Artigos em Revistas

This paper presents a specific method to improve the reliability of the equipment and the quality of power supplied to the electrical systems with the frequency and voltage control of a thermoelectric plant, to guarantee a more stable system. The method has the novelty of combining Total Productive Maintenance (TPM) using only four pillars, with Electrical Predictive Maintenance based in failure analysis and diagnostic. It prevents voltage drops caused by excessive reactive consumption, thus guaranteeing the company a perfect functioning of its equipment and providing a longer life of them. The Maintenance Management Program (MMP) seeks to prevent failures from causing the equipment to be shut down from the electrical system, which means large financial losses, either by reducing billing or by paying fines to the regulatory agency, in addition to prejudice the reliability of the system. Using management tools, but applying only four TPM pillars, it was possible to achieve innovation in power plants with internal combustion engines. This study aims to provide maintenance with a more reliable process, through the implantation of measurement, control and diagnostic devices, thus allowing the management to reduce breakdown of plant equipment. Some results have been achieved after the implementation, such as reduction of annual maintenance cost, reduction of corrective maintenance, increase of MTBF (Mean Time between Failures) and reduction of MTTR (Mean Time to Repair) in all areas. Probabilistic models able to describe real processes in a more realistic way, and facilitate the optimization at maximum reliability or minimum costs are presented. Such results are reflected in more reliable and continual power generation.

MILTON FONSECA JUNIOR, UBIRATAN HOLANDA BEZERRA, JANDECY CABRAL LEITE, JORGE LAUREANO MOYA RODRÍGUEZ

The search for effective ways to promote the secure operation of power systems and to increase its understanding by operators has encouraged continuous research for new techniques and methods that can help in this task. In this paper, it is proposed an approach to assess power system operation security for multiple contingencies using a multiway decision tree (MDT). The MDT differs from other decision tree techniques for establishing, in the training step, one value of the categorical attributes by branch. This approach proposes the use of topologies (contingencies) as categorical attributes. In this way, it improves interpretability regarding the power system operational state, as the operator can see clearly the critical variables for each topology, such that the MDT rules can be used in aiding the decision-making. This proposal was used for security assessment of the Northern part of the Brazilian Interconnected Power System (BIPS), and it was tested with real data from one day operation, demonstrating good performance, with a set of simple and clear rules. It was also performed a comparison of the obtained results with other techniques based on DT and it turned out that MDT has resulted in a simpler procedure for power system security classification with good accuracy.

WERBESTON D. OLIVEIRA, JOÃO P.A. VIEIRA, UBIRATAN H. BEZERRA, DANIEL A. MARTINS, BENEDITO DAS G. RODRIGUES

In this paper, a methodology was developed to analyze the results of energy efficiency programs used in the electricity distribution sector in Brazil. Analyzing the gains obtained through the investments made, and classifying which actions resulted in the best performance, contributed to decision making on the best allocation of investments to obtain the greatest energy savings. The Brazilian Energy Efficiency program was analyzed with a developed non-parametric model, using the data envelopment analysis method, and the categories of projects with better performance were determined. A database of the results from 1704 projects, from 2008 to 2016 in the Energy Efficiency program in Brazil´s electricity distribution sector, was used. The results obtained show that the best performance was achieved by projects in the industrial and cogeneration categories; however, in Brazil these constitute only 4.24% of the projects presented and 5.28% of the total investments in the last eight years, indicating a need to review the regulatory strategies for energy efficiency in this country.

ROGERIO DIOGNE DE SOUZA E SILVA, ROSANA CAVALCANTE DE OLIVEIRA, MARIA EMÍLIA DE LIMA TOSTES

This study investigates the effects on the performance of a diesel generator set at constant electric power of 2.43 kW (approximately 60% nominal engine load condition) and rotation at 3600 rpm operating with a 7% biodiesel-diesel blend (B7) and being doped with hydrogen into the intake air. Hydrogen was injected continuously into the engine intake manifold at different mass concentrations of 2, 6, 8 and 10% of the total fuel mass (B7 + hydrogen) which represents energy fractions of 5, 15, 20 and 24% of total fuel energy. To this, a small L-shaped tube installed at the center of the pipe was used. It is anticipated that the intake air fluctuations at that location, due to opening and closing the intake valve, allows a rapid mixture of hydrogen and air. Due to the addition of hydrogen the total amount of energy in the fuel (B7 + hydrogen) introduced into the engine was increased, so that the engine speed tends to increase, but this was prevented by the governor of the fuel injection pump which decreases the amount of B7 injected until the working frequency of the generator was 60 Hz. The test results showed a reduction in the specific fuel consumption as a function of the increase of hydrogen concentrations. Likewise, CO2, CO and HC emissions decreased proportionately as the hydrogen concentration was increased. On the other hand, the emissions of nitrogen oxides (NOx) increased due to the increase in the average temperature inside the cylinder. There was also an increase in the peak pressure and in the heat release rate inside the cylinder, since B7 ignition delay was reduced due to the increase in hydrogen content.

HENDRICK MAXIL ZÁRATE ROCHA, RICARDO DA SILVA PEREIRA, MANOEL FERNANDES MARTINS NOGUEIRA, CARLOS RODRIGUES PEREIRA BELCHIOR, MARIA EMÍLIA DE LIMA TOSTES

This work presents a hybrid method to solve the protective devices allocation problem in electric distribution systems. Current methods only consider optimization results, without taking into account standards established by electric energy companies. These standards reflect distribution systems particularities observed by these companies. Firstly, recloser placementis determined through an optimization process, aiming to reduce reliability indices. Fuse links are placed according to heuristic rules established by electric companies. To validate the proposed methodology, a comparison with three other references from the literature is carried out, showing good results and proving the method's effectiveness.

FERNANDO GUILHERME KAEHLER GUARDA, GHENDY CARDOSO JUNIOR, ADRIANO PERES DE MORAIS, UBIRATAN HOLANDA BEZERRA, JOAO PAULO ABREU VIEIRA

This paper proposes a methodology for compression of electrical power signals from waveform records in electric systems, using genetic algorithm (GA) and artificial neural network (ANN). The genetic algorithm is used to select and preserve the points that better characterize the waveform contours; and the artificial neural network is used in the compression of other points as well as on the signal reconstruction process. Thus, the data resulting from the proposed methodology are formed by a part of the original signal and by a compressed complementary part in the form of synaptic weights. The proposed methodology selects and preserves a percentage of the original signal samples, which are aspects not explored in the literature. The method was tested using field data obtained from an oscillographic recorder installed in a 230 kV electrical power system. The results presented compression rates ranging from 8.59:1.00 to 24.16:1.00 for preservation rates ranging from 2.5% to 10%, respectively.

FABIOLA GRAZIELA NORONHA BARROS, WELLINGTON ALEX DOS SANTOS FONSECA, UBIRATAN HOLANDA BEZERRA, MARCUS VINÍCIUS ALVES NUNES

This paper proposes a decision tree (DT)-based security dispatch method applied to integrated electric power and natural-gas networks (IPGNs) against credible contingencies that may cause violations. Preventive adjustments to the optimal electric energy generation and gas production are carried out based on the security regions and boundaries of controllable variables determined by the DTs. The easily interpretable DT’s rules that describe the security regions are tractable constraints to be included in the optimization routines of electricity generation and gas production rescheduling. Some specific critical contingencies applied to the IEEE 118-bus test system integrated with the 15-node natural gas network are taken as examples to demonstrate a promising application of the proposed security dispatch method to restore IPGN security.

DENIS C.L. COSTA, MARCUS V.A. NUNES, JOÃO P.A. VIEIRA, UBIRATAN H. BEZERRA

Este artigo objetiva analisar as atividades desenvolvidas com os alunos da escola E.E.F.M. Eneida de Moraes no Jardim Botânico do Museu Emilio Goeldi. Com os resultados busca-se através de vivências nesses espaços educativos, práticas de ensino que visem a interdisciplinaridade e a conservação ambiental.

JANISE MARIA MONTEIRO RODRIGUES VIANA, SÉRGIO CARDOSO DE MORAES, WELLINGTON DA SILVA FONSECA

The main objective of this paper is to assist in the investigation of electromagnetic forces, structural deformation, stresses, and Safety factor when energizing unloaded transformers. The methodology is based on modeling of a single-phase 50 MVA transformer subjected to inrush currents through finite element method (FEM). In this perspective, the conditions of inrush currents are used to estimate the magnetic field density dispersion in the transformer and to find the values of forces in axial and radial directions. These components are distributed along the energized windings for observing the loads in high-voltage windings. Thus, this article will contributes with the investigations of a structural Analysis on transformers when subjected to inrush current.

WELLINGTON DA S. FONSECA, DIORGE DE S. LIMA, MARCUS V.A. NUNES, ADRY K.F. LIMA, NEWTON S. SOEIRO

The formulations employed to the optimization of passive filters can be classified as formulations of a single objective or formulations with multiple objectives. The single-objective formulations normally are devoted to determine the filters of lowest cost that assure the compliance with the power quality standards, while in the multi-objective approaches are added other goals that are related with the improvement of the power quality indexes. In the presented approach, the problem of the reactive power compensation and the problem of the harmonic distortion compensation are considered a unified multi-objective problem in which is determined a set of passive filters that allows the obtaining of the maximum economic benefits as well as the maximum improvement of the power quality of the circuit. While several previous contributions solve the multi-objective problem by minimizing a single function composed of several sub-objectives, this work employs the non-dominated sorting genetic algorithm (NSGA-II) for the optimization of three independent objective functions. This algorithm obtains the Pareto front of the problem and allows the selection of the most effective solutions. The optimization method that presented in this work allows the selection by the algorithm of the filter type proper for compensation in a node of the circuit as well as the obtaining of their parameters. The set of possible filter configurations to place in one candidate node is defined by the user before the optimization is done. This is a distinctive characteristic of the presented approach that is tested with a practical example.

JANDECY CABRAL LEITE, IGNACIO PÉREZ ABRIL, MARIA EMÍLIA DE LIMA TOSTES, ROBERTO CÉLIO LIMÃO DE OLIVEIRA