Licinius Dimitri Sá de Alcantara

In this work, we address partial discharge (PD) localization as an inverse problem, where the objective is to infer the probable position of a PD source from ozone concentrations at the hydrogenerator’s ventilation outlets. Our localization system comprises pre-processing of ozone concentration data, feature extraction based on a deep neural network and classification using conventional machine learning methods (Support Vector Machine and Random Forest). The proposed method is validated experimentally using a needle-plate setup and then extended to a large-scale computational fluid dynamic model of a 311 MVA hydrogenerator. Results show that the proposed approach can identify PD source locations, achieving overall accuracies of 0.87 for the needle–plate setup and 0.77 for the hydrogenerator model. Complementary metrics include precision, recall, and F1-score. The demonstratedperformance indicates that the proposed method can serve as a practical tool for predictive maintenance in large rotating machines.

In this work, an ozone reaction chamber was used to provide experimental data to numerically evaluate the ozone generation reaction rate in a high-voltage dielectric-barrier needle-plate setup operating at 60 Hz. Ozone is thus produced by partial discharges. Ozone concentrations were measured under controlled environmental conditions, with experiments conducted at four voltage levels in the range from 5.0 kV_RMS to 6.5 kV_RMS and under four relative humidity levels in the interval from 30% to 70%. The results demonstrate that increasing relative humidity along this range causes a reduction of up to 73% in the ozone production reaction rate and a 67% decrease in ozone concentration at 6.5 kV_RMS. In addition to ozone concentration, the average energy of partial discharge pulses was also recorded for each test condition. A finite element fluid dynamics model was developed and employed, providing a framework and a formula for calculating ozone production reaction rates based on experimental results of ozone concentrations.

A água é um recurso essencial para a vida humana, e é imprescindível discutir as consequências que o despejo de poluentes em canais e rios causam diretamente para quem utiliza dos recursos hídricos. O presente trabalho tem como tema simular o despejo de fenol no canal São Joaquim, em Belém-PA, usando recursos da área da Fluidodinâmica Computacional (CFD), que consiste em um conjunto de ferramentas essenciais para análise de transporte de espécies diluídas em fluidos, como por exemplo na dispersão de poluentes nos canais e rios. A metodologia adotada consistiu em mapear geograficamente a bacia e representar o corpo da água em malhas de elementos finitos, onde um trecho de 500 m do corpo de água do canal foi delimitado e discretizado em uma malha de 1928 elementos. De início, também foi necessário identificar pontos de dispersão de poluentes em canais e rios de Belém, para assim realizar a simulação. Os dados utilizados foram coletados a partir de informações da literatura, além da utilização de softwares, como o Google Earth, para imposição de condições de contornos, o SALOME para a construção de malha e definição das propriedades físicas, o OpenFoam para calcular a distribuição de vetores de velocidade da água no trecho considerado, além de analisar a dispersão e advecção do poluente no rio, e o Paraview para visualizar os resultados da simulação. Os resultados obtidos indicam como o modelo de Fluidodinâmica Computacional aplicado com a Computação de Alto Desempenho foram essenciais para modelar casos reais do transporte de contaminantes em cursos de água. Este estudo obteve resultados consistentes e estáveis a respeito da dispersão, onde um despejo de efluente com concentração de 15,26 mg/L de fenol resultou em uma concentração de estabilização do fenol em 2,41 mg/L ao longo do canal São Joaquim. Esses valores ultrapassam o limite de 0,03 mg/L estabelecidos pela legislação (CONAMA, 2005) para fenóis em águas superficiais classe 2. A velocidade média da água no trecho considerado foi de 0,312 m/s. Concluindo, a simulação do espalhamento de poluentes no canal permite identificar a devastação causada por despejos em áreas ambientais, compreendendo a dinâmica de poluentes em rios urbanos. Esse modelo também contribui para desenvolver soluções de preservação ambiental e gestão hídrica.

We suggest a new method of localization of partial discharges in high-power electrical systems. Ozone in a hydrogenerator is produced by chemical reactions induced by partial discharges in the stator region. The transport of ozone in an operating hydrogenerator is analyzed using a computational fluid dynamics model. The main aim of this work is to evaluate the ozone distribution in the generator radiators. Ozone sources are introduced into the stator model in different positions to analyze their effect on the measured values at the sensing points of radiators. Our results demonstrate a possibility of localization of partial discharges in hydrogenerator stator bars by ozone emission.

In recent years, grain storage in Brazil underwent a 1.5% increase in its available capacity, leading to a high demand for grain treatment in the country. This study aims to evaluate two computational models for grain distribution within stored maize, comparing their ability to predict the effectiveness of ozone application. Specifically, it was investigated whether a heterogeneous model, which accounts for variations in grain density and location, provides results more compatible with experimental observations in the literature. By comparing the predictive capabilities of both models, this study will contribute to developing more effective and targeted strategies for ozone-based pest control in stored grain. In the heterogeneous model, the smaller grains accumulate in the center of the container. The study uses the Stokes-Brinkman model and ozone transport equations in porous media. It was observed that the grain distribution model affects the spatial distribution of ozone concentration inside the container. In the heterogeneous grain distribution model, the region of larger grains presents a lower ozone absorption since supposedly a smaller number of ozone elimination reactions occur on the grain surfaces.

In this paper, a three-dimensional turbulent fluid dynamics numerical model of a 311 MVA full hydroelectric power plant unit is made, using the finite element method, to study and understand the ozone transport mechanisms inside the enclosured electric machine structure. In the real world, ozone is produced by partial discharges related to faults on stator bars. In order to analyse ozone transport from localised sources, a 3D fluid dynamic model of a complete hydrogenerator in operation is developed and presented for the first time. The model has a high level of geometric detail. Furthermore, a new proposal to simplify the modelling of radiators is implemented and validated. The modelled structure is based on a Campos Novos hydrogenerator electric machine and it consists of 378 coil-type stator bars made of copper covered by mica and, more externally, by a semiconductor coating layer. Other parts are also represented, including the stator core and air directors made of stainless steel, copper radiators, the rotor with its epoxy surface, and the concrete floor and concrete external walls. In the fluid dynamics model, a finite element mesh was designed to represent the air regions inside the hydrogenerator and the material surfaces that react with ozone (with their respective reaction rates), where the airflow and ozone transport are modelled using the Navier–Stokes equations and the mass conservation law. Partial discharge sources are represented by ozone sources with prismatic shapes, placed on surfaces of stator bars. Ozone concentrations have been calculated inside and around the generator machine. The rotor radius is 3.8075 m and its rotation frequency is 200 RPM. Radial air velocity due to interpole ventilation is also considered (2.2 m/s, as experimentally verified in loco. The radial velocity in the vicinity of the radiators is 3 m/s. It has been concluded that the ozone transport profile is influenced by the source positioning on the stator bars in such a way that source pinpointing is possible and it depends on determining the local and global maxima areas of ozone concentration at the radiators.

Resumo Muitas vezes comunidades agrícolas encontram-se em locais desassistidos em infraestrutura e fontes de energia. Dessa forma, um modelo energético autossustentável baseado em sistemas capazes de prover energias oriundas de fontes alternativas e de baixo custo de operação, como os sistemas fotovoltaicos, pode mudar o cenário de escassez e alavancar o desenvolvimento humano nessas localidades, ao mesmo tempo incentivando o uso consciente dos recursos disponíveis. Neste trabalho é feita uma análise técnica e de custos de um sistema fotovoltaico de bombeamento para fins de irrigação, que poderá servir como uma referência primária para agricultores familiares que almejam planejar-se a fim de obter pequenos incentivos e financiamentos no atendimento de sua demanda energética e estimular sua produtividade dentro de um bom custo/benefício. Observou-se através desta análise que é possível dimensionar um sistema para bombeamento fotovoltaico e irrigação de forma adequada, sem desperdícios de altos volumes diários de água na sua operação, e de baixo custos de instalação e manutenção para o agricultor familiar.

We present a synergistic investigation into ozone production dynamics within a high-voltage reaction chamber operating from 1.75 kV to 10 kV, at 60 Hz. The output ozone concentration dependence on a 60 Hz root mean square high-voltage for an air input pressure of 0.1 bar was measured using an ultraviolet-based sensor. A finite-element numerical model of the reaction chamber was developed and used for obtaining the reaction rate for the generated ozone for each level of input voltage and the internal distribution of the gas vector velocity field and ozone concentration. An expression to estimate the ozone reaction rates from the measured ozone concentrations was also derived. It was then compared and validated using the developed computational model. Therefore, in this work, a formula is proposed to estimate the ozone production by providing the experimental reaction rates. The other objective is to analyze the hysteresis phenomena observed in the partial discharges’ levels in the reaction chamber and in the output ozone concentration. Finally, we establish a connection between the total power of partial discharges and the consequent ozone production, clarifying the role of cumulative partial discharges’ power levels in governing the resultant output ozone concentration.

From Maxwell's equations, an analytical formulation is developed to calculate the propagation characteristics and field profiles of transverse magnetic (TM) modes on magneto-optical (MO) planar waveguides. Results show nonreciprocal behavior in terms of both modal effective index and field profile analyses. The proposed model can be used as a reference to assess the nonreciprocal potentialities of such structures.