Artigos em Revistas

Buildings' energy consumption has a great energetic and environmental impact worldwide. The architectural design has great potential to solve this problem because the building envelope exerts influence on the overall system performance, but this is a task that involves many objectives and constraints. In the last two decades, optimization studies applied to energy efficiency of buildings have helped specialists to choose the best design options. However, there is still a lack of optimization approaches applied to the design stage, which is the most influential stage for building energy efficiency over its entire life cycle. Therefore, this article presents a multi-objective optimization model to assist designers in the schematic building design, by means of the Pareto archived evolutionary strategies (PAES) algorithm with the EnergyPlus simulator coupled to evaluate the solutions. The search process is executed by a binary array where the array components evolve over the generations, together with the other building components. The methodology aims to find optimal solutions (OSs) with the lowest constructive cost associated with greater energy efficiency. In the case study, it was possible to simulate the process of using the optimization model and analyze the results in relation to: a standard building; energy consumption classification levels; passive design guidelines; usability and accuracy, proving that the tool serves as support in building design. The OSs reached an average of 50% energy savings over typical consumption, 50% reduction in CO2 operating emissions, and investment return less than 3 years in the four different weathers.

BRUNO RAMOS ZEMERO, MARIA EMÍLIA DE LIMA TOSTES, UBIRATAN HOLANDA BEZERRA, VITOR DOS SANTOS BATISTA, CARMINDA CÉLIA M. M. CARVALHO

This paper presents a procedure to estimate the impacts on voltage harmonic distortion at a point of interest due to multiple nonlinear loads in the electrical network. Despite artificial neural networks (ANN) being a widely used technique for the solution of a large amount and variety of issues in electric power systems, including harmonics modeling, its utilization to establish relationships among the harmonic voltage at a point of interest in the electric grid and the corresponding harmonic currents generated by nonlinear loads was not found in the literature, thus this innovative procedure is considered in this article. A simultaneous measurement campaign must be carried out in all nonlinear loads and at the point of interest for data acquisition to train and test the ANN model. A sensitivity analysis is proposed to establish the percent contribution of load currents on the observed voltage distortion, which constitutes an original definition presented in this paper. Initially, alternative transient program (ATP) simulations are used to calculate harmonic voltages at points of interest in an industrial test system due to nonlinear loads whose harmonic currents are known. The resulting impacts on voltage harmonic distortions obtained by the ATP simulations are taken as reference values to compare with those obtained by using the proposed procedure based on ANN. By comparing ATP results with those obtained by the ANN model, it is observed that the proposed methodology is able to classify correctly the impact degree of nonlinear load currents on voltage harmonic distortions at points of interest, as proposed in this paper.

ALLAN MANITO, UBIRATAN BEZERRA, MARIA TOSTES, EDSON MATOS, CARMINDA CARVALHO, THIAGO SOARES

Atualmente, são utilizados diversos processos para a geração de energia elétrica, como por exemplo: usinas hidrelétricas, termoelétricas, nucleares, eólicas, solares, entre outras. Também, neste atual cenário, podem-se ressaltar as usinas virtuais, pois estas são responsáveis por disponibilizar energia por meio de ações de eficiência energética. Portanto, este artigo apresenta o direcionamento a esta forma de geração de energia, a qual fica disponibilizada, por alguma ação de eficiência energética, para outro uso na sociedade. A usina virtual apresentada neste trabalho é baseada em pesquisas de ações de eficiências no sistema nacional de iluminação pública por meio do uso de lâmpadas com maior índice de eficiência e maior vida útil, o que permite a disponibilidade de energia a outros setores, reduzindo gastos quanto a investimentos e melhorando os níveis de tensões do sistema elétrico. Com isso, pode-se considerar como uma usina geradora de energia.

JORGE DE LIMA TOSTES, THIAGO OLIVEIRA COSTA, JOÃO VITOR DOS REIS ALVES, LAURO CORREA DOS SANTOS JUNIOR, PAULO DE LIMA TOSTES, CAROLINA GOMES, DIORGE DE SOUZA LIMA, WELLINGTON DA SILVA FONSECA, MARIA EMÍLIA DE LIMA TOSTES, UBIRATAN HOLANDA BEZERRA

This paper presents a new method for load pre-dispatch considering the technical conditions of engines in thermoelectric power plants by combining several maintenance and diagnostic techniques and using computational intelligence. A diagnosis of the technical conditions of the engines is performed using a lubricant analysis, vibration analysis, and thermography. With these data from a statistical analysis, it is possible to predict when an engine will fail and to consider this phenomenon in the load pre-dispatch. To increase the engine reliability and power supply, a maintenance management program is developed using MANAGEMENT tools, applying only 4 total productive maintenance pillars and combining them with predictive maintenance and diagnostics, thus reducing failures in plant equipment. Some results achieved after this implementation are as follows: a reduction in the annual cost of maintenance, a reduction in the corrective maintenance, an increase in the mean time between failures, and a decrease in the mean time to repair in all areas. In addition, the pre-dispatch ensures that the demanded power is met with a high degree of reliability and quality, and at minimal cost.

MILTON FONSECA, UBIRATAN HOLANDA BEZERRA, JORGE DE ALMEIDA BRITO, JANDECY CABRAL LEITE, MANOEL HENRIQUE REIS NASCIMENTO

The development of a preventive control methodology to increase the capacity of voltage sag recovery (Fault Ride Through Capability (FRTC)) of a doubly-fed induction generator (DFIG) connected in an electrical network is presented. This methodology, which is based on the decision trees (DT) technique, assists with monitoring and support for security and preventive control, ensuring that wind systems remain connected to the power system even after the occurrence of disturbances in the electric system. Based on offline studies, DT discovers inherent attributes of the FRTC scenario related to electrical system behavior and provides a quick prediction model for real-time applications. From the obtained results, it is possible to check that the DFIG is contributing to a system’s operation security from the availability of power dispatch and participation in the voltage control. It is also noted that the use of DT, in addition to classifying the system’s operational state with good accuracy, also significantly facilitates the operator´s task, by directing him to monitor the most critical variables of the monitored operation state for a given system’s topological configuration.

DIONE VIEIRA, MARCUS NUNES, UBIRATAN BEZERRA

This paper presents the definition of Equivalent Operational Impedance, which is a new concept established for distribution grids analysis with potential application in calculating technical and non-technical losses in Medium Voltage and Low Voltage distribution feeders. Considering a specified distribution network topology, the main feature of Equivalent Operational Impedance for this grid is that it is fairly constant even under varying load scenarios, once these scenarios present similar voltage solutions. This way, a load flow solution is used to obtain the Equivalent Operational Impedance of a specified grid topology and then the calculated Equivalent Operational Impedance can be used to obtain total technical and nontechnical losses for other load scenarios using only the calculated Equivalent Operational Impedance and the respective measurement of injected current at the Medium Voltage or Low Voltage distribution feeder. The use of this methodology by electric utilities allows the calculation of technical losses more accurately, as well as the inclusion of non-technical losses in the distribution networks operation planning. Results using the IEEE 13-bus test system are presented to demonstrate the effectiveness of the proposed methodology.

U. H. BEZERRA, T. M. SOARES, J. P. A. VIEIRA, M. E. L. TOSTES, A. R. R. MANITO, J. C. H. PAYE

The public buildings analysis with emphasis on energy efficiency policies, as recommended in the Brazilian Labeling Program (PBE-EDIFICA), represents an excellent opportunity for power managers to apply energy conservation measures, reducing the operating costs of organizations and to adequate the efficient use of electric power. Because of the Technical Quality Regulation for the Efficiency Level of Commercial Buildings, Services and Public Buildings (RTQ-C), it is possible to evaluate the construction and program actions in order to achieve the highest levels of power efficiency, which is the focus of the developed paper. In other words, it means the evaluation of the lighting and air conditioning systems of the Val de Cães Naval Base Command Building and the propose of retrofitting and energy efficiency actions to reach achieve PBE classification level A.

ANTONIO FELIX T. NEGRÃO, MARIA EMÍLIA DE LIMA TOSTES

The increasing use of equipment that employs electronic converters with high switching frequencies, in addition to the equipment that performs reactive compensation, has led to the appearance of harmonic components of orders higher than those normally observed in electrical systems. This phenomenon, called supraharmonics, is not yet fully understood and several questions related to its characteristics are being raised by several research groups. In this context, this paper presents a case study of the measurement of supraharmonics in a commercial installation of the banking sector and shows the analysis developed using Wavelet Packet Transform for the extraction of information that can efficiently characterize the phenomenon.

CARLOS EDUARDO MOREIRA RODRIGUES, MARIA EMÍLIA DE LIMA TOSTES

Economic‐emission load dispatch optimization problem is an essential task in power plants with internal combustion engines. In power plants, in addition to electricity, a lot of air pollution by exhaust gases is generated. There are many international standards that establish the permissible limits of different substances but still have not developed an expression to evaluate the environmental impact caused by all components of the exhaust gases as a whole. A new method to evaluate this impact is developed in this paper. The developed mathematical expression was called “emission index.” To get a better idea of the environmental impact of each type of engine, the “specific emission index”, which is the emission index divided by the power delivered by the engine. This paper also presents a mathematical model for a multiobjective optimization of economic‐emission load dispatch using nondominated sorting genetic algorithm II.

NADIME MUSTAFA MORAES, UBIRATAN HOLANDA BEZERRA, JORGE LAUREANO MOYA RODRÍGUEZ, JANDECY CABRAL LEITE, MANOEL HENRIQUE REIS NASCIMENTO

The objective of this paper is to investigate the behavior of electromagnetic forces during the occurrence of faults inside transformers as result of transients in the electrical systems. The methodology is based on the modeling of a single-phase 50-MVA transformer subjected to inrush currents through finite-element method. In this perspective, the values of inrush currents, obtained by the alternative transient program software, 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 forces components are distributed along the energized windings for observing the loads behavior in high-voltage windings. This paper will thus present investigations of electromagnetic forces, structural deformation, stresses, and safety factor on transformer's winding when subjected to inrush current.

WELLINGTON SILVA FONSECA, DIORGE SOUZA LIMA, ADRY KLEBER FERREIRA LIMA, MARCUS VINÍCIUS ALVES NUNES, UBIRATAN HOLANDA BEZERRA, NEWTON SURE SOEIRO