Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2006. / Mooney, Vincent J., Committee Chair ; Chatterjee, Abhijit, Committee Member ; Hasler, Paul, Committee Member ; Dorsey, John, Committee Member ; Niemier, Michael, Committee Member.

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 72).

Thesis (MScIng)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

No description available.

High voltage direct current. (hvdc) transmission of electrical paver has been made possible with the recent advent of multi-anode mercury arc valves with grading electrodes. However, mercury are valves do suffer from random phenomena such as arcback, which requires special bracing for the converter transformer. In addition, mercury arc valves need considerable auxiliaries, including cooling and vacuum plants. Research and development directed towards the improvement in the voltage and current capabilities of thyristors are yielding encouraging results. In contrast to mercury arc valves, thyristors do not suffer from random phenomena and require minim auxiliaries. Considering these advantages, thyristors offer a viable alternative to mercury arc valves for hvdc converters. The comparatively low ratings of thyristors necessitate series and parallel connection of thyristors in order to construct a valve of sufficient rating for hvdc operation. The design of thyristor valve should ensure even distribution of voltage and current among all thyristors of the valve, during all operating conditions. To achieve this objective transmission of the firing signal to the gate of each thyristors should have good coherence. The thesis examines design aspects, and considers the different methods of firing both theoretically and practically. Finally, the design and subsequent experimental results of the prototype thyristors valve rated at 10kv and 10A are also included.

Society has an every increasing thirst for electrical energy; this is only set to increase as the 21st Century progresses. In order to sustain this increasing demand, the power industry needs to consider a number of factors; adding generation capacity and maintaining the transmission and distribution networks that connect the producers to the consumers. This work focuses on the development of systems to aid maintenance operations. Parts of the transmission network in the UK date back to the 1950's and 60's, consisting of over 22,500 circuit km of overhead lines. The monitoring of this network is a significant ongoing task and needs to locate potential problems prior to failure. Numerous assessment techniques are presented in literature which discuss the examination of line components from the air or ground using the visual, infra-red or ultra-violet spectrums. Of particular interest in this work is the live-line inspection of composite insulators; thereby aligning with other ongoing work at The University of Manchester. While existing techniques have proved adequate to date, not all insulator surfaces can be appropriately seen. The ideal solution would be a device capable of photographing all insulator surfaces from a camera mounted on the insulator itself. While a number of live-line robotic systems are both in development and use around the world, operation and performance information is lacking; possibly due to commercial sensitivity issues. This work aims to clarify this situation, in particular focusing on the nature of broadband communication from, and survivability of complex electronics in areas of intense electric field strength and partial discharges. These areas are explored through the development of a technology demonstrator, a robot capable of imaging composite insulator surfaces in real-time and transmitting them to a ground station. Knowledge gained can then be adapted to create systems for other high-voltage monitoring situations. A systems level approach is taken whereby the technology demonstrator is divided into its constituent functional components. The requirements of each are assessed and research and development needs are detailed. Literature is reviewed to collate existing knowledge and enable comparison with the envisaged requirements. Prototype systems are developed to test the selected communication mechanism under high voltage conditions, while designs are created and fabricated for imaging and mechanical needs. The separate systems are then combined into the technology demonstrator and examined as a single unit under energised conditions. The author presents extensive results on the capability and nature of broadband radio frequency communication from areas of high electric field strength and partial discharges. They show that high data rates from such environments is possible up to a certain point at which high enhanced shield and antenna protection needs to be considered. They additionally demonstrate the transmission of live video from an energised composite insulator. This knowledge can be used to both improve the current system and as a basis to create additional monitoring solutions for high voltage situations. As such a new method of electric field distribution assessment is proposed.

This research is devoted to an investigation on the attractive width of high voltage transmission lines to lightning strikes. In order to design the optimal lightning protection, the estimated number of lightning flashes on the line, which is based on its attractive width, needs to be determined. The investigation was performed using experiments with model tests at the Mississippi State University High Voltage Laboratory. For laboratory experiments, a total of 2,100 negative and positive switching impulse voltages were applied to transmission line models from a conducting rod, which represented a lightning downward leader. Different tested models of transmission lines on a scale of 1:100 were used. The effects of overhead ground wires, phase conductors, tower structures, and the magnitude and polarity of lightning strokes were also studied. The attractive width increased gradually with the height of overhead ground wires and towers as well as the magnitude of the lightning stroke current. Impulse polarity had an impact on the attractive width, and the attractive width for negative polarity was larger than that for positive polarity. The taller tower had more effect on flash distribution to transmission lines than the shorter one. The experimental results agree with the actual transmission line observations published in literature. The new expressions for the attractive width of transmission lines, based on the experimental results, were established. The accurate estimation of the attractive width can help electric power utilities plan transmission systems reliably and economically. The detailed description of the background problem, proposed method, experimental results, and analysis are presented in this dissertation.

Recently there has been increasing interest in using glycerol as a substrate on steam reforming due to the increase of biodiesel production. With the increase of biodiesel production a glut of glycerol has resulted and this would be a more suitable substrate for value added production of hydrogen from reforming. Reforming biorenewable viscous fluids such as glycerol is difficult due to mass transfer limitations associated with vaporizing glycerol to gas phase before steam reforming. This study was to evaluate the feasibility of reforming electrically atomized liquid phase glycerol by means of a technique called electro-spray. It was hypothesized that reforming electrically charged glycerol nanodroplets on an oppositely charged conductive catalyst will increase the reforming performance as opposed to a neutral catalyst-substrate system. Hydrogen yield, selectivity was increased by 20%, 25% respectively when nanodroplets introduced. Exerting an electrical charge to the substrate-catalytic system significantly enhanced the reforming performance irrespective of the physical phase.

As the scale and complexity of an interconnected power grid has increased significantly, power systems can be operated close to the verge of voltage instability. With the application of Phasor Measurement Units (PMUs), dispatchers are able to monitor long term voltage stability in a real time operational environment. This research addresses the critical issues by proposing three different methods. Voltage Stability Assessment Index (VSAI) is a Thévenin Equivalent (TE) based method considering voltage dynamic mechanisms. To extend the model from one load bus to a critical load center, Optimal Power Flow-Loading limit (OPF-LI) is developed to assess the voltage stability margin. To utilize limited available PMU measurements, State Calculator (SC) is included in the algorithm to approximate the dynamic states at the buses where PMU measurements are not available. The online voltage regulating method in terms of On-load Tap Changer (OLTC) control is also investigated. The methods proposed in this research have been validated with the test cases from the WECC 179 bus system. / M.S. / This thesis proposed a hybrid solution of voltage stability monitoring and control in a power system. For the performance of motors, heaters or other loads in the power system, it is important that the customers are supplied with stable voltage. The variation of the voltage may cause damages to the load. Therefore, the methods in this thesis provides a feasible solution to monitor voltage stability of load centers in a power system. In addition, a novel approach for voltage control is proposed to prevent a voltage collapse of the system. The simulation results illustrate that the approach introduced in this thesis is promising for real time application.

[pt] O crescente aumento da complexidade dos sistemas elétricos de potência gera a necessidade de desenvolvimento de ferramentas que melhorem as condições de análise. O objetivo deste trabalho é aprimorar a ferramenta computacional de avaliação das condições de segurança (ou estabilidade) de tensão. No que diz respeito às barras associadas ao controle remoto de tensão por geração de potência reativa, são propostos novos modelos que representam mais adequadamente as condições operativas no momento do cálculo dos índices de segurança de tensão. Em relação à barra associada ao controle local de tensão por geração de potência reativa é proposta nova modelagem, aplicável tanto no problema de fluxo de potência, utilizando o método de Newton- Raphson, quanto no cálculo dos índices de segurança de tensão. Este modelo,mais robusto e flexível, inclui o controle de tensão local da barra no problema geral de fluxo de potência, formando um sistema de equações de ordem (2*número de barras+número de barras controladas localmente). Para o tratamento de múltiplas barras swing, é proposto um novo modelo, de novo para representar mais adequadamente as condições operativas. É aplicável tanto no problema básico de fluxo de potência, como no cálculo dos índices de segurança de tensão. O modelo proposto considera que apenas o ângulo de uma barra swing é especificado, com os ângulos das demais barras swing livres para variar. Testes numéricos com sistemas-teste (5 e 6 barras) comprovam a aplicabilidade e adequação dos modelos propostos comparando-os aos modelos usados atualmente. / [en] The crescent increase of the complexity of the electric power systems generates the need of development of tools to improve the analysis conditions. The objective of this work is to improve the computational tool of voltage security (stability) conditions assessment. As regards to the buses associated to remote voltage control by reactive power generation, new models that represent more appropriately the operatives conditions at the moment of the calculations of the voltage security indexes, are proposed. As regards to the bus associated to local voltage control by reactive power generation, it is proposed a new modeling, applicable as much in the power flow problem, using the Newton-Raphson method, as in the calculation of the voltage security indexes. This model, more robust and flexible, includes the local voltage control of the bus in the general power flow problem, constituting an equations system of order (2*number of system buses + number of buses with local voltage control). As regard to the multiples swing buses, it is proposed a new model, again to represents more appropriately the operatives conditions. It is applicable as much in the basic power flow problem, as in the calculation of the voltage security indexes. The proposed model considers that just one swing bus has your voltage angle specified and the others swing buses of the power system have your voltage angles free to vary.