Esta dissertação apresenta um modelo aproximado de rede desenvolvido para análise de sistemas de distribuição em regime permanente. O modelo é detalhado do ponto de vista matemático e teórico considerando a representação dos elementos em derivação da rede (cargas e geradores) e dos limites operacionais empregando aproximações lineares. A modelagem linear permite determinar de forma simples os valores das tensões e correntes do sistema, podendo ser empregada em problemas de otimização relacionados ao planejamento e expansão de sistemas de distribuição. A representação da carga considera a influência da variação da tensão, fator determinante nas redes de distribuição. Também é considerada a inclusão de geração distribuída (GD) sendo implementada para diferentes modos de operação, permitindo ainda a minimização das perdas para a barra onde a GD está alocada. Para validar a abordagem proposta, os resultados do modelo apresentado foram comparados em termos de tensões, correntes e perdas com resultados obtidos com o modelo convencional de fluxo de carga, solucionado pelo algoritmo de varredura. Os testes foram realizados em dois sistemas de distribuição conhecidos, um de 70 barras e um de 135 barras. Para o sistema de 70 barras foi avaliado o uso de diferentes modos de operação da GD. Finalmente, para o sistema de 135 barras foram comparados os resultados do modelo proposto com o fluxo de carga convencional caracterizando a GD como uma barra de tensão controlada (PV) para diversos valores de injeção ativa na barra selecionada. As conclusões confirmam a validade e as vantagens que o modelo desenvolvido neste trabalho proporciona. / This work presents an approximate model developed to the analysis of electrical distribution systems at steady state. Both mathematical and theoretical details are given considering the representation of the shunt elements (loads and generators) and the operating limits of the network, using linear approximations. The linear modeling adopted resulted in a simple way to determine the values of the voltages and currents of the system; further the model can be applied to optimization problems related to optimal operation and expansion planning of distribution systems. The load representation considers the influence of voltage variations, which play an important role in the distribution networks. This work also considers the inclusion of distributed generation (DG), which is assessed under several modes of operation, including one mode which allows to minimize the losses at the node where the DG is located. To validate the proposed approach, the results for two example networks, given in terms of voltages, currents and losses, were compared with corresponding results obtained with conventional load flow model, solved by the backward-forward sweep method. The examples networks used to test and validate the model are known distribution systems, one having 70 and the other 135 nodes. Regarding the system with 70 nodes, the inclusion of DG was studied for several operational modes. Finally, the system of 135 nodes were used to compare the results of the proposed model with the results of the conventional load flow; in this case, the GD was characterized as a controlled-voltage bar (PV) for various levels of active power injection into the bar where the GD is located. The conclusions show the validity and advantages of the proposed model.

abstract: Electric power systems are facing great challenges from environmental regulations, changes in demand due to new technologies like electric vehicle, as well as the integration of various renewable energy sources. These factors taken together require the development of new tools to help make policy and investment decisions for the future power grid. The requirements of a network equivalent to be used in such planning tools are very different from those assumed in the development of traditional equivalencing procedures. This dissertation is focused on the development, implementation and verification of two network equivalencing approaches on large power systems, such as the Eastern Interconnection. Traditional Ward-type equivalences are a class of equivalencing approaches but this class has some significant drawbacks. It is well known that Ward-type equivalents "smear" the injections of external generators over a large number of boundary buses. For newer long-term investment applications that take into account such things as greenhouse gas (GHG) regulations and generator availability, it is computationally impractical to model fractions of generators located at many buses. A modified-Ward equivalent is proposed to address this limitation such that the external generators are moved wholesale to some internal buses based on electrical distance. This proposed equivalencing procedure is designed so that the retained-line power flows in the equivalent match those in the unreduced (full) model exactly. During the reduction process, accommodations for special system elements are addressed, including static VAr compensators (SVCs), high voltage dc (HVDC) transmission lines, and phase angle regulators. Another network equivalencing approach based on the dc power flow assumptions and the power transfer distribution factors (PTDFs) is proposed. This method, rather than eliminate buses via Gauss-reduction, aggregates buses on a zonal basis. The bus aggregation approach proposed here is superior to the existing bus aggregation methods in that a) under the base case, the equivalent-system inter-zonal power flows exactly match those calculated using the full-network-model b) as the operating conditions change, errors in line flows are reduced using the proposed bus clustering algorithm c) this method is computationally more efficient than other bus aggregation methods proposed heretofore. A critical step in achieving accuracy with a bus aggregation approach is selecting which buses to cluster together and how many clusters are needed. Clustering in this context refers to the process of partitioning a network into subsets of buses. An efficient network clustering method is proposed based on the PTDFs and the data mining techniques. This method is applied to the EI topology using the "Saguaro" supercomputer at ASU, a resource with sufficient memory and computational capability for handling this 60,000-bus and 80,000-branch system. The network equivalents generated by the proposed approaches are verified and tested for different operating conditions and promising results have been observed. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

abstract: Photovoltaic (PV) power generation has the potential to cause a significant impact on power system reliability since its total installed capacity is projected to increase at a significant rate. PV generation can be described as an intermittent and variable resource because its production is influenced by ever-changing environmental conditions. The study in this dissertation focuses on the influence of PV generation on trans-mission system reliability. This is a concern because PV generation output is integrated into present power systems at various voltage levels and may significantly affect the power flow patterns. This dissertation applies a probabilistic power flow (PPF) algorithm to evaluate the influence of PV generation uncertainty on transmission system perfor-mance. A cumulant-based PPF algorithm suitable for large systems is used. Correlation among adjacent PV resources is considered. Three types of approximation expansions based on cumulants namely Gram-Charlier expansion, Edgeworth expansion and Cor-nish-Fisher expansion are compared, and their properties, advantages and deficiencies are discussed. Additionally, a novel probabilistic model of PV generation is developed to obtain the probability density function (PDF) of the PV generation production based on environmental conditions. Besides, this dissertation proposes a novel PPF algorithm considering the conven-tional generation dispatching operation to balance PV generation uncertainties. It is pru-dent to include generation dispatch in the PPF algorithm since the dispatching strategy compensates for PV generation injections and influences the uncertainty results. Fur-thermore, this dissertation also proposes a probabilistic optimal power dispatching strat-egy which considers uncertainty problems in the economic dispatch and optimizes the expected value of the total cost with the overload probability as a constraint. The proposed PPF algorithm with the three expansions is compared with Monte Carlo simulations (MCS) with results for a 2497-bus representation of the Arizona area of the Western Electricity Coordinating Council (WECC) system. The PDFs of the bus voltages, line flows and slack bus production are computed, and are used to identify the confidence interval, the over limit probability and the expected over limit time of the ob-jective variables. The proposed algorithm is of significant relevance to the operating and planning studies of the transmission systems with PV generation installed. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

Esta dissertação apresenta um modelo aproximado de rede desenvolvido para análise de sistemas de distribuição em regime permanente. O modelo é detalhado do ponto de vista matemático e teórico considerando a representação dos elementos em derivação da rede (cargas e geradores) e dos limites operacionais empregando aproximações lineares. A modelagem linear permite determinar de forma simples os valores das tensões e correntes do sistema, podendo ser empregada em problemas de otimização relacionados ao planejamento e expansão de sistemas de distribuição. A representação da carga considera a influência da variação da tensão, fator determinante nas redes de distribuição. Também é considerada a inclusão de geração distribuída (GD) sendo implementada para diferentes modos de operação, permitindo ainda a minimização das perdas para a barra onde a GD está alocada. Para validar a abordagem proposta, os resultados do modelo apresentado foram comparados em termos de tensões, correntes e perdas com resultados obtidos com o modelo convencional de fluxo de carga, solucionado pelo algoritmo de varredura. Os testes foram realizados em dois sistemas de distribuição conhecidos, um de 70 barras e um de 135 barras. Para o sistema de 70 barras foi avaliado o uso de diferentes modos de operação da GD. Finalmente, para o sistema de 135 barras foram comparados os resultados do modelo proposto com o fluxo de carga convencional caracterizando a GD como uma barra de tensão controlada (PV) para diversos valores de injeção ativa na barra selecionada. As conclusões confirmam a validade e as vantagens que o modelo desenvolvido neste trabalho proporciona. / This work presents an approximate model developed to the analysis of electrical distribution systems at steady state. Both mathematical and theoretical details are given considering the representation of the shunt elements (loads and generators) and the operating limits of the network, using linear approximations. The linear modeling adopted resulted in a simple way to determine the values of the voltages and currents of the system; further the model can be applied to optimization problems related to optimal operation and expansion planning of distribution systems. The load representation considers the influence of voltage variations, which play an important role in the distribution networks. This work also considers the inclusion of distributed generation (DG), which is assessed under several modes of operation, including one mode which allows to minimize the losses at the node where the DG is located. To validate the proposed approach, the results for two example networks, given in terms of voltages, currents and losses, were compared with corresponding results obtained with conventional load flow model, solved by the backward-forward sweep method. The examples networks used to test and validate the model are known distribution systems, one having 70 and the other 135 nodes. Regarding the system with 70 nodes, the inclusion of DG was studied for several operational modes. Finally, the system of 135 nodes were used to compare the results of the proposed model with the results of the conventional load flow; in this case, the GD was characterized as a controlled-voltage bar (PV) for various levels of active power injection into the bar where the GD is located. The conclusions show the validity and advantages of the proposed model.

Este trabalho tem por meta focalizar a adaptação necessária na metodologia de planejamento atual, norteada segundo uma ótica determinística e conservadora, afim de permitir a elaboração de Programas de Obras de Transmissão/Subtransmissão, condicionados por limitações de teto no montante de investimento a curto e médio prazos. Para tanto, como tema central, busca-se desenvolver uma base conceitual e metodológica, para permitir uma exploração maximizada das possibilidades de carregamento de equipamentos e instalações do sistema de transmissão, contemplando a especificação das ferramentas computacionais necessárias para dar consequência prática à proposta. Considerando o potencial de análise proporcionado por métodos e técnicas de natureza probabilística, aplicados ao planejamento de Sistemas Elétricos, a espinha dorsal da evolução metodológica delineada no texto repousa sobre a avaliação de confiabilidade global e quantificação de riscos operativos. O texto foi estruturado em 8 capítulos onde, a partir de um capítulo introdutório, enfoca-se sequencialmente os temas: * Conceitos e Metodologias para Maximização do Carregamento de Transformadores de Potência. * Conceitos e Metodologias para Maximização do Carregamento de Linhas aéreas de Transmissão. * Impacto das Restrições Financeiras no planejamento e possibilidade de atuação a nível técnico para administrar o conflito entre qualidade de serviço e recursos limitados. * Conceitos e Metodologias para relaxação dos Critérios limitantes para o carregamento máximo de componentes do sistema, em ambiente de severas restrições financeiras, no horizonte de curto prazo. * Resultados obtidos em aplicações concretas a situações do Setor Elétrico, visando caracterizar o alcance do ferramental preconizado nos capítulos anteriores. * Critérios e Procedimentos para Padronização de Subestações e Linhas de Transmissão , coerentes com os conceitos de maximização de carregamento introduzidos nos dois primeiros capítulos. Ao final do texto, incluiu-se um capítulo de \"Conclusões\", com o objetivo de sumarizar os aspectos mais relevantes abordados no texto, assim como indicar linhas de ação e novos desenvolvimentos, necessários para permitir a efetivação prática da metodologia proposta. / An important problem posed to power system planners in developing countries is now becoming commonplace, even in developed countries, and concerns on how to fit an expansion plan into a tight budget, with the least reduction in reliability levels. This problem is known as power system planning under financial constraints and a series of methods is now available to deal with it. So, this work addresses the necessary adjustments in order to permit the Transmission / Sub-transmission Expansion Program establishment when there are investments constraints in a medium/short term range. The main emphasis is on the development of a methodological and conceptual framework, aiming at a maximizes exploration of the loading capability of transformers and transmission lines of the power network. In this context, a new methodological framework for transmission system planning in a financial constrained environment is presented. The proposed approach combines transmission projects priority evaluation and ranking as well as criteria flexibilization, being particularly suitable for short-term planning. The problem to be faced is to operate the system after a project postponement, while the service quality is kept so adequate as it is possible. One of the main issues to be focused is the transmission system uprating since a maximized equipment utilization can contribute to avoid a more significant restriction to the costumers. Therefore, a detailed description of the models for transmission lines and transformers loading limits assessment is presented, with emphasis on the main concepts and the application of probabilistic tools to circumvent the inherent conservatism of deterministic methods. A summary of the contents is presented in what follows: * Concepts and Methodology for Transformers loading maximization. * Concepts and Methodology for Transmission Lines loading maximization. * Financial Restrictions impacts on Expansion Planning Process and the possibilities to manager the conflict between service quality and investment constraints. * Concepts and Methodologies to the relaxation of Criteria that limits the loading capability of transmission lines, aiming at short term Planning under severe financial restrictions, * Obtained results in concrete applications of the proposed methodology and computational tools to Brazilian Electric Power System. * Methods and Criteria to standardization of Substations and Transmission Lines, according the main issues formerly introduced. * Conclusion and Future Research.

The thesis aims to introduce an efficient resource development strategy in electric utility long term planning under uncertainty considerations. In recent years, electric utilities have recognized the concepts of robustness, flexibility, and risk exposure, to be considered in their resource development strategy. The concept of robustness means to develop resource plans that can perform well for most, if not all futures, while flexibility is to allow inexpensive changes to be made if the future conditions deviate from the base assumptions. A risk exposure concept is used to quantify the risk hazards in planning alternatives for different kinds of future conditions. This study focuses on two technical issues identified to be important to the process of efficient resource development: decision-making analysis considering robustness and flexibility, and decision-making analysis considering risk exposure. The technique combines probabilistic methods and tradeoff analysis, thereby producing a decision set analysis concept to determine robustness that includes flexibility measures. In addition, risk impact analysis is incorporated to identify the risk exposure in planning alternatives. Contributions of the work are summarized as follows. First, an efficient resource development framework for planning under uncertainty is developed that combines features of utility function, tradeoff analysis, and the analytical hierarchy process, incorporating a performance evaluation approach. Second, the multi-attribute risk-impact analysis method is investigated to handle the risk hazards exposed in power system resource planning. Third, the penetration levels of wind and photovoltaic generation technologies into the total generation system mix, with their constraints, are determined using the decision-making model. The results from two case studies show the benefits of the proposed framework by offering the decision makers various options for lower cost, lower emission, better reliability, and higher efficiency plans. / Ph. D.

Solar DEC (Desiccant and Evaporative Cooling) air-conditioning is a renewable technological approach to the future air-conditioning of buildings driven with solar-thermal heat. The principal acceptance of solar airconditioning has led to system prototypes mainly across Europe, however the diffusion of this innovative technology is proceeding slowly due to little field testing experience. In climates with coexisting heating demand particularly, a multivalent system approach that utilizes solar-heat not only for air-conditioning but also for hot water preparation and heating has potential as a feasible concept. However, previous research focused on systems using solar heat exclusively for the DEC-process. This research contributes to the advancement of the solar DEC-technology with multivalent use of solar thermal heat. The investigation consists of an initial detailed in-situ monitoring analysis of a system prototype operated in an industrial environment, followed by the development of optimised system concepts and a climate-specific analysis of the solar DEC-technology. The monitoring provided in-depth knowledge about the system operation, revealing the reasons for the insufficient refrigeration capacity achieved in practice. A detailed simulation model for an entire multivalent solar DEC-system including the heat sinks, DEC-system, heating and hot-water preparation was developed and a DEC-control strategy has been formulated. A new optimised control strategy for multivalent systems with simultaneous sink supply concept was devised. A sensitivity analysis was carried out to investigate the key design parameters for the dimensioning of multivalent solar DEC-systems. The research concluded that the auxiliary primary energy consumption of the optimised system was lower by one third compared to the initial system. Finally, a methodological zoning approach was developed, to systematically produce design-specific outline data for the application of the solar DEC-technology at climatically different sites.

This quantitative research study investigated the impact of organisational context on the process and success of strategic IS planning (SISP) in post-implementation information systems in Libyan organisations. A set of direct and indirect relationships were investigated in the research model. The organisational context presented as a contingent situational variable mediated by SISP process and predicted by SISP success (the criterion variable). The causality of the relationship set was developed from the contingency theory of information systems and supported by fit models in strategic management research. The study deployed multivariate analysis represented in the structural equation modelling (SEM) to develop robust construct measurements and analyse data collected from executives responsible for information systems planning in both public and private Libyan organisations. Multi-dimensional multi-items constructs were used in the path analysis model after they were extensively validated. The path analysis model represented as mediation model, where hypothesise suggest that SISP context has an impact SISP success, through the influence of the SISP process. In the model, four dimensions of the SISP context construct were found to have a significant impact on SISP success directly and indirectly through the SISP process. Two of these dimensions are components of the leadership orientation construct, namely “Creative and Controlling” leadership. The other two dimensions are “Organisation centralisation structure and the Riskiness of organisation strategies”. The environmental uncertainty and planning resource constructs were found to have no impact on SISP success in Libyan organisations. Furthermore, this study validated six out of seven dimensions of SISP process construct measurement; only five exhibited acceptable fit level in the path analysis model and all were affected by the SISP context. However, just three out of five SISP process constructs had an impact on SISP success namely “Comprehensiveness, Focus and Intuition planning process”. Different SISP processes were associated with different levels of SISP success, “Intuition” was the most effective SISP process approach. The second most effective SISP process approach was the “Focus on innovation”, followed by “Limited comprehensiveness”. The SISP success measured by the fulfilment of key objectives that has three measurements constructs namely “Analysis, Alignment, and Cooperation”. The research suggest that under the effect of organisation context the most successful SISP produced by (CIO, CEO, or top executives) who rely less on personal judgment, focus more on innovation rather than control and limit their comprehensiveness of information systems planning process.

Esta dissertação aborda o cálculo da taxa de crescimento da tensão de restabelecimento transitória (TCTRT), considerando o caso de falha na barra, durante a abertura do primeiro polo e o cálculo da tensão de restabelecimento transitória (TRT) nos primeiros instantes de tempo, incluindo o efeito da capacitância. Os principais casos possíveis de falha na barra foram analisados e os resultados demonstraram a precisão das expressões obtidas. Normalmente, o cálculo da TCTRT e da TRT é feito por meio de simulações em programas de transitórios eletromagnéticos em que há rotinas específicas para a extração dos valores destas, porém, em determinadas condições, podem ocorrer oscilações ou imprecisões numéricas. Por ser um assunto de grande interesse convém desenvolver expressões que possam esclarecer resultados duvidosos sem a necessidade de artifícios de redução do passo de integração a valores muitas vezes não factíveis. As expressões obtidas neste trabalho podem ser utilizadas não só para se obter de forma precisa e simplificada os valores da taxa de crescimento da tensão de restabelecimento transitória de um circuito real, assim como os valores da TRT nos primeiros instantes de tempo. / This study is focused on the rate of rise of transient recovery voltage (RRTRV) calculation considering the case of bus fault, during the first pole to open, and also includes the transient recovery voltage (TRV) calculation, in the first instants of time, including the capacitance effect. The main cases of bus fault have been evaluated and demonstrate that the expressions developed in this study are relevant and with good precision. Usually, the RRTRV and the TRV are calculated with the use of simulation programs, using specific routines, nevertheless, in certain conditions, there might be oscillations and numeric imprecisions which requires a mathematic expression. This topic is of great interest and it is important to have mathematical expressions that could clarify doubtful results. The expressions obtained in this study can be use in a very simples and effective mode to calculate RRTRV and the TRV in the first instants of time, considering a real life circuit.

O sistema elétrico brasileiro utiliza o custo do déficit como parâmetro no seu planejamento da expansão e operação para indicar o custo econômico da escassez de energia elétrica para a sociedade. Para o desenvolvimento de um método confiável de cálculo deste parâmetro, é importante compreender a dependência do suprimento de energia nos diversos setores econômicos. Este trabalho apresenta e discute a percepção das empresas do setor de telecomunicações dos impactos resultantes de restrições no fornecimento de energia elétrica. O trabalho foi desenvolvido em duas etapas: revisão da literatura referente aos métodos utilizados para o cálculo do custo do déficit no modelo brasileiro e na experiência internacional e, em seguida, pesquisa empírica com realização de estudos de casos em duas empresas de telecomunicações. As informações obtidas mostram que, no setor de serviços de telecomunicações, qualquer nível de interrupção ou restrição de energia tem impacto econômico para as empresas. Tendo em vista o caráter de serviço essencial para a população, as empresas investem em estruturas de contingenciamento que mitigam os riscos em caso de pequenas restrições ou interrupções curtas de energia. Indisponibilidade de energia acima da capacidade de contingenciamento prevista pelas empresas requer investimentos adicionais e implica em aumento dos custos operacionais para redução dos riscos de falhas na prestação dos serviços e suas consequentes sanções regulatórias. Em relação aos métodos para o cálculo do custo do déficit, concluiu-se que, baseado nas análises dos casos estudados, no perfil de consumo de energia e nas características de negócio do setor de telecomunicações, para pesquisas diretas ao consumidor, o método de preferência revelada é o mais adequado para este setor econômico e possivelmente outros com as mesmas características. Neste método o custo da insuficiência de energia é inferido através das decisões de investimento feitas pelo consumidor em equipamentos de contingência, tais como geradores de reserva. / The Brazilian electricity system uses the deficit cost as a parameter in its planning processes to indicate the economic cost for the society of electricity shortages. In developing a reliable method of calculating this parameter, it is important to understand the dependence of different economic sectors on the energy supply. This work presents and discusses the telecommunication companies\' perception of the impacts resulting from restrictions to the power supply. It was developed in two stages: a literature review on the methods used to calculate the deficit cost in Brazil and other countries, followed by an empirical research with case studies in two telecommunication companies. The research showed that for the telecommunication service providers, any level of power interruption or restriction has an economic impact. In view of the essential nature of the service to the population, companies invest in contingency structures to mitigate the risks for small power restrictions and short interruptions. Providing mitigation measures for larger levels of power shortage would require additional investments and result in higher operational costs, in order to decrease the risk of service interruption and consequent regulatory sanctions. Regarding the deficit cost calculation method, it is shown, based on the case studies analysis, the power consumption profile, and the business characteristics, that for consumer surveys, the revealed preference method is most suitable for the telecommunications economic sector, and possibly for other similar ones. In this method, the power shortage cost is inferred from the investment decisions made by the company in power contingency equipment, such as backup generators.