Thesis (D. Tech. Electrical engineering) --Vaal University of Technology / A comprehensive study upon "Non-conventional methods for energy extraction from the high voltage transmission lines" was addressed in this thesis. As defined in this study, a non-conventional method to extract energy is one that does not touch the conductors of the line. The theoretical framework which originated in the Maxwell's equations was presented as a base for discussion of all the methods and the conditions for the extraction to be possible. This study presents various methods such as capacitive and inductive to extract energy from high voltage alternating current transmission lines (HVAC). Although in theory, for high voltage direct current transmission lines (HVDC), the conditions for extraction are not matched, there remain some methods that could still attract interest. The centre point of this thesis is the new power application of the Rogowski coil. This method is analysed in full extent starting from theoretical modelling, computer simulations, design of the actual Rogowski coil and power electronics associated with it, and experimental results on a reduced scale model. In doing this, strong mathematical tools and computer software such as Matlab 6, Quick Field and MathCAD were used. At the end of this thesis, some conclusions are presented together with new ideas for further research in the field.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της λειτουργίας των καθοδικών αλεξικεραύνων κατά την προστασία γραμμών μεταφοράς υψηλής τάσης. Ειδικότερα, λόγω της ιδιαίτερης φύσης των κεραυνών και των πληγμάτων που αυτοί επιφέρουν, γίνεται μελέτη μοντέλων που έχουν προταθεί για την προσομείωση των αλεξικεραύνων κατά την λειτουργία τους. / The purpose of this paper is to study the function of surge arresters protecting high voltage transmission lines. Specifically, given the particular nature of lightning strikes and the blows they bring, models that have been proposed for the simulation of surge arrestes during operation are being studied.

Στην παρούσα διπλωματική εργασία μελετάται η ικανότητα συμπεριφοράς γραμμών μεταφοράς υψηλής τάσης έναντι κεραυνών. Αρχικά γίνεται μια ιστορική αναδρομή για τον κεραυνό. Στη συνέχεια, εξετάζονται οι κεραυνοί και παρατίθενται μια ενδελεχής παρουσίαση των ειδών των κεραυνικών αλλά και των ατμοσφαιρικών εκκενώσεων, προχωρώντας μετά στην αναφορά των κύριων χαρακτηριστικών των κεραυνών, των αποτελεσμάτων τα οποία προκαλούν, αλλά και των παραμέτρων από τις οποίες εξαρτώνται και χαρακτηρίζονται. Έπειτα, γίνεται μια αναλυτική περιγραφή των γραμμών μεταφοράς, παρουσιάζοντας τις κατηγοριοποιήσεις στις οποίες υπόκεινται, με κύρια κριτήρια αυτών να είναι η ονομαστική τάση υπό την οποία είναι φορτισμένες, το μήκος αλλά και την ικανότητα τους στην μεταφορά ηλεκτρικής ενέργειας. Επίσης, γίνεται αναφορά στις καταπονήσεις τις οποίες δέχονται οι γραμμές αλλά και στην μόνωση, όπως και στα χαρακτηριστικά τους. Παρακάτω, βλέπουμε ποια είναι τα κύρια είδη σφαλμάτων στις εναέριες γραμμές μεταφοράς και από ποιες αιτίες αυτά προκαλούνται. Το επόμενο κεφάλαιο πραγματεύεται τη μόνωση των γραμμών αλλά και τα κεραυνικά πλήγματα, ενώ εξετάζονται οι μηχανισμοί που προκαλούν την παραγωγή υπερτάσεων στις γραμμές. Έπειτα, για το καθορισμό της θέσης του αγωγού προστασίας της γραμμής παρουσιάζονται οι μέθοδοι της μέγιστης γωνίας και η ηλεκτρογεωμετρική μέθοδος. Στο προτελευταίο κεφάλαιο , υπάρχει μια εκτενής αναφορά στο πρόγραμμα ATP-EMTP και τα στοιχεία του. Τέλος, παρουσιάζεται μια εξομοίωση μιας γραμμής μεταφοράς υψηλής τάσης με τη χρήση του συγκεκριμένου προγράμματος και κυρίως του γραφικού προεπεξεργαστή του , που είναι το πρόγραμμα ATPDraw. Η εξομοίωση αυτή έγινε για διαφορετικών εντάσεων κεραυνικά ρεύματα τα οποία πλήττουν τον αγωγό προστασίας της γραμμής, και μελετά τις παραγόμενες υπερτάσεις σε τέσσερα διαφορετικά σημεία αυτής και το βαθμό επικινδυνότητάς τους. / In this diploma thesis is studied the ability to conduct high voltage transmission lines against lightning. Initially, there is a little historical background to the lightning. Afterwards there is a study about lightning and it is provided a thorough presentation of the types of lightning and atmospheric discharges, moving afterwards to the reference of the main lightning features, the results that they rise, as well as the parameters that they depend on and described from. Next, a more detailed description of the transmission lines, showing the classifications in which they are subject to, with main criteria, the nominal voltage in which they are charged, the length, but also their ability of electricity transmission. Moreover, there is a reference to the stresses, in which the lines are subjected to, as well as their insulation level and their characteristics. Below, we can see what the main types of outages in air transmission lines are and which are the causes that generate them. The next chapter deals with the isolation of lines, as well as with lightning strokes and described the mechanisms which cause the overvoltages on transmission lines. Then, in order to determine the position of the line protection conductor , the maximum angle method as well as the electrogeometrical method are presented. The fifth chapter contains an extended reference to the ATP-EMTP program and its components. Finally, a simulation of a high voltage transmission line is represented, with the use of this program and mainly its graphic preprocessor, which is the program ATPDraw. This simulation has been done for different intensities of lightning currents, which strike at the protection conductor of the line,and it is also studying overvoltages at four different points and the risk rate.

Thesis (D. Tech. Engineering : Electrical ; Dept. Applied Electronics and Electronic Communications) -- Vaal University of Technology / Two methods to convert an AC current source to an AC voltage source are presented. Both methods make use of a current transformer to provide energy extraction from the main system while maintaining galvanic isolation between the main system and the output system. Control is via a pulse width modulation scheme in both instances. The ftrst method uses a storage element to provide a DC voltage, which feeds an inverter that supplies the AC load with a voltage source. The second method does not use a storage element but is a direct AC current source to AC voltage source converter employing a current transformer. This has not been done before. A possible application of this study is in the extraction of power from high voltage transmission lines without the conventional substation and rural grid to supply small users such as the telecommunication industry.

Les phénomènes de couplage électromagnétique entre les lignes aé- riennes de transmission d\'énergie et des structures voisines sont inévitables, surtout dans les zones densément peuplées. Les effets indésirables découlants de cette proximité sont variés, allant de l\'établissement des tensions dangereuses à l\'apparition de phénomènes de corrosion dus au courant alternatif. L\'étude de cette classe de problèmes est nécessaire pour assurer la sécurité dans les alentours de la zone d\'interaction et aussi pour préserver l\'intégrité des équipements et des dispositifs présents. Cependant, la modélisation compl ète de ce type d\'application implique la représentation tridimensionnelle de la région d\'intérêt et nécessite des méthodes numériques de calcul de champs spécifiques. Dans ces travaux, des problèmes liés à la circulation de courants électriques dans le sol (ou de couplage dit conductif) seront abordés avec la méthode des éléments finis. D\'autres problèmes résultants de la variation temporelle des champs électromagnétiques (ou de couplage dit inductif) seront aussi considérés et traités avec la méthode PEEC (Partial Element Equivalent Circuit) généralisée. Plus précisément, une condition limite particulière sur le potentiel électrique est proposée pour tronquer le domaine de calcul dans l\'analyse par éléments finis des problèmes de couplage conductif et une formulation PEEC complète pour la modélisation de problèmes de couplage inductif est présentée. Des con gurations tests de complexités croissantes sont considérées pour valider les approches précédentes. Ces travaux visent ainsi à apporter une contribution à la modélisation de cette classe de problèmes, qui tendent à devenir communs avec l\'expansion des réseaux électriques. / Electromagnetic coupling phenomena between overhead power transmission lines and other nearby structures are inevitable, especially in densely populated areas. The undesired effects resulting from this proximity are manifold and range from the establishment of hazardous potentials to the outbreak of alternate current corrosion phenomena. The study of this class of problems is necessary for ensuring security in the vicinities of the interaction zone and also to preserve the integrity of the equipment and of the devices there present. However, the complete modeling of this type of application requires the three- -dimensional representation of the region of interest and needs specific numerical methods for field computation. In this work, the modeling of problems arising from the flow of electrical currents in the ground (the so-called conductive coupling) will be addressed with the finite element method. Those resulting from the time variation of the electromagnetic fields (the so-called inductive coupling) will be considered as well, and they will be treated with the generalized PEEC (Partial Element Equivalent Circuit) method. More specifically, a special boundary condition on the electric potential is proposed for truncating the computational domain in the finite element analysis of conductive coupling problems, and a complete PEEC formulation for modeling inductive coupling problems is presented. Test configurations of increasing complexities are considered for validating the foregoing approaches. These works aim to provide a contribution to the modeling of this class of problems, which tend to become common with the expansion of power grids.

The dissertation comprises the general characteristic of the work, 5 chapters, conclusions and recommendations, references and list of published works on the topic of the dissertation. The dissertation covers 149 pages, 78 illustrations, 17 tables. In introduction chapter the problem topicality is considered, the aims and tasks of the work are formulated, the novelty of the research is described, the author’s reports and publications as well as the dissertation structure are presented. Chapter 1 is intended for the review of literature. The survey of ozone sources in working premises and the environment air is presented as well as methods of the ozone concentration determination and its dispersion simulation are discussed. At the end of the chapter conclusions are formulated and the dissertation tasks are concretized. In chapter 2 the methodology of the ozone concentration determination with the ozone analyzer and passive samplers as well as the measurement methods of aerosol particles and meteorological, microclimatic parameters are described. In chapter 3 the results obtained during experimental investigations are discussed: the ozone concentration changes near technogenic sources of this pollutant, the influence of meteorological and microclimatic parameters on the ozone concentrations changes, the relation of aerosol particles with the ozone concentration. Ozone concentrations measured by different methods are compared and the results of comparative measurements are... [to full text] / Disertaciją sudaro įvadas, 5 pagrindiniai skyriai, darbo išvados ir rekomendacijos, literatūros sąrašas, publikacijų sąrašas. Bendra disertacijos apimtis – 149 puslapiai, 80 iliustracijų, 17 lentelių. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, formuluojamas darbo tikslas bei uždaviniai, aprašomas mokslinis darbo naujumas, pristatomi autoriaus pranešimai ir publikacijos, disertacijos struktūra. Pirmasis skyrius skirtas literatūros apžvalgai. Jame pateikta ozono šaltinių darbo patalpose ir aplinkos ore apžvalga, aptariami ozono koncentracijos nustatymo ir jos sklaidos modeliavimo metodai. Skyriaus pabaigoje formuluojamos išvados ir konkretinami disertacijos uždaviniai. Antrajame skyriuje aprašomi ozono koncentracijos nustatymo ozono analizatoriumi ir pasyviaisiais kaupikliais metodika bei aerozolio dalelių ir meteorologinių, mikroklimato parametrų matavimo metodai. Trečiajame skyriuje aptariami eksperimentinių tyrimų metu gauti rezultatai apie: ozono koncentracijos kitimą prie technogeninių šio teršalo šaltinių, meteorologinių ir mikroklimato parametrų įtaką ozono koncentracijos pokyčiams, aerozolio dalelių sąryšį su ozono koncentracija. Lyginamos ozono koncentracijos matuotos skirtingais metodais ir aptariami lyginamųjų matavimų rezultatai. Ketvirtajame skyriuje pateikti RISK programa sumodeliuoti ozono sklaidos nuo šaltinio rezultatai. Penktajame skyriuje pasiūlytas technologinis sprendimo variantas, leidžiantis sumažinti ozono koncentracijas prie technogeninių... [toliau žr. visą tekstą]

A majority of utilities conduct maintenance of transmission line components based on the results of routine visual inspection. The inspection is normally done by inspectors who detect defects by visually checking transmission line components either from the air (in helicopters), from the ground (by using high-powered binoculars) or from the top of the structure (by climbing the structure). The main problems with visual inspection of transmission lines are that the determination of the defects varies depending on the inspectors' knowledge and experience and that the defects are often reported qualitatively using vague and linguistic terms such as "medium crack", "heavy rust", "small deflection". As a result of these drawbacks, there is a large variance and inconsistency in defect reporting (which, in time, makes it difficult for the utility to monitor the condition of the components) leading to ineffective or wrong maintenance decisions. The use of inspection guides has not been able to fully address these uncertainties. This thesis reports on the application of a visual inspection methodology that is aimed at addressing the above-mentioned problems. A knowledge-based Fuzzy Inference System (FIS) is designed using Matlab's Fuzzy Logic Toolbox as part of the methodology and its application is demonstrated on utility visual inspection practice of porcelain cap and pin insulators. The FIS consists of expert-specified input membership functions (representing various insulator defect levels), output membership functions (indicating the overall conditions of the insulator) and IF-THEN rules. Consistency in the inspection results is achieved because the condition of the insulator is inferred using the same knowledge-base in the FIS rather than by individual inspectors. The output of the FIS is also used in a mathematical model that is developed to suggest appropriate component replacement date. It is hoped that the methodology that is introduced in this research will help utilities achieve better maintenance management of transmission line assets.

Cette thèse s’inscrit dans le cadre de l’amélioration du comportement électrique des isolateurs de lignes haute tension ; l’objectif est d’assurer une meilleure fiabilité et qualité d’alimentation en énergie électrique. Ce travail a été motivé par la nécessité de répondre à trois questions liées au comportement des isolateurs verre en zone polluée. La première porte sur la recherche d’une méthode permettant de calculer la tension de contournement des chaînes polluées selon le type d’isolateur et ses caractéristiques. La deuxième question concerne la différence de comportement entre les isolateurs en verre et les isolateurs en porcelaine de type « outerrib » ; ce type d’isolateurs présente une forme spécifique adaptée aux environnements à forte pollution. Les tensions de contournement ainsi que les trajectoires de l’arc sur les isolateurs en verre sont très différentes de celles observées avec les isolateurs en porcelaine. Et la troisième question est relative à la défaillance des isolateurs recouverts de silicone lors des essais en chocs (des impulsions de tension) à front raide. En effet, les isolateurs recouverts d’une couche de 0.3 mm (ou plus) de silicone hydrophobe explosent lorsqu’ils sont soumis à des impulsions de tension à front raide d’amplitude très élevée pendant un temps très court. Différents mécanismes pouvant être à l’origine de l’explosion/éclatement des isolateurs recouverts d’une couche de silicone sont discutés. Il ressort des différents tests et analyses que le mécanisme le plus probable semble être la fragmentation par plasma. En effet, suite à l’application d’une tension à front raide, d’amplitude très élevée, des canaux (fissures) microscopiques prennent naissance là où le champ électrique est le plus intense. L’application répétitive des chocs de tension conduit au développement de décharges dans ces canaux (rupture diélectrique de l’air) c’est-à-dire des arcs (canaux de plasma) qui se développent/propagent dans le volume de l’isolateur. La puissance déchargée (c’est-à-dire l’énergie stockée dans les condensateurs du générateur en des temps très courts) dans ces canaux à chaque choc étant très élevée, elle conduit à l’explosion de l’isolateur après quelques chocs (parfois 5 ou 6 suffisent): c’est la fragmentation par plasma. / This thesis deals with the improvement of the electrical behavior of insulators of high voltage lines; the objective is to ensure better reliability and quality of power supply. This work was motivated by the need to answer three questions related to the behavior of glass insulators in polluted areas. The first one concerns the search for method for calculating the flashover voltage of polluted chains according to the type of insulator and its characteristics. The second question concerns the difference in behavior between glass insulators and "outerrib" porcelain insulators; this type of insulator has a specific shape adapted to environments with high pollution. The flashover voltages as well as the trajectories of the arc on glass insulators are very different from those observed with porcelain insulators. And the third issue is the failure of silicon-coated insulators during shock tests (pulses) with a steep front. Indeed, insulators coated with a layer of 0.3 mm (or more) of hydrophobic silicone explode when subjected to very high amplitude steep-edge voltage pulses for a very short time. Different mechanisms that may be responsible for the explosion / puncturing of insulators covered with a layer of silicone are discussed. It appears from the various tests and analyzes that the most probable mechanism seems to be plasma fragmentation (cracking). Indeed, following the application of a steep front voltage, of very high amplitude, microscopic channels (fissures) originate where the electric field is most intense. The repetitive application of impulse voltages (shocks) leads to the development of discharges in these channels (breakdown of the air), i.e.; arcs (plasma channels) which develop / propagate in the volume of the insulator. The discharged power (i.e.; the energy stored in the capacitors of the generator in a very short times) in these channels (cracks) at each shock being very high, leads to the explosion of the insulator after some shocks (5 to 6 sometimes): it is the fragmentation by plasma or plasma cracking.

Electromagnetic coupling phenomena between overhead power transmission lines and other nearby structures are inevitable, especially in densely populated areas. The undesired effects resulting from this proximity are manifold and range from the establishment of hazardous potentials to the outbreak of alternate current corrosion phenomena. The study of this class of problems is necessary for ensuring security in the vicinities of the interaction zone and also to preserve the integrity of the equipment and of the devices there present. However, the complete modeling of this type of application requires the three- -dimensional representation of the region of interest and needs specific numerical methods for field computation. In this work, the modeling of problems arising from the flow of electrical currents in the ground (the so-called conductive coupling) will be addressed with the finite element method. Those resulting from the time variation of the electromagnetic fields (the so-called inductive coupling) will be considered as well, and they will be treated with the generalized PEEC (Partial Element Equivalent Circuit) method. More specifically, a special boundary condition on the electric potential is proposed for truncating the computational domain in the finite element analysis of conductive coupling problems, and a complete PEEC formulation for modeling inductive coupling problems is presented. Test configurations of increasing complexities are considered for validating the foregoing approaches. These works aim to provide a contribution to the modeling of this class of problems, which tend to become common with the expansion of power grids. / Les phénomènes de couplage électromagnétique entre les lignes aé- riennes de transmission d\'énergie et des structures voisines sont inévitables, surtout dans les zones densément peuplées. Les effets indésirables découlants de cette proximité sont variés, allant de l\'établissement des tensions dangereuses à l\'apparition de phénomènes de corrosion dus au courant alternatif. L\'étude de cette classe de problèmes est nécessaire pour assurer la sécurité dans les alentours de la zone d\'interaction et aussi pour préserver l\'intégrité des équipements et des dispositifs présents. Cependant, la modélisation compl ète de ce type d\'application implique la représentation tridimensionnelle de la région d\'intérêt et nécessite des méthodes numériques de calcul de champs spécifiques. Dans ces travaux, des problèmes liés à la circulation de courants électriques dans le sol (ou de couplage dit conductif) seront abordés avec la méthode des éléments finis. D\'autres problèmes résultants de la variation temporelle des champs électromagnétiques (ou de couplage dit inductif) seront aussi considérés et traités avec la méthode PEEC (Partial Element Equivalent Circuit) généralisée. Plus précisément, une condition limite particulière sur le potentiel électrique est proposée pour tronquer le domaine de calcul dans l\'analyse par éléments finis des problèmes de couplage conductif et une formulation PEEC complète pour la modélisation de problèmes de couplage inductif est présentée. Des con gurations tests de complexités croissantes sont considérées pour valider les approches précédentes. Ces travaux visent ainsi à apporter une contribution à la modélisation de cette classe de problèmes, qui tendent à devenir communs avec l\'expansion des réseaux électriques.

In India, the natural energy resources (thermal and hydro) are unevenly distributed and are mostly present in the remote areas and the load centers are distributed across various regions of the country. Therefore high voltage lines have become necessary for the devel-opment of large interconnected power networks and for the reliable and economic transfer of power. The increase in electric power demand due to the electric load growth has lead to the expansion of the transmission systems to ultra high voltage levels. Presently, Ultra High Voltage (UHV) power transmission lines are being built to transfer large electric power to distant load centers from the generating stations. Increasing the line voltage increases the surge impedance loading, stability and the thermal capacity of the line. Lightning is one of the major causes for the line outages and interruptions of UHV power lines. A lightning strike generates a very large voltage leading to insulator puncture, melting, burning and pitting of conductors and the supporting hardware. Lightning can lead to transient over-voltages thus leading to ash-over in the power transmission lines which are dangerous for the power equipments as well as for the human beings working in the vicinity. Ground wires are used for the protection of overhead power transmission lines against a lightning stroke. The overhead ground wires are installed such that the lightning attaches to it and shunts the lightning current to the ground through the tower, thus protecting the phase conductors. Shielding failure happens when the lightning strikes the phase conductor instead of the ground wires. Lightning shielding failure is a major con-cern in UHV lines due to their large height, very high operating voltage and wide exposure area of the phase conductors. The lightning over-voltages injected on the phase conductor (shielding failure) nally reaches the substation causing serious threat to the substation components and can lead to temporary or permanent outage of the power transmission system. There have been cases of very high shielding failure ash-overs of UHV lines and thus lightning attachment to power transmission lines need to be studied in detail to reduce the power system line outages. Several models such as electro-geometric model (EGM) and leader progression model (LPM) have been developed to study the shielding failure of power transmission lines. EGM has been extensively used to obtain lightning attachment to power transmission lines but in recent years it is seen that EGM is unable to accurately predict the lightning attach-ment to UHVAC lines. The shielding failure rates obtained by EGM does not match with the observed shielding failure rate for UHV lines. For this reason LPM is considered to obtain lightning attachment to UHV lines but LPM in its initial stage do not deal with the detailed physics of the upward leader inception, i.e., corona inception and unstable as well as stable upward leader inception from the object on the ground. In this thesis a model for the lightning attachment has been developed based on the present knowledge of the lightning physics. The thesis mainly focuses on the modelling of upward leader inception and propagation for lightning attachment to UHV power trans-mission lines. Upward leader inception is modeled based on the corona charge present near the conductor region and the upward leader propagation model is based on the correlation between the lightning induced voltage on the conductor and the voltage drop along the upward leader channel. The present model considers corona inception and modelling of unstable and stable upward leader inception from the ground object for the analysis of the lightning attachment process. The upward leader inception model developed is compared with the previous inception models and the results obtained using the present and previous models are found to be comparable. Lightning striking distances ( nal jump) for various lightning return stroke current were computed for di erent conductor heights using present lightning attachment model. It is seen that the striking distance increases with the increase in lightning re-turn stroke current and increases with increase in conductor heights. The striking distance computed using the present model matches with the value calculated using the equation proposed by the IEEE working group for the applicable conductor heights of up to 8 m. The in uence of the conductor operating voltage, cloud electric eld, lightning down-ward leader lateral distance, conductor length, transmission line tower and conductor sag on the upward lightning leader inception are analysed and reported in the thesis. It is found that the lightning attraction to power transmission line increases with increase in conductor positive operating voltage and decreases with increase in conductor negative op-erating voltage. The presence of transmission line tower reduces the lightning attachment to the conductor lines and the probability of lightning strike decreases with the increase in downward leader lateral distance from the conductor lines. The present lightning attachment model is applied to study the shielding failure of UHV power transmission lines rated for 1200 kV ac (delta and horizontal con guration) and for 800 kV dc (with and without a dedicated metallic return conductor) and thereby the lightning shielding failure ash-over rate is computed for the UHV power transmission lines. It is seen that the lightning shielding rate for UHV power transmission lines depend on the lateral distance of the downward leader channel, instantaneous 50 Hz voltage on the transmission line conductor, height of the transmission line conductor, induced voltages on the conductor and the lightning return stroke current.