Made available in DSpace on 2016-03-07T19:21:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-08-28. Added 1 bitstream(s) on 2016-03-07T19:24:56Z : No. of bitstreams: 1 000859497.pdf: 1029193 bytes, checksum: bf9e875b887e62d258a1ab378a66993e (MD5) / O setor de distribuição de energia elétrica vem apresentando constantes mudanças para se adaptar à necessidade de atendimento das crescentes demandas com recursos financeiros e energéticos cada vez mais escassos. Concessionárias têm buscado eficiência operacional em seus processos através de tecnologias que visam atender a um consumidor cada vez mais exigente por qualidade na utilização da energia elétrica. Neste cenário, a utilização de equipamentos que flexibilizem a operação das redes de distribuição apresentam-se como alternativas menos onerosas quando comparadas com a realização de grandes investimentos na expansão. O uso de equipamentos de flexibilização nas redes de distribuição possui peculiaridade específicas que prevê adaptações de natureza elétrica e física no sistema. O compensador série controlado a tiristores apresenta-se como uma alternativa a ser considerada para aplicação em redes de até 36kV. Aspectos de robustez face a necessidade de flexibilização são discutidos de modo a analisar sua postergação de investimentos visando mitigar ou diminuir o impacto de grandes alterações em redes de distribuição. Tais adaptações são comparadas com a sua viabilidade econômica, a partir da adequação da relação custo-benefício. Os resultados das análises apontam para uma tendência favorável à utilização do compensador série controlado a tiristores na rede de distribuição (D-TCSC), quando considerados os valores de implantação, tempo de execução física, instituição de condições mais favoráveis para realização de manobras e retorno mais rápido na imobilização de cálculos de tarifas e retorno do capital investido / The electrical distribution system has presented constant changes to adapt to the growth in power demand with reducing financial and energetic resources availability. Utilities are looking for improvement in operating conditions using new technologies to attend to high power quality by the most demanding consumer. The use of equipment to improve the flexibility of distribution systems is an alternative which postpone large investments in system expansion. The thyristor-controlled series compensator is an attractive option for networks up to 36 kV. In this work, flexible solutions are discussed to postpone investments. Economical viability of a series controlled compensator in a distribution system is presented. The results take in account the initial cost, time of implementation, return on invested capital, among others

Made available in DSpace on 2015-08-20T17:09:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-12-12. Added 1 bitstream(s) on 2015-08-20T17:26:50Z : No. of bitstreams: 1 000844250.pdf: 1828617 bytes, checksum: 76e731b5aec7d79741d059ecd22502c8 (MD5) / A presente pesquisa apresenta uma análise teórica de alguns tópicos relevantes de programação linear relacionados ao método simplex. A motivação de analisar esses tópicos é torná-los mais didáticos e incentivar a aplicação dos mesmos na otimização de sistemas de energia elétrica e, em geral, na aplicação na otimização de problemas de engenharia. O método simplex em programação linear (PL) que foi por muito tempo a principal técnica de otimização de problemas de otimização lineares e não lineares (usado após a linearização) ainda é o mais utilizado na otimização de muitos problemas reais na engenharia e particularmente na engenharia elétrica. O método simplex resolve um problema de programação linear usando uma estratégia conceitualmente refinada. Para conhecer todas as versões do método simplex que podem ser usadas para resolver um problema de programação linear e também para dominar a parte conceitual do mesmo é necessário entender o ótimo de um problema de programação linear, quando um problema de programação linear é ilimitado, a lógica de otimização do método primal simplex, as condições nas quais um método simplex precisa de variáveis artificiais, o método primal simplex revisado, a teoria da dualidade em programação linear, a lógica de otimização do método dual simplex, a teoria da análise de sensibilidade e p ́os-otimizac ̧ão em programação linear, a lógica de otimização do método primal simplex canalizado bem como do método dual simplex canalizado. O produto desta pesquisa consiste em gerar um material didático que ajude de forma mais eficiente aos iniciantes em tópicos de pesquisa operacional. Desta forma, apresenta-se uma análise teórica e a reformulação de alguns tópicos relevantes relacionados com o método simplex na resolução de problemas de PL / This research presents a theoretical analysis of some relevant topics related to linear programming via simplex method. The motivation of analyzing these topics makes them more didactic and easy to understand. As these kinds of methodologies are fast and unequivocal, they are applicable in various real-world engineering problems particularly in the field of power system optimization. In linear programming (LP), the simplex method has been the main technique to optimize the linear problem as well as the linearized problem (a problem with the nonlinear nature). The simplex method solves a linear programming problem using a conceptually refined strategy. In order to understand all of the available versions of the simplex method that can be used to find the solution of a linear programming problem and in order to have a detail study on them, it is necessary to understand: the optimality of such problems, where a linear programming problem is limited, the logic of optimization of the primal simplex method, in which condition a simplex method needs artificial variables, the revised primal simplex method, the duality theory in linear programming, the logic of optimization of the dual simplex methodology, the theory of sensitivity analysis and post-optimization in linear programming, and the logic of the primal or dual simplex for the boundary variables. The output of this research is to prepare a didactic reference and a user manual to help the beginner researchers in operations research. Therefore, a theoretical analysis and reformulation of some relevant topics related to the simplex method for solving LP problems is presented

Made available in DSpace on 2014-11-10T11:09:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-02-28Bitstream added on 2014-11-10T11:58:00Z : No. of bitstreams: 1 000794229.pdf: 1336859 bytes, checksum: 2709e1209d7b9c68eb2eec145dcde590 (MD5) / Neste trabalho, são propostas duas metodologias para resolver o problema de planejamento da expansão de sistemas de transmissão (PPEST). A primeira delas é uma apresentação de um algoritmo baseado em meta-heurística, Particle Swarm optimization (PSO), como ferramenta para resolver o PPEST estático. Nesta proposta são usados os modelos matemáticos de transporte e CC. Ambos os modelos foram implementados na linguagem de programação FORTRAN e o solver comercial MINOS foi usado para resolver os problemas de programação linear relacionados. A segunda proposta apresenta o PPEST considerando múltiplos cenários de geração usando o modelo linear disjuntivo. Este modelo foi implementado via AMPL e resolvido usando o solver comercial CPLEX. A fim de validar e qualificar a primeira metodologia proposta, cinco sistemas foram estudados, são eles: Garver, IEEE 24-barras, Sul Brasileiro, Colombiano e Norte-Nordeste Brasileiro. E para a segunda metodologia proposta, três sistemas foram estudados, são eles: Garver, IEEE 24-barras, Sul Brasileiro. Os resultados mostraram a eficiência e utilidade das duas metodologias propostas / In this work, two methodologies to solve the transmission network expansion planning (TNEP) problem have been proposed. The first one is a presentation of a meta-heuristic based algorithm, Particle Swarm Optimization (PSO), as a tool to solve static TNEP problems. In this proposition, the mathematical models of transportation model and the DC model have been used. Both the models have been implemented via the programming language of FORTRAN and the commercial solver of MINOS has been used to solve the related LP problems. The second proposal, presents the TNEP problem considering multiple generation scenarios using the disjunctive linear model. This model has been implemented via AMPL and solved by the commercial solver of CPLEX. In order to validate and qualify the first proposed methodology, five case studies have been carried out, these cases are: Garver, IEEE 24-bus, Southern Brazil, Colombian, and Brazilian North-Northeast systems. And for the second proposed methodology, 3 case studies have been used such as: Garver, IEEE 24-bus and Southern Brazil test systems. The results show the effectiveness and the usefulness of the proposed methodologies

Made available in DSpace on 2014-11-10T11:09:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-01-17Bitstream added on 2014-11-10T11:57:57Z : No. of bitstreams: 1 000794407.pdf: 4698769 bytes, checksum: 53c9b02bcf68c5d45e286aa866d2b61d (MD5) / Neste trabalho, o algoritmo genético de Chu-Beasley especializado foi utilizado para resolver o problema de reconfiguração de sistemas de distribuição de energia elétrica, que é modelado como um problema de programação não linear inteiro misto. Um objetivo do trabalho é definir um espaço de busca reduzido, para reduzir o tempo computacional do algoritmo genético de Chu-Beasley especializado para resolver um problema de reconfiguração de sistemas de distribuição de energia elétrica. Para avaliar a factibilidade em relação às restrições de operação dos sistemas de energia elétrica foi implementado um algoritmo de fluxo de carga radial, para calcular o estado deste sistema e, a partir deste, as perdas de potência ativa e as correntes nos ramos. São apresentados testes realizados utilizando os sistemas de 14, 33, 84, 119 e 417 barras para avaliar a eficiência e robustez da metodologia proposta. Os resultados obtidos foram apresentados e comparados com os resultados encontrados na literatura / In this paper, Chu-Beasley’s specialized genetic algorithm will be used to solve the reconfiguration of distribuition system problem, which was modeled such as mixed integer nonlinear programming problem. In this work was defined a reduced search space to reduce the computational time of genetic algorithm of Chu-Beasley’ specialized to solve the reconfiguration of distribution systems problem. To evaluate the feasibility regarding constraints of the electrical power systems' operation, an algorithm for radial load flow was implemented to calculate these nodal tensions of these systems and, losses and currents of the system. Tests are presented using the systems of 14, 33, 84, 119 and 417 buses to avaluate the efficiency and robustness of the proposed method. The results were presented and compared to those found in the literature

Orientador: Percival Bueno de Araujo / Banca: Laurence Duarte Colvara / Banca: Dilson Amancio Alves / Banca: Francisco Damasceno Freitas / Banca: George Lauro Ribeiro de Brito / Resumo: Este trabalho trata da análise da estabilidade a pequenas perturbações de sistemas elétricos de potência multimáquinas considerando a atuação de Estabilizadores de Sistemas de Potência (ESPs) e de controladores do tipo Power Oscillation Damping acoplados a dispositivos FACTS UPFC (conjunto UPFC/POD). Um de seus objetivos é analisar como o posicionamento dos zeros da função de transferência em malha aberta (FTMA) do sistema elétrico de potência influencia na localização e na capacidade dos controladores em introduzir amortecimento às oscilações de baixa frequência. De maneira usual, uma análise de sensibilidade, através do método dos resíduos fornece a localização para instalação do conjunto UPFC/POD e/ou ESP. Entretanto, será mostrado neste trabalho que a quantidade de amortecimento fornecido ao modo eletromecânico de interesse utilizando os controladores suplementares de amortecimento é limitada pelo zero da FTMA do controlador. Desta forma, o ESP ou o conjunto UPFC/POD instalado na melhor localização obtida através do método dos resíduos pode não fornecer o coeficiente de amortecimento desejado ao polo de interesse. Outro objetivo é o ajuste dos parâmetros destes controladores e são utilizadas duas técnicas, sendo uma baseada na compensação de fase e chamada de método dos resíduos. Também é proposta outra forma de ajuste, fundamentada em algoritmos genéticos. Para a execução desses estudos o Modelo de Sensibilidade de Potência é utilizado para a representação do sistema elétrico de potência. Resultados são apresentados para dois sistemas teste: sistema simétrico com 4 geradores, 10 barras e 9 linhas de transmissão e o sistema New England com 10 geradores, 39 barras e 46 linhas de transmissão / Abstract: This work deals with the small-signal stability analysis of multimachine power systems considering the Power System Stabilizers (PSS) and Power Oscillation Damping (POD) performance. POD is coupled to the FACTS (Flexible Alternating Current Transmission Systems) UPFC (Unified Power Flow Controller). An analysis of the open-loop transfer function (OLTF) zeros of the electric power systems is carried out aiming to verify the influence of the OLTF zeros placement on the controllers location and ability to introduce damping to low frequency oscillations. In the usual way, a sensitivity analysis, using the residue method, provides the UPFC/POD and/or PSS location. However, will be shown in this work that the damping provided to interest eigenvalue using a supplementary damping controller is limited by the OLTF zeros placement. Thus, the PSS or the UPFC/POD installed in the best location obtained by the residue method cannot provide the desired damping coefficient to the interest pole. Another objective of this work is to evalmate the performance of the controller parameters tuning. Two techniques are used with this objetive. One of then is based on phase compensation and called the residue method. The second one is based on genetic algorithm method. For the execution of these studies the Power Sensitivity Model (PSM) is used to represent the electric power system. Results are presented for two test systems: a test system with 4 generators, 10 buses and 9 transmission lines and the New England System that has 10 generators, 39 buses and 46 transmission lines / Doutor

Thesis submitted in partial fulfilment of the requirements for the degree Magister Technologiae: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2008 / Fuel cell technology is an emerging technology that provides a highly efficient, quiet operation, reliable, and environmentally friendly energy conversion system for stationary, automobile (vehicle), and portable applications. An electrochemical process combines hydrogen fuel and oxygen from air to produce water, and in the process it produces electricity and heat. Fuel cell stationary applications which include residential, office buildings, hospitals, hotels, airports and others have received greater attention for their ability to utilize the heat generated for space and water heating. This combined heat and power (CHP) process increases the energy conversion efficiency greatly which in turn save cost of energy usage. Different power converter topologies for fuel cell systems residential applications are presented in this thesis for efficiency, cost, component count, input ripple current minimization technique, reliability for comparison analysis. The commercial feasibility of fuel cells rests on the cost of the fuel cell system and operating efficiency and fuel cost. The proposed power converter topology consists of two front end DC-DC converters. The first front-end DC-Dc converter is tightly controlled while the second is a full bridge four interleaved DC-DC converters. Advantages of the proposed topology are reduced input ripple current, high efficiency, low maintenance cost, smaller size, modularity, redundancy. Design overview as well as simulation results are presented. Fuel cell simulation test results, including transient response are displayed and analyzed. The concept of interleaving of multiple units of the De-De converter is proposed. Interleaving enables paralleling multiple units of the converters to achieve a high combined power. This results in using semiconductor power devices of lower current rating, lowering sizes of input and output capacitors and reducing the output ripples. Simulations results are presented that verify the concept of interleaving. Preliminary work to implement interleaving is presented, and future work is recommended.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology / Traditionally, efficiency is defined for sinusoidal networks and not for non-sinusoidal networks. For this reason, the efficiency formula and indices for efficiency calculations are reviewed. The concepts for determining powers, efficiency and power direction of flow in a non-sinusoidal network are explained. A new index „True Efficiency‟ is introduced to represent efficiency in non-sinusoidal circuits. Harmonic filters are installed in networks with harmonic distortion levels above the set standards for harmonic mitigation. However, there are no specific indices for evaluating the effectiveness of filter(s), hence the introduction of the index „Filter Effectiveness‟. Two software tools are utilised to develop flow charts and indices for evaluating true efficiency and effectiveness of harmonic filters in a power system under distorted waveform conditions. In this way, the effect that distortions have on efficiency can be determined and the effectiveness of the mitigation measure in place can be evaluated. The methodologies are developed using a step-by-step approach for two software packages. Three case studies were conducted on a large network. This network has multiple harmonic sources and capacitor banks. The first case study considered a network with two harmonic sources and three capacitor banks of which two are at the point of common coupling (PCC) and one is at a load bus; the second case study considered Case 1 with two capacitor banks at the PCC used as components for the 2nd - order filter and the third case considered Case 2 with a Notch filter added at one of the load buses. The network was simulated using DIgSILENT and SuperHarm software packages. DIgSILENT can calculate powers while SuperHarm gives current and voltages and power is hand calculated. The two packages were used together to test their compatibility and verify the network modelling. For the different investigations conducted, the software-based methodologies developed to calculate true efficiency in a network with multiple harmonic sources and capacitor banks have been shown to be effective. The indices developed for evaluating the effectiveness of harmonic filters proved to be effective too. The two software packages used proved to be compatible as the results obtained are similar. The methodologies can easily be adapted for investigations of other large networks as demonstrated in this study. The true efficiency methodologies are thus recommended for application in this field as it will help determine efficiency for networks with non-linear loads and help mitigate the distortions.

Thesis (DTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / Geomagnetically induced currents (GIC) are currents induced in ground-based conductor networks in the Earth's surface. The GIC are driven by an electric eld induced by geomagnetic variations which are a result of time-varying magnetospheric-ionospheric currents during adverse space weather events. Several studies have shown that there is a likelihood of technological damage (the power grid) in the mid- and low-latitude regions that could be linked to GIC during some geomagnetic storms over the past solar cycles. The effects of GIC in the power system can range from temporary damage (e.g. protective relay tripping) to permanent damage (thermal transformer damage). Measurements of GIC in most substations are done on the neutral-to-ground connections of transformers using Hall-effect transducers. However, there is a need to understand the characteristics of GIC in the power lines connected to these transformers. Direct measurements of GIC in the power lines are not feasible due to the low frequencies of these currents which make current measurements using current transformers (CT) impractical. This thesis discusses two techniques that can be employed to enhance understanding GIC characteristics in mid-latitude regions. The techniques involve the measurement of GIC in a power line using differential magnetometer measurements and modelling GIC using the finite element method. Low frequency magnetometers are used to measure magnetic felds in the vicinity of the power lines and the GIC is inferred using the Biot-Savart law. A finite element model, using COMSOL-Multiphysics, is used to calculate GIC with the measured magnetic field and a realistic Earth conductivity profile as inputs. The finite element model is used for the computation of electric field associated with GIC modelling.

M.Ing. / Please refer to full text to view abstract

M.Ing. / Line commutated thyristor converters are proven to be natural line harmonic currentgenerating sources regardless of their operating modes. The quality of harmonic current components induced back to the lines is commonly described to be similar under both states of operation. This however does not seem to be quite obvious as far as the aggregate harmonic current contribution to the phase inputs per operating region of thyristor converters. It becomes thus important to examine the degree of association between thyristor converter operating states and the magnitude of current harmonic pollution induced back to the input lines to subsequently establish the most current harmonic polluting region of operation. For the purpose of this study, the Nyquist-Shannon theorem, best known as the sampling theorem, whereby the converter output signal or waveform is sampled by the switching function to reconstruct the input waveform, is numerically applied in conjunction with the MatLab/Simulink 7.0 which enables the simulation of the two-quadrant operation of direct current variable speed drive (DC VSD) and that of high voltage direct current link (HVDC) converter station operation, as well as physical measurements on the twoquadrant operation of the DC VSD (Saftronics DC2L) with the aid of the digital scope meter (DSO)1200 series. However, numerical analysis based on the sampling theorem, practical measurements obtained and the MatLab/Simulink simulations indicate that the converter operating states cause a randomly distributed harmonic current generation trend in the input lines as the firing angle is increased and the most harmonic current contribution cannot be attributed to a specific region of the controlled converter firing angle.