Αυτή η διπλωματική εργασία πραγματεύεται την διάδοση κρουστικών υπερτάσεων που προκαλούνται από κεραυνικά πλήγματα σε ένα δίκτυο χαμηλής τάσης, στο οποίο βρίσκονται εγκατεστημένοι απαγωγοί υπέρτασης. Σκοπός της διπλωματικής εργασίας είναι η εξαγωγή χρήσιμων συμπερασμάτων σχετικά με την προστασία που παρέχουν οι απαγωγοί σε ένα τέτοιο δίκτυο, μέσω αποτελεσμάτων που θα προκύψουν από προσομοιώσεις. / This diploma thesis deals with the propagation of impulse overvoltages caused by lightning strikes in a low voltage network, which is supllied with surge protective devices (SPDs). The goal of this thesis is the extraction of useful conclusions regarding the protection that SPDs can offer to such a network, by comparing various results that arise from simulations.

Στα πλαίσια της παρούσας διπλωματικής εργασίας γίνεται αναφορά και μελέτη στις επαγώμενες υπερτάσεις σε δίκτυα διανομής Χαμηλής Τάσης, όταν αυτές προκαλούνται από πτώση κεραυνού στις γραμμές μεταφοράς. Παράλληλα, γίνεται μελέτη της συμπεριφοράς ενός τύπου απαγωγέων υπερτάσεων (SPDs), ως μέρος του εσωτερικού συστήματος αντικεραυνικής προστασίας μιας εγκατάστασης. Όλα τα παραπάνω έγιναν μέσω προσομοιώσεων που πραγματοποιήθηκαν με χρήση του λογισμικού ATP – EMTP. Σκοπός της εργασίας είναι η μελέτη της αποτελεσματικότητας των απαγωγέων υπερτάσεων όσον αφορά την προστασία οικιακών καταναλωτών και η εξαγωγή παρατηρήσεων όσον αφορά την επιρροή των διαφόρων χρόνων μετώπου και ουράς ενός κεραυνού στην δημιουργία και εξάπλωση υπερτάσεων. Αρχικά, στο πρώτο κεφάλαιο, περιγράφεται το φυσικό φαινόμενο του κεραυνού, τα είδη του, ο μηχανισμός των ατμοσφαιρικών εκκενώσεων και τα φυσικά χαρακτηριστικά του. Επίσης γίνεται αναφορά στους παράγοντες που τον επηρεάζουν, αλλά και μια σύντομη παρουσίαση των επιπτώσεων των κεραυνικών πληγμάτων. Στο δεύτερο κεφάλαιο δίνεται μια συνοπτική εικόνα των δικτύων μεταφοράς ηλεκτρικής ενέργειας, και γίνεται εκτενέστερη αναφορά στις γραμμές μεταφοράς και διανομής ηλεκτρικής ενέργειας, τα χαρακτηριστικά τους και τον τρόπο μοντελοποίησής τους. Στο τρίτο κεφάλαιο γίνεται αναφορά στις υπερτάσεις και τις αιτίες από τις οποίες προκαλούνται. Στο τέταρτο κεφάλαιο κάνουμε μια εισαγωγή στους απαγωγείς υπερτάσεων και αναφορά στα χαρακτηριστικά τους, την τοποθέτηση, τον συγχρονισμό και τα διαφορετικά είδη τους. Στο πέμπτο κεφάλαιο περιγράφεται το μοντέλο που σχεδιάσαμε ώστε να πραγματοποιηθούν οι προσομοιώσεις, ο υπολογισμός των στοιχείων και των παραμέτρων του και παρουσιάζονται τα αποτελέσματα και οι γραφικές παραστάσεις των μεγεθών που προέκυψαν από τις δοκιμές, καθώς και τα συμπεράσματα που εξήγαμε. Τέλος παρατίθεται ένα παράρτημα όπου περιγράφεται εν συντομία το λογισμικό ATP – EMTP, το οποίο χρησιμοποιήθηκε για τις προσομοιώσεις / In this thesis reference and study is made concerning the induced over-voltages in Low - Voltage distribution networks, when such are caused by lightning strikes on the transmission lines. In parallel, there is made study of the behavior of one type of Surge Protection Devices (SPDs), as part of an internal lightning protection system. All of the above came as a result of simulations using the ATP – EMPT software. The main objective of this thesis is to study the effectiveness of surge arresters concerning the protection of home consumers (loads) and the observation of the impact of various lightning types in the emergence and spreading of over-voltages. Chapter 1 describes the natural phenomena of lightning, its categories, the mechanism of atmospheric discharges and natural features. There is also reference to the factors that affect such phenomena and the consequences of lightning strikes. Chapter 2 makes an introduction to the electrical energy distribution networks and a more detailed reference to the transmission lines, their characteristics and the way that can me modeled. Chapter 3 makes a reference to over-voltages and the reasons they are caused. Chapter 4 introduces the various types of surge arresters, their characteristics, installation and synchronization. Chapter 5 describes the model we designed in order to make the simulations and the calculation of its parameters and elements. In addition, the simulation results and graphs are presented along with our conclusions. Finally an appendix is cited, describing the basics of ATP – EMTP, the simulation software we used to study our case.

The thesis discusses the findings of an investigation into the use of novel condition monitoring techniques for oil-paper insulated high voltage equipment as used on the Eskom Main Transmission System. This research into the monitoring of the condition of high voltage (RV) insulation was undertaken because of the high failure rate of high voltage current transformers (eT's) and transformer bushings on the Eskom Transmission National Grid. These failures reached unacceptably high levels in the 1990's. The extent of failures has been quantified and was the driving motivation behind this research. Techniques for the condition assessment and condition monitoring of oil-paper filled high voltage equipment have traditionally focused on off-line techniques, in particular off-line tan delta measurements. This requires that the equipment be removed from service temporarily, but at widely spaced intervals before a measurement may be taken (typically every 3 to 6 years). Such techniques will not be able to detect faulty equipment where the insulation integrity deteriorates rapidly, resulting in catastrophic failure with risk to both adjoining equipment and personnel. The need for an on-line technique for detecting deteriorating insulation prior to failure was identified in the early 1990's and various systems were developed. This research investigation has focussed on assessing the use of on-line relative tan delta monitoring of RV insulation and compares this to off-line monitoring. In particular, the ability of such a relative tan delta measurement system to detect deteriorating oil-paper insulation has been assessed. The investigation has included the design, construction and commissioning of a dedicated test facility located at Eskom's Tugela substation. This test facility is unique in the world. This test facility has resulted in a number of experiments that have provided invaluable insight into possible failure modes of oil-filled high voltage equipment and the ability of on-line techniques to detect rapid failure modes has been carefully assessed. Further assessment of the on-line monitoring systems was also undertaken at various Eskom operational installations. The results of these tests and operational monitoring are addressed in this research. The research work and its findings are assessed against published literature and global activity in this important area. / Thesis (M.Sc.-Eng.)-University of KwaZulu-Natal, Durban, 2004.

Mémoire (Sc.A.)--Université du Québec à Chicoutimi, 1986. / Document électronique également accessible en format PDF. CaQCU

Thesis (Ph.D.) -- Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). "February 2006." Includes bibliographical references (p. [151]-160). Also available via the World Wide Web.

Στην παρούσα διπλωματική εργασία εξετάζεται το φαινόμενο του κεραυνού και οι επιπτώσεις αυτού του φαινομένου στα δίκτυα ηλεκτρικής ενέργειας. Για καλύτερη κατανόηση των διαφόρων ηλεκτρικών φαινομένων μοντελοποιήθηκε ένα τριφασικό δίκτυο μέσης και χαμηλής τάσης έτσι ώστε να εξαχθούν μετρήσεις που αντικατοπτρίζουν τις επιπτώσεις που έχουν τα κεραυνικά πλήγματα στον εξοπλισμό και στο φορτίο του δικτύου. Στο Κεφάλαιο 1 γίνεται μία σύντομη εισαγωγή στο φαινόμενο του κεραυνού. ΣτοΚεφάλαιο 2 δίνεται ένας ορισμός για να περιγραφεί ακριβέστερα το φαινόμενο του κεραυνού και παρουσιάζονται τα διάφορα είδη του. Στο Κεφάλαιο 3 μελετούνται τα ηλεκτρικά χαρακτηριστικά ενός κεραυνού οπότε παρουσιάζονται λεπτομερώς θέματα που έχουν να κάνουν με το ρεύμα, την τάση και το φορτίο που μπορεί να οδηγήσει ένας κεραυνός. Στο Κεφάλαιο 4 μελετούνται οι επιπτώσεις που προκαλούνται από κεραυνούς τόσο στη φύση όσο και στις τεχνικές υποδομές της περιοχής όπου πέφτει ο κεραυνός. Στο Κεφάλαιο 5 εισάγεται ο αναγνώστης στη θεωρία δικτύων ηλεκτρικής ενέργειας ενώ στο Κεφάλαιο 6 γίνεται εισαγωγή στη θεωρία υπερτάσεων. Στο Κεφάλαιο 7 παρουσιάζεται αναλυτικά το μοντέλο προσομοιώσεων που αναπτύχθηκε στα πλαίσια της εργασίας χρησιμοποιώντας το περιβάλλον προσομοίωσης Matlab/Simulink, παρατίθενται οι μετρήσεις που εξήχθησαν και παρουσιάζονται τα τελικά συμπεράσματα του πρακτικού μέρους της εργασίας. / This thesis examines the phenomenon of lightning and the effectsof this phenomenon in electricity networks. For a better understanding of the various electrical phenomena modeled a three-phase network medium and low voltage so as to extract measurements that reflect the impact of the lightning strike on equipment and network load. Chapter 1 gives a brief introduction to the lightning strike. Chapter 2 gives a definition to describ eaccurately the lightning strike and presents the various types of this. In Chapter 3 we study the electrical characteristics of a lightning strike. Are presented in detail issues that have to do with the current, voltage and the load can lead thunder bolt. In Chapter 4 we study the effects caused by lightning strike in both nature and the technical infrastructure of the area where the lightning falls. Chapter 5 introduces the reader to the theory of electricity networks while Chapter 6 is introduced in the theory over voltages. Chapter 7 presents detailed simulation model developed in this thesis using the simulation environment Matlab / Simulink, given the measurements obtained are presented and the final conclusions of the practical part of the work.

Thesis (MScEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Recent research has shown that standard substation capacitive voltage transformers (CVTs) and current transformers (CTs) can be used for the measurement of wideband high voltage phenomena by employing these apparatus in a transconductance topology. With this topology the voltage waveform can be obtained by integration of the ground return current in the earth straps of the CVT and the CT. This technique does, however, impose unique requirements on the amplification and integration instrumentation due to large dynamic range requirements and the strict offset specifications required for accurate integration. This thesis describes a programmable, wideband signal conditioning system for high voltage (HV) measurements using the transconductance topology. A suitable system topology, optimised to reduce the problems usually associated with grounding and electromagnetic interference (EMI) in HV environments, is proposed. This system consists of an analog signal conditioning subsystem, a digital signal conditioning subsystem and a high speed serial fibre-optic link. The analog signal conditioning subsystem conditions the signals from a sensor to levels suitable for the digitiser of the digital signal conditioning subsystem. The high bandwidth specification of the application made it necessary to consider both discrete and integrated implementation of the analog signal conditioning subsystem. Based on the simulated and laboratory test results of both implementations, the optimum design was chosen for the developed system. The digital signal conditioning subsystem, which performs the integration, as well as the serial optic-fibre link control logic was implemented using programmable logic array (PLA) technology. The digital data is transmitted across the fibre-optic link. This data is then converted back to an analog signal. Keywords: High voltage measurements, Transconductance topology. / AFRIKAANSE OPSOMMING: Onlangse navorsing het aangetoon dat standaard substasie kapasitiewe spanningstransformators en stroomtransformators gebruik kan word om wyeband hoogspanningsverskynsels te meet deur hierdie apparatuur in 'n transkonduktansie topologie aan te wend. Met hierdie topologie kan die spanningsgolfvorm verkry word deur die integrasie van die aardstrome in die aardverbindings van die kapasitiewe spanningstransformators en stroomtransformators. Hierdie tegniek stel egter unieke vereistes vir die versterkings- en integrasieinstrumentasie te wyte aan groot dinamiese bereik vereistes en die streng afset spesifikasies wat benodig word vir akkurate integrasie. Hierdie tesis beskryf 'n programmeerbare, wyeband seinkondisioneringstelsel vir hoogspanningsmetings deur van die transkonduktansie topologie gebruik te maak. 'n Geskikte stelseltopologie, wat geoptimiseer is om probleme, wat gewoonlik met aarding en elektromagnetiese interferensie in hoogspanningsomgewings geassosieer word, te verminder, is voorgestel. Die stelsel bestaan uit 'n analoog seinkondisioneringsubstelsel, 'n digitale seinkondisioneringsubstelsel en 'n hoëspoed seriële optiese vesel koppelvlak. Die analoog seinkondisioneringsubstelsel kondisioneer die seine vanaf 'n sensor na geskikte vlakke vir die versyferaar van die digitale seinkondisioneringsubstelsel. Die hoë bandwydte spesifikasie van die toepassing vereis die inagneming van beide diskrete en geïntegreerde implementerings van die analoog seinkondisioneringsubstelsel. Gebaseer op gesimuleerde en laboratorium toetsresultate van beide implementerings is die optimale ontwerp vir die ontwikkelde stelsel gekies. Die digitale seinkondisioneringsubstelsel wat die integrasie uitvoer, asook die seriële optiese vesel koppelvlak beheerlogika is geïmplementeer met behulp van programmeerbare logika skikking tegnologie. Die digitale data word gestuur oor die optiese vesel koppelvlak. Hierdie data word dan terug geskakel na 'n analoog sein. Sleutelwoorde: Hoogspanningsmetings, Transkonduktansie topologie.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / The industrial and population growth of a nation can cause power delivery problems to localized areas of a national grid through their increased demand for electrical energy. One reason for these power shortages is the insufficient current carrying capacity of existing high voltage alternating current, (HVAC), transmission lines supplying the area. High voltage direct current (HVDC) transmission lines are a possible solution as they provide better power delivery than HVAC lines. New or upgraded HVAC lines, or HVDC lines or combinations of HVAC and HVDC lines are possible solutions to improve power delivery. This research investigates the various line possibilities using theory. and cutting edge frequency and time domain software tools. The challenge is how to approach this problem. What methodology or structure should be used? Thus one of the contributions of this work is the development of a strategy (flow chart), for solving power delivery problems to localized areas of a national grid through individual or combinations (e.g. parallel operation) of HVAC and/or HVDC transmission lines. The main contribution is the evaluation of a HVDC system as a solution to overcoming power delivery shortages to a localized area of a national grid. Three different software packages (two industrial and one academic) namely, PSCAD/EMTDC (time domain), DlgSILENT PowerFactory (frequency domain) and MathCAD software are evaluated for their capability to perform the simulation studies necessary to prove the possible solutions given in the developed flow chart. The PSCAD/EMTDC software package is evaluated for integrated HVAC/HVDC load flow analyses, DlgSILENT for individual and parallel combinations of HVAC lines and MathCAD to prove hand calculations to software results. Five case studies are conducted. The first case study demonstrates a healthy system with no delivery shortcomings, the second case study portrays the delivery shortcoming due to increased localized area demand, and the remaining three case studies explore possible solutions to solve the problem. The first possible solution is to construct an identical HVAC line in parallel to the existing line.

Orientador: Jose Antenor Pomilio / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-11T05:49:41Z (GMT). No. of bitstreams: 1 Sperandio_GiulianoSalomao_M.pdf: 1492429 bytes, checksum: f30c57d63ec881417a2d7f6ebaf926c2 (MD5) Previous issue date: 2007 / Resumo: O ozônio se apresenta como um excelente produto químico para ser usado em substituição ou em conjunto com o cloro para o tratamento de água. O ozônio é um potente bactericida e viricida e não deixa resíduos no meio ambiente. A produção deve ser local e requer apenas ar e eletricidade. Um método simples e eficaz para a produção de ozônio é através de microdescargas em barreiras dielétricas em oxigênio. A produção da microdescarga é feita numa célula onde é aplicada uma alta tensão, da ordem de quilovolts. A alta tensão é gerada através de um circuito eletrônico de alto rendimento e interage com a carga para produzir a alta tensão desejada. A fonte de alta tensão foi projetada para fazer o uso das não idealidades do conjunto formado pelo transformador de alta tensão associado a célula ozonizadora. O comportamento da carga permite que a potência de saída seja ajustada pela freqüência de trabalho. A potência de saída é uma variável que está associada com a produção de ozônio a qual pode ser ajustada. O controle da potência foi realizado por um microcontrolador que também incorpora funções de proteção e comando remoto. Os resultados obtidos pela implementação prática do circuito eletrônico corroboram o modelo e as simulações feitas. O circuito foi desenvolvido por uma demanda da indÚstria. A etapa de desenvolvimento do circuito em laboratório atingiu uma maturidade satisfatória para industrialização / Abstract: The ozone gas is a powerful oxidizing substance and it can be used for the treatment of water. It is known to be a potent bactericide and viricide and leaves no harmful residues to the environment. Ozone has to be produced on-site and requires only air and eletricity. An efficient way to produce ozone is through diclectric-barrier discharge in oxigen. An electronic high-efficiency circuit is used to generate the necessary high- voltage to make the electric discharge. The circuit was designed to use the resonance of the transformer plus the silent-discharge ozone-generator tube. The transformer non-idealities are usefull for allowing the converter operation in the resonance region, minimizing the commutation losses. The output power can be adjusted setting the switching frequency. The circuit works properly and the practical results match to the simulations. This converter was developed according to the specification of an industry and it is now going into commercial production / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica