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.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / FundaÃÃo de Amparo a Pesquisa do Estado do Piauà / Objetivo: Investigar o potencial biotecnolÃgico do bagaÃo de uva, variedade Benitaka, cultivada no municÃpio de SÃo JoÃo do PiauÃ, PiauÃ, por meio de metodologias analÃticas cientificamente reconhecidas, buscando reconhecer os principais grupos de metabÃlitos responsÃveis por atividade antioxidante. Metodologia: As uvas (Vitis vinifera L.), variedade Benitaka, foram resultantes da safra 2011/2012 e coletadas no Polo de Viticultura do Assentamento Marrecas, no MunicÃpio de SÃo JoÃo do PiauÃ/PI e posteriormente higienizadas, prensadas em despolpadeira para separaÃÃo do bagaÃo, o qual foi submetido à desidrataÃÃo, trituraÃÃo, peneiramento e formaÃÃo do bagaÃo de uva em pÃ. A partir do bagaÃo de uva em pà foram realizadas anÃlises da composiÃÃo centesimal, conteÃdo de minerais, fibra dietÃtica total, solÃvel e insolÃvel, determinaÃÃo de Vitamina C, conteÃdo de antocianinas, perfil de Ãcidos graxos e investigaÃÃo de sua qualidade microbiolÃgica. Foram tambÃm elaborados extratos a partir de diferentes solventes, os quais foram analisados quanto à toxicidade frente à Artemia salina sp., conteÃdo de fenÃlicos totais, flavonÃides totais e taninos totais; atividade antioxidante in vitro pelos mÃtodos de DPPHâ e autooxidaÃÃo do sistema &#946;-caroteno/Ãcido linoleico; estabilidade oxidativa em Ãleo de soja e identificaÃÃo e quantificaÃÃo de polifenÃis por HPLC-UV. Os resultados foram expressos como mÃdia e desvio padrÃo (n=3) e utilizou-se o programa estatÃstico SAS para AnÃlise de VariÃncia e Teste de Tukey. Adotou-se o nÃvel de significÃncia de 5% (p<0,05). Resultados: Os resultados mostraram que no bagaÃo de uva em pà a quantidade de fibra dietÃtica total (46,17g/100g) se destacou quantitativamente em relaÃÃo aos carboidratos (29,2g/100g), proteÃnas (8,49g/100g) e lipÃdeos (8,16g/100g). O valor energÃtico total encontrado foi de 224Kcal/100g. A fraÃÃo fibra insolÃvel (79%) foi superior à fraÃÃo solÃvel (21%). O conteÃdo de Vitamina C foi de 26,25mg de Ãcido ascÃrbico/100g e de antocianinas, 131mg/100g. Os minerais ferro (18,08mg/100g), potÃssio (1,40mg/100g), zinco (0,98mg/100g), manganÃs (0,82mg/100g) e cÃlcio (0,44mg/100g) estavam presentes em maiores concentraÃÃes. A fraÃÃo lipÃdica foi composta principalmente por Ãcido linoleico (89,61%) e o teor de PUFA (89,61%) >MUFA (21,37%) >SFA (18,46%). O rendimento dos extratos variou de 6,85% a 45,5%, dependendo do solvente de extraÃÃo, sendo que o menor rendimento foi observado no extrato acetÃnico e o maior no extrato metanÃlico. O conteÃdo de fenÃlicos totais, flavonoides totais e taninos totais variaram em funÃÃo do solvente de extraÃÃo. Os extratos etanÃlico e acetÃnico conseguiram estabilizar o radical DPPHâ de forma eficiente, com valores de EC50 de 0,31 Âg/mL e 0,39 Âg/mL, os quais nÃo diferiram estatisticamente dos padrÃes quercetina (0,22 Âg/mL) e BHT (0,11 Âg/mL). Em relaÃÃo à avaliaÃÃo da atividade antioxidante pelo mÃtodo de autooxidaÃÃo do sistema &#946;-caroteno/Ãcido linolÃico, os extratos agiram de forma similar ao antioxidante sintÃtico BHT, com mÃdias de EC50 de 0.34 Âg/mL a 0.36 Âg/mL. O extrato etanÃlico aumentou a vida de prateleira do Ãleo de soja de forma similar ao BHT. O composto fenÃlico presente em maior concentraÃÃo foi isoquercitrina (12,94 mg/100g), seguido de rutina (7,54 mg/100g), quercetina (5,4 mg/100g) e resveratrol (2,5 mg/100g). ConclusÃo: Os resultados mostraram que o bagaÃo de uva representa uma fonte potencialmente importante de nutrientes e compostos fenÃlicos; alÃm de elevado potencial antioxidante, o que contribui para o seu elevado valor como um subproduto de frutos, com possibilidades de comercializaÃÃo como antioxidante natural.

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. / Libyan Government

The modern day power system is witnessing a tremendous change. There has been a rapid rise in the distributed generation, along with this the deregulation has resulted in a more complex system. The power demand is on a rise, the generation and trans-mission infrastructure hasn't yet adapted to this growing demand. The economic and operational constraints have forced the system to be operated close to its design limits, making the system vulnerable to disturbances and possible grid failure. This makes the study of voltage stability of the system important more than ever. Generally, voltage stability studies are carried on a single phase equivalent system assuming that the system is perfectly balanced. However, the three phase power system is not always in balanced state. There are a number of untransposed lines, single phase and double phase lines. This thesis deals with three phase voltage stability analysis, in particular the voltage stability index known as L-Index. The equivalent single phase analysis for voltage stability fails to work in case of any unbalance in the system or in presence of asymmetrical contingency. Moreover, as the system operators are giving importance to synchrophasor measurements, PMUs are being installed throughout the system. Hence, the three phase voltages can be obtained, making three phase analysis easier. To study the effect of unbalanced system on voltage stability a three phase L-Index based on traditional L-Index has been proposed. The proposed index takes into consideration the unbalance resulting due to untransposed transmission lines and unbalanced loads in the system. This index can handle any unbalance in the system and is much more realistic. To obtain bus voltages during unbalanced operation of the system a three phase decoupled Newton Raphson load ow was used. Reactive power distribution in a system can be altered using generators voltage set-ting, transformers OLTC settings and SVC settings. All these settings are usually in balanced mode i.e. all the phases have the same setting. Based on this reactive power optimization using LP technique on an equivalent single phase system is proposed. This method takes into account generator voltage settings, OLTC settings of transformers and SVC settings. The optimal settings so obtained are applied to corresponding three phase system. The effectiveness of the optimal settings during unbalanced scenario is studied. This method ensures better voltage pro les and decrease in power loss. Case studies of the proposed methods are carried on 12 bus and 24 bus EHV systems of southern Indian grid and a modified IEEE 30 bus system. Both balanced and unbalanced systems are studied and the results are compared.

This work presents new analytical and computational methods for operation security assessment of electric power systems by considering Angle and Voltage Stability Limits. In the context of Angle Stability, it was developed a method for estimating transient security margins based on equivalent network reduction techniques and coherent generators. The angle speed deviation was the criterion used to identify generators that swing together. The reduced order was accomplished by replacing two clusters of coherent generators by an One-Machine Infinite Bus equivalent system. With this equivalent, critical fault clearing times and security margins are calculated with the aid of the Equal Area Criterion. The results were in a good agreement when compared with others methods, especially those based on Transient Energy Function used as a Lyapunov function. The method was also applied for estimating security margins and critical fault clearing times of power systems in the presence of wind power generation. It was demonstrated that the proposed method can be used to select critical contingencies, where detailed power system models are needed such that it can reproduce the actual behavior of the system. With respect to Voltage Stability, it was developed an analytical and computational method for steady state voltage stability analysis on a P-Q plane. First of all, it was applied on a simple two-bus power system, and the analytical and computational results were compared. Then, a Voltage Stability Index was derived, in order to obtain the security margins of each bus for any operational state of an n-bus power system. It was carried out by using a power system reduction technique. With the Voltage Stability Index, it is possible to identify critical buses and the regions that are prone to voltage collapse. The voltage stability limits of a distribution power system was also analyzed by means of the P-Q curves, by considering different operation scenarios of wind power generation. It was demonstrated that the wind power can contribute to improve the voltage security margins. Finally, the method was applied to a real power system of Companhia Estadual de Distribuição de Energia Elétrica, in the presence of wind power generation. The methods are computationally efficient and suitable for planning, operation and real-time operation of electric power systems. / Este trabalho apresenta novos métodos analíticos e computacionais para a avaliação da segurança da operação de sistemas elétricos de potência considerando os Limites de Estabilidade Angular e de Tensão. No tema Estabilidade Angular, desenvolveu-se um método para a estimativa de margens de segurança transitória baseado em técnicas de redução de redes e geradores coerentes. O desvio de velocidade angular foi o critério usado para identificar geradores que oscilam juntos. A redução foi realizada substituindo-se dois grupos de geradores coerentes por um sistema Equivalente Máquina-Barra Infinita. Com este equivalente, os tempos críticos de abertura de falta e as margens de segurança são calculados com auxílio do Critério das Áreas Iguais. Os resultados encontrados foram muito satisfatórios quando comparados com aqueles obtidos por outros métodos, especialmente os que utilizam a função energia como função de Lyapunov. O método também foi aplicado para a estimativa de margens de segurança e tempos críticos de abertura de falta, em sistemas de potência na presença de geração eólica. Foi demonstrado que o método proposto é capaz de selecionar contingências críticas que precisam ser estudadas com modelos completos de modo a reproduzir o comportamento real do sistema elétrico. Com relação à Estabilidade Tensão, foi desenvolvido um método analítico e computacional para análise de estabilidade estática de tensão no plano P-Q. Primeiramente, o método foi aplicado em um sistema de potência simples com duas barras, e os resultados analíticos e computacionais foram comparados. Então, um Índice de Estabilidade de Tensão foi deduzido, para determinar a margem de segurança de cada barra para qualquer estado de operação de um sistema de potência com n-barras. Com o Índice de Estabilidade de Tensão, é possível identificar barras críticas e regiões com tendência ao colapso de tensão. Os limites de estabilidade de tensão de um sistema de distribuição foram analisados através das curvas P-Q , no qual foram considerados diferentes cenários de operação da geração eólica. Deste modo, foi demonstrado que a geração eólica pode contribuir para melhorar as margens de segurança de tensão. Finalmente, o método foi aplicado em um sistema de potência real pertencente à Companhia Estadual de Distribuição de Energia Elétrica. Os métodos desenvolvidos são computacionalmente eficientes e adequados para o planejamento da expansão e operação, bem como na operação em tempo real dos sistemas elétricos de potência.