A Geração Distribuída no Brasil tem crescido ao longo dos anos, especialmente na fonte fotovoltaica e na categoria que a ANEEL denomina microgeração distribuída, que são centrais geradoras de energia elétrica com potência instalada menor ou igual a 75 kW e conectada na rede de distribuição por meio de instalações de unidades consumidoras. Apesar dos problemas tradicionais que podem ocorrer com a inserção em larga escala, como maiores perdas e desvios de tensão, as placas fotovoltaicas, conectadas à rede de distribuição por meio de um inversor, trazem a possibilidade de controlar a tensão no ponto de conexão, manipulando-se o fator de potência de saída do inversor, controlando a potência reativa. Neste contexto, considerando o uso dos inversores inteligentes com possibilidade de envio de sinal remotamente ao operador e a possibilidade de criação de Centros de Despacho de Geração Distribuída (CDGD), este trabalho tem por objetivo propor uma metodologia de regulação de tensão centralizada utilizando unidades de microgeração fotovoltaicas, em redes de distribuição com larga inserção. A metodologia proposta utiliza o conceito de despacho de potência reativa e fluxo de potência reativa ótimo, por meio de uma abordagem centralizada da rede, utilizando-se o software OpenDSS e MatLab, equipado com Algoritmo Genético (AG) para solucionar o problema de otimização. Para avaliar o desempenho do modelo, foram feitos estudos de caso no sistema IEEE 123 barras e em uma rede real em Alegrete. Os resultados obtidos validam a abordagem proposta, demonstra a aplicabilidade e limitações em casos reais. / The distributed generation in Brazil has increased in the past years, specially in photovoltaic power generation, at the category that Brazilian Electric Regulator ANEEL classifies as "distributed micro-generation", i.e., generation units in which the active power capacity is equal or bellow 75kW and conected on distribution network by the consumers. Despite the traditional problems that might occur due to high penetration of the units, e.g., higher losses and voltage sags and swells, they are conected to the network through an inverter that can be controlled in order to provide or consume reactive power, providing voltage regulation. In that context, considering the use of intelligent inverters that can be remotely operated by a centralized utility operator, this work aims to propose a centralized voltage regulation methodology using distributed micro-generation in distribution networks. The proposed methodology uses the concept of reactive power dispatch and optimal power flow, from a centralized view of the network, using the software MatLab and OpenDSS with Genetic Algorithm to solve the optimization problem. To evaluate the model, simulations were performed with the IEEE 123 bus system and with a real distribution network from the Alegrete city, in the Brazilian state of Rio Grande do Sul. The results show the proposed is valid, despite some limitations on real cases.

The objective of this thesis is to investigate the transient response and optimal economic dispatch of an isolated power system with wind generators. Different types of wind turbines and the classification of Stability are introduced. Then, the process of Transient stability analysis and the concept of Genetic Algorithms are given for explanation. In this thesis, the practical power system of Kinmen is selected for case study. The disturbances introduced by gusting wind and N-1 system contingency are considered in the transient stability analysis. Furthermore, in order to obtain both accuracy and feasibility of the Optimal power dispatch by using Real-parameter Genetic Algorithms, the simulation results should be tested for the restrictions and requirements of the actual operation.

A Geração Distribuída no Brasil tem crescido ao longo dos anos, especialmente na fonte fotovoltaica e na categoria que a ANEEL denomina microgeração distribuída, que são centrais geradoras de energia elétrica com potência instalada menor ou igual a 75 kW e conectada na rede de distribuição por meio de instalações de unidades consumidoras. Apesar dos problemas tradicionais que podem ocorrer com a inserção em larga escala, como maiores perdas e desvios de tensão, as placas fotovoltaicas, conectadas à rede de distribuição por meio de um inversor, trazem a possibilidade de controlar a tensão no ponto de conexão, manipulando-se o fator de potência de saída do inversor, controlando a potência reativa. Neste contexto, considerando o uso dos inversores inteligentes com possibilidade de envio de sinal remotamente ao operador e a possibilidade de criação de Centros de Despacho de Geração Distribuída (CDGD), este trabalho tem por objetivo propor uma metodologia de regulação de tensão centralizada utilizando unidades de microgeração fotovoltaicas, em redes de distribuição com larga inserção. A metodologia proposta utiliza o conceito de despacho de potência reativa e fluxo de potência reativa ótimo, por meio de uma abordagem centralizada da rede, utilizando-se o software OpenDSS e MatLab, equipado com Algoritmo Genético (AG) para solucionar o problema de otimização. Para avaliar o desempenho do modelo, foram feitos estudos de caso no sistema IEEE 123 barras e em uma rede real em Alegrete. Os resultados obtidos validam a abordagem proposta, demonstra a aplicabilidade e limitações em casos reais. / The distributed generation in Brazil has increased in the past years, specially in photovoltaic power generation, at the category that Brazilian Electric Regulator ANEEL classifies as "distributed micro-generation", i.e., generation units in which the active power capacity is equal or bellow 75kW and conected on distribution network by the consumers. Despite the traditional problems that might occur due to high penetration of the units, e.g., higher losses and voltage sags and swells, they are conected to the network through an inverter that can be controlled in order to provide or consume reactive power, providing voltage regulation. In that context, considering the use of intelligent inverters that can be remotely operated by a centralized utility operator, this work aims to propose a centralized voltage regulation methodology using distributed micro-generation in distribution networks. The proposed methodology uses the concept of reactive power dispatch and optimal power flow, from a centralized view of the network, using the software MatLab and OpenDSS with Genetic Algorithm to solve the optimization problem. To evaluate the model, simulations were performed with the IEEE 123 bus system and with a real distribution network from the Alegrete city, in the Brazilian state of Rio Grande do Sul. The results show the proposed is valid, despite some limitations on real cases.

A Geração Distribuída no Brasil tem crescido ao longo dos anos, especialmente na fonte fotovoltaica e na categoria que a ANEEL denomina microgeração distribuída, que são centrais geradoras de energia elétrica com potência instalada menor ou igual a 75 kW e conectada na rede de distribuição por meio de instalações de unidades consumidoras. Apesar dos problemas tradicionais que podem ocorrer com a inserção em larga escala, como maiores perdas e desvios de tensão, as placas fotovoltaicas, conectadas à rede de distribuição por meio de um inversor, trazem a possibilidade de controlar a tensão no ponto de conexão, manipulando-se o fator de potência de saída do inversor, controlando a potência reativa. Neste contexto, considerando o uso dos inversores inteligentes com possibilidade de envio de sinal remotamente ao operador e a possibilidade de criação de Centros de Despacho de Geração Distribuída (CDGD), este trabalho tem por objetivo propor uma metodologia de regulação de tensão centralizada utilizando unidades de microgeração fotovoltaicas, em redes de distribuição com larga inserção. A metodologia proposta utiliza o conceito de despacho de potência reativa e fluxo de potência reativa ótimo, por meio de uma abordagem centralizada da rede, utilizando-se o software OpenDSS e MatLab, equipado com Algoritmo Genético (AG) para solucionar o problema de otimização. Para avaliar o desempenho do modelo, foram feitos estudos de caso no sistema IEEE 123 barras e em uma rede real em Alegrete. Os resultados obtidos validam a abordagem proposta, demonstra a aplicabilidade e limitações em casos reais. / The distributed generation in Brazil has increased in the past years, specially in photovoltaic power generation, at the category that Brazilian Electric Regulator ANEEL classifies as "distributed micro-generation", i.e., generation units in which the active power capacity is equal or bellow 75kW and conected on distribution network by the consumers. Despite the traditional problems that might occur due to high penetration of the units, e.g., higher losses and voltage sags and swells, they are conected to the network through an inverter that can be controlled in order to provide or consume reactive power, providing voltage regulation. In that context, considering the use of intelligent inverters that can be remotely operated by a centralized utility operator, this work aims to propose a centralized voltage regulation methodology using distributed micro-generation in distribution networks. The proposed methodology uses the concept of reactive power dispatch and optimal power flow, from a centralized view of the network, using the software MatLab and OpenDSS with Genetic Algorithm to solve the optimization problem. To evaluate the model, simulations were performed with the IEEE 123 bus system and with a real distribution network from the Alegrete city, in the Brazilian state of Rio Grande do Sul. The results show the proposed is valid, despite some limitations on real cases.

Neste trabalho realizamos um estudo do Despacho de Potência Ativa AC, o qual é uma estratégia de alocação da geração de potência entre as usinas de um sistema. Para isto, obtivemos dados teóricos, a partir de levantamento bibliográfico, que explicitaram os conceitos de Despacho Ativo. Fundamentamos, metodologicamente, nossa pesquisa no Método da Função Lagrangeana Aumentada. O sistema de equações resultantes das condições de otimalidade foram resolvidos pelo Método de Newton Modificado. Apresentamos os resultados de estudos de casos acadêmicos para a validação e verificação da eficiência da abordagem proposta. Os resultados indicaram uma coerência com as perspectivas reais de contribuição na resolução do Despacho Ótimo de Potência Ativa AC. / In this work we accomplished a study of the AC Active Power Dispatch, which is a strategy of distribution of the power generation among the plants of a system. For this, we obtained theoretical data, starting from bibliographical investigation, that elucidated the concepts of Active Dispatch. We based our research in the Method of the Augmented Lagrangian Function. The equation system originated of the optimal conditions was solved for Modified Newton\'s Method. We presented the results of studies of academic cases for the validation and verification of the efficiency of the proposal approach. The results indicated a coherence with the real perspectives of contribution in the resolution of the AC Active Optimal Power Dispatch.

Atualmente, a geração eólica é a forma de geração de energia elétrica de maior crescimento no mundo. Não obstante, dependendo da forma em que é gerenciado este tipo de geração, pode causar impactos significativos no sistema de energia elétrica. Este trabalho estuda o comportamento da geração eólica nos sistemas de potência do ponto de vista dos aerogeradores e dos parques eólicos. É realizada uma modelagem dos principais componentes dos sistemas de geração eólica, particularmente dos aerogeradores de velocidade variável equipados com geradores de indução de dupla alimentação, com o intuito de aplicar estratégias de controle para a operação dos mesmos e estudar as suas características de funcionamento. São propostos métodos para a regulação da potência ativa gerada por estes aerogeradores e para a regulação da potência ativa gerada por parques eólicos compostos por vários aerogeradores de velocidade variável, com o objetivo de permitir um maior índice de penetração da geração eólica nos sistemas de energia elétrica. Usando a modelagem elaborada, são efetuadas rigorosas simulações computacionais do comportamento destas instalações eólicas funcionando com os métodos de regulação propostos. Os resultados obtidos nestas simulações mostram que o impacto da geração eólica pode ser consideravelmente diminuído, logrando atribuições semelhantes aos produtores de energia convencionais. Observa-se que estes métodos permitiriam flexibilizar a operação dos sistemas de geração eólica, possibilitando gerenciamentos mais adequados aos novos requerimentos exigidos pelos operadores dos sistemas de energia. / Nowadays, the wind power generation is the fastest growing electric power source in the world. Nevertheless, depending on the management of this kind of generation, it may cause significant impact in the power system. In this work, a modeling of the main components of wind power generation was performed, particularly of variable speed wind turbines with doubly fed induction generators, aiming to apply control strategies for its operation and to study its functional characteristics. Methods to regulate the active power generated by variable speed wind turbines, and to regulate the active power of wind farms composed of several of this turbines, are proposed with the objective to allow an increase in the level of penetration of wind generation in the power systems. Using the elaborated modeling, rigorous computational simulations of operation of these types of power stations, operating with the proposed methods, were accomplished. The obtained results in these simulations shows that it is possible to considerably minimize the wind power generation impacts, obtaining attributions similarly to conventional energy producers. It is observed that the proposed methods allows an operational flexibility of wind power generation, enabling a better management according to the new requirement of the power system operators.

Atualmente, a geração eólica é a forma de geração de energia elétrica de maior crescimento no mundo. Não obstante, dependendo da forma em que é gerenciado este tipo de geração, pode causar impactos significativos no sistema de energia elétrica. Este trabalho estuda o comportamento da geração eólica nos sistemas de potência do ponto de vista dos aerogeradores e dos parques eólicos. É realizada uma modelagem dos principais componentes dos sistemas de geração eólica, particularmente dos aerogeradores de velocidade variável equipados com geradores de indução de dupla alimentação, com o intuito de aplicar estratégias de controle para a operação dos mesmos e estudar as suas características de funcionamento. São propostos métodos para a regulação da potência ativa gerada por estes aerogeradores e para a regulação da potência ativa gerada por parques eólicos compostos por vários aerogeradores de velocidade variável, com o objetivo de permitir um maior índice de penetração da geração eólica nos sistemas de energia elétrica. Usando a modelagem elaborada, são efetuadas rigorosas simulações computacionais do comportamento destas instalações eólicas funcionando com os métodos de regulação propostos. Os resultados obtidos nestas simulações mostram que o impacto da geração eólica pode ser consideravelmente diminuído, logrando atribuições semelhantes aos produtores de energia convencionais. Observa-se que estes métodos permitiriam flexibilizar a operação dos sistemas de geração eólica, possibilitando gerenciamentos mais adequados aos novos requerimentos exigidos pelos operadores dos sistemas de energia. / Nowadays, the wind power generation is the fastest growing electric power source in the world. Nevertheless, depending on the management of this kind of generation, it may cause significant impact in the power system. In this work, a modeling of the main components of wind power generation was performed, particularly of variable speed wind turbines with doubly fed induction generators, aiming to apply control strategies for its operation and to study its functional characteristics. Methods to regulate the active power generated by variable speed wind turbines, and to regulate the active power of wind farms composed of several of this turbines, are proposed with the objective to allow an increase in the level of penetration of wind generation in the power systems. Using the elaborated modeling, rigorous computational simulations of operation of these types of power stations, operating with the proposed methods, were accomplished. The obtained results in these simulations shows that it is possible to considerably minimize the wind power generation impacts, obtaining attributions similarly to conventional energy producers. It is observed that the proposed methods allows an operational flexibility of wind power generation, enabling a better management according to the new requirement of the power system operators.

Neste trabalho realizamos um estudo do Despacho de Potência Ativa AC, o qual é uma estratégia de alocação da geração de potência entre as usinas de um sistema. Para isto, obtivemos dados teóricos, a partir de levantamento bibliográfico, que explicitaram os conceitos de Despacho Ativo. Fundamentamos, metodologicamente, nossa pesquisa no Método da Função Lagrangeana Aumentada. O sistema de equações resultantes das condições de otimalidade foram resolvidos pelo Método de Newton Modificado. Apresentamos os resultados de estudos de casos acadêmicos para a validação e verificação da eficiência da abordagem proposta. Os resultados indicaram uma coerência com as perspectivas reais de contribuição na resolução do Despacho Ótimo de Potência Ativa AC. / In this work we accomplished a study of the AC Active Power Dispatch, which is a strategy of distribution of the power generation among the plants of a system. For this, we obtained theoretical data, starting from bibliographical investigation, that elucidated the concepts of Active Dispatch. We based our research in the Method of the Augmented Lagrangian Function. The equation system originated of the optimal conditions was solved for Modified Newton\'s Method. We presented the results of studies of academic cases for the validation and verification of the efficiency of the proposal approach. The results indicated a coherence with the real perspectives of contribution in the resolution of the AC Active Optimal Power Dispatch.

Atualmente, a geração eólica é a forma de geração de energia elétrica de maior crescimento no mundo. Não obstante, dependendo da forma em que é gerenciado este tipo de geração, pode causar impactos significativos no sistema de energia elétrica. Este trabalho estuda o comportamento da geração eólica nos sistemas de potência do ponto de vista dos aerogeradores e dos parques eólicos. É realizada uma modelagem dos principais componentes dos sistemas de geração eólica, particularmente dos aerogeradores de velocidade variável equipados com geradores de indução de dupla alimentação, com o intuito de aplicar estratégias de controle para a operação dos mesmos e estudar as suas características de funcionamento. São propostos métodos para a regulação da potência ativa gerada por estes aerogeradores e para a regulação da potência ativa gerada por parques eólicos compostos por vários aerogeradores de velocidade variável, com o objetivo de permitir um maior índice de penetração da geração eólica nos sistemas de energia elétrica. Usando a modelagem elaborada, são efetuadas rigorosas simulações computacionais do comportamento destas instalações eólicas funcionando com os métodos de regulação propostos. Os resultados obtidos nestas simulações mostram que o impacto da geração eólica pode ser consideravelmente diminuído, logrando atribuições semelhantes aos produtores de energia convencionais. Observa-se que estes métodos permitiriam flexibilizar a operação dos sistemas de geração eólica, possibilitando gerenciamentos mais adequados aos novos requerimentos exigidos pelos operadores dos sistemas de energia. / Nowadays, the wind power generation is the fastest growing electric power source in the world. Nevertheless, depending on the management of this kind of generation, it may cause significant impact in the power system. In this work, a modeling of the main components of wind power generation was performed, particularly of variable speed wind turbines with doubly fed induction generators, aiming to apply control strategies for its operation and to study its functional characteristics. Methods to regulate the active power generated by variable speed wind turbines, and to regulate the active power of wind farms composed of several of this turbines, are proposed with the objective to allow an increase in the level of penetration of wind generation in the power systems. Using the elaborated modeling, rigorous computational simulations of operation of these types of power stations, operating with the proposed methods, were accomplished. The obtained results in these simulations shows that it is possible to considerably minimize the wind power generation impacts, obtaining attributions similarly to conventional energy producers. It is observed that the proposed methods allows an operational flexibility of wind power generation, enabling a better management according to the new requirement of the power system operators.

The objective of an Energy Control Center (ECC) is to ensure secure and economic operation of power system. The challenge to optimize power system operation, while maintaining system security and quality of power supply to customers, is increasing. Growing demand without matching expansion of generation and transmission facilities and more tightly interconnected power systems contribute to the increased complexity of system operation. Rising costs due to inflation and increased environmental concerns has made transmission, as well as generation systems to be operated closure to design limits, with smaller safety margins and hence greater exposure to unsatisfactory operating conditions following a disturbance. Investigations of recent blackouts indicate that the root cause of most of these major power system disturbances is voltage collapse. Information gathered and preliminary analysis, from the most recent blackout incident in North America on 14th August 2003, is pointing the finger on voltage instability due to some unexpected contingency. In this incident, reports indicate that approximately 50 million people were affected interruption from continuous supply for more than 15 hours. Most of the incidents are related to heavily stressed system where large amounts of real and reactive power are transported over long transmission lines while appropriate real and reactive power resources are not available to maintain normal system conditions. Hence, the problem of voltage stability and voltage collapse has become a major concern in power system planning and operation. Reliable operation of large scale electric power networks requires that system voltages and currents stay within design limits. Operation beyond those limits can lead to equipment failures and blackouts. In the last few decades, the problem of reactive power control for improving economy and security of power system operation has received much attention. Generally, the load bus voltages can be maintained within their permissible limits by reallocating reactive power generations in the system. This can be achieved by adjusting transformer taps, generator voltages, and switchable Ar sources. In addition, the system losses can be minimized via redistribution of reactive power in the system. Therefore, the problem of the reactive power dispatch can be optimized to improve the voltage profile and minimize the system losses as well. The Instability in power system could be relieved or at least minimized with the help of most recent developed devices called Flexible AC Transmission System (FACTS) controllers. The use of Flexible AC Transmission System (FACTS) controllers in power transmission system have led to many applications of these controllers not only to improve the stability of the existing power network resources but also provide operating flexibility to the power system. In the past, transmission systems were owned by regulated, vertically integrated utility companies. They have been designed and operated so that conditions in close proximity to security boundaries are not frequently encountered. However, in the new open access environment, operating conditions tend to be much closer to security boundaries, as transmission use is increasing in sudden and unpredictable directions. Transmission unbundling, coupled with other regulatory requirements, has made new transmission facility construction more difficult. In fact, there are numerous technical challenges emerging from the new market structure. There is an acute need for research work in the new market structure, especially in the areas of voltage security, reactive power support and congestion management. In the last few decades more attention was paid to optimal reactive power dispatch. Since the problem of reactive power optimization is non-linear in nature, nonlinear programming methods have been used to solve it. These methods work quite well for small power systems but may develop convergence problems as system size increases. Linear programming techniques with iterative schemes are certainly the most promising tools for solving these types of problems. The thesis presents efficient algorithms with different objectives for reactive power optimization. The approach adopted is an iterative scheme with successive power-flow analysis using decoupled technique, formulation and solution of the linear-programmingproblem with only upper-bound limits on the state variables. Further the thesispresents critical analysis of the three following objectives, Viz., •Minimization of the sum of the squares of the voltage deviations (Vdesired) •Minimization of sum of the squares of the voltage stability L indices (Vstability) •Minimization of real power losses (Ploss) Voltage stability problems normally occur in heavily stressed systems. While the disturbance leading to voltage collapse may be initiated by a variety of causes, the underlying problem is an inherent weakness in the power system. The factors contributing to voltage collapse are the generator reactive power /voltage control limits, load characteristics, characteristics of reactive compensation devices, and the action of the voltage control devices such as transformer On Load Tap Changers (OLTCs). Power system experiences abnormal operating conditions following a disturbance, and subsequently a reduction in the EHV level voltages at load centers will be reflected on the distribution system. The OLTCs of distribution transformers would restore distribution voltages. With each tap change operation, the MW and MVAR loading on the EHV lines would increase, thereby causing great voltage drops in EHV levels and increasing the losses. As a result, with each tap changing operation, the reactive output of generators throughout the system would increase gradually and the generators may hit their reactive power capability limits, causing voltage instability problems. Thus, the operation of certain OLTCs has a significant influence on voltage instability under some operating conditions. These transformers can be made manual to avoid possible voltage instability due to their operation during heavy load conditions. Tap blocking, based on local measurement of high voltage side of load tap changers, is a common practice of power utilities to prevent voltage collapse. The great advantage of this method is that it can be easily implemented, but does not guarantee voltage stability. So a proper approach for identification of critical OLTC s based on voltage stability criteria is essential to guide the operator in ECC, which has been proposed in this thesis. It discusses the effect of OLTCs with different objectives of reactive power dispatch and proposes a technique to identify critical OLTCs based on voltage stability criteria. The fast development of power electronics based on new and powerful semiconductor devices has led to innovative technologies, such as High Voltage DC transmission (HVDC) and Flexible AC Transmission System (FACTS), which can be applied in transmission and distribution systems. The technical and economicalBenefits of these technologies represent an alternative to the application in AC systems. Deregulation in the power industry and opening of the market for delivery of cheaper energy to the customers is creating additional requirements for the operation of power systems. HVDC and FACTS offer major advantages in meeting these requirements. .A method for co-ordinated optimum allocation of reactive power in AC/DC power systems by including FACTS controller UPFC, with an objective of minimization of the sum of the squares of the voltage deviations of all the load buses has been proposed in this thesis. The study results show that under contingency conditions, the presence of FACTS controllers has considerable impact on over all system voltage stability and also on power loss minimization.minimization of the sum of the squares of the voltage deviations of all the load buses has been proposed in this thesis. The study results show that under contingency conditions, the presence of FACTS controllers has considerable impact on over all system voltage stability and also on power loss minimization. As power systems grow in their size and interconnections, their complexity increases. For secure operation and control of power systems under normal and contingency conditions, it is essential to provide solutions in real time to the operator in ECC. For real time control of power systems, the conventional algorithmic software available in ECC are found to be inadequate as they are computationally very intensive and not organized to guide the operator during contingency conditions. Artificial Intelligence (AI) techniques such as, Expert systems, Neural Networks, Fuzzy systems are emerging decision support system tools which give fast, though approximate, but acceptable right solutions in real time as they mostly use symbolic processing with a minimum number of numeric computations. The solution thus obtained can be used as a guide by the operator in ECC for power system control. Optimum real and reactive power dispatch play an important role in the day-to-day operation of power systems. Existing conventional Optimal Power Flow (OPF) methods use all of the controls in solving the optimization problem. The operators can not move so many control devices within a reasonable time. In this context an algorithm using fuzzy-expert approach has been proposed in this thesis to curtail the number of control actions, in order to realize real time objectives in voltage/reactive power control. The technique is formulated using membership functions of linguistic variables such as voltage deviations at all the load buses and the voltage deviation sensitivity to control variables. Voltage deviations and controlling variables are translated into fuzzy set notations to formulate the relation between voltage deviations and controlling ability of controlling devices. Control variables considered are switchable VAR compensators, OLTC transformers and generator excitations. A fuzzy rule based system is formed to select the critical controllers, their movement direction and step size. Results show that the proposed approach is effective for improving voltage security to acceptable levels with fewer numbers of controllers. So, under emergency conditions the operator need not move all the controllers to different settings and the solution obtained is fast with significant speedups. Hence, the proposed method has the potential to be integrated for on-line implementation in energy management systems to achieve the goals of secure power system operation. In a deregulated electricity market, it may not be always possible to dispatch all of the contracted power transactions due to congestion of the transmission corridors. System operators try to manage congestion, which otherwise increases the cost of the electricity and also threatens the system security and stability. An approach for alleviation of network over loads in the day-to-day operation of power systems under deregulated environment is presented in this thesis. The control used for overload alleviation is real power generation rescheduling based on Relative Electrical Distance (RED) concept. The method estimates the relative location of load nodes with respect to the generator nodes. The contribution of each generator for a particular over loaded line is first identified , then based on RED concept the desired proportions of generations for the desired overload relieving is obtained, so that the system will have minimum transmission losses and more stability margins with respect to voltage profiles, bus angles and better transmission tariff. The results obtained reveal that the proposed method is not only effective for overload relieving but also reduces the system power loss and improves the voltage stability margin. The presented concepts are better suited for finding the utilization of resources generation/load and network by various players involved in the day-to-day operation of the system under normal and contingency conditions. This will help in finding the contribution by various players involved in the congestion management and the deviations can be used for proper tariff purposes. Suitable computer programs have been developed based on the algorithms presented in various chapters and thoroughly tested. Studies have been carried out on various equivalent systems of practical real life Indian power networks and also on some standard IEEE systems under simulated conditions. Results obtained on a modified IEEE 30 bus system, IEEE 39 bus New England system and four Indian power networks of EHV 24 bus real life equivalent power network, an equivalent of 36 bus EHV Indian western grid, Uttar Pradesh 96 bus AC/DC system and 205 Bus real life interconnected grid system of Indian southern region are presented for illustration purposes.