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This thesis documents a research study of High Voltage transmission line faults induced by fire. Conductor to conductor and conductor to ground flashovers have been experienced by electricity utilities around the world under conditions of veld and sugar cane fires. These types of faults are unpredictable and negatively impact line reliability and quality of supply. This is a crucial problem when the revenue of the industry is sensitive to voltage dips. Electricity utilities have taken a preventative approach, like clearing vegetation from the line servitude in order to decrease the frequency of line faults. There has also been a drive to collaborate with sugarcane farmers in order to have harvesting fires planned with utilities. Some success has been achieved with these initiatives however there still remains a large number of faults. The focus of this study is on the mechanism of fire-induced flashover. Previou s work has displayed the existence of two theories. The first theory suggests that flashover is due to the reduction in air insulation strength caused by a reduced air density that results from the thermal effect of the fire. The second theory suggests that small particles present in the fire cause electric field distortions that induce flashover. This study is focused on a theory , which indicates that flashover is induced due to an enhanced electric field which is a result of the conductive properties of the flames present in the air gap (the flame conductivity theory). The effects of particles and a reduced air density is said to support this mechanism that is the primary reason for flashover. This thesis present s a summary of the literature where firstly an understanding of air insulation behavior is displayed. Thereafter specific interest is given to the effect of fire and flames wherein the physics of flames are discussed. This then leads to the description of the flame conductivity theory. Chapter 4 deals with a simulative investigation into the effect a conducting flame has on the electric field distribution. This is looked at with a varying flame conductivity and gap length in mind. The simulations specifically cover the 275 kV and 400 kV line configurations. The simulative investigation results in a mapping of electric field enhancement against conductivity values and gap sizes. Thus a flashover probability is assessed by using the two factor flashover criteria when analyzing the electric field stresses. The objective of the experimental work in this study is to obtain insight on how the flame geometry and orientation affects flashover and the dependence of flashover on gap size. Tests involving a fire beneath a conductor were carried out for different gap sizes . Experimentation with particles above a flame was also conducted. It was concluded that flame structure does have an impact on flashover since a flame with sharp edges is more likely to cause flashover. Particles have a reducing effect on air insulation strength. This is mainly due to the fact that the particle reduces the effective air-gap size. No significant effect over and above this is noticed . For gaps spanned by clean Liquid Petroleum Gas (LPG) flames flashover voltage increases as gap-length increases with some degree of nonlinearity. Flame resistances and conductivity were approximated from measured currents and voltages. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

The overhead transmission line is a fundamental component in the power supply system as it links electricity supply to the various points on the electrical network. Failure of the transmission overhead line will result in interruption of supply and depending on the network configuration may result in long term outages. It is therefore essential that the overhead transmission line asset is inspected and maintained regularly to prevent premature failure. Newer approaches to maintenance management are required to improve the overhead transmission lines performance and reduce the cost and risk associated with the asset. Asset management is seen as the process that can be adopted to enhance overall management of the overhead transmission line. The review of maintenance practices of various Utility’s and that of a pilot site made up of selected lines within Eskom’s North East Transmission Grid revealed numerous shortcomings in the current practices largely due to the application of traditional (non-holistic) methods. This situation supports the development of asset management plans which will cater for improvement in performance, reduction in the risk and cost and achieving service level targets. This research has used asset management principles to design a guideline in the form of a flowchart for effective maintenance management for overhead transmission lines. The key benefits/advantages of the maintenance management guideline are as follows: It is closed loop and process driven. Decision making is more scientific because it requires the use of historical performance data, detailed asset condition information and encourages quantitative analysis. Promotes defect and condition assessment tracking via the condition database. Rather than focusing mainly on defect management, the asset manager will be directed towards the performance specifications and the condition database to establish individual action plans which can be prioritized against short, medium and long term improvement plans per specific asset. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.

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.

Shape memory alloys (SMA’s) are a family of metals that exhibit properties of pseudo-elasticity / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

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Thesis (Ph. D.) -- McMaster University, 1997. / Includes bibliographical references (leaves 165-168). Also available via World Wide Web.

Orientador: Maria Cristina Dias Tavares / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-13T12:17:57Z (GMT). No. of bitstreams: 1 Montanari_AllanAlves_M.pdf: 7585929 bytes, checksum: 4c00ba94f40e488cc4da50c4089e8630 (MD5) Previous issue date: 2009 / Resumo: Este trabalho apresenta um esquema de religamento monopolar adaptativo rápido para otimizar o tempo compreendido entre a abertura e o religamento da fase sob falta. A proteção adaptativa recompõe rapidamente o sistema de transmissão de energia elétrica, minimizando a probabilidade de propagação de perturbações severas no sistema. O método é fundamentado na análise de dados de ensaios de arco secundário gerados e monitorados numa estrutura de testes construída em campo, composta por um trecho real de linha de transmissão (três torres e dois vãos). Analisou-se o conteúdo harmônico da tensão e da corrente de arco secundário através da aplicação da Transformada de Fourier Janelada. Tais análises viabilizaram a realização de um tratamento estatístico para a caracterização da assinatura harmônica de arco secundário. Simulações de faltas monofásicas foram realizadas utilizando dados provenientes dos Ensaios de arco secundário. Desenvolveu-se um algoritmo baseado nas características Harmônicas da tensão da fase sob falta, calculadas através do deslocamento de uma janela de tempo sobre os sinais analisados (Transformada de Fourier Janelada). O algoritmo determina a existência do arco secundário e fornece informações a respeito do instante no qual o religamento pode ser realizado com sucesso. O método apresenta também um mecanismo para a detecção da característica permanente ou transitória da falta. / Abstract: This work presents a fast adaptive single-phase autorec1osingseheme to optimize the period between the tripping operation and the rec10sure of the faulted phase breakers. The adaptive proteetion quiekly reeomposes the eleetric power transmission, minimizing the probability of severe damages propagation in the system. The method is based on the analysis of secondary are field tests data that were generated and monitored in an infra-structure which consists of a real transmission line section (three towers and two spans). The harmonic content of the secondary are voltage and eurrent was analyzed by the application of Short Time Discrete Fourier Transform. Such analysis made it possible to implement a statistical approach in order to obtain the secondary are harmonic signature. Single-phase faults computer simulations were performed using the data obtained from the secondary are tests. It was developed an algorithm based on the voltage harmonic content of the faulted phase, which was ea1culated by shifting a window on the analyzed signals (Short Time Discrete Fourier Transform). The algorithm determines the secondary are existence and provides information in order to suceessfully rec10se the circuit breaker. The method also presents a control mechanism responsible for identifying whether the fault is a permanent one or a transient fault. / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

The central problem which overhead electric transmission lines pose for suburban areas is that right of way location decisions made in earlier years have influenced, and sometimes determined, the present overall pattern of suburban development and especially its residential aspects. The study is therefore limited to considerations of the impact on residential areas. The result has been that past decisions made by one agency on the basis of technical determinants and economic criteria applicable to a utility project have often been responsible for the present form and pattern of urban areas. Another problem is that in the suburban areas near those lines which have ugly structures and unmaintained rights of way, there is an adverse effect upon the quality of adjacent residential development. This effect is most marked in those areas which are striving for urban standards of residential density and neighbourhood amenity. Almost equally important with the effects which power lines may have on the areas they pass through is the simple fact of the tremendous amount of land which they use and alienate for most other urban uses. The study is concerned with the impact of overhead electric transmission lines on suburban areas, and not with electric lines at distribution voltages. Extra high voltage lines are of special interest to planning, for they present technical and economic problems which either preclude or make impractical converting them to underground forms. Accordingly, as overhead transmission lines are likely to have continuing effect, the following hypothesis is advanced. Because the location of overhead electric transmission lines has had considerable influence (sometimes adverse) on the spatial pattern of residential development, there is need for coordinating the requirements of the utility agency and the appropriate planning agencies. The study describes in some detail those locational requirements and standards of electric transmission lines which have a bearing upon the use of land. The optimum locational requirements for overhead electric transmission line rights of way and suburban density and types of residential development are shown to be nearly identical. The two are therefore in competition for the use of land, and this competition is most marked in suburban areas where land values are lower than in the central city. A specific examination is carried out of transmission line effects on the suburban residential area of Surrey, British Columbia, which is an urbanizing municipality on the fringes of the Vancouver metropolitan area. The case study shows that there is a significant correlation between the present pattern of residential development, as measured by assessment values and population distribution, and the presence of transmission line rights of way. The study concludes that the presence of the lines is the most likely causal factor. That the influence has been sometimes adverse is not as definitely established, but the conclusion may be inferred from subjective evaluation of the aesthetic evidence presented. Further study of objective evidence is called for. The statement in the hypothesis that it is necessary to coordinate the requirements of the utility agency and the appropriate planning agencies is basically valid, but is felt to be inadequate. It is concluded that the activity must, wherever possible, be an integrative one, and involve many other departments of government, including the federal. It is suggested that an integrative Provincial Development Department could well be the most effective method of controlling the more unfavourable aspects of electric transmission line right of way location and appearance. / Applied Science, Faculty of / Community and Regional Planning (SCARP), School of / Graduate

Several methods for calculating the electrical phase and modal parameters of overhead transmission lines are described in this thesis; then, a graphical method for evaluating communication frequency response of delta transmission lines -based on the guidelines given by W. H. Senn [12,13,14]- is developed. The graphical method, combined with the parameters calculation methods, obviates the need of large mainframe computers for the analysis of power line carrier (PLC) systems. A new technique for assessing coupling alternatives, based on Senn's method, is developed. The technique is applied to generate coupling recommendations; it is found that many of the current recommendations given elsewhere [21] are not reliable. Finally, future work to be done in this field is proposed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate