"As new, smaller satellites are built, the need for improved on-board propulsion systems has grown. The pulsed plasma thruster has received attention due to its low power requirements, its simple propellant management, and the success of initial flight tests. Successful integration of PPTs on spacecraft requires the comprehensive evaluation of possible plume-spacecraft interactions. The PPT plume consists of neutrals and ions from the decomposition of the Teflon propellant, material from electrode erosion, as well as electromagnetic fields and optical emissions. To investigate the PPT plume, an on-going program is underway at WPI that combines experimental and computational investigations. Experimental investigation of the PPT plume is challenging due to the unsteady, pulsed as well as the partially ionized character of the plume. In this thesis, a triple Langmuir probe apparatus was designed and used to obtain electron temperature and density measurements in the plume of a PPT. This experimental investigation provides further characterization of the plume, much needed validation data for computational models, and is useful in thruster optimization studies. The pulsed plasma thruster used in this study is a rectangular geometry laboratory model built at NASA Lewis Research Center for component lifetime tests and plume studies. It is almost identical in size and performance to the LES 8/9 thruster, ablating 26.6 ug of Teflon, producing an impulse bit of 256 uN-s and a specific impulse of 986 s at 20 J. All experiments were carried out at NASA LeRC Electric Propulsion Laboratory. The experimental setup included triple Langmuir probes mounted on a moveable probe stand, to collect data over a wide range of locations and operating conditions. Triple probes have the ability to instantaneously measure electron temperature and density, and have the benefit of being relatively simple to use, compared to other methods used to measure these same properties. The implementation of this measuring technique is discussed in detail, to aid future work that utilizes these devices. Electron temperature and density was measured from up to 45 degrees from the centerline on planes parallel and perpendicular to the thruster electrodes, for thruster energy levels of 5, 20 and 40 J. Radial distances extend from 6 to 20 cm downstream from the Teflon surface. These locations cover the core of the PPT plume, over a range of energy levels that corresponds to proposed mission operating conditions. Data analysis shows the spatial and temporal variation of the plume. Maximum electron density near the exit of the thruster is 1.6 x 1020, 1.6 x 1021, and 1.8 x 1021 m-3 for the 5, 20 and 40 J discharges, respectively. At 20 cm downstream from the Teflon surface, densities are 1 x 1019, 1.5 x 1020 and 4.2 x 1020 for the 5, 20 and 40 J discharges, respectively. The average electron temperature at maximum density was found to vary between 3.75 and 4.0 eV for the above density measurements at the thruster exit, and 20 cm from the Teflon surface the temperatures are 0.5, 2.5, and 3 eV for the 5, 20 and 40 J discharges. Plume properties show a great degree of angular variation in the perpendicular plane and very little in the parallel plane, most likely due to the rectangular geometry of the PPT electrodes. Simultaneous electron temperature and density traces for a single thruster discharge show that the hottest electrons populate the leading edge of the plume. Analysis between pulses shows a 50% variation in density and a 25% variation in electron temperature. Error analysis estimates that maximum uncertainty in the temperature measurements to be approximately +/- 0.75 eV due to noise smoothing, and the maximum uncertainty in electron density to be +/- 60%, due to assumptions related to the triple probe theory. In addition, analysis of previously observed slow and fast ion components in the PPT plume was performed. The analysis shows that there is approximately a 3 us difference in creation time between the fast and slow ions, and that this correlates almost exactly with the half period of the oscillations in the thruster discharge current."

Many new technologies are being introduced to the electrical power grid at the distribution voltage level. These technologies include electric vehicles (EVs), distributed generation, and battery energy storage systems (BESS) This thesis investigates how these various technologies can be harmoniously integrated into the electric grid. Therefore, a modeling environment that can simulate scenarios involving the above technologies in durations from hours to years was created. This modeling system is modular so that any feeder configuration can be simulated by the user and each module has individual user defined parameters or curves that define their operation. Optimum economic dispatch, stability enhancement, renewable generation smoothing, and peak-shaving algorithms were implemented into the modeling environment. With the use of the built in algorithms, or custom input, the simulation tool produces the necessary electrical and economic values to fully evaluate the system’s feasibility. Other algorithms created include renewable generation smoothing and stability enhancement.

Devido à crescente demanda por energia elétrica na sociedade atual e o potencial congestionamento dos sistemas de transmissão, os aspectos de segurança no fornecimento de energia, de confiabilidade e da estabilidade dos sistemas elétricos de potência tornam-se cada vez mais prementes. Considerando o tamanho e complexidade crescentes e o seu uso em situações limites, os estudos e avaliações do SEP (Sistema Elétrico de Potência) demandam considerável poder computacional, além de utilização de modelos matemáticos para os diversos equipamentos que o compõe. Necessária, portanto, tanto a representação correta do SEP com as interligações (topologia da rede elétrica) de seus elementos constituintes, quanto a exatidão dos modelos matemáticos dos geradores, estabilizadores, compensadores, transformadores e linhas de transmissão, dentre outros equipamentos. A proposta deste trabalho é a definição de uma metodologia para análise e estudo do SEP que independa: dos modelos matemáticos dos equipamentos, do conhecimento prévio da topologia da rede elétrica e dos equivalentes adotados para as redes externas (de outras empresas). A metodologia é uma abordagem Model-Free no sentido em que busca a partir das informações aquisitadas do processo elétrico, determinar o comportamento do SEP, de modo totalmente independente dos modelos matemáticos dos equipamentos, do conhecimento prévio da sua topologia e da existência ou não de redes externas. A metodologia fornece informações quanto à instabilidade do SEP, ao identificar \"assinaturas\" caraterísticas da evolução de seu comportamento, seja em operação normal ou sob contingências, as quais podem ou não resultar em uma condição de instabilidade do mesmo. As assinaturas são identificadas ao se analisar o comportamento das tensões das barras do SEP, dentro de uma abordagem Fuzzy que classifica as barras coerentes em tensão. A dinâmica do estado operacional do SEP é, então, obtida à partir do comportamento desta classificação. / Due to the growing demand for electric power in today\'s society and the potential congestion of transmission systems, security aspects in power supply, reliability and stability of power systems are becoming more and more pressing. Considering the increasing size and complexity and its use in limit situations, the studies and evaluations of the EPS (Electrical Power System) require considerable computational power, as well as the use of mathematical models for the various equipment that compose it. Therefore, it is necessary the correct representation of the EPS with the interconnections (topology of the electrical network) of its constituent elements, as well as the accuracy of the mathematical models of generators, stabilizers, compensators, transformers and transmission lines, among other equipment. The purpose of this work is the definition of a methodology for the analysis and study of EPS, independent of: mathematical models of the equipment, previous knowledge of the topology of the electrical network and the equivalents adopted for the extern networks (of other companies). The methodology is a Model-Free approach in the sense that it searches from the acquired information of the electrical process, to determine the behavior of the EPS, totally independently of the mathematical models of the equipment, the previous knowledge of its topology and the existence or not of external networks. The methodology provides information on the instability of the EPS by identifying \"signatures\" characteristic of the evolution of its behavior, whether in normal operation or under contingencies, which may or may not result in a condition of instability of the same. The signatures are identified by analyzing the behavior of the EPS busbar voltages, within a Fuzzy approach that classifies the coherent buses into voltage. The dynamics of the operational state of the EPS is then obtained from the behavior of this classification.

Digitized by Kansas Correctional Industries / Department: Electrical Engineering.

O presente trabalho tem por objetivo propor uma metodologia de estimação de estado (EE) para sistemas de distribuição de energia que auxilie na identificação das regiões de fornecimento das concessionárias de distribuição que possam conter perdas não técnicas, de modo a orientar as ações para sua redução. As perdas não técnicas de energia elétrica são um grande desafio não só no Brasil como também em outros países em desenvolvimento. Face à dificuldade e ao custo para fiscalizar anualmente toda a área de concessão, faz-se necessário um diagnóstico para avaliar em quais grupos de clientes e regiões encontram-se este tipo de perda. Destarte, fica evidenciada a necessidade do desenvolvimento de uma ferramenta que, além de tratar de uma modelagem completa do sistema, utilize informações provenientes de medições diversas. Para isso, a estimação de estado se torna a metodologia ideal. A metodologia utilizada na estimação de estados foi a dos Mínimos Quadrados Ponderados (do inglês, Weighted Least Squares - WLS) (Schweppe & Wildes, 1970) e algumas técnicas foram aplicadas para permitir a EE em sistemas de distribuição, tais como a utilização da corrente complexa dos trechos como variáveis de estado, que decompõe a estimação de estados em três subproblemas, um para cada fase, permitindo a utilização de uma modelagem trifásica da rede e a introdução de pseudomedidas obtidas dos dados de faturamento dos clientes através de um processo estatístico. O trabalho apresenta exemplos de aplicação, sendo estes em sistemas de distribuição reais, mostrando os resultados obtidos e termina destacando as principais vantagens da metodologia. / This work focuses on the development of a distribution system state estimation (SE) algorithm for application to radial distribution networks which assists the identification of regions of the distribution network containing non-technical energy losses, helping the electric utilities to evaluate and reduce it. Non-technical energy losses represent an important challenge for distribution companies in developing countries, such as Brazil. However, economical limitations and measurement problems make impossible to have a perfect picture of the complete system, then a diagnoses method is required to evaluate which group of consumers and the regions have that type of loss. Therefore, is evidenced the necessity of a tool development which, farther on using the complete system modeling, works with information from various measurement instruments. Consequently, the SE becomes the ideal method. The SE applied is the Weighted Least Square approach (WLS) (Schweppe & Wildes, 1970) and some techniques where applied to allow the SE for distribution systems, such as, using the branch currents as the system state, which decouples the state estimation problem into three sub problems, one for each phase, allowing the three phase system modelling and the introduction of pseudo measurements from historical load data produced based on customer billing data through statistical processes. This work shows the results obtained by applying the computational tool to a real distribution system. Such results are compared with the ones obtained by using other methodologies, and the main advantages of this new methodology are outlined.

As one of the main contributors to greenhouse gas emissions, the electricity sector is anticipated to go through the following transitions in order to meet deep decarbonization targets for a sustainable future: 1) on the supply side, the electric grid is increasing its reliance on renewable generation, such as wind and solar; 2) on the demand side, heating is shifting from direct burning of fuel on site to electric, namely heat pumps. This dissertation evaluates the benefits of selected methods to alleviate pressing challenges associated with the electricity sector transitions on both the supply side and the demand side. First, on the supply side, the benefits of renewable generation forecasting coupled with storage are evaluated for an electric grid with high wind energy penetration and load following generation served by fossil fuels. A time series based forecasting method is found to have high forecasting accuracy and low computational costs. This methodology is applied to a real world situation in Sao Vicente, an island with 30% current wind energy penetration. The simulation results show that coupling forecasting and energy storage would further increase the wind penetration up to 38% without additional installation of wind turbines. Second, on the demand side, the benefits of demand side management using heat pumps enabled by the inherent thermal storage of the building envelope are evaluated during extreme cold events when the electric demand peaks and the wind power is often highly fluctuating. A second order thermal model is developed to thoroughly characterize the thermal inertia and leakage of the building envelope and quantify the amount of flexibility the building envelope is able to provide. This methodology is applied to five historical extreme cold events in New York City and the simulation results show that the requirements for short term ramping due to high wind variability are greatly reduced through the sequential controls of the heat pumps. This dissertation also studies the implications of the electricity sector transitions on the residential sector with regard to costs, energy, missions, and policy. Four representative residential city blocks located in three different climate regions of the United States are analyzed using fine spatial and temporal real historical consumption and weather data. Residential blocks in different climate regions have different weather patterns, demand profiles, and local renewable resources. Future energy scenarios with electric heating at high renewable penetration levels are modeled and compared for the representative residential city blocks. Detailed costs comparisons are evaluated for various technological interventions including 1) air source and ground source heat pumps; 2) battery and thermal storage; and 3) wind and solar generation. This dissertation finds that 1) the optimal wind and solar generation mix varies with location and amount of storage and 2) battery storage is more cost effective than thermal storage, ground source heat pumps, and overbuilt renewable generation. In addition, optimal pathways to deep decarbonization for these representative residential city blocks are proposed and compared. Strategic actions are identified for the homes and suggestions are discussed for policy makers and local utilities. This dissertation through its methodologies and analysis enables home owners and policy makers to make cost assessments in achieving the goals of deep decarbonization.

Subestações blindadas são utilizadas por empresas de energia há mais de 50 anos. Muitas destas subestações estão em operação até os dias de hoje, sem qualquer modificação em seu projeto original, e ainda assim continuam operando sem apresentar problemas ou indícios de fadiga. Isto pode ser atribuído a sua qualidade construtiva em conjunto com o material isolante utilizado por este tipo de equipamento, o Hexafluoreto de Enxofre (SF6). Este gás possui todas as características desejáveis para manter adequadas as propriedades dielétricas da subestação, além de ser inerte e extremamente estável. O tempo de vida nominal de uma subestação blindada pode ser de 30 a 50 anos, dependendo de suas características ou recomendação do fabricante. A proximidade, ou até a ultrapassagem, do final do tempo de vida gera preocupação às empresas detentoras destes equipamentos antigos no que diz respeito a operação da subestação com segurança. Outro aspecto importante está relacionado a vazamentos de gás na atmosfera, pois o SF6 está entre os elementos mais danosos para o efeito estufa. Por estas razões este trabalho apresenta o desenvolvimento de um sistema para monitoramento de vazamentos e também de parâmetros indicativos do gás SF6 em uma subestação blindada antiga. O objetivo principal foi de desenvolver um sistema com dados históricos para se realizar estudos a respeito do comportamento do gás. A subestação utilizada neste trabalho não possuía nenhum sistema de monitoramento online. Assim, foi desenvolvido um sistema de tempo real para coletar dados de densidade do gás e de ponto de orvalho nos compartimentos da subestação. O sistema de coleta de dados foi instalado em três bays de uma subestação. Foram instalados sensores para medir estas duas grandezas, e também, módulos de aquisição de dados de baixo custo que se comunicam por meio de protocolos padrão e abertos. A partir do sistema instalado, no longo prazo, se espera a redução de vazamentos de gás com a possibilidade de inspeções online. Pode ser atribuído como resultado do trabalho a redução de custos, pois os dados históricos com indicativos favoráveis permitem estender o tempo entre manutenções preventivas. Como resultado complementar deste trabalho, o monitoramento de perdas de gás se torna mais eficiente e rápido, colaborando, assim com as expectativas ambientais atuais. / Gas Insulated Substations (GIS) are used by energy companies for over 50 years. Many early substations have been in operation until the present day, without any modification in its original design, and still are operating without problems or indications of fatigue. This can be attributed to its constructive quality along with the insulating material used for this type of equipment, the gas sulfur hexafluoride (SF6). This gas has all the desirable features for maintaining the dielectric of the substation as well as being inert and extremely stable. The nominal lifetime of a GIS substation can be 30 to 50 years, depending on their characteristics or manufacturer\'s recommendation. The proximity, or even exceeding, the lifetime generates concern to companies holding these old equipment as regards the operation of the substation safely. Another important aspect is related to gas leakages into the atmosphere because SF6 is among the most damaging elements to the greenhouse effect. Therefore, this work presents the development of a system for monitoring leakage and also indicative parameters of SF6 gas at an old GIS. The main objective was to develop a system with historical data to conduct studies about the behavior of the gas. The substation used for this work had no online monitoring system. Thus, it was developed a real-time system for collecting data of gas density and dew point in the compartments of the substation. The data collection system was installed in three bays of the substation. Sensors were installed to measure these two quantities, and also low cost data acquisition modules which communicate via standard and open protocols. In long term, with the system, there should be a reduction of gas leakages with the possibility of online inspections of the gas. May be assigned as a result the reduction of costs, since the historical data with good indicative allows extending the time for preventative maintenance. As additional result of this work, it is expected that the monitoring of leakage become more efficient and faster, thus contributing to the current environmental expectations.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Includes bibliographical references. / by Joseph Vito Minervini. / Ph.D.

The rapid development in renewable generation technologies and flexible distribution networks requires current infrastructure to be modified and developed to adapt high penetration levels of distributed generation. Existing distribution networks were not initially designed and anticipated to accommodate generators on large scale. Short circuit studies ensure the effectiveness of protection equipment settings and coordination is maintained in case of short circuit, despite any additional distributed generation is connected to the distribution network. This research aims to study and compare the different network fault situations for wind energy systems with induction generators, photovoltaic energy systems, and diesel generators connected to distribution networks. The simulation study will be conducted on the existing IEEE case study systems including 13 bus and 30 bus distribution test systems, using ETAP software. Short circuit analysis will be performed twice to include the ANSI/IEEE and the IEC methods for short circuit currents calculation. Simulated results showed that the wind energy systems have significant impact on the short circuit currents, whereas the photovoltaic energy systems are found to have inconsequential effect. The most moderate solution is found to be a distributed generation mix.

Harmônicos e desequilíbrios podem causar uma série de problemas a equipamentos conectados a rede elétrica. Este trabalho propõe um método de extração em tempo real das componentes de seqüência positiva, negativa e/ou harmônicos que não requer transformações de coordenadas ou filtragem de sinais. O método proposto é verificado via simulação numérica e implementado experimentalmente em um DSP. Como exemplos de aplicação apresentam-se: a simulação de um Filtro Ativo de Potência utilizando-se um conversor do tipo fonte de tensão operando em PWM e um Relé de Seqüência Negativa. / Harmonics and unbalances cause several problems to equipments connected to AC mains. This work proposes a real time method to obtain the positive and negative sequence components and/or harmonics that requires no coordinate transformation neither signal filtering. Numerical simulation and experimental results are shown to validate the proposed method. As examples of application an Active Power Filter using a voltage source converter operating with PWM and an Negative Sequence Power Relay are presented.