Reliability assessment methods allow the evaluation of the reliability of systems and provide important information on how to improve a system‟s life to reduce risk and hazards. With the advancement in technology, the existing methods were extended and new methods were adopted. The advancement from mechanical to numerical and analog to digital system in many applications, and deregulation of energy sector brought the need to further modify the reliability analysis methods. The scope of this research is to demonstrate the advancement of the Dynamic Flowgraph Methodology (DFM) to reliability modeling of Smart Electrical Transmission System. The reason behind this is the successful operation of electric power under a deregulated electricity market depends on transmission system reliability management. Besides this, analog electro-mechanical systems in existing power system are aging and becoming obsolete. This thesis also illustrates how the electrical transmission system can be renovated into smart electrical transmission system and evaluates the reliability measures. / UOIT

Power transmission network is the most important link in the country’s energy system as they carry large amounts of power at high voltages from generators to substations. Modern power system is a complex network and requires high-speed, precise, and reliable protective system. Faults in power system are unavoidable and overhead transmission line faults are generally higher compare to other major components. They not only affect the reliability of the system but also cause widespread impact on the end users. Additionally, the complexity of protecting transmission line configurations increases with as the configurations get more complex. Therefore, prediction of faults (type and location) with high accuracy increases the operational stability and reliability of the power system and helps to avoid huge power failure. Furthermore, proper operation of the protective relays requires the correct determination of the fault type as quickly as possible (e.g., reclosing relays). With advent of smart grid, digital technology is implemented allowing deployment of sensors along the transmission lines which can collect live fault data as they contain useful information which can be used for analyzing disturbances that occur in transmission lines. In this thesis, application of machine learning algorithms for fault classification and location identification on the transmission line has been explored. They have ability to “learn” from the data without explicitly programmed and can independently adapt when exposed to new data. The work presented makes following contributions: 1) Two different architectures are proposed which adapts to any N-terminal in the transmission line. 2) The models proposed do not require large dataset or high sampling frequency. Additionally, they can be trained quickly and generalize well to the problem. 3) The first architecture is based off decision trees for its simplicity, easy visualization which have not been used earlier. Fault location method uses traveling wave-based approach for location of faults. The method is tested with performance better than expected accuracy and fault location error is less than ±1%. 4) The second architecture uses single support vector machine to classify ten types of shunt faults and Regression model for fault location which eliminates manual work. The architecture was tested on real data and has proven to be better than first architecture. The regression model has fault location error less than ±1% for both three and two terminals. 5) Both the architectures are tested on real fault data which gives a substantial evidence of its application.

Please read the abstract in the front matter this document / Dissertation (M Eng (Electronic Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

Orientador: Fábio Bertequini Leão / Resumo: Este trabalho apresenta modelos de programação não linear e linear inteira binária como novos métodos para resolver o problema de diagnóstico de faltas em sistemas de transmissão de energia elétrica. Os modelos de otimização são desenvolvidos com base no conjunto de coberturas mínimas e possui como restrições as equações que descrevem a lógica e a filosofia de proteção empregadas por empresas de energia elétrica. As equações de restrições modelam a associação dos alarmes dos relés de proteção informados pelo sistema de supervisão e aquisição de dados (SCADA) com os estados esperados das funções dos relés de proteção. Os modelos de programação matemática realizam o diagnóstico de falta em uma única etapa, identificando a seção em falta através da análise dos estados dos disjuntores e das funções de proteção associadas a cada equipamento do sistema elétrico. O modelo proposto é um problema muito complexo de programação não linear inteira binária, portanto é reformulado como outro problema, em que algumas expressões são linearizadas, o que resulta em um modelo matemático de programação linear inteiro binário. A solução ótima obtida pelo modelo proposto é encontrada utilizando solvers comerciais de programação matemática. Os resultados obtidos mostram eficiência e robustez do modelo matemático. Na literatura, o problema de diagnóstico de falta é resolvido principalmente por técnicas heurísticas, portanto, o método proposto é inovador. / Doutor

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.

This thesis deals with a system for operation of directly driven offshore wave energy converters. The work that has been carried out includes laboratory testing of a permanent magnet linear generator, wave energy converter mechanical design and offshore testing, and finally design, implementation, and offshore testing of an underwater collector substation. Long-term testing of a single point absorber, which was installed in March 2006, has been performed in real ocean waves in linear and in non-linear damping mode. The two different damping modes were realized by, first, a resistive load, and second, a rectifier with voltage smoothing capacitors and a resistive load in the DC-link. The loads are placed on land about 2 km east of the Lysekil wave energy research site, where the offshore experiments have been conducted. In the spring of 2009, another two wave energy converter prototypes were installed. Records of array operation were taken with two and three devices in the array. With two units, non-linear damping was used, and with three units, linear damping was employed. The point absorbers in the array are connected to the underwater substation, which is based on a 3 m3 pressure vessel standing on the seabed. In the substation, rectification of the frequency and amplitude modulated voltages from the linear generators is made. The DC voltage is smoothened by capacitors and inverted to 50 Hz electrical frequency, transformed and finally transmitted to the on-shore measuring station. Results show that the absorption is heavily dependent on the damping. It has also been shown that by increasing the damping, the standard deviation of electrical power can be reduced. The standard deviation of electrical power is reduced by array operation compared to single unit operation. Ongoing and future work include the construction and installation of a second underwater substation, which will connect the first substation and seven new WECs.