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Substations are joints in the power system that represent nodes that are vital to stable and reliable operation of the power system. They contrast the rest of the power system in that they are a dense combination of critical components causing all of them to be simultaneously vulnerable to one isolated incident: weather, attack, or other common failure modes. Undoubtedly, the loss of these vital links will have a severe impact to the to the power grid to varying degrees. This work creates a cascading model based on protection system misoperations to estimate system risk from loss-of-substation events in order to assess each substation's criticality. A continuation power flow method is utilized for estimating voltage collapse during cascades. Transient stability is included through the use of a supervised machine learning algorithm called random forests. These forests allow for fast, robust and accurate prediction of transient stability during loss-of-substation initiated cascades. Substation risk indices are incorporated into a preventative optimal power flow (OPF) to reduce the risk of critical substations. This risk-based dispatch represents an easily scalable, robust algorithm for reducing risk associated with substation losses. This new dispatch allows operators to operate at a higher cost operating point for short periods in which substations may likely be lost, such as large weather events, likely attacks, etc. and significantly reduce system risk associated with those losses. System risk is then studied considering the interaction of a power grid utility trying to protect their critical substations under a constrained budget and a potential attacker with insider information on critical substations. This is studied under a zero-sum game theoretic framework in which the utility is trying to confuse the attacker. A model is then developed to analyze how a utility may create a robust strategy of protection that cannot be heavily exploited while taking advantage of any mistakes potential attackers may make. / Ph. D. / Substations are key components to the continued and reliable operation of the power system. Their removal from the power system would severely hinder the system’s ability to transport power from power producers to end consumers. As larger weather events and potential threats to the power system are being considered, power system engineers to start considering the impact that losing substations would cause on the system. This work studies the impact on the system associated with losing substation and ranks them to find the most important ones. A probabilistic model is created based on incorrect operations in power system protection elements that historically have exacerbated large events in the power system. Mitigation of this impact is then studied through two preventative means: changing the operating condition of the current system and adding protection to the substations. This is in order to secure the system before potentially losing the operation of a substation. The operating point change is formulated as a new optimization problem that helps alleviate stress on the system close to the most critical substations found in the earlier model. Protection of these substations is analyzed through game-theoretic means where the utility tries to confuse any potential attackers on which substations actually have true, rigid protection on them. In doing so, on expectation, the damage done to the system may be reduced significantly.

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In order to identify the weakest bus in a power system so that the Unified Power Flow Controller could be connected, an investigation of static and dynamic voltage stability is presented. Two stability indices, static and dynamic, have been proposed in the thesis. Multi-Input Multi-Output (MIMO) analysis has been used for the dynamic stability analysis. Results based on the Western System Coordinate Council (WSCC) 3-machine, 9-bus test system and IEEE 14 bus Reliability Test System (RTS) shows that these indices detect with the degree of accuracy the weakest bus, the weakest line and the voltage stability margin in the test system before suffering from voltage collapse. Recently, Flexible Alternating Current Transmission systems (FACTs) have become significant due to the need to strengthen existing power systems. The UPFC has been identified in literature as the most comprehensive and complex FACTs equipment that has emerged for the control and optimization of power flow in AC transmission systems. Significant research has been done on the UPFC. However, the extent of UPFC capability, connected to the weakest bus in maintaining the power flows under fault conditions, not only in the line where it is installed, but also in adjacent parallel lines, remains to be studied. In the literature, it has normally been assumed the UPFC is disconnected during a fault period. In this investigation it has been shown that fault conditions can affect the UPFC significantly, even if it occurred on far buses of the power system. This forms the main contribution presented in this thesis. The impact of UPFC in minimizing the disturbances in voltages, currents and power flows under fault conditions are investigated. The WSCC 3-machine, 9-bus test system is used to investigate the effect of an unsymmetrical fault type and position on the operation of UPFC controller in accordance to the G59 protection, stability and regulation. Results show that it is necessary to disconnect the UPFC controller from the power system during unsymmetrical fault conditions.

Este trabalho traz um estudo inicial do acoplamento elétrico-energético no planejamento da operação de curto-curtíssimo prazo utilizando Fluxo de Potência Ótimo em Corrente Alternada (FPOCA) com o objetivo de averiguar possíveis desvios entre o planejamento energético e o planejamento elétrico. É feita uma análise da influência dos aspectos elétricos do sistema de transmissão no planejamento energético de curto prazo utilizando-se um FPOCA, juntamente com a minimização do custo da geração e das perdas na transmissão. A minimização do custo da geração é feita através de uma otimização do sistema hidrotérmico utilizando-se um Programa de Otimização de Sistema Hidrotérmico (POSH) baseado em um algoritmo simplex convexo e na aplicação da teoria de fluxo em rede, enquanto que a minimização das perdas na transmissão é feita utilizando-se um FPOCA baseado no método Dual-Newton. Estas ferramentas permitem analisar a necessidade de ajustes para compatibilizar a otimização energética e a otimização elétrica de um sistema eletroenergético, e buscar um planejamento \"ótimo\" que atenda os planejamentos energético e elétrico. Dessa forma, a interface elétrico-energética se torna mais \"forte\", pois as metas de geração obtidas pelo planejamento de curto prazo que serão passadas para o planejamento de curtíssimo prazo, já incluem o efeito dos aspectos elétricos do sistema. Isto proporciona um controle dos desvios da trajetória \"ótima\" do sistema, o que contribui para melhorar a otimização global do planejamento da operação eletroenergética. / This work brings a beginning study of the electric-energetic coupling in the short-shortest term operation planning using Optimal Power Flow in Alternate Current (OPFAC) aiming to inquire possible mismatches between the energetic planning and the eletric planning. It is made an analysis of the electrical aspects influence in the short term energetic planning using OPFAC together with the minimization of generation cost and the transmission losses. The generation cost minimization is made for the hidrothermal system optimization using a Hydrothermal System Optimization Program (POSH) based on a convex simplex algorithm and the application of the network flow theory, while the transmission losses minimization is made using an OPFAC based on the Dual-Newton method. These tools allow to analyze the necessity of adjustments to make compatible the energetic optimization and the electric optimization of the power system, and to search an \"optimal\" planning that attends both the energetic planning and electric planning. Like this, the electric-energetic interface becomes strongest, therefore the generation goals gotten by the short-term planning, that will be passed to the shortest-term planning, already includes the effect of the electric system aspects. These one provide the mismatches control in the optimal trajectory of the system and it contributes to improve the global optimization of power system operation planning. The analyzed system is the 440 kV Equivalent System of CESP (Energetic Company of São Paulo), with 53 bus, being 7 generation bus, 85 transmission lines and 48 transformers.

Este trabalho tem como objetivo realizar um estudo de alocação de unidades termoelétricas em sistemas elétricos de potência (SEP). O fluxo de potencia ótimo (FPO) foi utilizado para se obter o ponto ótimo de operação para o sistema e os multiplicadores de Lagrange associados às restrições. Os multiplicadores de Lagrange indicam a sensibilidade entre a função objetivo e a restrição a ele associada. Esta sensibilidade indica, quais as barras do sistema, são candidatas à alocação de novas usinas termoelétricas. Testes nos sistemas de 5 barras, IEEE 14 barras, IEEE 30 barras, equivalente CESP 440 kV de 53 barras e IEEE 118 barras comprovam a eficiência da abordagem, a qual poderá ser utilizada em estudos de planejamento da expansão do sistema. / The aim of this paper is to present a study of thermoelectrical generation allocation in electric power systems. The optimal power flow (OPF) was used to evaluate the optimal operation point for the power system and also Lagrange multipliers associated with the constraints. The Lagrange multipliers are the sensitivity between the objective function and its constraints. This sensitivity is used to verify in a power system where is the best place to incentive the allocation of new thermoelectrical power plants. Tests on the systems: 5 buses, IEEE 14 buses, IEEE 30 buses, equivalent CESP 440kV 53 buses and IEEE 118 buses showed the efficiency of the presented approach. This method of analyzing the system can be used in study of expansion planning system.

Este trabalho apresenta um estudo sobre o método da continuação aplicado ao problema de fluxo de potência. Definições e conceitos de estabilidade de tensão são descritos de forma a explicitar as diferenças e semelhanças existentes com relação ao estudo de máximo carregamento em sistemas de energia elétrica. Uma síntese da teoria da bifurcação aborda sua importância em estudos de colapso de tensão. É proposta uma técnica de controle do tamanho do passo para o método da continuação com o objetivo de determinar o ponto de máximo carregamento (PMC) sem a necessidade de especificar, por meio do usuário, um valor para o tamanho inicial do passo. Os resultados dos estudos realizados em sistemas testes do IEEE (14, 30, 57 e 118 barras) mostram a aplicação do método da continuação convencional e de sua associação à técnica de controle do tamanho do passo. / This work presents a research about the continuation method applied to the power flow problem. Voltage stability definitions and concepts are described in a way to highlight and point out the differences and the similarities among several methods used to determine the maximum loading of electrical power systems. A short description of the bifurcation theory is also presented in order to show its importance to the voltage collapse studies. A technique based on automatically controlling the step size is proposed as an innovation of the continuation method. The objective of this technique is to determine the maximum loading point without the traditional need of asking the user for the initial step size. The results compare the performance between the conventional and the new method. These methods are analyzed using IEEE test systems (14, 30, 57 and 118-bus).

Neste trabalho propomos uma abordagem para a resolução do problema de Fluxo de Potência Ótimo (FPO) perturbado. A metodologia consiste na obtenção da solução ótima para o problema inicial via um programa de FPO, e na utilização de sensibilidade para estimar novas soluções depois de ocorridas algumas perturbações no problema. Essas perturbações são variações de carga em uma ou mais barras do sistema. A técnica de sensibilidade está baseada nas informações de segunda ordem e nas condições de otimalidade. A obtenção da solução após ocorrerem perturbações no sistema é direta e não necessita de parâmetros iniciais e de correção, como penalidade e barreira, utilizados nos programas de FPO convencionais. Os resultados numéricos apresentados evidenciam o potencial desta metodologia para resolução do problema de FPO perturbado. / An approach to solve the perturbated Optimal Power Flow (OPF) problem is proposed in this study. The methodology consists in obtaining the optimal solution for the initial problem via a program of OPF, and using sensitivity to estimate new solutions after the occurrence of some perturbations in the problem. These perturbations consist in load variations in some buses of the system. The sensitivity technique is based on both the information of second order and otimality conditions. The computation of the solutions after the occurrence of perturbations in the system does not depend of initial and correction parameters such as penalty and barrier used in the conventional OPF programs. The numerical results demonstrate the potential of this methodology for the solution of the perturbated OPF problem.