ett kort avbrott av nätets driftspänning uppstår innan en återinkoppling kan ske och normal drift åter föreligger. Arbetet är avgränsat genom att det endast handlar om avbrott orsakade av åsköverspänningar samt endast spänningsnivåer över 1000V. Utifrån litteraturstudier som är gjorda på kurslitteratur, forskning samt Vattenfalls eget material i ämnet, har arbetet resulterat i ett antal olika återgärder som skulle kunna minska antalet korta avbrott i högspänningsnätet. Detta examensarbete förordar att arbetet med att identifiera och analysera bakomliggande orsaker och möjliga åtgärder för att kunna minska antalet återinkopplingar fortsätter. I en fortsatt fördjupad analys bör även ekonomiska aspekter vägas mot nyttan av åtgärderna för både kunder och nätbolag.<br>In Sweden Vattenfall Eldistribution AB provides electrical power to approximatly 900000 customers, both private customers and business customers. The grid is operated from Trollhättan and it is the division Nätdrift's main purpose to, beside keeping the grid operating with a minimum of disturbances, to plan, optimize, manage and develop the operating systems. The society today is increasingly depending of an uninterrupted transmission of electricity and therefore it is important to make a survey of the factors that causes short interruptions in the grid. A short interruption is defined as an interruption that has a duration between 100 ms and 3 min. The regulations provided by the authorities do not include any demands regarding how frequent these short interruptions may occure in the grid. This is due to the fact that they are mostly caused by overvoltage from lightning storms, and therefore hard to predict. When lightning strikes on an overhead line, a breakdown of the insulation will occur due to overcurrent and a shortcut will ignite an arc between the wire and earth. This will start the phase-fault protection system to react and activate the feeder circuit breakers involved. This protection of the grid will cause a short interruption of the power supply before the automatic reclosing repowers the overhead line back to normal operating voltage. This thesis has been based on short interruptions caused by lightning and there has been no considerations taken to short interruptions occurring in grids with a voltage level below 1000 V. In this thesis a study of literature has been conducted from course literature, research and Vattenfalls internal documents. The result has been that a number of possible actions can be taken in consideration for making short interruptions less frequent. This thesis is also recommending that the survey of actors which are causing short interruptions continues. When doing so, the economical aspects should also be taken in consideration regarding the customers as well as the network company.

This master´s thesis deals with the designing process of surge protection for the object potentially explosive atmospheres and according to a set of standards ČEN EN 62305 and ČSN EN 60079. This work consists of four main parts. The first part deals with the theory of lightning and surges. Subsequently, in the second part is devoted to the theory of protection against these phenomena and proposals for external and internal lightning protection and surge. This chapter also deals with more demands on electrical installations in hazardous areas. The third part deals with the analysis of the risks to the subject paint and according to ČSN EN 62305-2 ed.2 and at the conclusion of the study is a proposal for external lightning protection and internal surge protection.

Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-12-03Bitstream added on 2014-06-13T18:52:41Z : No. of bitstreams: 1 thomazella_r_me_bauru_prot.pdf: 788309 bytes, checksum: a630d7e9326542247d07d560a3da2dd5 (MD5)<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>O presente trabalho visa o desenvolvimento de uma ferramenta computacional confiável na análise e estimação dos níveis de tensões induzidas em linhas de distribuição. Neste contexto, utilizam-se ferramentas computacionais consolidadas, como o ATP (Alternative Transients Program), que combinado a um software desenvolvido em Visual Basic, permitem quantificar e avaliar o nível de sobretensões nas linhas de distribuição. Por meio de modificações nas técnicas clássicas de modelagem das descargas atmosféricas, foi possível a construção de um software em Visual Basic capaz de quantificar os valores das tensões induzidas em linhas de distribuição finitas. A avaliação dos níveis de sobretensões induzidas nas mesmas foi implementada pela associação deste software a um programa de simulação (ATP), a fim de se obter resultados fidedignos deste transitório. Tais resultados foram utilizados para se avaliar o desempenho das...<br>The present work aims at the development of a trustworthy computacional tool in the analysis and estimate of the levels of induced overvoltage in distribution network. In this context, consolidated computacional tools are used, as ATP (Alternative Transients Program), that combined with a software developed in Visual Basic (beginner's all-purpose symbolic instruction code), they allow to quantify and to evaluate the level of overvoltage in the distribution network. By the means of modifications in the classic techniques of modeling of the atmospheric discharges, the construction of a software in Visual Basic was possible to quantify the values of the induced overvoltage in a finite... (Complete abstract click electronic access below)

As tensões induzidas e sobretensões geradas por descarga atmosféricas diretas e indiretas são um dos principais causadores de desligamentos não programados em redes de transmissão e distribuição. Estes desligamentos comprometem o fornecimento de energia a milhares de consumidores, sobretudo em regiões com constantes variações climáticas e com características orográficas bastante diversificadas, como apresentado no território brasileiro. Desse modo, cada vez mais esses fenômenos são estudados a fim de desenvolverem-se procedimentos para proteção contra distúrbios causados por descargas atmosféricas. Neste contexto, esta pesquisa contempla o estudo do estabelecimento das descargas atmosféricas indiretas e das tensões por elas induzidas em linhas de distribuição, assim como o assentamento das mesmas nestas redes de energia. Não obstante, utilizando-se um software capaz de representar transitórios eletromagnéticos são modelados e implementados um alimentador teste de distribuição e um sistema para estimação de tensões induzidas no domínio do tempo baseado no modelo de Sune Rusck. Também são modelados e implementados para-raios de óxido de zinco, de forma a representar suas características dinâmicas, para proteger a linha sob apreciação dos distúrbios provocados pelas tensões induzidas. A partir de uma análise comparativa entre a operação do sistema de distribuição em regime permanente e frente aos desdobramentos promovidos pelas tensões induzidas, é determinada a melhor configuração, localização e quantificação dos para-raios a serem instalados para proteção do sistema teste. Por meio da avaliação dos resultados das simulações computacionais observa-se a robustez da subestação e quais os ramos e cargas mais suscetíveis a perturbações frente às tensões induzidas, bem como a maior proteção oferecida pelos para-raios aos elementos conectados próximos aos seus nós de alocação.<br>The induced voltages and overvoltages generated by direct and indirect lightning are a major cause of not programmed shutdowns in transmission and distribution networks. These shutdowns compromise the power supply of thousands of consumers, especially in regions with frequent climatic variations and quite diverse orographic characteristics, as occurred on Brazilian soil. Thus, these phenomena are more and more studied in order to develop procedures for protection against disturbances caused by lightning. In this context, this research focuses on the study of the establishment of indirect lightning and the voltage induced by them on distribution lines, as well as their settlement on energy networks. However, using a software able to represent electromagnetic transients, a distribution test feeder and a system for estimating induced voltages in the time domain based on the Sune Rusck model are modeled and implemented. In addition, metal oxide surge arresters are modeled and implemented to represent its dynamic characteristics, in order to protect the line under consideration of disturbances caused by induced voltages. From a comparative analysis between the operation of the distribution system in steady state and facing the developments promoted by induced voltages, it is determined the best configuration, as well as the location and quantification of the surge arrester to be installed to protect the test system. Through evaluation of the results of computer simulations, it is observed the robustness of the substation and which branches and loads are more susceptible to the disturbances facing the induced voltages, and the greater protection offered by the surge arresters elements connected near to its nodes allocation.

There is great concern by the power systems utilities related to disturbances that generate induced overvoltages in the power network, as they reach the consumer sensitive equipment, causing damage and losses. In consequence of this framework, the power systems utilities get large financial losses every year due to indemnity for damage to such equipments. Among the disturbances that lead to induced overvoltages are lightning. Thus, in this work it was developed the study and analysis of the lightning´s effect on loads allocated on average (11kV/15kV) and low voltage (below 600V) under the influence caused by the resistance of grounding. For modeling and simulation of the system under analysis, the program for transient study ATP (Alternative Transient Program) was used. To develop the study, it was designed a system comprising of an 88kV transmission line, a substation, a distribution line of 13.8 kV and loads representing residential consumers. It was also analyzed the use of surge suppressor in the low voltage distribution transformers as a way to mitigate the induced overvoltages that reach consumers.<br>Existe uma grande preocupação por parte das concessionárias de energia relacionada aos distúrbios que geram sobretensões induzidas na rede elétrica, pois estas atingem os equipamentos sensíveis dos consumidores, causando danos e perdas. Em conseqüência deste quadro, as concessionárias contraem grandes prejuízos financeiros todos os anos devido ao ressarcimento por danos a tais equipamentos. Dentre os distúrbios causadores de sobretensões induzidas destacam-se as descargas atmosféricas. Sendo assim, neste trabalho foi desenvolvido o estudo e análise do efeito de descargas atmosféricas em cargas alocadas em média (11kV/15kV) e baixa tensão (abaixo de 600V) relacionada a influência causada pela resistência de aterramento. Para a modelagem e simulações do sistema sob análise utilizou-se o programa para estudo de transitórios ATP (Alternative Transient Program). Para a realização do estudo modelou-se um sistema composto de uma linha de transmissão de 88kV, uma subestação, uma linha de distribuição de 13,8kV e cargas que representam os consumidores residenciais. É analisada também a utilização de supressores de surto na baixa tensão dos transformadores de distribuição como forma de atenuar as sobretensões induzidas que atingem os consumidores.<br>Mestre em Ciências

Orientador: André Nunes de Souza<br>Banca: Ivan Nunes da Silva<br>Banca: Luiz Gonzaga Campos Porto<br>Resumo: O presente trabalho visa o desenvolvimento de uma ferramenta computacional confiável na análise e estimação dos níveis de tensões induzidas em linhas de distribuição. Neste contexto, utilizam-se ferramentas computacionais consolidadas, como o ATP (Alternative Transients Program), que combinado a um software desenvolvido em Visual Basic, permitem quantificar e avaliar o nível de sobretensões nas linhas de distribuição. Por meio de modificações nas técnicas clássicas de modelagem das descargas atmosféricas, foi possível a construção de um software em Visual Basic capaz de quantificar os valores das tensões induzidas em linhas de distribuição finitas. A avaliação dos níveis de sobretensões induzidas nas mesmas foi implementada pela associação deste software a um programa de simulação (ATP), a fim de se obter resultados fidedignos deste transitório. Tais resultados foram utilizados para se avaliar o desempenho das... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: The present work aims at the development of a trustworthy computacional tool in the analysis and estimate of the levels of induced overvoltage in distribution network. In this context, consolidated computacional tools are used, as ATP (Alternative Transients Program), that combined with a software developed in Visual Basic (beginner's all-purpose symbolic instruction code), they allow to quantify and to evaluate the level of overvoltage in the distribution network. By the means of modifications in the classic techniques of modeling of the atmospheric discharges, the construction of a software in Visual Basic was possible to quantify the values of the induced overvoltage in a finite... (Complete abstract click electronic access below)<br>Mestre

風力発電システムは、現在世界中で普及しているが、その地上高と立地条件からしばしば落雷の被害を受け、稼働率の低下が問題視されている。本論文は、垂直導体である風力発電タワーにおける雷サージ解析の高精度化、高速化を目的とした垂直導体回路解析モデルの提案、およびその有用性のについて述べるとともに、風力発電所や洋上風車への拡張性についてまとめたものである。<br>博士(工学)<br>Doctor of Philosophy in Engineering<br>同志社大学<br>Doshisha University

Este trabalho apresenta uma análise dos surtos em redes aéreas secundárias de distribuição causados por descargas atmosféricas diretas no circuito primário. Alguns trabalhos publicados sobre o fenômeno são comentados, sendo também analisados vários outros estudos relativos à modelagem de componentes. No trabalho, os principais componentes da rede foram modelados e incluídos na representação de uma topologia típica (com as linhas primária e secundária). Assim, foram considerados: transformador de distribuição, isoladores, pára-raios, cargas (consumidores) e resistências de aterramento. Os modelos foram validados, quando possível, através de ensaios em laboratório. Algumas alternativas de proteção da rede secundária foram consideradas. Foi verificada a influência de alguns parâmetros relevantes tais como amplitude e tempo de frente da corrente da descarga, resistências de aterramento, modelos de cargas e posição da descarga. Os resultados foram obtidos por simulações computacionais realizadas através do programa ATP (Alternative Transients Program). São apresentadas formas de onda de sobretensões nos consumidores. Também são apresentados e discutidos valores de corrente e energia nos dispositivos de proteção, fornecendo informações sobre as alternativas de proteção.<br>This work presents an evaluation of surges in low-voltage overhead distribution lines caused by direct lightning strikes in medium voltage lines. Some publications concerning the phenomenon are commented and several other studies used during the process of modeling of the components are also analysed. The main components of the distribution system were modeled and included. So, a typical distribution network topology (with the primary and secondary lines) was represented including its components: distribution transformer, insulators, surge arresters, loads and ground resistances. The performance of the developed models, whenever possible, was verified by laboratory tests. Some possibilities of the secondary protection were included. Parameters having major effect on the results, such as the lightning current amplitude and front time, the values of grounding resistances, the models of the loads and the lightning strike position were taken into consideration in the study. The results were obtained by simulations performed using the ATP (Alternative Transients Program). Waveforms are presented in order to provide information on the characteristics of the overvoltages in the consumers along the line. Currents, as well as energy absorbed by the low-voltage surge arresters are aldo presented and discussed, providing useful information about the performance of some protection alternatives.

Este trabalho apresenta um estudo de caracterização das impedâncias de entrada, em função da frequência, de instalações residenciais de baixa tensão e diversos equipamentos eletro-eletrônicos comumente encontrados. As respostas em frequência medidas são ajustadas e modeladas por redes RLC simples, mas efetivas, que podem ser utilizadas em qualquer programa computacional para simulações de transitórios. A faixa de frequências, até 5 MHz, permite o uso desses modelos em estudos associados a transitórios atmosféricos ou causados por chaveamentos. É importante ressaltar a existência de muito poucos trabalhos nesse assunto, pois, usualmente, as instalações de baixa tensão, ou os equipamentos conectados, são representadas por simples elementos concentrados, resistores, indutores ou capacitores. Por outro lado, sabe-se que os níveis de sobretensões em um sistema, ou instalação, são fortemente dependentes das cargas conectadas e, quanto mais precisos os modelos, melhores e mais confiáveis simulações são obtidas. Este trabalho inclui simulações com o programa computacional ATP utilizando os modelos desenvolvidos para avaliação de surtos em uma rede de distribuição típica submetida a descargas atmosféricas diretas no circuito primário. Além disso, utilizando o programa Pspice, são realizadas simulações da resposta interna de uma instalação residencial, com diversos equipamentos conectados, e submetida a surtos atmosféricos em sua entrada. O trabalho concentra informações práticas e úteis sobre estudos de surtos em sistemas e instalações de baixa tensão<br>This work presents a study of impedance characteristics, over a wide range of frequencies, of residential low-voltage installations and electric-electronic appliances, commonly found in residential installations. The measured frequency responses are fitted and modeled by simple, but effective, RLC networks, that can be used in any software for transient simulations. The range of frequencies, up to 5 MHz, allows the use of these models considering lightning or switching studies. It is of importance to point the lack of publications focusing this topic, because usually the low-voltage installations, or connected equipment, are represented by simple lumped components inductances, resistances or capacitances. Otherwise, it is well known that the overvoltage level of a system, or installation, is strongly dependent on the connected loads and for more precise models, better and more reliable simulation results are obtained. This work includes ATP software simulations using the developed models for evaluation of surges in a typical distribution network subjected to direct lightning strikes at the primary circuit. Furthermore, simulations of internal response of a low-voltage installation with connected equipment and subjected to lightning surges in its entrance is performed using the Pspice software. The work summarizes practical and useful information about the low-voltage surge studies on low-voltage systems.

電気鉄道の安全安定輸送を確保するため，雷害防止が求められている。本論文では，電気鉄道設備の雷サージ特性実測を行い，接地インピーダンス特性を雷サージの視点から検討した。さらに，電力系統解析技術を応用して鉄道特有機器の回路解析モデルを開発し，その精度を実測で確認し，鉄道設備雷電流侵入時の応答を実測および計算結果より明らかにした。これらの成果は，電気鉄道の設計・保守・解析に十分に生かすことが可能である。<br>Lightning protection is required to ensure safe and stable electric railway transportation. In this thesis, the lightning surge characteristics of the facilities in electric railway systems were measured. The characteristic of earthing impedance was also investigated from the viewpoint of lightning surge. In addition, some numerical models of railway specific apparatuses for circuit analysis method were developed by applying simulation technology for power system and confirmed their accuracies by actual measurements. The responses to lightning currents invaded into the facilities were clarified by the measured and calculated results. These results can be fully utilized in the design, maintenance and analysis of electric railway systems.<br>博士(工学)<br>Doctor of Philosophy in Engineering<br>同志社大学<br>Doshisha University

A maior parte das concessionárias de energia elétrica brasileiras normalmente não trata as falhas em transformadores de distribuição como um problema relevante sob ponto de vista financeiro, uma vez que qualquer ação preventiva para minimizar o problema dentro da realidade atual pode ser mais onerosa. Portanto, políticas adequadas para investigar as falhas de transformadores de distribuição são geralmente relegadas a segundo plano ou às vezes nem existem. Neste contexto, a informação existente em falhas de transformadores pode não conter dados importantes. No entanto, novas leis que afetam as concessionárias de energia estão mais severas e demandam por maior eficiência por parte delas. Neste novo cenário, uma metodologia forense, criada há muitos anos por várias concessionárias para analisar falhas em transformadores de distribuição, foi recentemente resgatada com a análise de 3159 equipamentos. Essa metodologia é conhecida como Metodologia Forense para Transformadores de Distribuição (MFTD) e será utilizada como ferramenta de diagnóstico para estudos de casos. Novos testes e ensaios como medição de resistência de isolamento, índice de absorção dielétrica e polarização, análise físico-química entre outros, serão agregados à metodologia forense para aprimorá-la. Além disso, os para-raios, sendo parte do sistema de proteção de transformadores de distribuição, também são estudados com o objetivo de verificar possíveis falhas de projeto e desafios a serem superados.<br>Most Brazilian utility companies normally do not treat failures in distribution transformers as a relevant problem in large financial point of view, since any preventive action to minimize them within the current reality can be more costly. Thus, proper policies for investigating faults in distribution transformers are usually disregarded by the power utilities and sometimes policies may not even exist. In this context, existing information on faulty distribution transformers may not contain important data. However, new laws affecting power distribution companies are becoming more severe and there are demands for greater efficiency. In this new scenario, a forensic methodology to analyse faults in distribution transformers, created some years ago by many utilities, has recently been resurrected with the analysis of 3,159 distribution transformers. This methodology is known as Forensic Analysis Applied to Distribution Transformers (FAADT). New tests and trials as measuring insulation resistance, polarization index and dielectric absorption, physical and chemical analysis among others, will be added to the forensic methodology to improve it. Moreover, the surge-arresters, being part of the system of protection of distribution transformers, are also studied in order to evaluate possible design flaws and challenges to overcome.

碩士<br>國立臺北科技大學<br>電機工程系所<br>94<br>In Taiwan, lightning stroke is the natural calamity that happen the most in power systems. It occupied more than 50% in power system accidents every year. There are three ways of lightning surge invade methods – Indirect Lightning Stroke, Direct Lightning Stroke, and Back Flash Lightning Stroke. And the Back Flash Lightning Stroke near the transmission tower of substation is most gravity. The surge might destroy the insulation of device and influence the service reliability of power system. In order to protect the transformer, the Tai-Power Company''s substation installs the arrester neat the main transformer as close as possible. The protecting range for the arrester is finite; therefore, the electrical equipments near the current entrance may exceed in the protecting range of arrester and be destroyed by the lightning stroke. This article is aimed at Tai-power Company’s Nan-Hu and Song-Shan primary substation (outdoor substation), to probe into the transient overvoltage phenomenon whiles the lightning stroke happening by the simulation of ATP/EMTP–the electromagnet transient analysis program. To simulate the situation of different lightning strokes and different lightning stroke points and analyze the protection of arrester in substation. The result of the analysis shows that if we locate the arrester next to the main transformer in substation only, it can not protect all the equipments in substation at all. Therefore, we can consider assembling arrester at the transmission entrance in order to protect the equipments in the substation which located in the area that suffer the lightning strokes the most.

Lightning is a natural phenomenon involving transient high current discharge in the atmosphere. Cloud-to-ground lightning, wherein the discharge occurs between the cloud and the ground is quite hazardous to systems on the ground. Apart from threat to life, the devastating effects of lightning can be mainly of thermal, mechanical and electromagnetic origin. Many a times, thermal and electromagnetic effects are of main concern. A direct hit, wherein the system under consideration becomes a part of the lightning path, could be quite catastrophic to many vulnerable systems like oil rigs, chemical factories, missile/satellite launch pads. From the safety and operational point of view, lightning is of serious concern for electrical systems including transmission lines and substations, nuclear power stations, telecommunication station and data banks. Lightning cannot be avoided, however, by employing a suitable Lightning Protection System (LPS), adequate protection against a direct hit can be provided to ground based systems. A typical lightning protection system involves: 1) Air termination network, which is responsible for stroke interception, 2) Down conductor system, which provides to the stroke current a minimal impedance path to the ground and 3) Earth termination network, for safe dissipation of current into the ground. Similarly, for the indirect effects, which are basically of electromagnetic origin, suitable protection can be designed. The key factors in a protective action involve interception of the dangerous strokes, minimization of the consequential potential rise on down conductors, as well as, at earth termination and keeping the field in the protective volume within an acceptable level. The last aspect can be generally categorized into secondary level protection. For critical systems, the lightning protection system is generally isolated from it. In such designs, potential rise on LPS governs the physical isolation required between the protected and protection system. For a given level of bypass strokes, cost of the LPS increases with the amount of physical separation employed. All most all of the earlier works have concentrated on lightning surge response of power transmission line towers. Apart from their relatively moderate heights, the intention was to arrive at a model, which can be incorporated in circuit simulation software like EMTP. Consequently, they envisage or approximate the mode of propagation to be TEM. In reality, for down conductors of height greater than say 30 m, only TM mode prevails during the initial critical time period. Hence the earlier models cannot be extended to general lightning protection schemes and for down conductor of larger lengths. Only limited literature seems to be available on the characteristics of general down conductor configurations. The problem in hand is very important and some serious research efforts are very much essential. In view of the above, the present work aims to evaluate the rise in potential as well as current injected into the soil at the base for: (i) practical range of down conductor configurations involving single down conductor (with height exceeding 30 m) and (ii) pertinent values of stroke current parameters. The protection schemes considered are isolated vertical down conductor, isolated tower (both square and triangular cross-section) and, tower with insulated lightning mast carrying ground wires. The parameters under consideration are: (i) height and cross section for the down conductor, (ii) clearance between the down conductor and the protected system, (iii) channel geometry, wherein only inclination is to be considered, (iv) velocity of current along the channel and (v) wave shape and rise time for the stroke current. For the evaluation of lightning surge response of transmission line towers, many theoretical and experimental approaches are found in the literature. However, works considering the TM mode of current propagation is relatively limited. In that both experimental and theoretical approaches have been adopted. Theoretical approach invariably adopted numerical field computation in frequency domain using Numerical Electromagnetic code (NEC-2). Fourier Transform techniques are employed to extract the time domain quantities. This approach is very economical, free from experimental errors and least time consuming. Hence it is selected for the present work. However, there are certain limitations in this approach. In NEC simulation, there is a restriction on the size and the arrangement of individual elements. Therefore, although fairly complex tower structures can be simulated, some simplification in the geometry is unavoidable. Such an approximation has been reported to cause insignificant error. NEC is not accurate for calculations in low frequency regime. But in the present work, the initial time regime is of concern wherein the high frequency components dominate. Therefore the above said limitation is not of any serious concern. In order to validate the approach, potential rise is computed for 120 m tall cylindrical down conductor and tower. Results are compared favorably with earlier works, which are based on potential lead wire method. A careful re-look into the ’potential rise’ on the down conductors reveal several things. The electric field in the region between the protection system and protected system is the root cause for the breakdown/flashover. For a given geometry, the integral of the electric field along the shortest path between the two systems must be representing the overall stress on the air gap. Further, for the later time periods, this integral coincides with the well-known quasi-static potential. All the available data and models for breakdown of long air gaps are basically in terms of this quasi-static potential. In view of this, the above path integral is defined as ’equivalent potential rise’ (which will be hereafter termed as ’potential rise’), and taken as the index for surge response. Further, observation of the computed spatio-temporal radial electric field around the down conductor reveals some additional features, which are not common in the quasi-static regime. Electric field reverses its polarity in space, which is due to the opposite current flowing in the lightning channel. Therefore, ’potential rise’, which is taken as the representative for the dielectric stress on the air, should not be evaluated for larger distances. Considering this and noting that the protected system generally lies well within a distance of 50% of the H, height of the down conductor, potential rise is evaluated by integrating electric field within this distance (12.5%H, 25%H, 50%H). Three heights (100%H, 75%H, 50%H) are considered for the evaluation of the potential. The influences of various down conductor and lightning channel parameters are analyzed. Finally vertical channel with full velocity for current propagation is arrived for the investigations. Also, the influence of neighboring conducting objects is briefly studied. It is argued that it needs to be ignored for the general study. Analysis is carried out for a range of down conductor configurations of heights ranging from 45 m to 120 m. Cylindrical down conductor is selected for the detailed study on the overall characteristics and its dependency on pertinent parameters. The characteristics of potential rise are found to be significantly different from that given by the commonly employed uniform transmission line model. In the regime of very fast front currents, down conductor of comparable heights have comparable potential rise. For the larger time to crest, behavior tends more to wards that for quasi-static regime. The dependency of the potential rise on radius of the down conductor seems to be logarithmic in nature. Surge response of isolated towers of both square and triangular cross sections is studied for heights ranging from 45 m to 120 m. The overall characteristics are found to be similar to cylindrical down conductor. Dispersive propagation is found to exist on towers. As a result, the base currents are slightly lower and potential rise exhibits less oscillations. Data curves on potential rise at three different heights and for three different spatial extents are generated for the range of down conductor heights with rise time of the stroke current as the variable. Several interesting observations have been made. Next the investigation is taken up for the insulated mast scheme. The parameters of the study are taken as the number of ground wires, grounding location of ground wires and length of the insulation cylinder. Potential across the insulation, tower base currents, and ground wire end currents are deduced. The basic characteristics of the potential rise are shown to be quite similar to that for the transmission line. For fast front currents the temporal variation is bipolar with a smooth decay. In other words, oscillations are sustained for considerably longer duration. Voltage stress across the insulation surface for one ground wire design is found to be higher by 1.4 - 2.4 times than that for isolated tower. The highest amplification of the ground end current, which occurs for fast front currents, is about 1.8 times. Potential difference across the insulation for two-ground wire design is higher by a factor of 1.3 - 1.85 than that for isolated tower. For the design with four ground wires, potential across the insulation is comparable with that for the tower. However, the mechanical strength of the insulating support should also be considered in the selection of number of ground wires. There exists, especially for fast front strokes, significant induction to the supporting tower. The height of the insulation seems to possess no appreciable influence on the potential rise and base currents. Several issues need to be considered before selecting this design. The contribution made by the present work can be summarized as follows. It basically deals with lightning surge response of isolated down conductors of height in the range 45 - 120 m. The configurations considered are, cylindrical down conductor, tower with both square and triangular cross section and insulated mast scheme. It makes a careful study on the ’potential rise’ on down conductors and a suitable definition for the same is proposed. Basic characteristics of potential rise and ground end currents are studied for the above-mentioned designs. Their salient features are enumerated. For the towers, design data curves are provided for relevant range of stroke current rise time. The issues that need to be considered in the insulated mast scheme are discussed along with the data on potential rise and base currents. The findings of this work are believed to be very useful for the design of lightning protection scheme involving isolated down conductor. Further the results are useful in analyzing the consequential lightning generated threat of being close to tall towers.

Lightning is a natural phenomenon involving transient high current discharge in the atmosphere. Cloud-to-ground lightning, wherein the discharge occurs between the cloud and the ground is quite hazardous to systems on the ground. Apart from threat to life, the devastating effects of lightning can be mainly of thermal, mechanical and electromagnetic origin. Many a times, thermal and electromagnetic effects are of main concern. A direct hit, wherein the system under consideration becomes a part of the lightning path, could be quite catastrophic to many vulnerable systems like oil rigs, chemical factories, missile/satellite launch pads. From the safety and operational point of view, lightning is of serious concern for electrical systems including transmission lines and substations, nuclear power stations, telecommunication station and data banks. Lightning cannot be avoided, however, by employing a suitable Lightning Protection System (LPS), adequate protection against a direct hit can be provided to ground based systems. A typical lightning protection system involves: 1) Air termination network, which is responsible for stroke interception, 2) Down conductor system, which provides to the stroke current a minimal impedance path to the ground and 3) Earth termination network, for safe dissipation of current into the ground. Similarly, for the indirect effects, which are basically of electromagnetic origin, suitable protection can be designed. The key factors in a protective action involve interception of the dangerous strokes, minimization of the consequential potential rise on down conductors, as well as, at earth termination and keeping the field in the protective volume within an acceptable level. The last aspect can be generally categorized into secondary level protection. For critical systems, the lightning protection system is generally isolated from it. In such designs, potential rise on LPS governs the physical isolation required between the protected and protection system. For a given level of bypass strokes, cost of the LPS increases with the amount of physical separation employed. All most all of the earlier works have concentrated on lightning surge response of power transmission line towers. Apart from their relatively moderate heights, the intention was to arrive at a model, which can be incorporated in circuit simulation software like EMTP. Consequently, they envisage or approximate the mode of propagation to be TEM. In reality, for down conductors of height greater than say 30 m, only TM mode prevails during the initial critical time period. Hence the earlier models cannot be extended to general lightning protection schemes and for down conductor of larger lengths. Only limited literature seems to be available on the characteristics of general down conductor configurations. The problem in hand is very important and some serious research efforts are very much essential. In view of the above, the present work aims to evaluate the rise in potential as well as current injected into the soil at the base for: (i) practical range of down conductor configurations involving single down conductor (with height exceeding 30 m) and (ii) pertinent values of stroke current parameters. The protection schemes considered are isolated vertical down conductor, isolated tower (both square and triangular cross-section) and, tower with insulated lightning mast carrying ground wires. The parameters under consideration are: (i) height and cross section for the down conductor, (ii) clearance between the down conductor and the protected system, (iii) channel geometry, wherein only inclination is to be considered, (iv) velocity of current along the channel and (v) wave shape and rise time for the stroke current. For the evaluation of lightning surge response of transmission line towers, many theoretical and experimental approaches are found in the literature. However, works considering the TM mode of current propagation is relatively limited. In that both experimental and theoretical approaches have been adopted. Theoretical approach invariably adopted numerical field computation in frequency domain using Numerical Electromagnetic code (NEC-2). Fourier Transform techniques are employed to extract the time domain quantities. This approach is very economical, free from experimental errors and least time consuming. Hence it is selected for the present work. However, there are certain limitations in this approach. In NEC simulation, there is a restriction on the size and the arrangement of individual elements. Therefore, although fairly complex tower structures can be simulated, some simplification in the geometry is unavoidable. Such an approximation has been reported to cause insignificant error. NEC is not accurate for calculations in low frequency regime. But in the present work, the initial time regime is of concern wherein the high frequency components dominate. Therefore the above said limitation is not of any serious concern. In order to validate the approach, potential rise is computed for 120 m tall cylindrical down conductor and tower. Results are compared favorably with earlier works, which are based on potential lead wire method. A careful re-look into the ’potential rise’ on the down conductors reveal several things. The electric field in the region between the protection system and protected system is the root cause for the breakdown/flashover. For a given geometry, the integral of the electric field along the shortest path between the two systems must be representing the overall stress on the air gap. Further, for the later time periods, this integral coincides with the well-known quasi-static potential. All the available data and models for breakdown of long air gaps are basically in terms of this quasi-static potential. In view of this, the above path integral is defined as ’equivalent potential rise’ (which will be hereafter termed as ’potential rise’), and taken as the index for surge response. Further, observation of the computed spatio-temporal radial electric field around the down conductor reveals some additional features, which are not common in the quasi-static regime. Electric field reverses its polarity in space, which is due to the opposite current flowing in the lightning channel. Therefore, ’potential rise’, which is taken as the representative for the dielectric stress on the air, should not be evaluated for larger distances. Considering this and noting that the protected system generally lies well within a distance of 50% of the H, height of the down conductor, potential rise is evaluated by integrating electric field within this distance (12.5%H, 25%H, 50%H). Three heights (100%H, 75%H, 50%H) are considered for the evaluation of the potential. The influences of various down conductor and lightning channel parameters are analyzed. Finally vertical channel with full velocity for current propagation is arrived for the investigations. Also, the influence of neighboring conducting objects is briefly studied. It is argued that it needs to be ignored for the general study. Analysis is carried out for a range of down conductor configurations of heights ranging from 45 m to 120 m. Cylindrical down conductor is selected for the detailed study on the overall characteristics and its dependency on pertinent parameters. The characteristics of potential rise are found to be significantly different from that given by the commonly employed uniform transmission line model. In the regime of very fast front currents, down conductor of comparable heights have comparable potential rise. For the larger time to crest, behavior tends more to wards that for quasi-static regime. The dependency of the potential rise on radius of the down conductor seems to be logarithmic in nature. Surge response of isolated towers of both square and triangular cross sections is studied for heights ranging from 45 m to 120 m. The overall characteristics are found to be similar to cylindrical down conductor. Dispersive propagation is found to exist on towers. As a result, the base currents are slightly lower and potential rise exhibits less oscillations. Data curves on potential rise at three different heights and for three different spatial extents are generated for the range of down conductor heights with rise time of the stroke current as the variable. Several interesting observations have been made. Next the investigation is taken up for the insulated mast scheme. The parameters of the study are taken as the number of ground wires, grounding location of ground wires and length of the insulation cylinder. Potential across the insulation, tower base currents, and ground wire end currents are deduced. The basic characteristics of the potential rise are shown to be quite similar to that for the transmission line. For fast front currents the temporal variation is bipolar with a smooth decay. In other words, oscillations are sustained for considerably longer duration. Voltage stress across the insulation surface for one ground wire design is found to be higher by 1.4 - 2.4 times than that for isolated tower. The highest amplification of the ground end current, which occurs for fast front currents, is about 1.8 times. Potential difference across the insulation for two-ground wire design is higher by a factor of 1.3 - 1.85 than that for isolated tower. For the design with four ground wires, potential across the insulation is comparable with that for the tower. However, the mechanical strength of the insulating support should also be considered in the selection of number of ground wires. There exists, especially for fast front strokes, significant induction to the supporting tower. The height of the insulation seems to possess no appreciable influence on the potential rise and base currents. Several issues need to be considered before selecting this design. The contribution made by the present work can be summarized as follows. It basically deals with lightning surge response of isolated down conductors of height in the range 45 - 120 m. The configurations considered are, cylindrical down conductor, tower with both square and triangular cross section and insulated mast scheme. It makes a careful study on the ’potential rise’ on down conductors and a suitable definition for the same is proposed. Basic characteristics of potential rise and ground end currents are studied for the above-mentioned designs. Their salient features are enumerated. For the towers, design data curves are provided for relevant range of stroke current rise time. The issues that need to be considered in the insulated mast scheme are discussed along with the data on potential rise and base currents. The findings of this work are believed to be very useful for the design of lightning protection scheme involving isolated down conductor. Further the results are useful in analyzing the consequential lightning generated threat of being close to tall towers.

碩士<br>大同大學<br>電機工程學系(所)<br>94<br>This thesis will be utilizing ATP-EMTP as analytic tool, performing overvoltage analysis, regarding 345kV voltage grade level of the Mai-Liao Power Plant; especially its EHV No. 1 Station, concerning switching surge and lightening surge. The overall purpose is to evaluate whether the insulation strength of the 345kV system, is strong enough to withstand overvoltage threats of lightening surge and switching surge. Based on suggestions of ANSI/IEEE Std. C62.22 and outcomes of analysis of this research, relevant assessment will be made in regards to whether or not, the circuit breaker and transformer installations of the GIS system, possess sufficient protection margin; further alternation suggestions will also be made concerning the simulation methodologies and respective models to be applied, for lightening surge and switching surge. Various models for lightening surge simulation include: transmission line model, tower model, lightening current source model, archorn flashover model and substation model. Various models for switching surge simulation include: transmission line model, time-controlled switching model, statistic switching model and transformer model. Deriving from analytical results, one is made aware of the fact that, when conducting lightening surge overvoltage simulation, if one employs “Ramp 1/70μs” as lightening current waveform, as well as Multistory Tower Model as the tower model of lightening analysis, one can obtain much more rigorous outcomes. Furthermore, deriving from analytical results of energizing surge simulation, by using statistic switching model, provided that the simulation trials is over 100 times, the final results obtained are more accurate, when compared to using time controlled switching model. Whereas when conducting analysis for reclosing overvoltage simulation, if one applies the Bergeron Model as transmission line model, then a more reasonable decay phenomenon of residual voltage can be presented, which is much more realistic in relation to the actual reclosing overvoltage. The final outcome of this research study clearly shows that, the lightening surge overvoltage and the switching surge overvoltage derived from such operations of reclosing, as well as Jia-Min substation’s energizing, will not bear direct impact or damage, neither to the GIS system nor to the primary transformers at the Mai-Liao Power Plant. Nevertheless, when the Mai-Liao Power Plant and the Jia-Min substation are in shunt liaison, if the voltage phase angles at the 2 extremes of the circuit breaker are non-synchronous, then this will lead to an overcurrent invasion of the primary transformers at the Mai-Liao Power Plant.

碩士<br>國立中正大學<br>電機工程研究所<br>93<br>Abstract The insulation strength of electric power equipments should not only endure normal operation voltage for a long period time, but also endure the possible temporary overvoltages arisen in the systems. By means of understanding the insulation strength of electric power equipments, temporary overvoltags arisen in the systems, and the characteristics of surge protective devices, appropriate arresters may be selected to protect the overall system under on acceptable level of both security and economy. These are the major issues that insulation coordination concerns. This study also discusses the determination of protection margin under probabilistic lightning model. Based on the log-normal distribution lightning model, simulations are conducted using Electro Magnetic Transient Program (EMTP) to observe the protection margin for transformers at a 69 kV substation, as lightning strikes its nearby overhead lines. The simulation results show that whether or not the arresters are installed, the protection margin for transformers may be expressed as a random distribution. Therefore, under the probabilistic lightning model, the protection margin is better to be represented probabilisticly, not just a number. Generally speaking, the equipment’s withstanding voltage is in proportion to the system’s voltage class. So, under the same lightning conditions, the higher voltage class the system is, the higher probability satisfying the protection margin is. The results also show that the threat of lightning surge to 69kV systems is serious and is even more than that to 345kV and 161kV systems.

碩士<br>中原大學<br>電機工程學系<br>87<br>The performance of grounding system is very important to the safety of human and equipments. A grounding system is conventionally characterized by its grounding resistance , but more and more damages occurred on grounding system due to lightning surge can not be evaluated only by using grounding resistance. The thesis analyzes the lightning surge characteristics of grounding system directly form the view point of electromagnetic principles, i.e. analyzes the electromagnetic characteristics of grounding system with respect to the lightning surge current. The analysis items include the potential and electromagnetic fields due to lightning surge current, and next, based on the analysis results , the step voltage and touch voltage related to human safety , and the ground potential rise(GPR) and ground potential difference(GPD) related to equipment protection are analyzed ; from which , we can assess the damages of personnel and equipments on a grounding system. The analysis results have shown that the danger step and touch voltages will be produced to threaten the safety of personnel when the lightning surge current injects into the grounding system, the GPR and GPD will also damage the low voltage and weak systems. These hazards will increase with the increasions of the peak value, wavefront steepness and the duration time of lightning surge current. For protecting personnel, low voltage and weak systems and equipments from the lightning surge current, this thesis proposes two methods namely conduction method and insulation method to enhance the protection performances of grounding system, and this will contribute to upgrading the power quality.

碩士<br>國立清華大學<br>電機工程學系<br>90<br>From north to south, the length of the operation route of Taiwan High Speed Railway (THSR) which has seven power substations is about 340 km. Every substation is supplied by TPC’s 161kV buses via three-phase double-circuit transmission lines. By Scott main transformer, the three-phase power is transferred to two single-phase power (2×27.5kV、60Hz) and then fed to the catenary system. Although the electrical system of Shinkansen Sysyem (SKS) is adopted by THSR, there are some differences between them. For example, the midpoints of autotransformers in THSR are directly grounded compared to SKS ones which are grounded via protection gaps. Due to the above reason, the thesis analyzes and simulates the overvoltage phenomenon which may happen in the power system of THSR according to the relative data and assumptions. As for using ElectroMagnetic Transient Program (EMTP) to simulate the lightning surge, the thesis explains the modeling methods, parameters and the simulation results. Finally the thesis discusses the characteristics of overvoltage and evaluates the insulation coordination conditions of THSR according to simulation results. At the present time, the adopted power system configuration of THSR is still in planning and construction phase. In order to provide a reference to THSR, the thesis analyzes and simulates possible overvoltage phenomenon according to the limited information we have. Besides all above, the thesis systematically discusses overvoltage phenomenon including Temporary OverVoltage (TOV), Switching OverVoltage (SOV) and Lightning OverVoltage (LOV) on the basis of gathered information and publications. A new way for modeling the two-terminal-ungrounded voltage source to simulate the lightning induced voltage by EMTP is also presented, which contributes to the EMTP modeling technique.

碩士<br>中原大學<br>電機工程研究所<br>89<br>In this thesis, the lightning characteristics of large grounding system with multi-grid are analyzed based on the electromagnetic theory. The study is aimed to the grounding system in the Mucha factory of Taipei-Rapid-Transit System (TRTS) which is composed of seven ground grids. To study the lightning characteristics of this grounding system, the ground potential rises (GPRs), ground surface potentials, ground potential differences (GPDs) between different grids, step voltages and touch voltages on each grid when the lightning is striking on one of the grids is analyzed and the hazards to personnel and equipments are evaluated. The study will consider that all the grids are connected together and disconnected from each other, respectively. The study results have shown that the GPR, GPD and touch voltages on the grid to be stricken by lightning will be reduced with small degree when all the grids are connected together. These results will contribute to the protections of equipments and the safety of personnel on the grid to be stricken by lightning, but the GPR of step voltage and touch voltages on other grids without lightning striking will be slightly risen. In summary, whether all the grids are connected together or not, the protection measures are still required to enhance the personnel and equipments to protect against lightning. Many protection measures had been proposed by the literatures. This thesis will integrate then and list out for application references.

Student Number : 0418388R - MSc(Eng) research report - School of Electrical and Information Engineering - Faculty of Engineering and the Built Environment<br>Due to the high soil resistivities and high frequency of lightning strikes in South Africa, the background theory about the effect of soil resistivity on the LV surge environment is important, but the present local and international standards do not give reasonable explanations for this effect. The previously published experimental results and research results related to this effect were investigated. From these investigations, it can be shown that the soil resistivity can affect surge generation, surge propagation and surge attenuation significantly. Also, soil resistivity plays a main role in the lightning surges caused by both direct strikes and indirect strikes, which can cause severe damage to the LV distribution system. Soil resistivity also has a significant impact on the resistance of an earth electrode.

碩士<br>國立臺灣科技大學<br>電機工程系<br>99<br>The lightning strikes are natural phenomenon has been a major concern in every Countries. How to lower the surge voltage and complete lightning protection is the first consideration during building design and implementation. The lightning-protection rod of the building is grounded directly through the grounding conductor. It is seldom to ground the lightning rod via the steel structure of the building. The thesis discussed the difference between direct-grounded method and building-steel-structure-grounded method. The construction is simulated with an eight floors Reinforce Concrete (RC) structure using EMTP software. Every section of the column and beam of steel structure is simulated with resistance and inductance. The lightning model of the Heilder-type is used to simulate the lightning current. Lightning surge voltage distribution on RC structure building grounding is studied in this thesis. The results show that surge voltage of direct-grounded method is lower than that of RC-structure- grounded method in terms of building lightning-protection rod. According to the advantages for direct-grounded method, the rising rate of surge voltages are lowered which are much more safe to mechanic equipment and working environment to employee. Furthermore, the surge voltage of neutral grounded is lower than that of neutral non-grounded in a 3-phase power supply of building; meanwhile, the different connection of 3-phase-load, Y or Δ, will affect the surge voltage distribution when lightning strikes.

碩士<br>中原大學<br>電機工程研究所<br>90<br>This study is to analyze the lightning and switching surges characteristics of grounding system of typical large integrated circuit (IC) manufacturing plants fed with 161kV power. The thesis analyzes lightning and switching surges characteristics of grounding system directly form the view point of electromagnetic principles, i.e. analyzes the electromagnetic characteristics of grounding system with respect to the lightning surges and switching surges. The analysis items included the ground surface potentials and electromagnetic fields. Based on the analysis results, the step and touch voltages related to human safety, and the transient ground potential rise (GPR´s) and ground potential difference (GPD´s) related to equipment protection are analyzed; from which, we can assess the damages of personnel and equipments on the grounding system. The analysis results have shown that the GPD´s produced by switching operation and lightning will threaten the safety of personnel, low voltage equipments and weak systems. For improving the protection performances of grounding system against the lightning and switching surges, the improving methods are proposed here. The improving methods will also contribute to upgrading the power quality.

碩士<br>國立臺灣科技大學<br>電機工程系<br>94<br>The main purpose of this thesis is to simulate the transient over-voltage on the 345kV and 161kV cable, while the lighting striking on the cable connection station by using the Electro-Magnetic Transients Program (EMTP). The feasibility of cable connection station to reduce the damage caused by lightning striking will also be conducted. In the process of the research, the components of the study system include lighting surge, transmission line, transmission tower, lightning surge, arrester, and cable are first modeled. Secondly, the voltage value in the cable will be analyzed by the different connection methods of ground wire, altering the length of the grounding wire of the arrester, and changing the value of the grounding resistance while the lighting striking on the different place. Simulation r4esults show that the voltage value be influenced by the grounding wire changed and reduction of the grounding resistance value can effectively decrease the over-voltage caused by lighting striking using the independent grounding method. The independent grounding also can avoid to exceed the metallic shield voltage caused by ground potential rise.

碩士<br>國立臺北科技大學<br>電資碩士在職專班研究所<br>102<br>The lightning characteristics of 161kV cable connection stations(CCS) and the affections are evaluated.The improved strategies are also proposed.The study mainly focus on the analysis of voltage and current variations on the overhead lines,CCS and underground cable relative equipments with respect to the lightning on the overhead ground wire(OGW)and phase conductor,and to evaluate the affections equipments,based on the analysis results. First of all,modeling and simulation of lightning characteristics by alternative transient program(ATP) are presented,in which the 161kV overhead line,CCS and underground cable will be considered in the model.In addition,different lightning currents,different lightning points and different system conditions will be considered for the lightning characteristics simulation.The different system conditions means that different improved strategies which include overhead line with or without line arresters,different tower foot resistances,different numbers of OGW,CCS with or without arresters and tower arms with or without capacitors.Analysis results show that line arresters and reducing tower foot ground resistances are more effective than others for protecting overhead line and underground cable of lightning point on OGW of CCS.While,if lightning point on phase conductors of CCS,to install capacitors between tower arms and reducing tower foot ground resistances are prefer for increasing the protection of underground cables.The study results are valuable for the study of CCS improvement devices in the future.

abstract: Prior work in literature has illustrated the benefits of using surge arrester as a way to improve the lighting performance of the substation and transmission line. Installing surge arresters would enhance the system reliability but it comes with an extra capital expenditure. This thesis provides simulation analysis to examine substation-specific applications of surge arrester as a way of determining the optimal, cost-effective placement of surge arresters. Four different surge arrester installation configurations are examined for the 500/230 kV Rudd substation which belongs to the utility, Salt River Project (SRP). The most efficient configuration is identified in this thesis. A new method “voltage-distance curve” is proposed in this work to evaluate different surge arrester installation configurations. Simulation results show that surge arresters only need to be equipped on certain location of the substation and can still ensure sufficient lightning protection. With lower tower footing resistance, the lightning performance of the transmission line can typically be improved. However, when surge arresters are installed in the system, the footing resistance may have either negative or positive effect on the lightning performance. Different situations for both effects are studied in this thesis. This thesis proposes a surge arrester installation strategy for the overhead transmission line lightning protection. In order to determine the most efficient surge arrester configuration of transmission line, the entire transmission line is divided into several line sections according to the footing resistance of its towers. A line section consists of the towers which have similar footing resistance. Two different designs are considered for transmission line lightning protection, they include: equip different number of surge arrester on selected phase of every tower, equip surge arresters on all phases of selected towers. By varying the number of the towers or the number of phases needs to be equipped with surge arresters, the threshold voltage for line insulator flashover is used to evaluate different surge arrester installation configurations. The way to determine the optimal surge arresters configuration for each line section is then introduced in this thesis.<br>Dissertation/Thesis<br>Masters Thesis Electrical Engineering 2018

碩士<br>國立高雄應用科技大學<br>電機工程系<br>96<br>In this thesis,the transient over-voltage phenomenon is simulated by Alterative Transient Program Electromagnetic Transient Program (ATP-EMTP) as a transmission line or tower is struck by a lightning. The models of tower, line and arrester are established, and different protection strategies are added to the simulation system, these strategies include reducing the foot resistance of a tower and installing line arrester,etc. Then the scheme is applied to some 161kV transmission line sections, and the results can be very important reference for other parts of Taipower system to improve stability and power quality.

碩士<br>國立中正大學<br>電機工程研究所<br>103<br>In this thesis, the electro magnetic transient program (ATP-EMTP) is used to simulate the transient behaviors of switching surge and lighting surge for offshore wind farm. The Graphical User Interface ATPDraw demonstrates the equipment transient model of the offshore farm. The electrical equipment includes wind generator, wind generator step-up transformer, submarine cable, underground cable, onshore distribution station, circuit breaker, and arrester. Proper system is selected according to the pertinent literature and data provided from the manufacturer for setting the equipment transient models to simulate the switching surge and lightning transient. The simulation is composed of cable system energization, circuit breaker disconnection, fault clearing, lightning surge. The potential transient voltage of all electrical equipment is assessed by the selected BSL of whether it exceeds the specification or not. Lastly, the arrester is assessed of whether or not it can bear the transient energy. The result of this simulation reveals that when increasing the voltage to the operation breaker, there is no obvious increase of the transient overvoltage. However,  if increasing voltage when the cable still have residual voltage, the significant increase of transient voltage can be noticed. This significant transient voltage, nevertheless, can be eliminated by the arrester. The lightning simulation indicates that when the wind power plant is struck, the grounding potential of the plant might be rising and influenced as well as the cable system and cause a certain degree of overvoltage.

Eskom (Electricity Supply Commission of South Africa) is the national electrical utility that provides the generation, transmission and distribution of electricity in South Africa. The majority of Eskom's electricity distribution is done with either 11 kV or 22kV electrical overhead networks. An unacceptable number of Eskom's pole mounted power transformers on these networks have been failing over the past six years in the Kwa-Zulu Natal region. The average transformer failure rate for the Distribution Eastern Region was calculated to be 2.4% per annum. International norms seem to indicate a transformer failure rate of between 0.5% and 1.0% per annum as acceptable. The estimated cost of these transformer failures was between R9 million and R13 million per annum for the Eastern Region. Eskom Distribution has seven regions and the total cost of these failures was considerable to the business. These transformer failures contributed an average of 5.3% per month of the Supply Loss Index (SLI) for the Eastern Region, with a maximum contribution of 14.5% per month of the SLI for the region. The SLI is an Eskom performance measure of the unavailability of supply of the networks. The Eskom plant performance database (NAPI) was statistically analysed in detail and a number of field investigations conducted at transformer installations that had failed in the past. Transformer earth electrode resistance measurements were taken in an attempt to identify the cause of these transformer failures. Local transformer manufacturers were consulted and a national transformer refurbishment company's database was analysed during the investigation as part of a holistic approach to the industry related dissertation. The main finding of the NAPI data analysis was that the majority of the transformers failed during lightning storm periods. Another similar Eskom investigation had a sample of failed transformers opened for internal inspection. Signs of lightning damage to either the primary side winding or the primary lead were found. The proposed failure hypothesis was that the transformers required additional lightning protection of the primary side to protect the transformer against lightning. It seemed that the current specification of the Eskom distribution class surge arresters was inadequate to offer sufficient lightning protection of the pole mounted transformers. Practical measures were implemented on existing Eskom 11 kV networks in the Glencoe area as part of an Eskom research project to reduce the high failure rates of transformers. Two experimental networks were established and one control network was used as a reference line. The project implementation was completed at the end of October 1999. The experimental project looked at applying additional primary side lightning protection of the transformers. The main emphasis of the lightning protection on the first network was the use of two distribution class arresters in parallel (double arrester configuration) for each transformer and an understrung conductor connected to the prior structure back from the transformer installation. The second network had the standard single arresters installed on the transformers. A 600mm wood path was placed in series with an earthed down conductor installed on each intermediate woodpole structure to ensure a basic insulation level of 300kV for the network. The control network also had single arresters installed and was a fully insulated network (no earthed down conductor on the woodpoles). Each network was carefully monitored in terms of equipment failures and the performance levels of each network was measured with installed voltage dip recorders near the individual network circuit breakers. The Eskom Lightning Position and Tracking System (LPATS) data was collected and analysed to quantify the lightning activity before the project implementation to that of after project implementation. For the period November 1999 to March 2002 not a single transformer or surge arrester had failed ,due to lightning on the double arrester and understrung conductor configuration experimental network. There were recorded transformer and surge arrester failures on the second experimental network and on the control network. It was found that the practical methods implemented on the networks did not have a negative impact on the performance levels of the networks. Laboratory work was conducted in the high voltage laboratory at the University of Natal, on various metal oxide varistor (MOV) blocks of opened up new and failed surge arresters. This was to determine the effect of MOV blocks in parallel under power frequency and current impulse conditions. In particular, to determine what the effect of parallel MOV blocks with different voltage-current (V-I) characteristics would have on the current sharing and energy absorption capabilities of the individual blocks. The work was performed to simulate the behaviour of two surge arresters in parallel as in the experimental project. The experimental project lines were modeled using the Alternative Transients Program (ATP) simulation package and various parametric studies performed in the single phase conductor simulations. Each network component (such as the line, transformer and surge arrester) and phenomena (such as the effect of corona, the transient earth electrode resistance and voltage flashover) were modeled. The effect of surge arresters in parallel and the use of an understrung conductor arrangement were quantified. A current sharing factor (k-factor) was introduced to quantify the sharing of currents through surge arresters in parallel with different V-I curves. The main finding from the impulse laboratory work was that current sharing between parallel MOV blocks became better at higher currents. This finding was supported by other research work findings, particularly in the field of nuclear fusion research with parallel arresters. The results of the ATP simulations showed that the experimental network with the parallel arresters and understrung conductor arrangement considerably reduced the energy absorbed by the individual arresters. The effect of the double arrester configuration was to reduce the energy absorbed by the individual arresters even with arresters with different V-I characteristics and different manufacturers. The understrung conductor arrangement was found to be the major contributor towards the reduction of the energy absorbed by the arresters. The equivalent circuit of a MOV block for transient studies was proposed and then simulated in ATP. The simulated results were compared to the measured waveforms obtained from the impulse laboratory work. A good agreement between the simulated and measured waveforms was obtained. For existing Eskom networks with high arrester and transformer failure rates, the double arrester (distribution class) configuration would be the most time and cost effective solution. The alternative of using a single station class arrester is not proposed due to the costs involved and the availability of stock. The understrung conductor arrangement did significantly reduce the energy absorbed by the arresters but due to high labour costs and time requirements this would not be recommended for existing networks. It is suggested that Eskom investigate this practical method for new lines to be built in high lightning areas. Even with arresters from different manufacturers, the use of the double arrester configuration would decrease the energy absorbed and hence reduce the risk of failure of the individual arresters protecting the transformer. This means that Eskom field staff can use different manufacturer arresters in parallel. This would be especially for times when replacing failed arresters or a faulty transformer under breakdown conditions and electrical supply has to be restored to the customer as soon as possible. It was proposed to perform arrester matching by ensuring that the both arresters were from the same manufacturer.<br>Thesis (M.Sc.Eng)-University of Natal, Durban, 2002.

碩士<br>國立臺北科技大學<br>電機工程系優質電力產業研發專班<br>99<br>In this thesis, the lightning surge characteristics of primary substation with voltage level 161/69kV are studied. The work mainly aims to analyze lightning current and voltage on the primary and secondary side (161kV side and 69kV side) and grounding system with respect to various lightning points on 69kV and 161kV ground wires and buses. First of all, modeling of primary substation based on alternative transient program (ATP) is presented. Then, the lightning characteristics are analyzed by ATP simulations for lightning currents and voltages on the different locations of system and on grounding points of power transformers. For the simulation, different lightning points aforementioned, lightning arresters of power transformers, load levels and the grounding type of 161kV winding neutral points of main transformers are all taken into account. Finally, based on the ATP analysis results, the risks on the equipments such as buses, switches, breakers, power transformers and arresters in the substations due to lightning are evaluated. The study results have shown that lightning damages are very severe at secondary side of substation under heavy lightning even though it has lightning arresters, hence further lightning protection is required. The data presented in this thesis is valuable for further study on enhancing lightning protection for primary substation.

碩士<br>國立臺北科技大學<br>電機工程系研究所<br>102<br>Nowadays, most of home-use electrical appliances are electronic products which usually have the advantages of multifunction and small size, but their capability to withstand the impacts of lightning and switching surges is usually low. Consequently,damage cases in the low voltage customers due to lightning and switching surges from feeder are frequent. In the thesis, the characteristics of lightning and switching surges of secondary substation and feeders are analyzed, and the surge voltages from feeder to low voltage customers are surveyed and the affections are evaluated. First of all, Modeling based on the alternative transient program (ATP) of electromagnetic transient program (EMTP) for secondary substation and the downstream feeders are presented. Then, the voltages at low voltage customer during various types of lightning and switching at substation and feeder are analyzed based on ATP simulations. For lightning surge simulation, different lightning points with different lightning strengths are considered. Also, for the switching surge simulation, the switch close and open operations at primary and secondary sides of substation and at the feeder under synchronous and non-synchronous operation are considered. Finally, the affections of lightning and switching surges on the low voltage customer will be assessed based on the comparisons between the simulation results and the surge voltage tolerances of low voltage equipments specified by IEC standard. The assessment results show that malfunction may be occurred on the sensitive equipments in low voltage customers due to surge voltage from the switch non-synchronous close operation, while various equipments will suffer form damages due to lightning on the nearby feeder. Thus, more attention should be given to the surge protection issues for low voltage customer, and the study can provide related information and numerical date.

碩士<br>華梵大學<br>機電工程學系博碩專班<br>99<br>The quality of electric power of power supply system is important for the project planning, design and analysis of Metro Rapid Transit. The quality of electric power is unstable because of an abnormal transient overvoltage. Lightning flashovers is an effective device to solve this problem. In this paper, the system model is established to simulate using electromagnetic transient program（ATP/EMTP） was used to simulate the lightning surge for transmission line system of the substation of Taipei Metro Rapid Transit. The lightning over-voltages of device endpoints were obtained for six conditions. The results were analyzed according to the obtained data. Finally, the simulation results show that the length of underground cables, the position and quality of arresters installation will change the value of the device endpoint voltage. In this study, the number five is the optimal design. Keywords: Electromagnetic, Bulk Supply Substation, Lightning Surge

Το θέμα της παρούσας διπλωματικής εργασίας είναι η αντικεραυνική προστασία όσον αφορά τα κυκλώματα γραμμής των ηλεκτρικών σιδηροδρομικών συστημάτων. Προτού όμως αναφερθούν τρόποι και συσκευές προστασίας ή δoθούν κάποια παραδείγματα εφαρμογών στις σιδηροδρομικές γραμμές κάποιων χωρών, πρέπει να γίνει μια εισαγωγική αναφορά γύρω από τον πυρήνα αυτής της εργασίας: τον κεραυνό. Έτσι, στο 1 κεφάλαιο γίνεται περιγραφή κάποιων εισαγωγικών εννοιών σχετικά με τον κεραυνό. Ξεκινώντας από τη φόρτιση των σύννεφων και στο πως αυτή γίνεται, καταλήγουμε στα διάφορα είδη κεραυνών. Ακολουθεί η εξομοίωση στο εργαστήριο με ορισμένα μεγάλα διάκενα εκκένωσης για την εξαγωγή κάποιων συμπερασμάτων της εκκένωσης του κεραυνού. Στη συνέχεια αναλύεται ο μηχανισμός των ατμοσφαιρικών εκκενώσεων μέσα από τρεις φάσεις: έναρξη οχετού (οχετός προεκκένωσης), φάση του οχετού επιστροφής και ο συνδετικός οχετός. Τέλος γίνεται ανάλυση του ρεύματος κεραυνού και των παραμέτρων του, ενώ δίνονται και κάποιες σχέσεις για τη συχνότητα εμφάνισης των κεραυνών. Στο 2 κεφάλαιο γίνεται ανάλυση των συνδέσεων ασφαλειών (fuse link), μιας εφαρμογής που χρησιμοποιείται για την αντικεραυνική προστασία των κυκλωμάτων γραμμής. Αρχικά γίνεται περιγραφή των ειδικών παραμέτρων του συστήματος της συγκεκριμένης εφαρμογής που χρησιμοποιείται στα κινητήρια συστήματα. Στη συνέχεια δίνεται μια σύντομη επισκόπηση του πλήρους σχεδίου. Ακολούθως περιγράφονται οι προσομοιώσεις υπολογιστών, στις οποίες καθορίστηκε η κατανομή του ρεύματος κεραυνού σ’ ένα κινητήριο σύστημα. Στην παράγραφο 2.1.3.δ, εξηγείται η εργαστηριακή δοκιμή της συσκευής περιορισμού της τάσης, ειδικά της συμπεριφοράς (με τη χαρακτηριστική) του ρεύματος κεραυνού. Επιπλέον, γίνεται περιγραφή της πρακτικής εφαρμογής των ασφαλειών που είναι ανθεκτικές σε κεραυνούς, παρουσιάζοντας μια πρακτική δοκιμή. Δίνονται επίσης ορισμένες τυποποιημένες εφαρμογές. Τέλος, εξηγείται το σχέδιο των συνδέσεων των ασφαλειών που είναι ανθεκτικές σε κεραυνούς. Στο 3 κεφάλαιο αναλύονται τα αλεξικέραυνα μεταλλικών οξειδίων (ΜΟ). Τα συστήματα ισχύος των ηλεκτρικών σιδηρόδρομων μπορούν να προστατευτούν έναντι υπερτάσεων με τη χρήση αυτών των συσκευών. Στο κεφάλαιο περιγράφεται η αρχή λειτουργίας των αλεξικέραυνων ΜΟ, η οποία βασίζεται στη μη γραμμική χαρακτηριστική τάσης - ρεύματος συγκεκριμένων κεραμικών στοιχείων, αποκαλούμενα MO varistors. Ακολουθούν οι τρεις τύποι αλεξικέραυνων υπέρτασης ΜΟ για τα ηλεκτρικά συστήματα σιδηρόδρομων: με περίβλημα πορσελάνης, με συνθετικό πολυμερές περίβλημα και με άμεσα διαμορφωμένο πολυμερές περίβλημα. Τέλος, γίνεται λόγος για τη χρήση των αλεξικέραυνων ΜΟ στα DC κινητήρια συστήματα σύμφωνα με την Ένωση των Γερμανικών Επιχειρήσεων Μεταφορών (VDV), σε διάφορες σιδηροδρομικές εφαρμογές. Στο 4 κεφάλαιο γίνεται ανάλυση ενός πλάνου αντικεραυνικής προστασίας για τα συνεχούς ρεύματος (DC) σιδηροδρομικά συστήματα. Αρχικά, γίνεται μια αναφορά στις τάσεις του συστήματος και τις διάφορες μορφές υπερτάσεων, των άμεσων και έμμεσων πληγμάτων κεραυνού. Στη συνέχεια περιγράφονται κάποιες συσκευές προστασίας (καθώς και τα χαρακτηριστικά αυτών), όπως είναι τα αλεξικέραυνα υπερτάσεων ΜΟ (τύπου Α1 και Α2), οι περιοριστές χαμηλής τάσης (LVL), ενώ εισάγεται ένας προσφάτως ανεπτυγμένος υβριδικός περιοριστής τάσης (HVL) ο οποίος συνδυάζει την προστασία από υπερτάσεις και την προστασία έναντι των επικίνδυνων τάσεων επαφής. Τέλος, γίνεται μία περιγραφή διαφόρων μέτρων προστασίας στις γραμμές μεταφοράς, στους υποσταθμούς καθώς επίσης και στα οχήματα κίνησης, ενώ δίνονται και κάποια αποτελέσματα δοκιμών με χρήση LVLs. Το 5 κεφάλαιο αναλύει την πρόβλεψη των σφοδρών εκκενώσεων κεραυνού που μπορούν να προκαλέσουν μια σοβαρή διαταραχή στη λειτουργία της αμαξοστοιχίας, με τη χρησιμοποίηση υπολογιστών βασισμένων στο Ιαπωνικό Δίκτυο Ανίχνευσης Κεραυνού (Japanese Lightning Detection Network - JLDN), προκειμένου να υποστηρίξουν πομπούς για να κάνουν μια αποτελεσματική λήψη απόφασης σχετικά με τη ρύθμιση των μηχανικών συντήρησης, τις γεννήτριες ηλεκτρικής ενέργειας έκτακτης ανάγκης και τις επιπλέον ηλεκτρικές συσκευές για γρήγορη ανάκτηση. Ένα πραγματικού χρόνου σύστημα υποστήριξης λήψης απόφασης έχει αναπτυχθεί. Τέλος, γίνεται αναφορά στις δύο κύριες τεχνικές εκτίμησης, που εχουν αποτιμηθεί με την εφαρμογή τους σε πραγματικά δεδομένα κεραυνού, οι οποίες χρησιμοποιούνται για την εκτίμηση της τροχιάς της περιοχής που κινείται επικίνδυνα και της διάρκειας της δραστηριότητας του κεραυνού. Στο 6 κεφάλαιο περιγράφονται οι λεπτομέρειες του αισθητήρα υπερτάσεων/υπερρευμάτων κεραυνού για το σιδηρόδρομο. Πρόκειται για ένα νέο σύστημα ελέγχου του σιδηροδρομικού σήματος, το οποίο ελέγχει σιδηροδρομικά σήματα, διακόπτες, κυκλώματα γραμμής βασισμένα στο πρωτόκολλο IP. Σε αυτό το σύστημα, πολλές ηλεκτρονικές συσκευές εγκαθίστανται κατά μήκος του σκληρού περιβάλλοντος του σιδηροδρόμου. Επομένως, αυτές οι ηλεκτρονικές συσκευές πρέπει να έχουν αντοχή προς το περιβάλλον για υπέρταση/υπέρρευμα κεραυνού, για θερμοκρασία, για δόνηση, για βροχή και για ηλεκτρομαγνητικό θόρυβο. Σαν αντίμετρο για την υπέρταση κεραυνού, χρησιμοποιούμε την προστατευτική συσκευή (το αλεξικέραυνο). Η υποβάθμιση της προστατευτικής συσκευής μπορεί να προκαλέσει την καταστροφή των ηλεκτρικών συσκευών. Έτσι αναπτύχθηκε ο αισθητήρας υπερτάσεων/υπερρευμάτων για την ανίχνευση της υποβάθμισης της προστατευτικής συσκευής. Στο 7 κεφάλαιο περιγράφονται οι μετρήσεις των υπερτάσεων και των μεταβατικών ρευμάτων κεραυνού που εισέρχονται σε μια εγκατάσταση σιδηροδρόμου κατά τη διάρκεια του καλοκαιριού του 2003 στο Tierp της Σουηδίας. Οι μετρήσεις υπερτάσεων έγιναν σε μια τεχνητή βάση που παρέχει έναν αδιάκοπο εφοσδιασμό για τα τηλεπικοινωνιακά συστήματα και τα συστήματα σηματοδότησης. Επίσης παρουσιάζονται και συζητούνται τα παραδείγματα των κυματομορφών των μεταβατικών ρευμάτων. Τέλος, το κεντρικό μήνυμα που περνάνε τα δύο τελευταία κεφάλαια, 8 και 9, είναι ότι πρέπει να ενισχυθούν τα αποτελεσματικά και οικονομικά αντίμετρα για την παρεμπόδιση των ζημιών κεραυνού στο σιδηροδρομικό σύστημα σηματοδότησης. Στο 8 κεφάλαιο μετρήθηκε η κατανομή του δυναμικού του κρασπέδου εδάφους όταν προκλήθηκε μια αύξηση δυναμικού της ράγας με την έγχυση ενός υπερρεύματος κεραυνού σε μια ράγα. Επιπλέον, διοχετεύθηκε ένα υπέρρευμα κεραυνού μέσα στη ράγα ή στο κράσπεδο εδάφους για να αυξηθεί το δυναμικό τους, προκειμένου να μετρηθούν οι υπερτάσεις κεραυνού σε μια ισόπεδη διάβαση έτσι ώστε να μπορέσουν να λάβουν βασικά δεδομένα για το σχεδιασμό της μόνωσης. Τέλος, αποδεικνύεται ότι ένα αποτελεσματικό αντίμετρο είναι να γειώσουμε τις συσκευές αντικεραυνικής προστασίας που συνδέονται με τους ηλεκτρονικούς ανιχνευτές τραίνων σε μια ισόπεδη διάβαση προκειμένου να κατασταλούν οι υπερτάσεις κεραυνού στην ισόπεδη διάβαση. Στο 9 κεφάλαιο μετρήθηκαν οι υπερτάσεις κεραυνού που προκλήθηκαν από την εισβολή των κυμάτων κεραυνού στο σιδηροδρομικό σύστημα ισόπεδης διάβασης, στην περίπτωση ενός πραγματικού πλήγματος κεραυνού, ώστε να μπορούν να κατανοηθούν οι υπερτάσεις αυτές ποσοτικά. Έτσι θα μπορούσαμε να διευκρινίσουμε τη συχνότητα εμφάνισης των υπερτάσεων κεραυνού στο σύστημα της ισόπεδης διάβασης στην κατάσταση του πραγματικού πλήγματος κεραυνού.<br>The subject of this project is the lightning protection for track circuits of electrical railway systems. But before being reported ways and protection devices or given some examples of applications for rail lines in some countries, should be an introductory reference around the core of this work: the lightning. Thus, chapter 1 contains a description of some import concepts about lightning. Starting from the charge of the clouds and how it is, we arrive at the different types of lightning. Here the simulation in the laboratory with some major gaps evacuation for some of the conclusions of the lightning discharges. Then analyze the mechanism of atmospheric discharges through three phases: entry drain, phase of the return drain and the connecting drain. Finally an analysis of lightning current and his parameters became, while some relationships are given about occurrence frequency of lightning. In the 2nd chapter an analysis of fuse link, an application used for lightning protection on track circuits, is described. First the special system parameters for this specific application, used in traction systems will be described. Then a brief overview of the complete project is given. Following computer simulations will be described, in which the lightning current distribution in a traction system was determined. In the paragraph 2.1.3.δ, the laboratory testing of the voltage limiting device, especially its lightning current behavior is explained. Moreover the practical application of the lightning resistant fuse link both in a field test and following in stand applications is described. Finally the design of this lightning resistant fuse link is explained. In the 3rd chapter Metal-Oxide (MO) surge arresters are described. Power systems of electric railways may be protected against overvoltages by using them. The operating principle of an MO surge arrester is essentially based on the strongly non-linear current-voltage characteristic of specific ceramic elements, so-called MO varistors, is described. Following the three types of (MO) surge arresters for electrical railway systems: with a Porcelain Housing, with a Polymer Composite Housing and with a Directly Moulded Polymer Housing. Finally, talk about use of MO surge arresters in DC traction systems as per Association of German Transport Undertakings (VDV), in various railway applications. In the 4th chapter an overvoltage protection concept for DC railway systems, is analyzed. First, there is a reference about system voltages and on various forms of overvoltages, of direct and indirect lightning strokes. Below, some protection devices (and their characteristics), such as the (MO) lightning surge arresters (A1 and A2 type), the Low Voltage Limiters (LVLs), while a newly developed Hybrid Voltage Limiter (HVL), which combines overvoltage protection and the protection against dangerous touch voltages, is introduced, are quoted. Finally, a description about some protection measures on overhead lines, for substations, and also on traction vehicles, while some test results using LVLs, are given. The 5th chapter investigates the prediction of severe lightning discharges that might cause a serious disturbance in train operation, by using computers based on the Japanese Lightning Detection Network (JLDN), in order to support dispatchers to make an effective decision about arranging maintenance engineers, emergency electrical power generators and extra electrical devices for quick recovery. A real-time decision support system has been developed. Two principal estimation techniques, which are used for estimating the trajectory of moving hazardous area and the lifetime of the lightning activity, have been evaluated by applying them to the real lightning data. In the 6th chapter details of the lightning surge sensor for railway are described. This is a new railway signal control system, which controls railway signals, switches, track circuits based on IP protocol. In this system, much electronic devices are installed along harsh railway environment. Therefore, these electronic devices must have environment resistance for lightning surge, temperature, vibration, waterproof, and electromagnetic noise. As a countermeasure for the lightning surge, we utilize the protective device (cable arrester). The degradation of the protective device may cause the damage of the electric devices. So we develop a lightning surge sensor to detect the degradation of a protective device. In the 7th chapter the measurements of lightning transients entering a railway facility during the summer of 2003, in Tierp, Sweden, are described. The measurements of the transients were made in a technical house that supplies an uninterrupted supply for the telecommunication systems and the signal systems. Examples of transient waveforms are presented and discussed. Finally, the major idea of chapters 8 and 9 is that it’s required to build up effective and economical countermeasures for preventing lightning damages on the railway signalling system. In the 8th chapter the wayside ground potential distribution when a rail potential rise was caused by injecting a lightning surge current into a rail, are measured. Moreover, a lightning surge current into the rail or wayside ground is injected, to raise their potential, in order to measure the lightning overvoltages on a level crossing so that we can obtain basic data for insulation design. It is shown in the paper that an effective countermeasure is to earth lightning protective devices attached to electronic train detectors for a level crossing in order to suppress the lightning overvoltages on the level crossing. In the 9th chapter the lightning overvoltages caused by invading lightning surges into the railway level crossing system in the event of real lightning stroke so that we can grasp the lightning overvoltages quantitatively, are measured. So, we could clarify the occurrence frequency of lightning overvoltages on the level crossing system in the condition of the real lightning stroke.

Σκοπός της εργασίας είναι η μελέτη της συμπεριφοράς απαγωγέων υπέρτασης στις γραμμές μεταφοράς υψηλής τάσης όταν αυτές καταπονούνται από κεραυνικά πλήγματα. Γίνεται μοντελοποίηση πραγματικών πυλώνων και γραμμών του Ελληνικού συστήματος μεταφοράς, καθώς και αλεξικέραυνων, προσομοίωσή τους στο πρόγραμμα ATP/EMTP και στη συνέχεια μελέτη των υπερτάσεων που εμφανίζονται κατά τη διάρκεια κεραυνικών πληγμάτων πάνω στους αγωγούς προστασίας.<br>The purpose of this thesis is the study of the behavior of surge arresters on high voltage transmission lines when they are strained by lightning strikes. Steel towers and transmission lines used in the Greek Transmission System and also surge arresters are simulated with ATP/EMTP and the overvoltages that occur during lightning strikes on the shielding wires are studied.

Computer simulations with programs such as the EMTP are widely accepted for lightning transient studies, to design the system in such a way that equipment failures and transmission line outages are prevented. In these studies, an accurate representation of the transmission lines and towers is required. Two new and improved time-domain models for the representation of these components are presented in this thesis. They are the frequency- dependent and the exponential transmission line models. The former is based on synthesizing the line functions directly in phase co-ordinates, and is used to represent multiphase transmission lines, while the latter is a single-phase model, which also synthesizes the line functions, to be used for tower representations. These models are valid for the required frequency range of 1 Hz to 1 MHz. They can be used for lightning studies as well as for many other types of transient studies. Extensive time-domain simulations have been performed to compare the results with those produced by existing line models. The results indicate that the new models are more accurate than some of the existing models, and numerically stable. Simulations of typical lightning surges have also been performed to compare the solutions produced by the developed models with actual measurements. With these new models, simulations match field recorded transient waveforms very well. In addition, a simple, fast and accurate method based on the Newton-Raphson iteration technique is introduced for finding transmission line modal parameters. It overcomes the eigenvector and eigenvalue switching problems experienced by most other methods. With a proper constraint equation for scaling the eigenvectors, this proposed method produces modal parameters which can reasonably be fitted with rational functions of minimum-phase type. With this, the modal transmission line modelling can be improved. The routine is very stable and can be used to diagonalize the Y Z product for uncommon lines with strong asymmetry. It has also been used to obtain the phase-domain parameters for the new frequency- dependent line model.

Το θέμα της παρούσας διπλωματικής εργασίας είναι η μελέτη της συμπεριφοράς απαγωγέων υπερτάσεων (SPD), όταν αυτοί αποτελούν μέρος του εσωτερικού συστήματος αντικεραυνικής προστασίας για μια οικιακή εγκατάσταση. Αρχικά γίνεται μια αναφορά στα αίτια δημιουργίας κρουστικών υπερτάσεων στο δίκτυο διανομής, ενώ στη συνέχεια δίνεται έμφαση στις υπερτάσεις που προκαλούνται από άμεσα ή έμμεσα κεραυνικά πλήγματα στο σύστημα. Στα πλαίσια της μελέτης δημιουργήθηκε ένα μοντέλο προσομοίωσης που αναπαριστά ένα δίκτυο χαμηλής τάσης TN-C-S με δύο πανομοιότυπους οικιακούς καταναλωτές, όσον αφορά τη δομή της εσωτερικής ηλεκτρικής εγκατάστασής τους παρουσία ή μη διατάξεων αντικεραυνικής προστασίας. Σκοπός της προκειμένης μελέτης είναι να δειχθεί η βέλτιστη συνδεσμολογία των διατάξεων προστασίας μέσα σε εσωτερικές ηλεκτρικές εγκαταστάσεις έτσι ώστε να αποτρέπεται η ανάπτυξη επικίνδυνων τάσεων και ρευμάτων για τον άνθρωπο και τον εξοπλισμό της οικιακής εγκατάστασης.<br>The subject of this project is a study upon the dynamic performance of surge arresters as a part of the internal lightning protection system for a residential electrical installation. At first, a reference about the actions or the natural phenomena that cause surge overvoltages in low voltage systems is given in detail and is followed by an essential theoretical approach on the lighning phenomenon. Both the causes, the consequences and the conditions in which a lightning occurs are being analysed. Furthermore, the characteristics and the qualifications a Lightning Protection System needs to comply with, are given, according to the Greek Standard ΕΛΟΤ-1197 and the European Standards IEC 62305-2, IEC 61643-12. Along with writing this essay, a simulation model using Simulink-Matlab was produced. The model represents a LV TN-C-S system that distributes power to two households with identical internal electrical installation. The aim of the present study is to indicate the optimal connection of the surge protective devices (SPDs) in the domestic electrical installation in order to prevent the appearance of potentially dangerous overvoltages to the humans or to the household equipment.

Σκοπός της παρούσας εργασίας είναι η μελέτη της συμπεριφοράς των καθοδικών αλεξικέραυνων στις γραμμές μεταφοράς ηλεκτρικής ενέργειας όταν καταπονούνται από κεραυνούς. Είναι γνωστό πως οι πειραματικές μετρήσεις που μπορούν να γίνουν για την διάγνωση της συμπεριφοράς των αλεξικέραυνων είναι επίπονες, λόγω της ίδιας της φύσης του κεραυνού, και βεβαίως δαπανηρές. Οπότε γεννάται η ανάγκη δημιουργίας κάποιων μοντέλων που προσεγγίζουν όσο πιο ρεαλιστικά γίνεται τις πραγματικές συνθήκες καταπόνησης των αλεξικέραυνων.<br>The purpose of this paper is to study the behavior of metal oxide surge arresters on power lines when they are strained by lightning. It is known that experimental measurements, which can be performed to diagnose the behavior of surge arresters are difficult, because of the very nature of lightning, and certainly costly. Thus rises the need for some models, which represent as much as possible realistically the real stress condition of surge arresters.

碩士<br>國立臺北科技大學<br>電機工程系研究所<br>100<br>The extra-high-voltage (EHV) substation(E/S) is erected continuously in each science park by Taiwan Power Company (TPC) for supplying power to substations and customers in the science park and nearby area. The lightning surges and switching surges of E/S are easily transferred to the downstream customers which are directly supplied by E/S. Thus, the impacts due to transferred surges will be more serious than that of other customers. The impacts will lead to damages on the insulation of distribution system and equipment and even threaten the safety of personnel. In thesis, the issue of surge damages of, the E/S in the science park and the E/S in the outside area of science Park (outside E/S) are studied. For both cases of customers directly supplied by E/S in the science park and indirectly supplied by outside E/S through distribution substation, the surge voltage and current are analyzed and compared, which include the analysis of lighting surges and switching surges transferred to the customers. Firstly, the circuit model of the system is constructed by the alternative transient program(ATP) of electromagnetic transient program(EMTP). Then, the surges at different locations due to lightning and switch operations are simulated and the characteristics of surge voltages and currents at customers are analyzed by ATP simulation. Based on the simulation results, the fault currents injected into grounding system at fault points are obtained. Finally, a software package for grounding system analysis, namely current distribution electromagnetic ground and soil structure analysis (CDEGS), is used to analyze the electromagnetic characteristics of ground grids of customer substations with respect to transient and steady states, which include the distribution of ground potential rise (GPR), potential on the ground surface, touch voltage, step voltage, conductor current and electromagnetic field (EMF) on the ground surface. According to the above analysis results, the risks of various surges are evaluated including the affections of lightning surges and switching surges on personnel, equipment and system.