Environmental concerns caused by burning fossil fuel and the safety concerns associated with nuclear power plants have led to increased interest and investment in wind power. Wind penetration in power systems is rapidly increasing world-wide and creating significant impacts on the overall system performance. The impact of wind generation on the overall system performance increases substantially as wind penetration in power systems continues to increase to relatively high levels. It becomes increasingly important to accurately model the wind behavior, the interaction with other wind sources and conventional sources, and incorporate the characteristics of the energy demand in order to carry out a realistic evaluation of system reliability. Analytical methods using annual wind models have generally been used for reliability evaluation of wind integrated power systems. These methods do not recognize the seasonal and diurnal load following capability of wind. In this thesis, the system adequacy indices are first evaluated on an annual and seasonal basis and then a technique is developed to incorporate the diurnal load following capability of wind. Power systems with high wind penetrations are often connected to multiple wind farms at different geographic locations. Wind speed correlations between the different wind farms largely affect the total wind power generation characteristics of such systems, and therefore should be an important parameter in the wind modeling process. Another concern that arises is the lack of time-synchronized data, especially at the planning phase, which limits the capability of system planners to accurately model multiple correlated wind farms using simple analytical methods. A simple and appropriate probabilistic analytical wind model which can be used for adequacy evaluation of multiple wind-integrated power systems is proposed in the thesis. A simple analytical method to develop an approximate wind model of multiple correlated wind farms when time-synchronized wind data is not available is also proposed in the thesis. The methods to incorporate correlations in the adequacy evaluations of wind integrated power systems presented in the thesis are expected to be highly useful for system planners and policy makers as wind penetration continues to increase.

Flexibility describes the system ability to cope with events that may cause imbalance between electricity supply and demand while maintaining the system reliability in a cost-effective manner. Flexibility has always been present in the power system to cater for unplanned generator outages and demand uncertainty and variability. The arrival of wind generation with its variable and hard to predict nature increases the overall needs for system flexibility. This thesis provides a systematic approach for investigating the role of flexibility in different power system activities including generation scheduling, generation planning and market operation, and furthermore proposes two 'offline' indices for flexibility evaluation. Using the tools and metrics presented in this thesis, it is possible to perform the following tasks: • Conduct generation scheduling simulation to evaluate the impacts of wind on the flexibility requirement of power systems; • Use the unit construction and commitment algorithm to 1) estimate the maximum allowable wind capacity for an existing system; 2) find the optimal investment of new flexible units for accommodating more wind generation; and 3) decide an optimal generation mix for integrating a given wind penetration; • Use the market model to reveal the value and profitability of flexibility and evaluate the corresponding effects of alternative market design; • Use the two proposed flexibility indices to quantitatively assess the flexibility of individual generators and power systems without undertaking complex and time consuming simulations.

This dissertation introduces a new planning and operational tool to integrate photovoltaic (PV) systems into the utility's generation mix. It is recognized that much of the existing research concentrated on the central PV system, its operations, and long-term planning with PV system and concluded that technical problems in PV_ operation. will _power was subtracted from the utility load with the expectation that conventional generation would meet the load. This approach is valid for small penetration levels and for PV facilities connected near the load centers. Second, PV system was studied on a case-by-case basis. This made the interactions between the PV systems and conventional power systems not well known to the operator in the dispatch center on one hand, and to the PV system manufacturer, on the other hand. In addition, several constraints such as thermal generation ramping capabilities, energy costs, tie-line interchange, spinning reserve requirements, hydro availability and generating capacity, and pumped-storage scheduling are not adequately represented in this process. These are real problems and their solutions are sought in this dissertation. Finally, the value of PV systems does not lie only in serving load, but also in reducing problems associated with emissions. It is felt that a comprehensive methodology that would take into account the PV system characteristics and the forth mentioned constraints, as well as more global penetration is developed. The proposed methodology is designed to handle load dynamics and PV fluctuations, so as to minimize operational problems. The objective of this study is to determine the economic and operational impacts when large photovoltaic systems are incorporated into the electric utility generation mix. The proposed methodology handles combustion turbines, hydro and pumped-storage hydro power systems. Performance analysis shows that hydro availability, generation mix and characteristics, PV power output dynamics and performance, time of the year, and energy costs influence the economic and operational impacts of large-scale PV generation. Results show that while hydro dispatching increases acceptable PV penetration levels, generation mix and energy costs influence the breakeven capital cost. According to this study, for a 10 percent PV penetration level (1200 MW) and high energy costs, the breakeven capital cost is $968/kW and $1200/kW for Richmond (Virginia) and Raleigh (North Carolina), respectively. This corresponds to an energy cost of 3.20 and 3.00 ¢/kWh for Richmond and Raleigh. / Ph. D.

Within the past two decades, the planning arena has changed considerably and increasing awareness of the impacts of utility generation, intensifying pressure from the public and regulators, and growing competition from other energy and electricity suppliers have made the utility planning process rather complex. The variety of players in utility planning has introduced new priorities and a new set of competing objectives. Increased resource scarcity, the requirement for economic efficiency and the need to view the electricity production and utilization process in its entirety also necessitate an integrated resource planning approach, resulting in a wider array of expansion alternatives that must be evaluated. Another characteristic that makes planning so complicated is the uncertainty in the factors that influence the cost of the power system plan. Public concern for the environment has resulted in a series of legislations for controlling emissions of acid rain precursors (SO₂ and NO_x) and other pollutants. More and more regulators are also requiring electric utilities to internalize environmental externalities in their planning processes. The potential for new legislation on currently uncontrolled effluents like CO₂ likewise remains. There is thus a need to examine the modeling of emissions that would reflect not only the cost of control but the environmental impacts of these emissions as well. This thesis combines the features of the trade-off and decision analysis techniques to address the multiplicity of objectives and the uncertainties of planning. It draws on Saaty's analytic hierarchy process (AHP) and the interdependent data analysis (IDA) technique developed at Virginia Tech to develop priority weights among objectives and probability distributions of uncertainties. It elucidates the relationship between the competing techniques of trade-off analysis and the method of weights in terms of the economic theory of the firm. The confidence intervals determined with the IDA technique are then used to obtain a range of alternatives that satisfy the requirements of both approaches for evaluation by the decision maker (DM). Special attention is given to the environmental impacts of the generation plan and the model accounts for these issues as attributes in the planning process as well as being legislation uncertainties. / Ph. D.

The objective of the proposed research is to quantify the limits of overstressed and aging circuit breakers in terms of probability of failure and to provide guidelines to determine network reconfigurations, generator commitment, and economic dispatch strategies that account for these limits. The proposed temporary power system operating strategies address circuit breaker adequacy issues and allow overstressed breakers to be operated longer and more reliably until they are replaced with adequate equipment. The expansion of electric networks with new power sources (nuclear plants, distributed generation) results in increased short-circuit or fault currents levels. As fault currents increase, they will eventually exceed circuit breaker ratings. Circuit breakers exposed to fault currents in excess of their ratings are said to be overstressed, underrated, or inadequate. Insufficient ratings expose overstressed breakers to increased failure probabilities. Extensive common-mode outages caused by circuit breaker failures reduce the reliability of power systems. To durably avoid outages and system unreliability, overstressed breakers must eventually be replaced. Large-scale replacements of overstressed breakers cannot be completed in a short time because of budgetary limits, capital improvement schedules, and manufacturer-imposed constraints. Meanwhile, to preserve the ability of old and overstressed breakers to safely interrupt faults, short-circuit currents must be kept within the limits imposed by the ratings and the age of these breakers by using the substation reconfiguration and generator commitment strategies described in this study. The immediate benefit of the above-mentioned operating strategies is a reduction of the failure probability of overstressed breakers obtained by avoiding the interruption of currents in excess of breaker ratings. Other benefits include (i) increased network reliability, (ii) restored operating margins with respect to existing equipment, and (iii) prioritized equipment upgrades that enhance the long-term planning of power systems.

Renewable Portfolio Standards (RPS) require electricity providers to supply a minimum fixed percentage or total quantity of customer load from designated renewable energy resources by a given date. These policies have become increasingly prevalent in the past decade as state governments seek to increase the use of renewable energy sources. As a policy tool, RPS provide a cost-effective, market-based approach for meeting targets which promote greater use of renewable energy in both regulated and deregulated markets. To facilitate the obtainment of Renewable Portfolio Standards, most states allow the trading of Renewable Energy Credits (RECs). RECs represent the environmental attributes of renewable energy generation which are decoupled from the generated power. These credits are created along with the generation of renewable energy, decoupled from energy generation, tracked by regional systems, and eventually purchased by retail suppliers to fulfill their RPS obligations. As of April 2010, RPS have been passed into law in 29 states and Washington D.C. and an additional 6 states have non-mandatory renewable portfolio goals however the U.S. government has yet to enact a Federal Renewable Portfolio Standard. Although the final requirements and details of a Federal RPS are undecided, federal standards would be unlikely to preempt or override state programs which are already in place. A key concern regarding the passage of a federal RPS is that a national REC market would result in a shift of wealth from states with few renewable energy resources and limited resource potential to regions richer in renewable resources. Because of the implications that a federal renewable portfolio standard would have on the economy, the environment, and the equitable treatment of all the states, many issues and concerns must be resolved before federal standards will be passed into law. A theoretical case study for an electric utility generation planning decision that includes obligations to meet Renewable Portfolio Standard is presented here. A framework is provided that allows decision makers and strategic planning teams to: assess their business situation, identify objectives of generation planning, determine the relative weights of the objectives, recognize tradeoffs, and create an efficient portfolio using Portfolio Theory. The case study follows the business situation for Austin Energy as it seeks to meet Texas State RPS and mandates set by Austin City Council and prepares for potential National RPS legislation. / text

A new Markov chain based energy storage model to evaluate the power supply availability of microgrids with renewable energy generation for critical loads is proposed. Since critical loads require above-average availability to ensure reliable operation during extreme events, e.g., natural disasters, using renewable energy generation has been considered to diversify sources. However, the low availability and high variability of renewable energy sources bring a challenge in achieving the required availability for critical loads. Hence, adding energy storage systems to renewable energy generation becomes vital for ensuring the generation of enough power during natural disasters. Although adding energy storage systems would instantaneously increase power supply availability, there is another critical aspect that should be carefully considered; energy storage sizing to meet certain availability must be taken into account in order to avoid oversizing or undersizing capacity, which are two undesirable conditions leading to inadequate availability or increased system cost, respectively. This dissertation proposes to develop a power supply availability framework for renewable energy generation in a given location and to suggest the optimal size of energy storage for the required availability to power critical loads. In particular, a new Markov chain based energy storage model is presented in order to model energy states in energy storage system, which provides an understanding of the nature of charge and discharge rates for energy storage that affect the system's power output. Practical applications of the model are exemplified using electrical vehicles with photovoltaic roofs. Moreover, the minimal cut sets method is used to analyze the effects of microgrid architectures on availability characteristics of the microgrid power supply in the presence of renewable energy sources and energy storage. In addition, design considerations for energy storage power electronics interfaces and a comparison of various energy storage methods are also presented. / text

Made available in DSpace on 2014-07-29T15:08:18Z (GMT). No. of bitstreams: 1 Previsao de Vazoes Naturais Diarias.pdf: 3835466 bytes, checksum: f927e5c8c3a89c73430512243b55c36c (MD5) Previous issue date: 2012-09-05 / The forecast of natural flows to hydroelectric plant reservoirs is an essential input to the planning and programming of the SIN´s operation. Various computer models are used to determine these forecasts, including physical models, statistical models and the ones developed with the RNA´s techniques. Currently, the ONS performs daily forecasts of natural flows to the UHE Tucuruí based on the univariate stochastic model named PREVIVAZH, developed by Electric Energy Research Center - Eletrobras CEPEL. Throughout the last decade, several papers have shown evolution in the application of neural networks methodology in many areas, specially in the prediction of flows on a daily, weekly and monthly basis. The goal of this dissertation is to present and calibrate a model of natural flow forecast using the RNA´s methodology, more specifically the NSRBN (Non-Linear Sigmoidal Regression Blocks Networks) (VALENCA; LUDERMIR, 2001), on a time lapse from 1 to 12 days forward to the Tucuruí Hydroelectric Plant, considering the hydrometric stations data located upstream from it s reservoir. In addition, a comparative analysis of results found throughout the calibrated neural network and the ones released by ONS is performed. The results show the advantage of the methodology of artificial neural networks on autoregressive models. The Mean Absolute Percentage Error - MAPE values obtained were, on average, 48 % lower than those released by the ONS. / A previsão de vazões naturais aos reservatórios das usinas hidrelétricas é insumo fundamental para o planejamento e operação do SIN. Diversos modelos são utilizados na determinação dessas previsões, entre os quais podem ser citados os modelos físicos, os estatísticos e aqueles baseados na técnica de Redes Neurais Artificiais. Atualmente, o ONS realiza as previsões diárias de vazões naturais para a Usina Hidrelétrica Tucuruí com base no modelo estocástico univariado denominado PREVIVAZH, desenvolvido pelo CEPEL. Ao longo da última década, muitos trabalhos têm mostrado a evolução da aplicação da metodologia de Redes Neurais Artificiais em diversas áreas e em particular na previsão de vazões naturais, para intervalos de tempo diários, semanais e mensais. O objetivo deste trabalho foi calibrar e avaliar um modelo de previsão de vazões naturais, utilizando a metodologia de RNA, mais especificamente as redes construtivas do tipo NSRBN(Non-Linear Sigmoidal Regression Blocks Networks) (VALENCA; LUDERMIR, 2001), no horizonte de 1 até 12 dias à frente, para a Usina Hidrelétrica Tucuruí, considerando as informações advindas de postos hidrométricos localizados à montante do seu reservatório. Adicionalmente, foi realizada uma análise comparativa dos resultados encontrados pela rede neural calibrada e aqueles obtidos e divulgados pelo ONS. Os resultados obtidos mostram a vantagem da metodologia de redes neurais artificiais sobre os modelos auto-regressivos. Os valores do Erro Percentual Médio Absoluto - MAPE foram, em média, 48% inferiores aos divulgados pelo ONS.

Made available in DSpace on 2015-04-11T13:52:31Z (GMT). No. of bitstreams: 1 renato.pdf: 918334 bytes, checksum: c22232e1466b4c7d89bbbe00975b8a09 (MD5) Previous issue date: 2011-07-15 / Understanding the intricacies of the production structure of a given region or country is as important as the planning and action phases, and as complex in terms of implementation and deepening processes. It was with this kind of motivation that this project examined in some detail the production structure of the Amazon state, choosing as time reference the year 2006. To reach the main objective of this project, it was left aside the technique of Regional Social Accounting to be able to order in a more coherent and consistent manner the necessary information that resulted in macroeconomic aggregates. The main tool used was the construction of some quadrants as of production (A1), intermediate consumption (B1) and value added components (C), all of those components of the Table of Uses and Resources of goods and services of the Amazon. The results generated tabulations producing levels of aggregation in ranges of 110 products by 56 activities, 17 products by 17 activities and 12 products by 12 activities, respecting in all cases statistical confidentiality due to imposition of non-identification in some specific cases. Furthermore, the project followed with analysis and discussions, in which were always presented comparisons that refer to the information contained in the Brazil´s TRU. Finally, the results point out to several future possibilities of use of this project, and also of its future developments, aiming mainly at its application in planning activities and public policy making. / Entender os meandros da estrutura produtiva de determinada região ou país é importante como instrumento de planejamento e de ação, assim como complexo em sua efetivação e aprofundamento. Foi com essa motivação que este trabalho buscou analisar com certo nível de detalhe a estrutura produtiva do estado do Amazonas, escolhendo como referência temporal o ano de 2006. Para atingir o objetivo proposto, apropriaram-se das técnicas da Contabilidade Social para ordenar com coerência e consistência as informações necessárias que resultem em agregados macroeconômicos. O principal ferramental utilizado foi a construção dos quadrantes de produção (A1), consumo intermediário (B1) e componentes do valor adicionado (C), todos eles elementos da Tabela de Recursos e Usos de bens e serviços do Amazonas (TRU-AM/2006). Os resultados gerados produziram tabulações de agregação em níveis de abertura de 110 produtos por 56 atividades, 17 produtos por 17 atividades e 12 produtos por 12 atividades, respeitando em todos os casos o devido sigilo estatístico por imposição da desidentificação em casos específicos. Seguiram-se as análises e discussões, apresentando sempre comparações referenciadas às informações contidas na TRU do Brasil. Por fim, o estudo aponta para diversas possibilidades futuras de utilização e aprofundamento do ferramental visando, principalmente, a sua aplicação nas atividades de planejamento e políticas públicas.

[pt] A reserva girante é a parcela da geração que deve estar sincronizada, ou que seja possível sincronizar em tempo hábil, de forma a repor a perda de unidades de geração, suprir acréscimos de demanda devido aos erros de previsão, ou ainda lidar com possíveis flutuações na capacidade de geração de fontes renováveis. Desta forma, é crucial que tal parcela esteja dimensionada de modo a suprir tais necessidades de forma adequada. Para tal, deve-se considerar o perfil da demanda do sistema e também as características do sistema de geração. Estimativas imprecisas da carga elétrica podem levar a ocorrências de cortes de carga. Da mesma forma, um superdimensionamento da reserva pode ter como consequência custos excessivos para o consumidor de energia. Uma representação aceitável para carga é considerá-la como uma variável aleatória. Este tipo de modelagem permite que o valor do pico de carga estimado tenha suas incertezas intrinsecamente consideradas. Assim, considerando as variabilidades inerentes à demanda e à geração, é então possível estimar o risco de não suprimento do sistema por meio de métodos baseados em Simulação Monte Carlo (SMC). Tais métodos têm como principal vantagem uma relativa robustez para avaliação de índices que mensuram numericamente o nível de confiabilidade do sistema: e.g., LOLP (loss of load probability). Nesta dissertação será avaliado o impacto das incertezas associadas à demanda, à variabilidade das fontes renováveis e às falhas em equipamentos no dimensionamento da reserva de geração no âmbito da operação de sistemas elétricos. Serão empregadas técnicas baseadas em SMC para avaliar os níveis de confiabilidade, considerando diversas possibilidades de representação da carga em sistemas multiárea. Dentre os cenários testados e discutidos, calculam-se índices de risco para o sistema e por áreas, para avaliar se o sistema é confiável não apenas como um todo, mas também em cada uma de suas regiões operativas. Para avaliar a metodologia proposta, são realizados testes com o sistema IEEE-RTS (Reliability Test System) de modo a responder se os índices de risco por área/sistema estão dentro de níveis aceitáveis. Por fim, é avaliado também o efeito da inserção de fontes renováveis intermitentes na reserva do sistema. / [en] The spinning reserve is the generation quota that must be synchronized (or that can be synchronized in a timely manner) with the aim to restore the loss of generation units, to supply increases in demand due to forecast errors, or to cope with generation capacity fluctuations of renewable sources. Thus, it is crucial that such amount is defined so as to adequately meet the required needs. For this, the system load profile and also the generating system characteristics must be duly considered. Inaccurate estimates of electrical demand can lead to the occurrence of load shedding. Similarly, overinvestment in capacity reserve may result in excessive costs to electric energy consumers. An acceptable representation for the load profile is to consider it as a random variable. This type of modeling allows the estimated peak load value to have its uncertainties intrinsically considered. Therefore, considering the inherent variability of demand and generation, it is then possible to estimate the risk of not supplying the system load through methods based on Monte Carlo simulation (SMC). Such methods have as their main advantage a relative robustness for evaluating indices that numerically measure the reliability level of the system; e.g., LOLP (loss of load probability). In this dissertation, the impact of uncertainties associated with demand, the variability of renewable sources and equipment failures will be evaluated in order to size the amount of generating reserve, within the scope of the operation of electric systems. SMC techniques are used to evaluate the reliability levels, considering several possibilities of load representation in a multi-area system. Among different scenarios analyzed, risk indices are calculated for system and areas, in order to assess whether the grid is reliable as a whole and also for all operating regions. In order to evaluate the proposed methodology, tests are performed with the IEEE-RTS (Reliability Test System) to respond if the area/system risk indices are within acceptable levels. Finally, the effect of inserting intermittent renewable sources into the system reserve is also discussed.