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[pt] No novo modelo para o setor elétrico brasileiro a operação do sistema é de responsabilidade do Operador Independente do Sistema enquanto que a propriedade do equipamento e os gastos com a sua manutenção são de responsabilidade do agente prestador do serviço ancilar.Desta forma, o lucro do agente prestador do serviço ancilar de potência reativa será função do custo deste serviço uma vez que a sua remuneração é previamente definida pelo agente regulador. Dentro desta ótica os riscos operacionais dos equipamentos de compensação de potência reativa, se não forem convenientemente mitigados,poderão aumentar os gastos com a manutenção e o pagamento de multa pela indisponibilidade do equipamento.Riscos operacionais são situações de sistema que estão fora da responsabilidade do agente mas que poderão reduzir o seu faturamento.Esta dissertação descreve os riscos operacionais e faz algumas sugestões para proteger o agente da redução do seu faturamento. / [en] In the new brazilian deregulated electrical network, system operation is under Independent System Operator responsibility while the ancillary service agent is the owner of the reactive power equipment and, as a consequence, is responsible for its maintenance costs. In the new model, the profit of the agent is a function of the maintenance costs because his payment is previously defined by the authorities. The operational risks of the reactive power equipments, if not conveniently mitigated, may increase the maintenance frequency and may also result in the payment of a fee due to the equipment unavailability.Operational risks are events in the electrical transmission system that are not under the responsibility of the agent but may reduce his profits. This report describes these operational risks and makes some suggestions to protect the agent against the reduction in his profits.

Total phosphorus concentrations in the open waters of the Laurentian Great Lakes are currently at or beneath target concentrations set by international agreement. Despite the success of phosphorus loading controls in remediating nearshore eutrophication problems in the past, nuisance growth of Cladophora has recently returned to the lower Great Lakes. This thesis examines soluble reactive phosphorus (SRP) in a northwestern segment of Lake Ontario to assess whether allochthonous or autochthonous sources of phosphate lead to localized areas of PO43- enrichment that may help to explain the seemingly paradoxical resurgence of Cladophora. As SRP is often an overestimate of PO43- in P-limited waters, measures of SRP made with the standard method were compared with measures of SRP made with modified methods (i.e., using dialysis and magnesium-induced co-precipitation) designed to more accurately measure phosphate when it was expected to be at low concentrations. Measures of SRP made with standard and modified methods did not differ, however, SRP was 1 to 3 orders of magnitude higher than a more sensitive steady-state radiobioassay for PO43- used for comparison in offshore waters. Although the utility of SRP is limited when phosphate concentrations are very low, SRP is useful to measure localized areas of phosphate enrichment, and its relative concentrations can be compared in time and space. To quantify the degree to which allochthonous inputs and dreissenids contribute to PO43- concentrations that permit Cladophora growth, intensive sampling for SRP was carried out prior to, during and following the Cladophora growing season. SRP was higher in the nearshore than offshore and near the mouth of a large tributary and a treated wastewater outfall than in samples from other locations along the shoreline, but only in the spring and autumn. Phosphate turnover times indicated lower P-limitation in the nearshore and near local inputs versus the offshore. Higher concentrations of SRP were measured in samples taken 15 cm and 50 cm above dreissenid mussel-beds than in those obtained at corresponding depths over other substrata and from higher up in the water column through the Cladophora growing season, while Chl a concentrations displayed the reverse trend. These results suggest that PO43- excreted by dreissenids could be more important in time and space than external inputs in supporting nuisance Cladophora growth in the current nearshore environment. Continued research and monitoring of P dynamics in the nearshore combined with model approaches should better predict whether more stringent P controls would be effective in managing Cladophora growth.

Total phosphorus concentrations in the open waters of the Laurentian Great Lakes are currently at or beneath target concentrations set by international agreement. Despite the success of phosphorus loading controls in remediating nearshore eutrophication problems in the past, nuisance growth of Cladophora has recently returned to the lower Great Lakes. This thesis examines soluble reactive phosphorus (SRP) in a northwestern segment of Lake Ontario to assess whether allochthonous or autochthonous sources of phosphate lead to localized areas of PO43- enrichment that may help to explain the seemingly paradoxical resurgence of Cladophora. As SRP is often an overestimate of PO43- in P-limited waters, measures of SRP made with the standard method were compared with measures of SRP made with modified methods (i.e., using dialysis and magnesium-induced co-precipitation) designed to more accurately measure phosphate when it was expected to be at low concentrations. Measures of SRP made with standard and modified methods did not differ, however, SRP was 1 to 3 orders of magnitude higher than a more sensitive steady-state radiobioassay for PO43- used for comparison in offshore waters. Although the utility of SRP is limited when phosphate concentrations are very low, SRP is useful to measure localized areas of phosphate enrichment, and its relative concentrations can be compared in time and space. To quantify the degree to which allochthonous inputs and dreissenids contribute to PO43- concentrations that permit Cladophora growth, intensive sampling for SRP was carried out prior to, during and following the Cladophora growing season. SRP was higher in the nearshore than offshore and near the mouth of a large tributary and a treated wastewater outfall than in samples from other locations along the shoreline, but only in the spring and autumn. Phosphate turnover times indicated lower P-limitation in the nearshore and near local inputs versus the offshore. Higher concentrations of SRP were measured in samples taken 15 cm and 50 cm above dreissenid mussel-beds than in those obtained at corresponding depths over other substrata and from higher up in the water column through the Cladophora growing season, while Chl a concentrations displayed the reverse trend. These results suggest that PO43- excreted by dreissenids could be more important in time and space than external inputs in supporting nuisance Cladophora growth in the current nearshore environment. Continued research and monitoring of P dynamics in the nearshore combined with model approaches should better predict whether more stringent P controls would be effective in managing Cladophora growth.

Switching of shunt reactors and capacitor banks is known to cause a very high rate of rise of transient recovery voltage across the circuit breaker contacts. With improvements in circuit breaker technology, modern SF6 puffer circuits have been designed with less interrupter per pole than previous generations of SF6 circuit breakers. This has caused modern circuit breakers to operate with higher voltage stress in the dielectric recovery region after current interruption. Catastrophic failures of modern SF6 circuit breakers have been reported during shunt reactor and capacitor bank de-energisation. In those cases, evidence of cumulative re-strikes has been found to be the main cause of interrupter failure. Monitoring of voltage waveforms during switching would provide information about the magnitude and frequency of small re-ignitions and re-strikes. However, measuring waveforms at a moderately high frequency require plant outages to connect equipment. In recent years, there have been increasing interests in using RF measurements in condition monitoring of switchgear. The RF measurement technique used for measuring circuit breaker inter-pole switching time during capacitor bank closing is of particular interest. In this thesis, research has been carried out to investigate switching transients produced during circuit breaker switching capacitor banks and shunt reactors using a non-intrusive measurement technique. The proposed technique measures the high frequency and low frequency voltage waveforms during switching operations without the need of an outage. The principles of this measurement technique are discussed and field measurements were carried out at shunt rector and capacitor bank installation in two 275 kV air insulated substations. Results of the measurements are presented and discussed in this thesis. The proposed technique shows that it is relatively easy to monitor circuit breaker switching transients and useful information on switching instances can be extracted from the measured waveforms. Further research works are discussed to realise the full potential of the measuring technique.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Engineering composite structures containing piezoelectric elements coupled with the so-named shunt circuits, with the aim of passive vibration attenuation, are characterized by inherent uncertainties in their parameters, which can affect significantly performance of the passive shunt circuit. In this context, this work presents the stochastic finite element modeling of a composite structure containing piezoelectric element to be coupled with a shunt circuit, in such a way, that uncertain parameters such as the fiber s orientation, layer thicknesses and the resistance and inductance in the shunt circuit are assumed as uncertain variables and, their corresponding dispersion, is characterized in the stochastic response by propagating the uncertainties into the model. First, the deterministic electromechanical problem is modeled by combining the First-Order Shear Deformation Theory and the concept of Equivalent Single Layer, in order to approximate the mechanical displacement fields, with the so-called Layerwise Theory used to model the discrete electric fields within the composite element. In the sequence, the shunt circuits coupled to the piezoelectric element are introduced in the model. The deterministic finite element modeling procedure was performed taking into the parameterization process of the design variables of interest to be further assumed as random variables in a straightforward way. In the present stochastic finite element modeling procedure, the uncertain variables are modeled as Gaussian stochastic homogeneous fields and discretized according to the Karhunen-Loève expansion method, with the aim of generating the exact stochastic matrices. The obtained results, in terms of the envelopes of the frequency response functions for a composite beam incorporating piezoelectric material coupled with a shunt circuit, demonstrate the interest in considering the uncertainties in the preliminary design phase of the shunt circuits to control the undesired vibrations. / Estruturas compósitas em engenharia contendo elementos piezelétricos acoplados a circuitos elétricos shunt, para fins de atenuação passiva dos níveis de vibração, apresentam incertezas inerentes em seus parâmetros de projeto, as quais, podem afetar significativamente a eficiência dos circuitos elétricos passivos. Neste contexto, este trabalho apresenta a modelagem por elementos finitos estocásticos de uma estrutura em material compósito laminado contendo elemento piezelétrico acoplado a circuitos elétricos shunt, de modo que, parâmetros incertos, como direções das fibras, espessuras das camadas e a resistência e indutância do circuito shunt, são assumidos como sendo variáveis aleatórias e, a dispersão destas variáveis, é caracterizada nas respostas estocásticas obtidas após a propagação das incertezas no modelo. Desta forma, realiza-se em um primeiro momento a modelagem do problema eletromecânico determinístico. Para tal, há combinação das teorias de Deformação Cisalhante de Primeira Ordem e da Camada Equivalente Única para aproximação dos campos de deslocamentos mecânicos, com a Teoria Layerwise, que utiliza o conceito de Camadas Equivalentes Discretas na consideração dos campos elétricos, os quais, são assumidos discretos ao longo da espessura da estrutura do laminado. Na sequência, faz-se a inclusão dos circuitos elétricos shunt no modelo eletromecânico. A modelagem determinística é realizada de forma parametrizada para que se possa realizar a introdução a posteriori das incertezas no modelo de forma mais eficiente. Utilizando-se do Método dos Elementos Finitos Estocásticos, os parâmetros fatorados das matrizes e os elementos do circuito são considerados como variáveis aleatórias e modelados como campos homogêneos estocásticos gaussianos. Estes campos são então discretizados de acordo com o método de expansão em série de Karhunen-Loève, onde são geradas as matrizes estocásticas exatas do sistema eletromecânico via modificação do processo de integração pelas funções de covariância. Os resultados obtidos, em termos dos envelopes das respostas em frequência para uma viga compósita contendo um elemento piezelétrico acoplado ao circuito shunt, evidenciam a importância de se considerar as incertezas durante as fases de concepção inicial e/ou pré-projeto de sistemas dinâmicos incorporando circuitos shunt para o controle passivo de vibrações. / Mestre em Engenharia Mecânica

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This work deals with the description and analysis of suitable methods for measurement of non-periodical high-level current pulses. For pulsed current source design and development a suitable measurement system is required. In this work shunt resistor, Rogowski sensor and magneto-optic sensor are presented. The analysis of their properties is performed in order to design a suitable sensor for test current pulse measurement. A design of Rogowski coil sensor has been made. An experimental measurement of current pulses with short time relations has been performed. The suitability of the coil sensor for non-harmonic waveforms measurement has been evaluated on the basis of measurement results. In case of the magneto-optic sensor a concept utilizing an optical fiber has been proposed. The design of the sensor has been performed also. Individual parts of the sensor were verified. Experimental magneto-optic sensors have been built and their properties have been studied.

This master’s thesis deals with the design of autonomous monitoring system electronics which will be used for diagnostics of the electromagnetic vibration generator developed at Brno University of Technology. This generator should be used in a practical application where frequent mechanical shocks are present, for example in vehicle or goods transportation. For such an application, the goal of the monitoring system is to find out whether generator is capable of producing enough electrical energy for smooth operation of wireless sensors used in similar applications. The first part of the thesis consists of the autonomous diagnostics system overview from both commercial and scientific spheres, brief description of the vibration generator used and also a summary of commercially available power management electronics. The next chapters present the detailed description of each functional element of energy harvesting system, the simulation of generator’s behaviour for optimal load in three different model applications and the most important part – design of the autonomous monitoring system. In the end, achieved results are evaluated and it is considered whether the shock-driven generator is suitable for use in a given application.