This dissertation is focused on design of compact electromagnetic magnetic band-gap structures (EBG). Several popular compact techniques are introduced and analyzed with equivalent surface impedance model. A novel compact EBG structure is investigated. Compared to the conventional uniplanar compact photonic band gap (UC-PBG) structure, a size reduction of 64.7% is achieved. A distinctive band gap is observed at 2.45 GHz with around 100 MHz bandwidth and zero reflection phase. Antenna applications of this novel EBG structure, including EBG patch antenna and EBG antenna array, have been presented. Simulation results further verify its characteristic of suppressing surface waves. For the EBG patch antenna, a more focused radiation pattern is obtained compared to a normal patch antenna. For an antenna array, the presence of EBG structure reduces the mutual coupling between the two radiating elements by 6 dB.

abstract: Antennas are required now to be compact and mobile. Traditional horizontally polarized antennas are placed in a quarter wave distance from a ground plane making the antenna system quite bulky. High impedance surfaces are proposed for an antenna ground in close proximity. A new method to achieve a high impedance surface is suggested using a metamaterial comprising an infinite periodic array of conducting loops each of which is loaded with a non-Foster element. The non-Foster element cancels the loop's inductance resulting in a material with high effective permeability. Using this material as a spacer layer, it is possible to achieve a high impedance surface over a broad bandwidth. The proposed structure is different from Sievenpiper's high impedance surface because it has no need for a capacitive layer. As a result, however, it does not suppress the propagation of surface wave modes. The proposed structure is compared to another structure with frequency selective surface loaded with a non-Foster element on a simple spacer layer. In particular, the sensitivity of each structure to component tolerances is considered. The proposed structure shows a high impedance surface over broadband frequency but is much more sensitive than the frequency selective surface structure. / Dissertation/Thesis / M.S. Electrical Engineering 2010

Orientador: Carlos Roberto Minussi / Banca: Anna Diva Plasencia Lotufo / Banca: Sandra Cristina Marchiori de Brito / Resumo: Este trabalho tem por objetivo apresentar uma metodologia, para detecção e classificação de faltas de curto-circuito, direcionada para os eventos de alta impedância em subestações de energia elétrica. A detecção é executada por um cálculo algébrico simples via observação da diferença absoluta entre o valor eficaz médio estimado e o valor eficaz medido a partir da oscilografia das correntes trifásicas. Caso seja detectada a anomalia de corrente, procede-se a sua classificação baseada na lógica fuzzy. Trata-se de um problema que apresenta maiores dificuldades de identificação e classificação, tendo em vista que tais perturbações são sutis, o que se diferenciam em relação aos eventos caracterizados como de baixa e ou de média impedância. Os distúrbios de alta impedância, muitas vezes, não são detectados pelo sistema proteção. Neste caso, o sistema de proteção consideraos como uma operação em regime permanente, não distinguindo entre uma falta de alta impedância e um aumento/diminuição da corrente elétrica em decorrência das variações da demanda solicitada pelos consumidores. Ressalta-se que a metodologia, aqui proposta, segue os princípios formulados na referência Decanini (2008), com as devidas adaptações ao problema associado às faltas de alta impedância. A metodologia, proposta neste trabalho, usa dados oscilográficos que são processados de modo que a detecção e classificação das faltas possam ser estimadas através de um conjunto de características extraídas dos sinais de correntes. Este conjunto de característica é classificado pela lógica nebulosa e sua saída resulta na indicação do tipo da falta. Deve-se ressaltar que este algoritmo além de ser eficiente na detecção e classificação de faltas de alta impedância, sua eficiência destacase também na localização e detecção de faltas de baixa impedância... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work presents a methodology to detect and classify short circuit faults principally for high impedance occurrences in electrical power systems. The detection is executed by a simple algebraic calculus observing the absolute difference with the efficient medium estimated value and the efficient value measured from the oscillogram of the three-phase currents. When a current anomaly is detected the classification is based on the fuzzy logic. It is a problem that presents some difficulties in identification and classification, considering that these perturbations are little which are different from the events characterized as low or medium impedance. The high impedance perturbations sometimes are not detected by the protection system. In this case, the protection system considers as one operation in steady state, and do not distinguish with a high impedance fault or an increasing/ decreasing of the electrical current due to the demand variation requested by the users. It is emphasized that the proposed methodology follows the fundamentals according the reference Decanini (2008), with the adaptations to the associated problem to the high impedance faults. The proposed methodology use oscillogram data that are processed in a way that the detection and classification of the faults are estimated by a set of characteristics from the current signals. This set is classified by logic fuzzy and the output results on the type of the fault. It is emphasized that this algorithm besides being efficient is detecting and classifying high impedance faults, is also efficient in localizing and detecting low impedance faults. The necessary data for the diagnosis of the faults were obtained by simulation of a radial feeder model with the ATP software. Results are satisfactory and show the viability of the proposed methodology that is faster for obtaining the solutions and is able to detect... (Complete abstract click electronic access below) / Mestre

High Impedance Faults (HIFs) are undetectable by conventional protection technology under certain<p>conditions. These faults occur when an energized conductor makes undesired contact with a<p>quasi-insulating object, such as a tree or a road. This contact restricts the level of the fault current to a very low value, from a few mA up to 75A. In solidly grounded distribution networks where the value of the residual current under normal conditions is considerable, overcurrent devices do not protect against HIFs. However, such a protection is essential for guaranteeing public security, because of the possibility of reaching the fallen conductor and the risk of fire. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The scope of this thesis was to develop a prototype high-impedance arc detection system that a utility worker could use as an early warning system while working in a manhole environment. As part of this system sensors and algorithms were developed to increase the sensitivity of detecting an arc while ignoring loads that can give false positive signatures for arcing. The latest technology was used to repeat measurements performed in previous research from decades ago that lacked in sampling speed and amplitude resolution. Several types of arcs were produced and analyzed so to establish a library of various waveform and frequency signatures. The system was constructed as a development unit and is currently gathering information in the field. Data being collected will be analyzed so future revisions will give higher confidence levels of arc detection. Other future plans involve designing a more compact and portable unit.

The most common fault type in electric power systems is the line to groundfault. In this type of faults, an electrical arc is usually developed. The thesispresents a mathematical model that describes the behavior of the arc during afault. The arc model has been verified based on real and simulated tests thatwere conducted on a system that has resonant earthing coil.In addition, two studies have been conducted on the same verified system.The first studied was implemented to see the effect of detuning the resonantearthing coil at different levels. It was noted that detuning the coil affected ACand the DC components in the arc faults. Also, the detuning affected the arcextinction.The second study has been looking at the effects of implementing a parallelresistor to the resonant earthing coil. The tests have been conducted usingdifferent set values of the resistor. In some of the studied cases and during thetesting period, the resistor has affected the self-extinguish behavior of the arc. / Den vanligaste feltypen i elektriska kraftsystem är fas till jord. I denna typ avfel utvecklas vanligtvis en elektrisk ljusbåge. Examensarbetet presenterar enmatematisk modell som beskriver ljusbågens beteende under ett fel. Bågmodellenhar verifierats baserat på verkliga tester och simuleringar som utfördespå ett system som har resonansjordningsspole.Dessutom har två studier genomförts på samma verifierade system. Denförsta studien genomfördes för att se effekten av avstämning av den resonantajordningspolen på olika nivåer. Det noterades att avstämning av spolen påverkadeACoch DC-komponenterna i ljusbågsfel.Avstämningen påverkade ocksåljusbågens släckning.Den andra studien har tittat på effekterna av att implementera ett parallelltmotstånd till den resonanta jordningsspolen. Testen har utförts med olikainställda värden på motståndet. I några av de studerade fallen och under testperiodenhar motståndet påverkat ljusbågens självsläckande beteende.

Increasing modernization of the world has brought about a human component to natural disasters, which are exacerbated by the growing threat of climate change. The Western United States and Australia have witnessed some of the deadliest, costliest, and destructive wildfires in the recent past with downed electric power lines being a significant factor amongst the causes. The relationship between wildfires and powerlines is not a newly discovered phenomenon, however, utilities across the globe are struggling to find an optimal solution to this problem. While existing regulations allow utilities to schedule power shutdowns, they are often accompanied by massive financial losses and discomfort to consumers. Utilities also need to factor in the climatic conditions in the region of their service and the flammability of the vegetation surrounding their lines while making decisions pertaining to system planning, load shedding, and protection. This multi-faceted problem can be dealt with in multiple ways – one such technique involves detection of a falling line into sensitive vegetation before it encounters the earth. This approach essentially boils down the problem into detecting a single line open circuit fault. The open circuit is momentary and hence, speed is of the essence in such a protection scheme. In this thesis, detection of an open circuit is carried out in two different ways, viz., with and without communication support between the various elements of the system, with the latter technique being a novel proposal with the aim of achieving a secure protection scheme with minimal additional infrastructural requirements. / Master of Science / The contact of a live wire with the earth is a fault. While most faults can be cleared using traditional protection techniques, there is a higher risk associated with power lines that come in contact with dry surfaces, flammable plants, and bushes, which cannot be detected that easily. These surfaces offer very high resistance to the flow of current and are hence termed high impedance faults. These high impedance faults have the potential to spark and cause a fire, which can snowball into a wildfire depending on the geography and climatic conditions of the area. For years, this has been a major problem in places like Australia and California leading to loss of lives, power, and money, but the optimal solution is evasive. While several techniques to combat this problem exist, the focus of this thesis is essentially what is known as the Open Circuit Fault. The technique revolves around the detection of the fault while the falling conductor is midair. Given the short time frame, high-speed detection is of the essence. This thesis will focus on achieving open circuit detection without the need for any communication support and is a novel contribution to this field.

Les Surfaces à Haute Impédance (SHI) ont été largement étudiées pour améliorer toutes sortes de performances des antennes, comme le gain, le facteur de qualité, les formes et dimensions. L'objectif de cette thèse est de modéliser les structures de SHI et de caractériser leurs performances en vue de futures applications aux antennes.Après une brève introduction aux structures SHI et une étude de quelques modèles analytiques fréquemment traités dans la littérature, deux nouvelles méthodes numériques sont proposées pour calculer l'impédance de surface de structures SHI. Ces deux méthodes (dites « méthode du flux de Poynting » et « méthode <E>/<H> ») sont validées sur des structures symétriques, puis mises en service sur des structures de SHI asymétriques. Elles sont également validées par comparaison de résultats analytiques, numériques et expérimentaux.Nous présentons ensuite un modèle équivalent basé sur l'idée de remplacer les structures hétérogènes de SHI par une surface homogène, caractérisée par son impédance surfacique. Ce modèle nous permet d'avoir une prédiction avec un temps de calcul et une occupation de mémoire PC largement réduits. / High impedance surfaces (HIS) have proved good candidates for antenna miniaturization or antennas performance improvement. Within a certain frequency band, they can enhance the gain of an antenna while simultaneously suppressing the unwanted surface waves.In this thesis, the focus of our work is on numerical modeling of these structures by using the finite element method (FEM) based on edge elements.One of our contributions is that we propose two new numerical methods (the Poynting flux method and <E>/<H> method) to calculate the surface impedance not only for HIS structures with symmetric geometries, but also for those with asymmetric geometries. These two numerical methods have been validated by comparing analytical, numerical and experimental results.Another significant contribution of the thesis is that we introduce an equivalent model, based on the idea of replacing the heterogeneous HIS structures by a homogeneous surface, characterized by its surface impedance. Compared with the normal model, this equivalent model can save computing time and memory space.

O conhecimento das características experimentais das faltas de alta impedância é de suma importância para o desenvolvimento de sistemas e equipamentos voltados a detecção eficiente das mesmas em sistemas de distribuição de energia elétrica. Este trabalho apresenta um conjunto de estratégias experimentais que visam orientar passo a passo a realização de ensaios de faltas fase-terra com alta impedância, contemplando-se desde os dispositivos de proteção usados na viabilização dos experimentos até os equipamentos de oscilografias utilizados para registrar as grandezas elétricas advindas dessas situações de faltas. São ainda apresentados os resultados obtidos pelos ensaios realizados de queda de condutor energizado (lado fonte) em solo seco, queda de condutor energizado (lado fonte) em brita seca, queda de condutor energizado sobre a cruzeta e queda de condutor energizado (lado carga) em solo seco. / The knowledge of experimental characteristics of high-impedance fault is of highest importance for developing both systems and equipments addressed to its efficient detection in electric power distribution systems. This work presents a set of practical strategies to guide step by step the accomplishment of experiments involving phase-ground faults with high impedance, being also contemplated from protection devices used in the experiments to oscillograph equipments dedicated to register the electric signals produced in those situations. It is still presented the results produced by fault experiments involving drop of energized cable (source side) in dry soil, drop of energized cable (source side) in dry broken stones, drop of energized cable on crossarm and drop of energized cable (load side) in dry soil.

Monitoring of abnormal events in a distribution feeder by using a single technique is a challenging task. Many abnormal events can cause unsafe operation, including a high impedance fault (HIF) caused by a downed conductor touch ground surface, an incipient fault (IF) caused by partial breakdown to a cable insulation, and a circuit breaker (CB) malfunction due to capacitor bank de-energization to cause current restrikes. These abnormal events are not detectable by conventional protection schemes. In this dissertation, a new technique to identify distribution feeder events is proposed based on the complex Morlet wavelet (CMW) and on a decision tree (DT) classifier. First, the event is detected using CMW. Subsequently, a DT using event signatures classifies the event as normal operation, continuous and non-continuous arcing events (C.A.E. and N.C.A.E.). Additional information from the supervisory control and data acquisition (SCADA) can be used to precisely identify the event. The proposed method is meticulously tested on the IEEE 13- and IEEE 34-bus systems and has shown to correctly classify those events. Furthermore, the proposed method is capable of detecting very high impedance incipient faults (IFs) and CB restrikes at the substation level with relatively short detection time. The proposed method uses only current measurements at a low sampling rate of 1440 Hz yielding an improvement of existing methods that require much higher sampling rates.