Dissertations / Theses on the topic 'Overhead conductors'

Overhead conductors used in the transmission of power in grids around the world are generally subjected to ageing, which is the time-based change of their properties. Important properties such as corona discharge, audible noise, hydrophobicity and corrosion are usually considered and investigated. On some conductors such as the aluminium conductor steel reinforced (ACSR), a reduction in audible noise over exposure time to the service environment has been noted to occur. However, the converse has been observed for the gap-type thermal resistant aluminium conductor steel reinforced (GTACSR or “Matthew” conductor), although this conductor is preferred due to its high ampacity. The relationship between conductor hydrophobicity, audible noise, surface contamination and roughness, wettability and corrosion were investigated using All Aluminium Alloy Conductor (AAAC), Aluminium Conductor Composite Core (ACCC) and GTACSR samples. Findings from Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectric Spectroscopy (XPS) and contact angle measurements revealed that carbon, hydrocarbon and silicone contamination was responsible for the hydrophobic nature of the surface. Furthermore, electrochemical investigations and electron microscopy showed that pitting or/and crevice corrosion were the predominant corrosion mechanisms on these conductors. Exposure to simulated industrial and marine environments further confirmed this finding and also showed that general corrosion also occurs on relatively uncontaminated conductors, thereby changing their surface roughness, as seen from the White Light Interferometry results. Corrosion was observed to be accelerated by the presence of surface contaminants such as oils and carbon, as these facilitated water (droplet) retention by reducing the conductor’s surface energy. Reduction/elimination of surface contamination/hydrophobicity were the desired solutions to the problem, and this was achieved by grit blasting. Partial/complete oxidation of the silicones resulted in the reduction/elimination of sample hydrophobicity – this was seen from more contact angles measurements and XPS data. Grit blasting also restored conductor cleanliness and roughened the surface sufficiently to produce surface run-off.

The developments of new types of conductors and increase of voltage level have driven the need to carry out research on evaluating overhead line acoustic noise. The surface potential gradient of a conductor is a critical design parameter for planning overhead lines, as it determines the level of corona loss (CL), radio interference (RI), and audible noise (AN). The majority of existing models for surface gradient calculation are based on analytical methods which restrict their application in simulating complex surface geometries. This thesis proposes a novel method which utilizes both analytical and numerical procedures to predict the surface gradient. Stranding shape, proximity of tower, protrusions and bundle arrangements are considered within this model. One of UK National Grid's transmission line configurations has been selected as an example to compare the results for different methods. The different stranding shapes are a key variable in determining dry surface fields. The dynamic behaviour of water droplets subject to AC electric fields is investigated by experiment and finite element modelling. The motion of a water droplet is considered on the surface of a metallic sphere. To understand the consequences of vibration, the FEA model is introduced to study the dynamics of a single droplet in terms of phase shift between vibration and exciting voltage. Moreover, the evolution of electric field within the whole cycle of vibration is investigated. The profile of the electric field and the characteristics of mechanical vibration are evaluated. Surprisingly the phase shift between these characteristics results in the maximum field occurring when the droplet is in a flattened profile rather than when it is ‘pointed’.Research work on audible noise emitted from overhead line conductors is reviewed, and a unique experimental set up employing a semi-anechoic chamber and corona cage is described. Acoustically, this facility isolates undesirable background noise and provides a free-field test space inside the anechoic chamber. Electrically, the corona cage simulates a 3 m section of 400 kV overhead line conductors by achieving the equivalent surface gradient. UV imaging, acoustic measurements and a partial discharge detection system are employed as instrumentation. The acoustic and electrical performance is demonstrated through a series of experiments. Results are discussed, and the mechanisms for acoustic noise are considered. A strategy for evaluating the noise emission level for overhead line conductors is developed. Comments are made on predicting acoustic noise from overhead lines. The technical achievements of this thesis are summarized in three aspects. First of all, an FEA model is developed to calculate the surface electric field for overhead line conductors and this has been demonstrated as an efficient tool for power utilities in computing surface electric field especially for dry condition. The second achievement is the droplet vibration study which describes the droplets' behaviour under rain conditions, such as the phase shift between the voltage and the vibration magnitude, the ejection phenomena and the electric field enhancement due to the shape change of droplets. The third contribution is the development of a standardized procedure in assessing noise emission level and the characteristics of noise emissions for various types of existing conductors in National Grid.

In cold climate regions, overhead transmission lines are prone to atmospheric icing which can be a source of several dynamic effects. The work presented in this study is concerned with accurate numerical modelling of the propagation or progression of ice shedding phenomena following an initial trigger such as a controlled shock load applied locally with a cable de-icing device, or uncontrolled shocks due to cable rupture or random ice dropping. An improved ice failure model for glaze ice cylindrical deposits on a stranded wire is proposed to study ice shedding effects. The model is verified with the results of forced ice shedding experiments on a reduced-scale single-span model tested by Kálmán (2007) at CIGELE Laboratory of Université du Québec at Chicoutimi (UQAC). The physical model is a 4 m span of a 4.1 mm diameter flexible stainless cable with an initial sag-to-span ratio of 6%. In the present study, the ice deposit is assumed elastic-plastic and the failure criterion is based on maximum normal strains; the numerical results are in better agreement with the experimental data as compared to the previous study by Kálmán (2007) who assumed a maximum normal stress failure criterion. The challenge is to predict not only the fracture of the ice deposits but also whether the fractured deposits will remain attached to the conductor or will fall off. In the tests, iced spans (loaded with different ice thicknesses) were subjected to a concentrated shock load applied at the mid span. Commercial software ADINA is used to simulate the nonlinear dynamic response of the iced cable to the shock load and subsequent ice-shedding transient effects.This new iced cable model and failure criterion is implemented to conduct numerical simulations of real-scale single spans subjected to shock loads, and the results are compared with previous work by Kálmán (2007).Following the improved performance of the new ice failure model, it has been applied to the case study of a Hydro-Québec 120 kV two-circuit line section that failed during an ice storm event in the spring of 1997. This line has suffered two conductor ruptures that initiated the subsequent failure of two suspension structures. A nonlinear dynamic analysis is performed which considers ice-shedding effects following the conductor ruptures. The results are compared with those of Lapointe (2003) who considered only conductor rupture effects on the fully iced line section.
En régions froides, les lignes aériennes de transport sont exposées au givrage atmosphérique qui peut devenir la source de plusieurs effets dynamiques. Cette étude porte sur la modélisation numérique de la progression des phénomènes de délestage de glace des conducteurs de ligne suivant l'application d'un choc mécanique local généré par un dispositif de dégivrage de câble, ou l'effet des chocs non contrôlés dus à la rupture de câbles ou au délestage aléatoire naturel de la glace. Un modèle amélioré pour simuler la rupture du manchon cylindrique de glace accumulé sur un câble est proposé dans cette étude et vérifié à l'aide de résultats expérimentaux obtenus par Kálmán (2007) sur un modèle réduit d'une portée unique au laboratoire CIGELE de l'Université du Québec à Chicoutimi (UQAC). Le modèle physique a une portée de 4 m et est composé d'un câble en acier inoxydable flexible de 4.1 mm de diamètre avec un rapport flèche/portée de 6%. Dans le modèle proposé, le dépôt de glace est supposé élastique-plastique et le critère de rupture est basé sur les déformations normales; les résultats des simulations numériques sont en meilleur accord avec les données expérimentales que celles de l'étude précédente de Kálmán (2007) qui utilisait un critère de rupture basé sur les contraintes normales. Le défi des simulations numériques du délestage de glace est de prévoir non seulement la fissuration des dépôts de glace mais également si leur détachement est complet du conducteur. Lors des essais, des portées de câble glacé (chargées avec différentes épaisseurs de glace) ont été soumises à un choc appliqué à mi-portée. L'étude utilise le logiciel commercial ADINA AUI 8.5 pour simuler la réponse dynamique non linéaire du câble glacé suite au choc appliqué. Le nouveau critère proposé pour la rupture du dépôt de glace est ensuite utilisé pour simuler la réponse de portées uniques à l'échelle réelle soumises à des chocs appliqués à mi-portée, et les résultats sont comparés à ceux de l'étude de Kálmán (2007).Finalement, le modèle amélioré a été appliqué à l'étude du cas d'une section de ligne biterne à 120 kV d'Hydro-Québec qui a été endommagée lors d'une tempête de verglas en 1997. Cette ligne de ligne a subi deux ruptures de conducteur qui ont causé l'effondrement de deux pylônes de suspension. Cet événement avait été déjà été modélisé par Lapointe (2003) mais sans la possibilité de tenir compte du délestage de glace suite aux chocs de rupture des conducteurs.

While great efforts have been made in the electrical utility industry to engineer various stranded conductors with enhanced strength and vibrational characteristics, research devoted to understanding the complex mechanical behavior of complete conductors has been scarce, especially from a computational mechanics perspective. In the meanwhile, the long-lasting problem of conductor fretting fatigue becomes increasingly critical for overhead line design and maintenance, especially with the world-wide aging of electrical transmission grids. Aging of conductors contributes to significant degradation of their local fatigue strength, leading to drastic reduction of their service life. However, the complex mechanical response of stranded conductors cannot be well predicted by either experimental testing or simplified theoretical models, owing to the physical complexity introduced by their multi-layer stranded geometry, nonlinear material properties, substantial frictions among the wires and between the wires and hardware clamping systems, as well as the comprehensive contact interactions amongst their components. Simplified beam models and coarse 3-D models of earlier computational studies also fail to calculate the accurate stress variations inside a conductor strand and capture the stress gradients near the contact interfaces. Moreover, the estimations of fretting fatigue life are very dependent on the high accuracy of the stress predictions in the conductor wires. Therefore, reliable high-fidelity computational models have been long expected for a better understanding of the contact damage of transmission line conductors under both design and fretting fatigue conditions. The main objective of this thesis is to study the complex stress states and relevant influencing factors of stranded electrical conductors, using finite element analysis approaches. The research was carried out in three stages. First of all, a study focused on the finite element (FE) modeling of an optical ground wire (OPGW) cable strand for its detailed stress analysis. A refined 3-D FE model including all essential nonlinear characteristics was successfully constructed. As a result, a high-fidelity physics-based macroscopic modeling methodology was developed for detailed and accurate computational stress analysis of stranded conductors. A 795 kcmil Drake ACSR conductor was then selected as a benchmark conductor to investigate the tensile strength and critical stress states of a complete conductor under extreme design conditions. Furthermore, a sensitivity study explored the relative importance of friction effects among conductor wires on the mechanical response.A large scale 3-D FE stress analysis model with comprehensive nonlinearities was developed and implemented to simulate an actual ACSR fretting fatigue test. The computational results showed good agreement with some experimental measurements and field observations reported in the open literature. Based on the accurate stress analysis, a practical multi-axial fatigue lifing methodology was developed to estimate local fretting fatigue strength of electrical conductors. Subsequently, a parametric study was performed to examine the influence of fretting amplitudes on the mechanical response of the conductor-clamp system.In conclusion, this research shows the reliability and significance of using reliable FE modeling in predicting the complex response of stranded conductors, which has contributed to fill some of the current knowledge gaps. Furthermore, the computational modeling and lifing approaches developed in this thesis provide a different perspective from existing practices and may become a starting block of further exploration of the mechanisms of conductor fretting fatigue and future development of improved fatigue lifing methods for the increasingly aging overhead transmission line conductors.
Malgré les efforts déployés par l'industrie des lignes de transport d'électricité pour la conception de conducteurs toronnés de haute résistance mécanique, la recherche dédiée à la compréhension physique du comportement mécanique des conducteurs s'est faite plus rare, surtout du point de vue de la mécanique computationnelle. Le problème du vieillissement des conducteurs de lignes aériennes à haute tension, en particulier celui de l'usure en fatigue des brins et torons, n'est toujours pas complètement compris ni donc résolu. Le vieillissement des conducteurs se manifeste par une dégradation importante de leur résistance locale à l'usure en fatigue, réduisant par le fait même leur vie utile et la robustesse mécanique de l'ensemble de la ligne. Il faut reconnaître que les études expérimentales et les modèles théoriques simplifiés ne peuvent pas prédire le comportement mécanique détaillé des conducteurs toronnés à cause de la complexité physique de ces câbles: torons et brins multicouches, matériaux inélastiques non-linéaires, effets des frictions substantielles entre les brins, torons et les surfaces des accessoires d'attache, ainsi que les interactions de contact entre ces éléments.Les travaux rapportés dans la thèse procèdent en trois étapes principales, décrites ci-après. La première partie consiste à préparer un modèle de section de câble de garde à fibre optique (CGFO) de construction complexe et d'en faire l'analyse détaillée sous déplacement axial contrôlé. Cette étape a servi à établir les bases de la méthodologie proposée, lesquelles sont discutées de manière exhaustive. La deuxième partie de la recherche porte sur la modélisation raffinée du conducteur de ligne ACSR 795 kcmil qui porte le nom de code « Drake », sélectionné comme cas de référence pour étudier la résistance en traction et les états de contraintes complexes du conducteur sous des conditions de conception extrêmes de conception. sensibilité a également exploré l'importance relative des effets frictionnels entre les brins du câble sur les contraintes calculées par le modèle. Finalement, un modèle détaillé 3-D est créé pour simuler les conditions précises d'un essai typique de fatigue en flexion pour le conducteur « Drake » jumelé à une pince de suspension. Le modèle retient toutes les non-linéarités du problème d'un point de vue mécanique. l'auteur suggère une méthode pratique pour évaluer la résistance locale en fatigue multiaxiale des conducteurs du type ACSR au droit des points de contact des pinces de suspension. Cette méthode est relativement simple d'application (une fois les analyses de contraintes disponibles) et donne des résultats en accord avec les valeurs recommandées par les manufacturiers pour le câble « Drake ». Par la suite, une étude paramétrique est faite pour vérifier l'influence de l'amplitude des mouvements de glissement sur les états de contraintes déterminés dans le conducteur dans la région de contact avec la pince sous l'effet d'un cycle complet de chargement flexionnel. En conclusion, cette recherche démontre la faisabilité et la pertinence de l'usage des méthodes computationnelles avancées pour l'analyse des contraintes d'un problème complexe comme celui des conducteurs toronnés multicouches. La méthodologie de construction des modèles est une contribution scientifique importante qui permet d'améliorer notre compréhension du comportement mécanique des conducteurs sous charges extrêmes ou dans des conditions de fatigue flexionnelle. La méthode proposée pour l'estimation de la résistance à l'usure en fatigue est également utile pour l'industrie des lignes de transport et pour les manufacturiers de câbles et il est envisageable que cette recherche servira de tremplins à plusieurs autres études computationnelles pertinentes sur les conducteurs de lignes afin d'améliorer leur fiabilité et leur robustesse mécanique.

An overhead power transmission conductor must maintain a safe distance from the objects underneath it. However, this distance decreases with time, even under conditions where metallurgical creep of the cable material does not occur, for instance, at room temperature. This phenomenon is first identified as "pseudo creep".
The creep behavior of a cable is directly related to its mechanical properties, which correspond to the applied loads under certain boundary conditions. Twist due to cable rotation and radial compression due to layer-to-layer contact are taken into consideration, so that a deeper understanding of what happens inside the cable and a quantitative assessment of their influence on the effective rigidity of the cable are obtained.
The radial creep of a cable is found to be more sensitive, since it takes a longer time to saturate owing to the accumulation of the radial deformations of individual wires and the time-dependent expansion and relocations of the hardened areas.
The time-dependent behavior of a cable is evaluated by experiments. Comparisons of the configurational parameters that determine the cable behavior are made for particular load types and boundary conditions.

It is important to keep an overhead power line within rated operating conditions. Thus,an accurate prediction of the conductor's thermal and electrical behavior leads to an increasein reliability and eciency. Under DLR operation, the current rating is adjustedbased on ambient weather and solar conditions to allow for dynamic line loading. Therating adjustment takes into account the cooling mechanisms acting on the conductor. Inthis thesis, cooling by means of convective heat transfer is studied based on wind tunnelexperimental measurements of three dierent conductor samples. Convection contributesto most of the cooling; however, it is aected by wind speed and direction. Two angle ofattacks were studied (40 and 90), where perpendicular ow was found to result in bettercooling. The location of boundary layer separation highly aects the surface distribution ofcooling, which is non-uniform. Oblique wind ow results in reduction in overall cooling dueto earlier boundary layer separation. Finally, the surface average convective heat transfercoecient correlates non-linearly with the Reynolds number, where higher wind speeds andlarger conductor diameters can lead to signicant improvements in cooling while keepingrelatively low current densities. The existing standards of IEEE and CIGRE were found tooverestimate the eect of convective cooling for the specic experimental cases.
Det är viktigt att hålla en kraftöverföringsledning inom nominella driftsförhållanden.Således leder en korrekt förutsägelse av ledarens termiska och elektriska beteende till en ökad tillförlitlighet och effektivitet. Under DLR-drift justeras nuvärdet baserat på omgivande väder och solförhållanden för att möjliggöra dynamisk belastning. Klassificeringsjusteringen tar hänsyn till de kylmekanismer som verkar på ledaren. I denna avhandling studeras kylning med hjälp av konvektiv värmeöverföring baserat på provning av vindtunnel av tre olika ledartyper. Konvektion bidrar till det mesta av kylningen. Det påverkas dock av vindhastighet och riktning. Två angreppsvinkelar studerades (40◦ och 90◦), där vinkelrätt flöde befanns resultera i bättre kylning. Placeringen av ytskiktseparationen har stor inverkan på ytfördelningen av kylning, vilken är ojämn. Skrå vindflöde resulterar i minskning av den totala kylningen på grund av tidigare separering av gränsskiktet. Slutligen korrelerar den ytvärdesöverföringskoefficienten för ytvärdet icke-linjärt med Reynolds-talet, där högre vindhastigheter och större ledardiametrar kan leda till signifikanta förbättringar i kylning samtidigt som relativt låga strömtäthet hålls. De befintliga standarderna för IEEE och CIGRE visade sig överskatta effekten av konvektiv kylning för de specifika experimentellafallen.

Thesis (M. Tech.) - Central University of Technology, Free State, 2011
The objectives of this research were to investigate and establish a procedure to determine the self-damping characteristics of transmission line conductors subjected to free and forced vibrations. The TERN and Aero-Z IEC62219-REV240609 conductor cables were the transmission line conductors that were readily available at the Vibration Research and Testing Centre (VTRC) of the University of KwaZulu-Natal (UKZN). The question to be answered was whether the self-damping characteristics of the TERN and Aero-Z IEC62219-REV240609 conductors were adequate to suppress Aeolian or wake-induced vibrations. In other words, is it necessary for external damping mechanisms to be used with these conductors? This study confirmed that the self-damping characteristics of conductors are not adequate to suppress Aeolian or wake-induced vibrations. Governing partial differential equations describing the characteristics of the catenary and parabolic cable conductors were developed to validate the experimental results. The experimental tests involved both conductors being subjected to an impulse function (a free vibration method) and also to a harmonic function (a forced vibration method). Measurements were carried out using accelerometers, and the recording equipment consisted of oscilloscopes and the PUMA system. With both the free and forced vibration methods, the damping factor of the TERN conductor was confirmed to be ζ ≤ 0.05, whereas the damping factor of the Aero-Z IEC62219-REV240609 was confirmed to be ζ ≤ 0.2. A procedure for determining the self-damping characteristics of the TERN and Aero-Z IEC62219-REV240609 conductors was developed, with the damping factor found to be ζ ≤ 0.2 for both conductors. These methods can assist in the implementation of procedural analysis of the self-damping behaviour of different types of transmission conductors and in finding the most suitable mass absorber (damper) to use in reducing the rate of failure of transmission line conductors. The results of this study can be used to improve the mathematical modelling of Aeolian and wind-induced vibrations where both self-damping properties and a mass absorber are incorporated.

Le fluage est l'un des phénomènes qui influencent le comportement des conducteurs aériens de transport d'énergie électrique. Il s'agit d'une déformation irréversible qui apparaît dans les structures soumises à des charges mécaniques permanentes. Ce phénomène commence à l'instant où la charge est appliquée et continue, à un taux décroissant, aussi longtemps que la charge et la température sont maintenues. Dans les conducteurs en portée, le fluage se manifeste par l'augmentation de la flèche et la réduction des distances sécuritaires entre les lignes et le sol. D'autre part, la température moyenne des conducteurs, transportant en continue un courant électrique important, peut être largement supérieure à la température ambiante, ce qui influence le phénomène de fluage des câbles. Dans ce cadre, s'inscrit ce projet de maîtrise qui consiste à évaluer l'effet de la température sur le comportement en fluage des conducteurs en mesurant l'allongement des fils qui les constituent. Pour ce faire, un banc d'essai de fluage des câbles a été conçu pour étudier le fluage sur les conducteurs et un banc d'essai de fluage des brins a été utilisé pour déterminer le comportement en fluage des fils. Pour les conducteurs, un essai préliminaire de fluage, de 400 heures, a été effectué sur un conducteur de type AAC (Orchid) pour valider le montage expérimental et vérifier l'effet de la mise en place des brins sur le fluage. Le câble a été testé à 38°C et à 25% de sa résistance à la traction assignée (RTA). Pour les essais sur les brins, les fils d'aluminium 1350-H19 et d'almélec ont été testés en fluage pendant 1000 heures. Les fils ont été soumis à quatre niveaux de température d'opération : 20°C, 38°C, 55°C et 70°C et à quatre niveaux de contrainte : 15%, 25%, 35% et 47% RTA pour l'aluminium et 8%, 15%, 25% et 35% RTA pour les fils en almélec. De plus, des essais de traction sur des fils en aluminium et en alliage d'aluminium ont été effectués pour évaluer l'effet du fluage et de la température sur le comportement mécanique des fils isolés. Ces résultats ont permis d'étudier l'effet de la température et de la contrainte sur le fluage des conducteurs à travers le fluage des fils. À partir des données expérimentales, une loi d'évolution de fluage a été établie et tient compte du taux de chargement et de la température.

Le vieillissement des lignes de transport d’énergie électrique est une problématique majeure des réseaux. D’ailleurs, des problèmes se posent au plan de l’évaluation de l’état des conducteurs qui, soumis aux vibrations éoliennes, sont vulnérables à l’endommagement en fatigue. Surtout présent aux pinces de suspension, ce phénomène est encore difficile à quantifier, notamment quant à la prédiction de la durée de vie résiduelle des conducteurs. D’autre part, avec le besoin croissant d’optimiser l’exploitation du réseau tout en maintenant sa fiabilité, une estimation précise de l’état d’endommagement des conducteurs est primordiale. Pour cela, une caractérisation des sollicitations à l’échelle des brins est d’abord requise. L’objectif principal de cette thèse vise donc le développement d’une stratégie de modélisation et d’analyse des conducteurs sollicités en vibrations éoliennes permettant une évaluation précise des conditions de chargement locales à l’échelle des brins, tout en tenant compte de l’effet de la géométrie des pinces de suspension. Une stratégie de modélisation 3D des solides toronnés est d’abord développée avec la méthode des éléments finis selon une discrétisation individuelle des brins par éléments poutres, capable de traiter toutes les interactions inter-filaires en frottement. Cette modélisation traduit efficacement la cinématique des torons tout en donnant accès aux charges locales. Son caractère général lui permet aussi d’être appliquée à tout problème impliquant des torons. Appliquée à l’étude des conducteurs sous l’effet des vibrations éoliennes, la stratégie conduit à une description précise de leur comportement tant au plan global en flexion que de la description des contraintes aux brins. Des estimations réalistes de durées de vie en fatigue des conducteurs sont même possibles par l’application de critères d’endommagement aux contraintes. Ensuite, les pinces de suspension sont intégrées à la stratégie de modélisation selon une représentation surfacique traitant le contact pince/conducteur. Une comparaison à des mesures expérimentales met en relief la précision de l’approche. L’analyse de la solution numérique permet l’identification des zones critiques d’endommagement en contact à chacune des couches du conducteur et révèle des informations nouvelles quant à la nature de la sollicitation des brins à la pince de suspension. Finalement, des travaux exploratoires proposent un nouveau concept d’analyse multi-échelles en combinant la modélisation numérique d’un système pince/conducteur à des essais de fatigue sur brins individuels. Une mise en œuvre préliminaire de l’approche permet de valider le concept et en jette les bases en vue de son application future. En somme, la stratégie de modélisation développée dans cette thèse constitue un puissant outil d’analyse qui ouvre maintenant la voie à une caractérisation appropriée de la fatigue des conducteurs en vue ultimement de prédire leur durée et vie résiduelle.
Abstract : The aging of overhead transmission lines is a major concern for utilities. In particular, problems arise in assessing the integrity of conductors whose exposure to Aeolian vibrations renders them vulnerable to fatigue damage. Occurring mainly at the suspension clamps, conductor fatigue is still difficult to quantify, especially regarding the prediction of their residual life. With the increasing need to optimize the power grid while maintaining its reliability, accurate evaluations of the conductor damage state become crucial. To this matter, a characterization of the stress levels at the wire scale is first required. The main objective of this thesis is therefore to develop a strategy for the modeling and analysis of conductors subjected to wind induced vibrations, allowing an accurate description of the local load conditions, while accounting for the effects of the suspension clamps. A finite element wire strand modeling strategy is first developed based on a 3D beam element discretization, considering all frictional wire interactions. The modeling approach efficiently reproduces the wire strand kinematics while giving access to the local loads. Its general formulation also allows it to be applied to any problem involving strands. Applied to the study of conductors subjected to Aeolian vibrations, the strategy leads to an accurate description of their behavior at both the global strand deformations and the wire stress description. Realistic conductor residual life estimates are even possible with the use of common damage criteria. The suspension clamps are then incorporated into the modeling strategy using a surface representation of the conductor/clamp contact. Comparisons with experimental measurements highlight the precision of the approach. The model response analysis allows now the identification of the critical damage zones within each conductor layers and reveals new information about the nature of the wire stresses at the suspension clamp. Finally, exploratory works propose a new concept of multi-scale analysis combining the numerical conductor/clamp modeling strategy to experimental fatigue tests on individual wires. A preliminary implementation of the approach validates the concept and lays the foundations for its future application. In summary, the modeling strategy developed in this thesis constitutes a powerful analytical tool which now opens the way to an appropriate characterization of conductor fatigue with the ultimate objective to eventually predict their residual life.

The master’s thesis deals with the topic new isolation lines of 110 kV. The aim is to propose new insulator hangers. The first, theoretical part focuses on the development of insulators, cutting and possibilities of application. They are the different materials that are used for the production of insulators HV, advantages and disadvantages long rod and cap and pin insulators. There are also described insulator hangers. The theoretical work is to describe thefittings for overhead transmission lines, which are, used to construct a insulator hanger. The last part of the theoretical work is intended distribution towers for overhead lines HV. The practical part deals with the design of new insulator suspensions for specific lines of 110 kV. The results are drawings newly designed hangers and a list of materials (fittings) for individual towers and the total amount of material. The practical part is calculating the differences in the conductor sag using old and new insulators hangers.

As the demand for energy increases, as well as the demand for renewable energy, Vattenfall, as network owner, receives many requests to connect new wind power to the grid. The limiting factor for how much wind power that can be connected to the grid is in this case the maximum current capacity of the overhead lines that is based on a line temperature limit. The temperature limit is set to ensure a safety distance between the lines and the ground. This master thesis project is a part of a research project at Vattenfall Research and Development that is examining the possibilities of increasing the allowed current on overhead lines in order to be able to connect more wind power to the existing network. Measured data from two overhead lines in southern Sweden is analyzed and the internal relations between the measured parameters are examined. The measured parameters are overhead line sag, line temperature, ambient temperature, solar radiation, wind speed and line current. The results indicate that there is a big load margin that could be utilized to increase the maximum current as long as further work could show that low winds at line height correlates with low wind at nacelle height. The results show that the sag versus line temperature is approximately linear within the measured temperature range. This means that a real-time-monitoring system measuring the line temperature should give adequate knowledge of the line position to ensure the safety distance. A model for the line temperature as a function of insolation, current, ambient temperature and wind speed has been estimated for one of the lines. Simulations show that a sudden increase in current at a worst-case scenario would give the operators about ten minutes to react before the line reaches the temperature limit.

This thesis describes an investigation into the influences of arcing and conductor deflection due to magnetic forces on the accuracy of fault locator algorithms in electrical distribution networks. The work also explores the possibilities of using the properties of an arc to identify two specific types of faults that may occur on an overhead distribution line. A new technique using the convolution operator is introduced for deriving differential equation algorithms. The first algorithm was derived by estimating the voltage as an array of impulse functions while the second algorithm was derived using a piecewise linear voltage signal. These algorithms were tested on a simulated single-phase circuit using a PI-model line. It was shown that the second algorithm gave identical results as the existing dynamic integration operator type algorithm. The first algorithm used a transformation to a three-phase circuit that did not require any matrix calculations as an equivalent sequence component circuit is utilised for a single-phase to ground fault. A simulated arc was used to test the influence of the non-linearity of an arc on the accuracy of this algorithm. The simulations showed that the variation in the resistance due to arcing causes large oscillations of the algorithm output and a 40th order mean filter was used to increase the accuracy and stability of the algorithm. The same tests were performed on a previously developed fault locator algorithm that includes a square-wave power frequency proximation of the fault arc. This algorithm gave more accurate and stable results even with large arc length variations. During phase-to-phase fault conditions, two opposing magnetic fields force the conductors outwards away from each other and this movement causes a change in the total inductance of the line. A three dimensional finite element line model based on standard wave equations but incorporating magnetic forces was used to evaluate this phenomenon. The results show that appreciable errors in the distance estimations can be expected especially on poorly tensioned di stribution lines.New techniques were also explored that are based on identification of the fault arc. Two methods were successfully tested on simulated networks to identify a breakingconductor. The methods are based on the rate of increase in arc length during the breaking of the conductor. The first method uses arc voltage increase as the basis of the detection while the second method make use of the increase in the non-linearity of the network resistance to identify a breaking conductor. An unsuccessful attempt was made to identifying conductor clashing caused by high winds: it was found that too many parameters influence the separation speed of the two conductors. No unique characteristic could be found to identify the conductor clashing using the speed of conductor separation. The existing algorithm was also used to estimate the voltage in a distribution network during a fault for power quality monitoring purposes.

Tahle práce se zabývá monitorováním venkovních vysokonapěťových vedeních, což mohou být vedení od 70kV do 400kV. Senzory jsou umístěny na vodiči a hlavní myšlenkou je vyhodnotit mechanické chování vodičů, a to od nízkých frekvencí (zlomky Hz) až po vysoké frekvence (desítky Hz). Tahle práce se zabývala pohyby o nízkých frekvencích a vysokých amplitudách a popsala možnosti sestavení těchto pohybů na základě měření ze senzorů. Konkrétně se jedná o pohyby v případě silného větru, zkratu, opadávání ledu nebo dalších. Všechno tohle pomáhá operátorů dělat rozhodnutí ohledně provozování sítí. Vývoj zahrnuje přidání/kombinaci nových senzorů, popsání matematického algoritmu potřebného k sestavení pohybu na základě toho co bylo změřeno, ať už se jedná o hodnoty získané simulací, laboratorním testem nebo reálným měřením na vedení.

Current flow in the electrical grid is changing due to the introduction of new generators and loads.Specifically, weak Overhead lines, are a constraint for the introduction of wind farms located farfrom the central network. The current situation requires smart solutions to improve the transportationcapabilities of these grid’s components. Among the different possibilities, Dynamic Line Rating(DLR), is emerging as the most interesting solution from both the economic and technical points ofview. The presented Thesis work investigates the performance of DLR from both the theoretical andpractical perspectives.The theory behind DLR is based on the development of a thermal model able to estimate the precisetemperature experienced by OHLs conductor under different climate conditions. Since 1972, whenthe first investigation on DLR have been published, different thermal models have been developed,each with a different precision level. The first part of the thesis concerns the investigation of IEEE738 standard accuracy.The standard analysis highlighted weaknesses on the theoretical approach employed on the forcedconvective cooling calculation. Specifically the wind direction effect is estimated as the conductorwas a perfect cylinder. A wind tunnel test has been performed in order to verify the effect of theconductor’s strands on the total thermal equilibrium. The results show that an inclined wind-conductor relative direction can have a more important impacton the line rating than foreseen with the IEEE thermal model. Since the wind tunnel test has been thefirst experience of this kind pursued at KTH, the presence of few different laboratory set-updeficiencies did not allow to draw a definitive and precise conclusion on the necessary IEEE formulacorrection.The practical side of the Thesis project includes an extensive literature research on the differentdevices that can be employed for dynamic line rating and a real-case study analysis. The analysis isperformed in order to evaluate which can be the best solution when the introduction of new windenergy supply increase the load on a pre-existent OHL. Results show that, in the selected region,Värmland, in the southwestern Sweden, DLR has the prerequisites to allow the exploitation of thehigh wind energy resource at the lower expenses. Wind energy production is often associated with anincreased cooling on the line’s conductors. This means that higher current levels can be withstoodavoiding the need for expensive lines’ upgrading. For the selected hot-spot, in 2015, DLR wouldhave allowed a transport capability improvement of 69.6% during the summer and of 26.7% duringthe winter. It is also reported that a load equal to the SLR during the winter period would have causedserious overheating transients of the conductor. Overall DLR proved to allow technical and economicbenefit for the system operator.
Flödet genom elnätet förändras på grund av införandet av ny generering och nya typer av laster.Specifikt är svaga luftledningar en begränsning för installation av vindkraft som ligger långt fråndet centrala nätet. Den nuvarande situationen kräver smarta lösningar för att förbättratransportkapaciteten i elnätet. Bland de olika möjligheterna finns Dynamic Line Rating (DLR) somframstår som den mest intressanta lösningen från både ekonomiska och tekniska synvinklar. Det härexamensarbetet behandlar resultatet av DLR från både teoretiska och praktiska perspektiv.Den teoretiska grunden för DLR är baserad på utvecklingen av en termisk modell som kan skattatemperaturen i luftledningar under olika klimatförhållanden. Examensarbetets första del behandlaren undersökning av IEEE 738 standarden (DLR standard). IEEE 738 standarden utgår från ledarensom en perfekt cylinder. Något som har en effekt bland annat i effekten av vindriktning. Ettvindtunnel test har utförts för att verifiera effekten av fler kardelers effekt på den totala termiskajämvikten. Resultaten visar att antalet kardeler har en betydande effekt på den termiska jämviktenoch då alltså även på DLR.Den andra delen av examensarbetet innehåller en omfattande litteratursökning på de olikaapparaterna som kan användas till DLR samt en praktik undersökning/analys. Analysen utförs föratt utvärdera vilken lösning som kan vara den bästa vid införandet av mer vindkraft, som ökarbelastningen på en redan existerande luftledning. Resultaten visar att, i det valda området,Värmland, i sydvästra Sverige, har DLR förutsättningar för att medge ökat utnyttjandet av den storavindkraft resurs som finns där till relativt låga kostnader. Slutsatsen av examensarbetet är att DLR ger tekniska och ekonomiska fördelar tillsystemoperatören.

Based on conventional static line rating method, the actual current carrying capability of overheadconductors cannot be judged. Due to continuous increment in electricity demand and the difficultiesassociated with new line constructions, the overhead lines are therefore required to be rated based on amethod that should establish their real-time capability in terms of electricity transmission. The methodused to determine the real-time ampacity of overhead conductors not only can enhance their transmissioncapacity but can also help in allowing excessive renewable generation in the electricity network. In thisdiploma work, the issues related to analyzing an impact of wind power on periodical loading of overheadline as well as finding its static and dynamic ampacities with line current are investigated in detail.Initially, in this project, the investigation related to finding a suitable location for the construction of a 60MW wind farm is taken on board. Thereafter, the wind park is integrated with a regional grid, owned byFortum Distribution AB. In addition to that, the electricity generated from the wind park is also calculatedin this project. Later on, the work is devoted to finding the static and dynamic line ratings for‘VL3’overhead conductor by using IEEE-738-2006 standard.Furthermore, the project also deals with finding the line current and making its comparison withmaximum capacity of overhead conductor (VL3) for loading it in such a way that no any violation of safeground clearance requirements is observed at all. Besides, the line current, knowing the conductortemperature when it transmits the required electricity in the presence of wind power generation is also animportant factor to be taken into consideration. Therefore, based on real-time ambient conditions withactual line loading and with the help of IEEE-738-2006 standard, the conductor temperature is alsocalculated in this project.At the end, an economic analysis is performed to evaluate the financial advantages related to applying thedynamic line ratings approach in place of traditional static line ratings technique across an overheadconductor (VL3) and to know how much beneficial it is to temporarily postpone the rebuilding and/orconstruction of a new transmission line. Furthermore, an economic analysis related to wind power systemis taken into consideration as well to get familiar with the costs related to building and connecting a 60MW wind farm with the regional grid.

In Deutschland und Europa ist im Zuge der Energiewende erforderlich, mehr Elektroenergie mit bestehenden Freileitungen zu transportieren. Eine technische Lösung, mit der dieses Ziel erreicht werden kann, ist das Umbeseilen der Freileitung mit Hochtemperatur-Leiterseilen mit geringem Durchhang (High Temperature Low Sag – HTLS conductors). Diese Leiterseile haben gegenüber konventionellen Leiterseilen (z. B. Aluminium/Stahl-Leiterseilen) höhere Bemessungsströme und temperaturen. Die stromführenden Verbindungen mit HTLS-Leiterseilen werden damit ebenfalls höher thermisch belastet. Diese sind für den zuverlässigen und sicheren Betrieb der Freileitung sehr wichtige Betriebsmittel. Neben anderen Verbindungstechnologien hat sich bei den stromführenden Verbindungen mit konventionellen Leiterseilen das Sechskantpressen seit Jahrzehnten bewährt. Aus der Literatur sind fast ausschließlich empirische Untersuchungen mit dieser Verbindungstechnologie bekannt. Das elektrische Kontaktverhalten von Pressverbindungen wurde bisher nur unzureichend untersucht. In dieser Arbeit wird dazu ein elektrisches Modell vorgestellt und weiterentwickelt, mit dem das elektrische Kontaktverhalten von Pressverbindungen genauer beschrieben werden kann. Weiterhin werden prinzipielle Zusammenhänge zwischen der Stromverteilung in den Kontaktpartnern und deren Einfluss auf den Verbindungswiderstand dargestellt. Als Ergebnis von theoretischen und experimentellen Untersuchungen konnten allgemeine Empfehlungen für das Dimensionieren von Pressverbindungen mit konventionellen und HTLS-Leiterseilen erarbeitet werden. Aus der prinzipiellen Funktionsweise einer Pressverbindung ist bekannt, dass der Form-, der Kraft- und der Stoffschluss in der Verbindung das elektrische Kontaktverhalten beeinflussen. Insbesondere der Kraftschluss wurde in der Literatur bislang nur näherungsweise berechnet. In den bekannten analytischen Modellen werden die Geometrie der Kontaktpartner sowie das Werkstoffverhalten vereinfacht und die mechanischen Belastungen beim Fügen der Verbindung nicht genau genug berücksichtigt. Aus den genannten Gründen wurde das Fügen von Pressverbindungen mit mehrdrähtigen Leiterseilen mit der Finite-Elemente-Methode (FEM) berechnet. Die Press- und Kontaktkräfte konnten damit für alle Kontaktflächen in einer Verbindung ermittelt werden. Es konnte gezeigt werden, dass insbesondere hohe Press- und Kontaktkräfte die Ursache für ein gutes elektrisches Kontaktverhalten einer Pressverbindung sind. Die physikalischen Ursachen dieses Zusammenhangs werden diskutiert. Das Langzeitverhalten von Pressverbindungen mit Verbund-Leiterseilen wurde experimentell untersucht. Die Ergebnisse der durchgeführten Langzeitversuche zeigen den Einfluss der Kontaktkraft im elektrischen Langzeitverhalten qualitativ auf. Bei den Pressverbindungen, für die nur sehr geringe Kontaktkräfte berechnet wurden, war das elektrische Langzeitverhalten weniger stabil
In Germany and in Europe it is due to the “Energiewende” necessary to transmit more electrical ener-gy with existing overhead transmission lines. One possible technical solution to reach this aim is the use of high temperature low sag conductors (HTLS-conductors). Compared to the common Aluminium Conductor Steel Reinforced (ACSR), HTLS-conductors have higher rated currents and rated tempera-tures. Thus the electrical connections for HTLS-conductors are stressed to higher temperatures too. These components are most important for the safe and reliable operation of an overhead transmission line. Besides other connection technologies, hexagonal compression connections with ordinary transmis-sion line conductors have proven themselves since decades. From the literature, mostly empirical stud-ies with electrical tests for compression connections are known. The electrical contact behaviour, i.e. the quality of the electrical contact after assembly, of these connections has been investigated insuffi-ciently. This work presents and enhances an electrical model of compression connections, so that the electrical contact behaviour can be determined more accurate. Based on this, principal considerations on the current distribution in the compression connection and its influence on the connection re-sistance are presented. As a result from the theoretical and the experimental work, recommendations for the design of hexagonal compression connections for transmission line conductors were devel-oped. Furthermore it is known from the functional principle of compression type connections, that the elec-trical contact behaviour can be influenced from their form fit, force fit and cold welding. In particular the forces in compression connections have been calculated up to now by approximation. The known ana-lytical calculations simplify the geometry and material behaviour and do not consider the correct me-chanical load during assembly. For these reasons the joining process of hexagonal compression con-nections with stranded overhead transmission line conductors was calculated with the finite element method. The compression forces and the residual contact forces were determined for all contacts be-tween barrel and conductor as well as between the wires of the conductor. It was shown, that high compression and residual contact forces are the main cause of good electrical contact behaviour. The physical relations are discussed. The electrical long-term behaviour was furthermore investigated in experiments. The results confirm the influence of the residual contact force on the long-term behaviour qualitatively. Those compression connections, which had only small residual contact forces, were less stable in the long-term tests

This diploma thesis is concerned with reconstruction of distribution network in Hruba Vrbka. The diploma thesis is divided in two parts. For better understanding to this issue, the first theoretical part is shortly dedicated to the history of electrical power system, to the several types of distribution network of low voltage and high voltage and their utilization in the area, considering the reliability and the quality of delivery of the electric energy. In this thesis there is mentioned division of distribution grids according to placing of cable lines, according to voltage and according to type of grid connection. Next part of this work is dedicated to the description of overhead lines and cable lines and their characteristics. For the proper concept of the grid we should know some characteristics of the electric line’s proposal: mechanical strength, warming, voltage drop, efficiency, degree of safety and provision of delivery. In the end of the theoretical part there are described methods for calculation of grid’s steady state as a linear task and also non-linear task, elimination of the balancing node, the iterative method, the reduction of external power take-off nodes and the solution of the steady state of the network through the direct current model. The second part of the diploma thesis is concerned with the calculation of the steady state in the village Hruba Vrbka. In this part is also described the KASI program which was used for the calculation of the grid’s steady state. Firstly low voltage grid’s balance in Hruba Vrbka was found out and evaluated and then there were proposed some solutions of the reconstruction for the grid improving. The suggested options of the reconstruction are considered from technical and economical point of view and the best solution is chosen. For this solution there is suggested the protection through program SICHR 9. In the end of this diploma thesis there is checked the load of the high voltage line.

The dissertation describes several types of low and high voltage distribution networks including their implementation in specified location with regards to the reliability and quality of electric power supply. The distributions networks are classified according to ways of cable routing, distribution line voltage levels as well as according to types of network interconnections. The high and low voltage distribution networks are further categorized based on used cable types, where, more attention is paid to insulated lines used in the Czech Republic, low voltage lines called „AES“ and „PAS“ high voltage lines used more and more during the distribution network reconstruction. Attention is also given to the description of used methodology for the calculation of network performance stability. An individual part of the dissertation is devoted to a low voltage distribution network proposal in the village of Kovalovice. Based on performed analysis of distribution network conditions, several reconstruction versions were proposed with the help of „KASI“ software, the description of which is also included. The proposed versions are further analysed for both, technical and economical aspects and is selected most suitable version of the distribution network.

The thesis aims to examine the impact of climate change on line rating and to investigate the possibility of a potential increase of capacity of an overhead line. The line rating of an overhead line determines how much current can be transmitted in the line. The weather parameters which affect the line rating are ambient temperature, solar radiation, wind speed, and wind direction. If the line rating is adapted to weather conditions, it is important to be able to predict how the weather will change in the future. Therefore, the impact of climate change on weather parameters is investigated. The ambient temperature and solar radiation are expected to change between different scenarios. However, it is unclear how wind speed and wind direction will be affected. Climate scenarios are designed that take these findings into account. The results show that wind speed has, by a large margin from other weather parameters, the largest impact on the dynamic line rating. This is followed by the wind's angle of attack to the conductor, ambient temperature, and finally solar radiation. For the designed climate scenarios, the dynamic line rating is almost the same in each case, which means that the calculated change in ambient temperature and solar radiation has no significant effect on the line rating. To further increase the capacity of the overhead line, the line could be upgraded with a conductor with a larger cross-sectional area.

The South African economy is an emerging market and as such there is a continued and growing need for the efficient supply of cost effective electricity. The capital investment involved in the design, construction, installation and commissioning of overhead transmission line networks are high and so too are the subsequent maintenance and operation costs, incurred over their life cycle periods. The need to improve the electrical operating efficiency of existing and future electrical transmission networks, through the reduction of electrical losses, focused and motivated the research in this particular area. The results and findings produced by this research study show that the magnetic induction produced by the steel core in ACSR (Aluminium conductor, steel reinforced) conductors cause in increase in the ac power losses, associated ac-dc resistance ratio and the effective ac resistance of the conductor, whilst the conductor is energised during normal operation. More specifically, the key parameters that cause this increase in the effective ac resistance of the conductor, as a result of the magnetic induction produced by the steel core, are those of hysterisis and eddy current power losses in the steel core and an added power loss caused by the non-uniform redistribution of current in the layers of aluminum wires, due to the ‘transformer effect’. Therefore the addition of the conductor dc resistance value to the component resistances produced by the current redistribution and magnetic hysterisis & eddy current power losses, form the total effective ac conductor resistance. This is contrary to standard practice where assumption is made that the conductor ac and dc resistance values are equal. The factors which influence the magnetic induction, include amongst others; the ferromagnetic properties of the steel core, the physical construction of the conductor, the conductor operating/core temperature and the load current. In order to calculate the effective ac-resistance of multi-layer ACSR conductors a computer simulation program was developed, which was largely based on determining the impact of varying these key factors, by evaluating its effect on the ac resistance of the conductor. It was found through manipulation of these factors that the total effective ac resistance of the conductor could be reduced and significantly so with higher load currents. The conductor sample used in this research study is commonly known as TERN ACSR conductor in the South African market and it was shown that with practical changes in lay ratios or lay lengths, one is able to reduce the total effective ac resistance of the conductor and associated power losses. Several software simulation exercises were performed using the developed software simulation program, to ultimately produce a set of optimised lay-lengths (lay-ratios) for the TERN ACSR conductor, with the intention that these simulated parameters would be employed in the production of actual conductor samples. The intention going forward after the planned production trial runs would be to test these conductor samples to verify compliance, in meeting both electrical and mechanical performance requirements. It should be noted that the planned production trials and relevant conductor-testing processes did not form part of the scope of this research report but are processes that have been planned for in the near future. Although testing to IEC 61089 are post processes that are planned for outside of this research scope, the specification requirements of IEC61089 were incorporated into the various computer simulation exercises.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

abstract: The future grid will face challenges to meet an increased power demand by the consumers. Various solutions were studied to address this issue. One alternative to realize increased power flow in the grid is to use High Temperature Low Sag (HTLS) since it fulfills essential criteria of less sag and good material performance with temperature. HTLS conductors like Aluminum Conductor Composite Reinforced (ACCR) and Aluminum Conductor Carbon Composite (ACCC) are expected to face high operating temperatures of 150-200 degree Celsius in order to achieve the desired increased power flow. Therefore, it is imperative to characterize the material performance of these conductors with temperature. The work presented in this thesis addresses the characterization of carbon composite core based and metal matrix core based HTLS conductors. The thesis focuses on the study of variation of tensile strength of the carbon composite core with temperature and the level of temperature rise of the HTLS conductors due to fault currents cleared by backup protection. In this thesis, Dynamic Mechanical Analysis (DMA) was used to quantify the loss in storage modulus of carbon composite cores with temperature. It has been previously shown in literature that storage modulus is correlated to the tensile strength of the composite. Current temperature relationships of HTLS conductors were determined using the IEEE 738-2006 standard. Temperature rise of these conductors due to fault currents were also simulated. All simulations were performed using Microsoft Visual C++ suite. Tensile testing of metal matrix core was also performed. Results of DMA on carbon composite cores show that the storage modulus, hence tensile strength, decreases rapidly in the temperature range of intended use. DMA on composite cores subjected to heat treatment were conducted to investigate any changes in the variation of storage modulus curves. The experiments also indicates that carbon composites cores subjected to temperatures at or above 250 degree Celsius can cause permanent loss of mechanical properties including tensile strength. The fault current temperature analysis of carbon composite based conductors reveal that fault currents eventually cleared by backup protection in the event of primary protection failure can cause damage to fiber matrix interface.
Dissertation/Thesis
Fault current temperature relationship program in C
Current temperature relationship program in C
M.S. Electrical Engineering 2014

L'objectif général de cette recherche était de développer des modèles capables de simuler les processus de fonte de la neige accumulée sur des conducteurs aériens et de prévoir leur délestage, dans diverses conditions météorologiques et types de transmission de courant. Dans le but de valider ce nouveau modèle, un certain nombre de tests expérimentaux ont été réalisés aux laboratoires de la CIGELE, à l'aide d'une chambre climatique et de la soufflerie réfrigérée, qui ont ensuite été comparés avec ceux simulés numériquement. Premièrement, des simulations en deux dimensions Reynolds Average Navier-Stokes (RANS) ont été effectuées avec FLUENT pour prédire le coefficient de distribution du transfert de chaleur local, le long de la surface du manchon avec flux transversal d'air, ainsi que le taux global de transfert de chaleur. Ces investigations permettent de connaître les caractéristiques de la convection forcée autour d'un manchon de neige, et également les effets dus à la rugosité de la surface de la neige et à la forme non-circulaire du manchon. Elles montrent aussi l'effet significatif de la rugosité de surface sur le taux de transfert de la chaleur. Deuxièmement, un modèle microstructural a été développé pour estimer la conductivité thermique équivalente de la neige sèche, qui établit la relation entre la conductivité thermique équivalente et la microstructure de la neige sèche dans divers régimes de température. Ces résultats ont été comparés avec ceux de recherches antérieures, montrant un bon accord. De plus, une série d'expériences a été réalisée dans les laboratoires de la CIGELE et leurs résultats ont été comparés avec ceux du modèle. Finalement, une relation entre le modèle de conductivité de la neige et la température a été proposée. Troisièmement, un modèle numérique 2-D en fonction du temps, de la percolation de l'eau dans un manchon de neige fondante a été établi sur la base de la méthode de Galerkin. L'influence de la vitesse du vent, de la température de l'air, de l'effet Joule, de la rugosité de la surface de la neige et de la dimension des grains de neige a été étudiée. Les résultats du modèle montrent que l'effet Joule et la rugosité de la surface de neige ont des effets notables sur la percolation de l'eau. Le temps requis pour parvenir à un état de quasiéquilibre est réduit de 50% ou plus, si le courant électrique ou la rugosité de surface excèdent certaines valeurs critiques. On a trouvé que les résultats du modèle concordaient bien avec ceux obtenus expérimentalement aux laboratoires de la CIGELE. Quatrièmement, la question de la détermination du déclenchement du délestage de la neige a été étudiée. Un tel modèle analytique est basé sur un modèle de défaillance de la neige sèche et sur des essais expérimentaux réalisés aux laboratoires de la CIGELE. Ce modèle prend en compte l'effet de l'écoulement de l'eau dans le manchon de neige. Les résultats montrent que le temps requis pour parvenir au délestage de la neige diminue de façon non linéaire alors que la teneur en eau initiale, la vitesse de l'air et l'intensité du courant électrique augmentent. Ce modèle peut fournir une estimation rapide de la chaleur de Joule ou du vent nécessaire pour déclencher le délestage de la neige sur un câble.

This dissertation deals with the challenge of power utility in South Africa which is on proactive detection of fallen power line conductors and real time sagging measurement together with slipping of such conductors. Various methods which are currently used for sag detection were characterized and evaluated to the aim of the research. A mathematical reconstruction done to estimate the lowest point of the conductor in a span is presented. Practical simulations and application of radio frequency identification (RFID) for sag detection is attempted through matlab software. RFID radar system is then analyzed in different modes and found to give precision measurement for sag in real time as opposed to global positioning system (GPS) if one dimension of the tag assumed fixed on the power line. Lastly errors detected on the measurements are corrected using a trainable artificial neural network. A conclusion is made by making recommendations in the advancement of the research.
Electrical Engineering
M. Tech. (Electrical Engineering)

博士
國立中正大學
電機工程所
98
The overhead distribution system has been constructed using mainly bare wires, and the bare wire is not insulated. The accidents occurred in overhead distribution lines are mostly caused by external contact faults which the public electric shock accident is one of reasons. These accidents will lead to reduce the reliability and the public safety of distribution systems. A modern distribution system should not only be concerned about how much economic benefit can be obtained from improving reliability, and must be able to give a guarantee of the safety level about the public lives. The reliability index is a time series to be observed and collected per year in distribution systems. In addition, another time series is to be concerned about the public safety on the occurred number of public received electric shocks per year in this dissertation. The covered conductors used in overhead lines have achieved in positive results during the recent years. For overhead distribution systems, the reliability of covered overhead lines could potentially be improved using various alternative technologies. Overhead distribution lines using the covered conductors can effectively reduce the number of the external contact faults, thus improve the reliability. Therefore, this dissertation tries to reflect on the effect of the reliability and the public safety for distribution systems using the covered conductors. The basic approaches of reliability assessment in power distribution systems are the analysis and the probabilistic simulation. This dissertation defines a set of endangered-life indices for public safety. The statistical two-sample t significance test presented in this dissertation can be used to determine the cause-and-effect relationships that exist between the covered rates and the reliability indices including public safety. In overhead distribution lines with different covered rates, the Poisson distribution, a probability statistics method, is used to analyze the probability distribution of the occurred numbers of endangered-life indices and to compare with simulations using discrete inverse transform method. Moreover, because outage events occur at unpredictable times and for different reasons, the Monte Carlo simulation approach (MCS) is a useful method that can use a computer to rapidly generate a large number of trials to simulate outage events. A practical test system is employed to analyze and simulate the reliability and safety indexes in this dissertation. The study results show that covered rates must increase greatly enough (approximately 40%) to improve the public safety. As covered rates increase, the levels of reliability and economic benefits increase. Thus, contact fault events in which a person receives an electric shock will decrease for distribution systems. Therefore, the effect of covered overhead lines cannot be described simplistically by economic quantification — the reduction in the annual number of people electrocuted is the most significant result of improving the public safety. Finally, this study focuses on how to predict the reliability and the public safety with respect to covered rates using time series modeling for the distribution system of TPC. We focus on how to forecast the reliability indices and public safety on covered rates using two regression models which are the logistic regression and dynamic regression models. The dynamic regression model is to combine the logistic regression model with time series errors in autoregressive-moving average analysis process. Results of the two fitted regression models for system reliability and public safety of TPC are presented with the square of the correlation, which are useful for planners to make decisions.

碩士
國立臺灣大學
生物產業機電工程學研究所
102
Dynamic thermal rating (DTR) technique is an effective and proper method to manage transmission lines in power system. Dynamic thermal rating utilizes on-line thermal sensors to monitor the operating temperature of overhead transmission lines, and calculates the ampacity margin of the transmission lines. The power transmission efficiency could be improved while under the safe condition. However, deploying a large number of thermal sensors may not be a viable option, because of high equipment costs and increasing the structural complexity of the power grid. A case study of the 345 kV extra high voltage transmission lines in central Taiwan was presented. The goal in this study is to allocate the minimum number of thermal sensors. Using the measurements where deploy the thermal sensor, the conductor temperature of whole transmission lines can be efficiently accurate estimation. This paper proposed an allocating placement method which is using the proper orthogonal decomposition (POD) for temperature feature extraction, and then using the memetic algorithm (MA) for determining the minimum number of thermal sensors and the optimal sensor placement to track the temperature of transmission lines and accurately estimate the full conductor temperatures. The results show that this method can be made only needs the one-fifth of sensors to estimate the conductor temperature of entire transmission line spans with high accuracy. The average mean square error is less than 1. This method can provide the operating power system a dependable technique for thermal capacity increment and the evaluation of overload risk.

In Deutschland und Europa ist im Zuge der Energiewende erforderlich, mehr Elektroenergie mit bestehenden Freileitungen zu transportieren. Eine technische Lösung, mit der dieses Ziel erreicht werden kann, ist das Umbeseilen der Freileitung mit Hochtemperatur-Leiterseilen mit geringem Durchhang (High Temperature Low Sag – HTLS conductors). Diese Leiterseile haben gegenüber konventionellen Leiterseilen (z. B. Aluminium/Stahl-Leiterseilen) höhere Bemessungsströme und temperaturen. Die stromführenden Verbindungen mit HTLS-Leiterseilen werden damit ebenfalls höher thermisch belastet. Diese sind für den zuverlässigen und sicheren Betrieb der Freileitung sehr wichtige Betriebsmittel. Neben anderen Verbindungstechnologien hat sich bei den stromführenden Verbindungen mit konventionellen Leiterseilen das Sechskantpressen seit Jahrzehnten bewährt. Aus der Literatur sind fast ausschließlich empirische Untersuchungen mit dieser Verbindungstechnologie bekannt. Das elektrische Kontaktverhalten von Pressverbindungen wurde bisher nur unzureichend untersucht. In dieser Arbeit wird dazu ein elektrisches Modell vorgestellt und weiterentwickelt, mit dem das elektrische Kontaktverhalten von Pressverbindungen genauer beschrieben werden kann. Weiterhin werden prinzipielle Zusammenhänge zwischen der Stromverteilung in den Kontaktpartnern und deren Einfluss auf den Verbindungswiderstand dargestellt. Als Ergebnis von theoretischen und experimentellen Untersuchungen konnten allgemeine Empfehlungen für das Dimensionieren von Pressverbindungen mit konventionellen und HTLS-Leiterseilen erarbeitet werden. Aus der prinzipiellen Funktionsweise einer Pressverbindung ist bekannt, dass der Form-, der Kraft- und der Stoffschluss in der Verbindung das elektrische Kontaktverhalten beeinflussen. Insbesondere der Kraftschluss wurde in der Literatur bislang nur näherungsweise berechnet. In den bekannten analytischen Modellen werden die Geometrie der Kontaktpartner sowie das Werkstoffverhalten vereinfacht und die mechanischen Belastungen beim Fügen der Verbindung nicht genau genug berücksichtigt. Aus den genannten Gründen wurde das Fügen von Pressverbindungen mit mehrdrähtigen Leiterseilen mit der Finite-Elemente-Methode (FEM) berechnet. Die Press- und Kontaktkräfte konnten damit für alle Kontaktflächen in einer Verbindung ermittelt werden. Es konnte gezeigt werden, dass insbesondere hohe Press- und Kontaktkräfte die Ursache für ein gutes elektrisches Kontaktverhalten einer Pressverbindung sind. Die physikalischen Ursachen dieses Zusammenhangs werden diskutiert. Das Langzeitverhalten von Pressverbindungen mit Verbund-Leiterseilen wurde experimentell untersucht. Die Ergebnisse der durchgeführten Langzeitversuche zeigen den Einfluss der Kontaktkraft im elektrischen Langzeitverhalten qualitativ auf. Bei den Pressverbindungen, für die nur sehr geringe Kontaktkräfte berechnet wurden, war das elektrische Langzeitverhalten weniger stabil.
In Germany and in Europe it is due to the “Energiewende” necessary to transmit more electrical ener-gy with existing overhead transmission lines. One possible technical solution to reach this aim is the use of high temperature low sag conductors (HTLS-conductors). Compared to the common Aluminium Conductor Steel Reinforced (ACSR), HTLS-conductors have higher rated currents and rated tempera-tures. Thus the electrical connections for HTLS-conductors are stressed to higher temperatures too. These components are most important for the safe and reliable operation of an overhead transmission line. Besides other connection technologies, hexagonal compression connections with ordinary transmis-sion line conductors have proven themselves since decades. From the literature, mostly empirical stud-ies with electrical tests for compression connections are known. The electrical contact behaviour, i.e. the quality of the electrical contact after assembly, of these connections has been investigated insuffi-ciently. This work presents and enhances an electrical model of compression connections, so that the electrical contact behaviour can be determined more accurate. Based on this, principal considerations on the current distribution in the compression connection and its influence on the connection re-sistance are presented. As a result from the theoretical and the experimental work, recommendations for the design of hexagonal compression connections for transmission line conductors were devel-oped. Furthermore it is known from the functional principle of compression type connections, that the elec-trical contact behaviour can be influenced from their form fit, force fit and cold welding. In particular the forces in compression connections have been calculated up to now by approximation. The known ana-lytical calculations simplify the geometry and material behaviour and do not consider the correct me-chanical load during assembly. For these reasons the joining process of hexagonal compression con-nections with stranded overhead transmission line conductors was calculated with the finite element method. The compression forces and the residual contact forces were determined for all contacts be-tween barrel and conductor as well as between the wires of the conductor. It was shown, that high compression and residual contact forces are the main cause of good electrical contact behaviour. The physical relations are discussed. The electrical long-term behaviour was furthermore investigated in experiments. The results confirm the influence of the residual contact force on the long-term behaviour qualitatively. Those compression connections, which had only small residual contact forces, were less stable in the long-term tests.