The objective of this research is to compare radio channel impulse response measurements with site-specific radio wave propagation prediction techniques. A wide band spread spectrum measurement system was developed, and desirable measurement locations were selected on the Virginia Tech campus. These measurements are designed togo beyond statistical characterizations of the channel and will aid in determining how the propagation environment is influencing the multi path propagation. The objective is to not only measure the delays and relative powers of multi path components, but to carefully document their angles of arrival and resolve the overall paths that these multipaths had to take to reach the receiver. This information will be used to compare with propagation prediction simulations using the modeled environment, and therefore, provide new insight into the nature of reflection and scattering of radio propagation in typical microcellular environments. As a first step in this endeavor, building surface characterizations are made in order to determine empirical reflection coefficients of common building materials. Propagation experiments have been designed to determine applicability of Fresnel reflection formulas to non-ideal conditions, such as waves that are not perfect plane waves, rough surfaces, etc. This information allows propagation prediction techniques to further quantify the site-specific mobile radio environment and yield more accurate propagation estimates. For this endeavor, Whittemore Hall and Squires Student Center were Chosen to provide reflection measurements from rough stone, glass, and brick surfaces. Detailed descriptions of measurement techniques, analysis and results are included. / Master of Science

No description available.

Electromagnetic pulse simulators are essential for testing the ability of electronic devices to withstand high intensity electromagnetic ends. This work presents the analysis of various parallel plate transmission lines used in electromagnetic pulse simulators. Numerical techniques are developed to obtain the characteristic impedance, field map, and cut-infrequencies for the higher order modes of these transmission lines as exact analytical methods are not available for the determination of these quantities. The field map and characteristic impedance are computed using both finite element method (FEM) and boundary element method (BEM). Cut-off frequencies of the higher order modes are computed using FEM. The analysis presented can handle very general transmission line geometries. This analysis is useful for the design of electromagnetic pulse simulators.

A computationally efficient, discrete model is presented for transmission line analysis and passive model order reduction of high-speed interconnect systems. The development of this model was motivated by the on-going efforts in chip/package co-design to route a major portion of the on-chip clock and high-speed data buses through the package in order to overcome the bandwidth reduction and delay caused by the high ohmic loss of on-chip wiring. The geometric complexity of the resulting interconnections is such that model order reduction is essential for rapid and accurate signal integrity assessment to support pre-layout design iteration and optimization. The modal network theory of the skin effect in conjunction with the theory of compact differences is used for the development of discrete models for dispersive, multi-conductor interconnects compatible with passive model order reduction algorithms. The passive reduced-order interconnect modeling algorithm, PRIMA, is then used on the resulting discrete model to generate a low-order, multi-port macromodel for interconnect networks. Numerical examples are used to demonstrate the validity and efficiency of the proposed model.

No description available.

Ces travaux de thèse portent sur la détection de défauts non francs dans des structures filaires particulières : les lignes de transmission a multiconducteurs (MTL), aussi appelées torons de câbles. Couramment employées pour le diagnostic de réseaux filaires, les méthodes par réflectométrie ne sont, pour l'heure, pas suffisamment performantes pour détecter de tels défauts. Par ailleurs, elles n'ont, en général, été étudiées et développées que pour des lignes simples, ou les phénomènes de couplages électromagnétiques entre les conducteurs (diaphonie) ne sont pas présents. Ces derniers sont cependant porteurs d'information supplémentaire sur l'état du câble. Les utiliser permettrait d'accroître la sensibilité de détection aux défauts. L'objectif est de proposer une nouvelle méthode de réflectométrie, tirant profit des signaux de diaphonie pour détecter les défauts non francs. Une telle méthode présente également l'avantage d'être adaptée aux structures en toron. Après avoir étudié l'impact d'un défaut non franc sur les paramètres caractéristiques d'une MTL et sur les signaux de diaphonie, une méthode, la "Cluster Time Frequency Domain Reflectometry ", a pu être proposée. Il s'agit d'un procédé en trois étapes. Des mesures par réflectométrie temporelle sont tout d'abord réalisées à l'entrée de la ligne à diagnostiquer. Tous les signaux présents, y compris ceux de diaphonie, sont enregistrés. Un traitement temps-fréquence leur est ensuite appliqué afin d'amplifier la présence d'éventuels défauts. Enfin, un algorithme de clustering, spécifiquement développé pour le diagnostic filaire, est utilisé de manière a bénéficier de l'ensemble de l'information disponible / Research works presented in this thesis rely on detecting soft faults (incipient faults) in specic wiring structures : multiconductor transmission lines (MTL), also known as bundles of wires. Reflectometry methods, often used for the diagnosis of wiring networks, aren't for now efficient enough at detecting such defects. Besides, they have been designed for single lines only, where electromagnetic coupling between conductors (crosstalk) is not to be considered. However such phenomenon can provide more information about the state of the cable. Using this information could enable us to detect soft faults more easily. Our goal is to propose a new reflectometry method, which takes advantage of crosstalk signals in order to detect incipient faults. Such a tool has also the advantage of being well-adapted to bundles of cables. Thanks to the preliminary study of the impact of soft faults on the characteristic parameters of a MTL and on crosstalk signals, a method called "Cluster Time Frequency Domain Reflectometry ", has been proposed. It is a three step process. Firts temporal reflectometry measurements are made at the beginning of the line under test. All the available signals, even crosstalk ones, are recorded. A time-frequency process is then applied on them, in order to amplify the presence of defects. Finally, a clustering algorithm, that has been specically developed for wiring diagnosis, is used to benefit from the whole available information

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

[pt] No projeto de estruturas treliçadas esbeltas, um ponto relativamente em aberto é quanto à resposta dinâmica dessas torres sob ação do vento. Já foram observadas várias ocorrências de queda de torres por tais efeitos no Brasil e ultimamente, essas incidências vêm aumentando, trazendo diversos transtornos e prejuízos significativos à sociedade e às empresas concessionárias. Nesse contexto, brotam dois aspectos centrais: a modelagem da estrutura e a discretização da ação do vento. A montagem desses dois cenários é feita com base em um modelo numérico, no SAP2000, de uma torre de 73,75 m de altura da linha de transmissão LT - 103, na Amazônia, e uma torre de TV com 192 m de altura, localizada em Brasília-DF, ambas no Brasil. Para avaliação da excitação do vento, é utilizada a norma brasileira NBR 6123. Em estudo preliminar, propõe-se uma forma de representação simplificada das forças do vento sobre a torre, de modo a serem utilizadas resultantes por módulos, convenientemente distribuídas por seus nós principais, visando-se quer a resposta estática, quer a dinâmica. A torre de TV é ensaiada sob a ação de pulsos isolados do vento de projeto e por sucessões diversas desses pulsos com o intuito de simular rajadas de vento. Investiga-se também, para a ação de ventos normalizados extremos, a resposta linear e não-linear P-Delta do sistema. Em consequência, identificam-se pontos de insuficiência estrutural e, para as ações extremas, ensaiam-se recursos mecânicos para controle dos deslocamentos e esforços máximos produzidos pela ação estática e dinâmica do vento. / [en] The dynamic response of slender latticed tower structures under wind excitation is still an open point in the design of such systems. In Brazil, an expressive number of accidents have been registered, in the last few decades, and a large number of material and financial losses have been equally reported, for both people and industrial plant owners. In the structural analysis scenario, two central points dominate the structural engineer concerns: the modeling of the structure and of the wind action. Two tower models are used, a 73,75m high transmission line trussed structure, LT 103, settled in the Brazilian Amazon Basin and a 193m tall trussed TV tower, built in Brasilia-DF. The wind action on the tower members is computed according to the brazilian recommendation, NBR- 6123. In a preliminary study, a simplified procedure is proposed to evaluate the wind forces on the LT-103 tower sections and to conveniently distribute them on the main tower model nodes (joints). The TV Tower is evaluated under the static and dynamic action of the wind forces, either by isolated pulses or by a train of them to model a wind gust. The tower response is computed under a linear and non-linear P-Delta behavior; some faulting spots are identified in the response reports and a combined vibration control solution is proposed incorporating steel tendons conjugated with multiple tuned mass absorbers. A comparison is also made with the NBR 15307 recommendation and a couple of comments are addressed to those who may intend to apply this regulation to investigate the behavior of slender trussed tower structures.

Atualmente, a intensidade de campo elétrico, campo magnético e campo eletromagnético é um fator determinante não só para a implantação de novas instalações, mas também, para as instalações existentes no sistema elétrico. Apesar de não existir nenhum estudo conclusivo que comprove a evidência direta entre a exposição a estes campos e os efeitos nocivos na saúde das pessoas, muitos países, inclusive o Brasil, definiram em suas legislações limites básicos à exposição de campos elétrico e magnético provenientes dos sistemas elétricos. Este trabalho tem como objetivo contribuir para análise de campo magnético de linhas subterrâneas de alta tensão existentes ou linhas em fase inicial de projeto, visando atender os limites de exposição vigentes na legislação local. Nele é apresentada a metodologia de cálculo de campo magnético baseada na Lei de Biot-Savart e no princípio da superposição. Estudos analíticos para verificação da influência dos parâmetros de instalação e elétricos de linhas sobre o campo magnético são apresentados para linhas subterrâneas de alta tensão compostas por um e dois circuitos com diferentes tipos de instalação e aterramentos. Comparações entre valores analíticos e valores de medições de campo magnético de linhas subterrâneas de alta tensão existentes em operação também são abordadas neste trabalho. As principais técnicas de mitigação de campo magnético utilizadas em linhas subterrâneas de alta tensão, tais como técnicas de compensação envolvendo laços de cabos e técnicas de blindagens com materiais metálicos externos aos cabos, também são apresentadas. Devido ao campo elétrico externo ao cabo isolado ser praticamente zero, assuntos referentes a este campo não são abordados neste trabalho. Por simplicidade, campo magnético refere-se à densidade de fluxo magnético neste documento. / Nowadays, the intensity of electric field, magnetic field and electromagnetic field is a determining factor, not only for implantation of new installations, but also for existing installations in the power system. Although no exist conclusive study that proves the direct evidence between exposure to these fields and adverse effects on human health, many countries, including Brazil, have defined in their laws basic limits for exposure to electric and magnetic fields produced by the electric system. This work aims to contribute to analysis of magnetic field for both existing high voltage underground lines and lines in initial stage of project, aiming the actual exposure limits of the local legislation. In it, is shown the magnetic field calculation methodology based on the Biot-Savart\'s law and the superposition principle. Analytical studies to verify the influence of installation and electrical parameters of lines on the magnetic field are presented for high voltage underground lines consist of one and two circuits with different types of installation and earthing. Comparisons between analytical and measurement values of magnetic field of existing high voltage underground lines in operation are also addressed in this work. The main mitigation techniques of magnetic field used in high voltage underground lines, such as compensation techniques by loop of cables and shielding by metallic materials, are also presented. Due the electric field outside the insulated cable be practically zero, issues related to the electric field are not addressed in this work. For simplicity, the magnetic field refers to the magnetic flux density in this document.

Este trabalho tem por objetivo apresentar o desenvolvimento e a implementação, em uma rotina computacional, de um algoritmo para localização de faltas em linhas de transmissão com compensação série baseado em método heurístico. O algoritmo de localização de faltas proposto neste trabalho é capaz de identificar o ponto de ocorrência da falta utilizando informações sobre os parâmetros da linha de transmissão, os sinais de tensões e correntes registrados nos terminais dessa linha, bem como as características das unidades de compensação série empregadas. O algoritmo desenvolvido no âmbito desta pesquisa foi codificado no ambiente Matrix Laboratory (MATLAB), bem como o método heurístico escolhido (pattern search) e a sua validação foi conduzida a partir de simulações computacionais utilizando modelos de rede implementados no Alternate Transient Program (ATP). / This work aims to describe the development and implementation in a computational routine, an algorithm to locate faults in series-compensated transmission lines based on an heuristic method. The fault location algorithm proposed in this work is capable of identifying the fault point using information about the parameters of the transmission line, voltages and currents signals recorded at the line terminals, as well as the characteristics of the series compensation units. The optimization method used for objective functions was pattern search. The algorithm developed during this research was coded using MATLAB, as well as the heuristic method chosen (pattern search) and its validation was based on computer simulations using network models implemented in ATP.