Overhead transmission lines are periodically inspected using both on-ground and helicopter-aided visual inspection. Factors including sun glare, cloud cover, close proximity to power lines and the rapidly changing visual circumstances make airborne inspection of power lines a particularly hazardous task. In this research, a finite element model is developed that can be used to create the theoretical dispersion curves of an overhead transmission line. The complex geometry of the overhead transmission line is the primary reason for absence of a theoretical solution to get the analytical dispersion curves. The numerical results are then verified with experimental tests using a non-contact and broadband laser detection technique. The methodology developed in this study can be further extended to a continuous monitoring system and be applied to other cable monitoring applications, such as bridge cable monitoring, which would otherwise put human inspectors at risk.

[pt] Vários aspectos de um sistema elétrico de potência devem ser avaliados em detalhe antes de sua construção e operação. A escolha dos níveis de isolamento utilizadas é editada pelas condições em regime permanente e de sobre tensões que poderão ocorrer no sistema. Naturalmente, as linhas de transmissão veículos de transporte de energia estão intimamente ligadas a este problema. A sua perfeita operação determina níveis de atendimento apropriados aos consumidores. Portanto, é de extrema importância que se conheça o comportamento do isolamento do sistema de transmissão. O presente trabalho tem por objetivo fornecer ao engenheiro condições d analisar a performance de uma linha de transmissão quando submetida a surtos atmosféricos e a surtos de manobra através de dois programas desenvolvidos para o computador digital HP- 2100. / [en] Many aspects of an electric utility power system design must be evaluated in detail prior to construction and operation. The choice of insulation requirements on eletric utility system equipment is dictated both by the steady state conditions as well as by overvoltages which can occur on the system. Transmission lines, which are the way to carry energy, are certainly involved in this problem. Therefore it is very important to know their insulation behavior. The purpose of this work is to give the engineer conditions to analyze transmission lines behavior, by way of two digital programs, one concerning lightining strokes and the other switching surges.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της συμπεριφοράς εναέριων γραμμών και υπόγειων καλωδίων μεταφοράς υψηλής τάσης έναντι κεραυνών. Για την εξυπηρέτηση του σκοπού αυτού, γίνεται προσομοίωση ενός υβριδικού δικτύου, αποτελούμενου τόσο από εναέριες γραμμές μεταφοράς όσο και από υπόγεια καλώδια, και μελέτη των μεταβατικών υπερτάσεων που εμφανίζονται σε αυτό λόγω κεραυνικών πληγμάτων σε έναν από τους αγωγούς προστασίας του τερματικού πυλώνα, όπου πραγματοποιείται η διασύνδεση εναέριας γραμμής-υπόγειου καλωδίου. Στο πρώτο κεφάλαιο παρατίθενται κάποια θεωρητικά στοιχεία σχετικά με τις ατμοσφαιρικές υπερτάσεις. Αναλύονται τα είδη των κεραυνών, οι βασικές παράμετροι και τα κύρια χαρακτηριστικά τους. Επιπλέον, περιγράφονται οι επιπτώσεις από κεραυνικά πλήγματα και ο τρόπος εύρεσης της συχνότητας με την οποία συμβαίνουν κεραυνοί ανά περιοχή. Στο δεύτερο κεφάλαιο γίνεται μία εισαγωγή στα Συστήματα Ηλεκτρικής Ενέργειας και αναπτύσσονται τα βασικά στοιχεία των εναέριων γραμμών και των υπόγειων καλωδίων μεταφοράς ηλεκτρικής ενέργειας. Επίσης, πραγματοποιείται μία σύγκριση αυτών των δύο τρόπων μεταφοράς ηλεκτρικής ενέργειας, παρουσιάζοντας τα θετικά και αρνητικά στοιχεία καθενός από αυτούς. Στο τρίτο κεφάλαιο εξετάζονται τα είδη σφαλμάτων και τα αίτια δημιουργίας αυτών στις γραμμές μεταφοράς ηλεκτρικής ενέργειας. Επιπλέον, δίνονται κάποια βασικά χαρακτηριστικά για την κυματομορφή του κεραυνικού ρεύματος. Στο τέταρτο κεφάλαιο αναλύεται η μόνωση και η προστασία τόσο των εναέριων γραμμών όσο και των υπόγειων καλωδίων έναντι κεραυνικών πληγμάτων. Εξετάζονται ακόμα οι μηχανισμοί που εγείρουν υπερτάσεις στη γραμμή μεταφοράς. Έπειτα, για τον καθορισμό της θέσης των αγωγών προστασίας της γραμμής, περιγράφονται οι μέθοδοι της μέγιστης γωνίας αλλά και η ηλεκτρογεωμετρική μέθοδος. Στο πέμπτο κεφάλαιο αναπτύσσονται τα επιμέρους στοιχεία του υπολογιστικού προγράμματος ATP-EMTP, το οποίο θα αποτελέσει το μέσο εξομοίωσης για την παρούσα εργασία. Αναφέρονται τα σημεία υπεροχής και η καταλληλότητά του για τέτοιου είδους αναλύσεις και παρουσιάζονται τα επιμέρους υποπρογράμματα από τα οποία αποτελείται. Ιδιαίτερη έμφαση δίνεται στο ATPDraw, το οποίο είναι το κύριο όργανο της εξομοίωσης. Στο έκτο κεφάλαιο περιγράφεται αναλυτικά το υβριδικό δίκτυο μεταφοράς υψηλής τάσης που χρησιμοποιείται στην εξομοίωση και αναλύονται τα στοιχεία που το αποτελούν, δηλαδή οι εναέριες γραμμές και τα υπόγεια καλώδια. Επιπλέον, παρουσιάζονται τα αποτελέσματα των εξομοιώσεων και οι γραφικές παραστάσεις των υπερτάσεων στα διάφορα σημεία του κυκλώματος, εξαιτίας κεραυνικών πληγμάτων, των οποίων το εύρος αυξάνει σε κάθε εξομοίωση. Στη συνέχεια ελέγχεται η επικινδυνότητα των υπερτάσεων που εγείρονται για τα διάφορα μεγέθη κεραυνικού ρεύματος και εάν ο εξοπλισμός σε διαφορετικά σημεία του δικτύου αντέχει τις υπερτάσεις αυτές ή καταστρέφεται. Από τα αποτελέσματα προκύπτει ότι επικίνδυνες υπερτάσεις παρατηρούνται σε τμήματα της εναέριας γραμμής μεταφοράς πλησίον του σημείου κεραυνικού πλήγματος. Αντίθετα, το υπόγειο τμήμα του δικτύου αποδεικνύεται πιο ανθεκτικό, καθώς δεν εγείρονται επικίνδυνες υπερτάσεις ακόμα και για πολύ υψηλό κεραυνικό ρεύμα. / The purpose of this diploma thesis is the study of the behavior of overhead transmission lines and underground transmission cables against lightning. In favor of this purpose, a simulation of a hybrid transmission network takes place, which is composed of both overhead lines and underground cables, in order to examine transient overvoltages. These overvoltages are raised due to a lightning that strikes the shield wire of the terminal tower, where the interconnection of overhead line to underground cable takes place. Chapter one presents the basic theory concerning atmospheric discharges. It describes the different types of lightning strikes, their parameters and basic characteristics. Furthermore, it analyzes the consequences of lightning and how to find the frequency that a lightning takes place in an area. At the second chapter there is an introduction in the systems of electric energy and a presentation of the basic characteristics of overhead lines and underground cables. In addition, there is a comparison between those two means of electricity transmission. Chapter three examines the types of errors and the causes of them at the electricity transmission lines. Moreover, it gives the basic parameters of the lightning current waveform. Chapter four analyzes the insulation and protection of both overhead lines and underground cables against lightning. It also examines the mechanisms that raise overvoltages at the transmission lines. Afterwards, there are described two methods on how to define the place of shield wires at a transmission line. Chapter five describes the ATP-EMTP simulation program, which is a specific software to simulate power systems. Its superiority for research like the present one is high lined and special emphasis is given to ATPDraw which is the main tool for the simulation. At chapter six there is a detailed analysis of the hybrid network used in this simulation and of its basic components, which are the overhead lines and the underground cables. Furthermore, there is a presentation of the results of the simulation and the graphs of the overvoltages at different spots of the network, due to lightning strikes. Afterwards, there is an evaluation of the risk of overvoltages that are raised for different lightning current sizes and if the equipment at different spots of the network sustains these overvoltages or it is destroyed. From the results, it is concluded that dangerous overvoltages are raised at sections of the overhead line near the lightning strike. On the contrary, the underground section of the network appears to be more resistant, as there are not raised dangerous overvoltages, even when the lightning current was too high.

[pt] A transmissão de energia elétrica através de linhas de transmissão aéreas encontra um grau de dificuldade muito grande na constituição de novas faixas de passagem e licenciamento de obras, devido, principalmente, à questão ambiental. Por outro lado, a crescente demanda de energia do sistema elétrico leva o sistema de transmissão a uma progressiva elevação do carregamento de seus componentes, incluindo linhas de transmissão. Desta forma, é fundamental o desenvolvimento de técnicas que permitam aumentar a capacidade de transporte de energia a baixo custo com as instalações existentes e a recapacitação de linhas existentes aparece como uma alternativa a ser analisada nos estudos da expansão do sistema de transmissão. O objetivo deste trabalho é apresentar alternativas de técnicas de recapacitação de linha de transmissão, segundo a ótica de dimensionamento elétrico e da determinação das distâncias mínimas de coordenação de isolamento necessárias na torre, visando maximizar a energia transportada por área ocupada pela faixa da linha de transmissão e com isso, reduzir a necessidade de negociação de novas faixas de passagem com os órgãos de licenciamento e a comunidade, diminuindo o impacto sobre o ambiente e dando maior agilidade na ampliação da capacidade de transporte da malha existente. Busca-se, além disso, identificar, para diferentes níveis de tensão, as possíveis alternativas de recapacitação aplicáveis à linha de transmissão. / [en] The construction of new overhead transmission lines is, nowadays, a difficult activity to achieve, as new right-of- ways are not easily being permitted, due to environmental restrictions. On the other hand, the increase of electrical energy demand leads the transmission system to over load its components, including transmission lines. Therefore, it is extremely important to develop techniques in order to raise energy transmission capacity in low costs using the existent components. Capability increase in existent transmission lines is an alternative to be analyzed in transmission system expansion studies. This dissertation presents techniques to increase capability in existent transmission lines, according to electrical dimensioning and minimum distances needed in towers evaluated in insulation coordination studies. The aim is to maximize the transport capacity of an existent transmission line, reducing the need of negotiating new right-of-ways permit. This study also identifies, for different voltage levels, te available alternatives of a technique to increase the transmission line capability.

[pt] As fundações dos elementos de apoio de uma linha aérea de transmissão de energia elétrica situam-se ao longo de extensos traçados, onde diferentes condições de apoio para as estruturas são encontradas em razão da variação natural dos horizontes. Tal configuração pode levar alternativamente a se programarem estudos e sondagens especiais em cada local de suporte, fazendo crescer os custos e prazos de projeto, ou ao contrário, reduzindo drasticamente a investigação, com prejuízos evidentes ao planejamento, execução e economia da obra de implantação da linha de transmissão. Dessa maneira, são organizados e propostos procedimentos para avaliação do terreno segundo as suas orografia, hidrografia, geologia e pedologia e do ambiente atmosférico local, cujas manifestações são capazes de impor severas solicitações às torres e, indiretamente, às fundações. É eleita a região da bacia do rio da Prata para constituir o grande cenário do estudo, quer pela abundância de dados e informações disponíveis sobre linhas de transmissão já em carga, ou ainda em construção, nessa região. Assim sendo, desenvolve-se uma metodização para orientar o estudo dessas fundações, considerando o conjunto torre x terreno x fundação e buscando soluções técnicas convenientes e economicamente aceitáveis, atendendo assim ao binário desempenho-custo. Para as torres são considerados os modelos auto-suportados e estaiados, o terreno é variado entre algumas categorias identificadas na região e as fundações são representadas pelas superficiais, em sapatas, e pelas profundas do tipo tubulão. Buscando, ainda, auxiliar no aprimoramento dos projetos de fundações para suportes de linhas de transmissão, é desenvolvido um estudo de confiabilidade estrutural tendo como modelo algumas das fundações pré-selecionadas para a metodização primariamente desenvolvida. São determinadas as probabilidades de falha dessas fundações através do programa FERUM e, a partir do levantamento dos prejuízos financeiros causados pela falha desses elementos, determina-se o risco de falha. Por último, é desenvolvido um estudo paramétrico para avaliar a influência do projeto de fundação, do tipo de solo e da velocidade de vento sobre a probabilidade de falha. / [en] The transmission line tower foundations are executed following extensive paths, where different structural foundation conditions are found, in reason of natural horizontal ground layer variations. Then, one may alternatively to schedule and to execute special and specific studies or, conversely, to substantially reduce the geothecnical investigation, with sensible economical loses in the transmission line design and behavior. In such way, a methodology is proposed to evaluate conveniently the site according to its geology, orography , hydrography and pedology as well to related atmospheric local manifestations, able to submit severe mechanical solicitations to the towers and their foundations. In this way, one proposes a methodology to govern the study of these foundations, considering the tower x site x foundation relations and searching for convenient technical and acceptable economical solutions. Guyed and self-supported models are considered for towers, and the foundations are represented by footings, as the superficial type, and piers, as the deep type. The rio do Prata basin is chosen to constitute the large scenery of the study, because its abundant available data concerned to already operational transmission lines, or still under design and construction ones. Moreover, seeking the improvement of the tower foundation design a study based on structural reliability is developed considering some foundation models selected as mentioned above. Foundation failure probabilities are determined by the FERUM computational program and the risk of failure is obtained from economical damages caused by foundation failures. In the last, a parametric study is developed to evaluate how does the failure probability behave according to variations in the foundation soil, wind velocity and footing dimensions and depth.

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