Artigos em Revistas

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

Industrial production has evolved significantly over the last decade. For this reason, it is necessary to obtain mathematical and computational tools that enable power systems engineers to make decisions that reduce harmonic distortions in accordance with international standards. This paper presents a total harmonic distortion (THD) assessment based on full knowledge discovery in databases (KDD) using power quality (PQ) standards and computational intelligence tools. The materials and methods of THD assessment consist of load and layout analysis; choice and installation of PQ analyzers; and the application of the full KDD process, including collection, selection, cleaning, integration, transformation and reduction, mining, interpretation, and evaluation of the data. This research methodology was used in an electrical and electronic industry; the results obtained have characteristics that can be used as a reference for other types of analyses. The results indicate that these methods can be applied to several industrial applications such as: 1) the description of the complete KDD process for THD assessment of the point of common coupling; 2) simultaneous collection using five PQ analyzers at several points in the electrical network; and (3) the use of a decision tree classifier.

EDSON FARIAS DE OLIVEIRA, MARIA EMÍLIA DE LIMA TOSTES, CARLOS ALBERTO OLIVEIRA DE FREITAS, JANDECY CABRAL LEITE

This paper proposes a new methodology based on the use of Resonance Index (RI) analysis as a posteriori decision-making procedure to check solutions of the optimization algorithm NSGA-II against resonance, when applied to the capacitor banks placement problem in radial distribution systems. Most of existing methodologies approach harmonic resonance in the referred problem through the inclusion of constraints in the optimization procedure with respect to the harmonic distortion indexes THD and IHD. However, monitoring only these two parameters is not sufficient to identify specific problems on capacitor banks due to harmonic resonance. To demonstrate this point, a RI analysis using the resonant chart was performed considering a 34-bus radial system. Also, the proposed a posteriori analysis is compared with the one that includes directly RI as a constraint in the optimization procedure, demonstrating that the proposed approach has a better performance with respect to computational time.

JOSE H.D. ONAKA, UBIRATAN H. BEZERRA, MARIA E.L. TOSTES, ÁTHILA S. LIMA

Partial discharge (PD) monitoring is widely used in rotating machines to evaluate the condition of stator winding insulation, but its practice on a large scale requires the development of intelligent systems that automatically process these measurement data. In this paper, it is proposed a methodology of automatic PD classification in hydro-generator stator windings using neural networks. The database is formed from online PD measurements in hydro-generators in a real setting. Noise filtering techniques are applied to these data. Then, based on the concept of image projection, novel features are extracted from the filtered samples. These features are used as inputs for training several neural networks. The best performance network, obtained using statistical procedures, presents a recognition rate of 98%.

RODRIGO M. S. DE OLIVEIRA, RAMON C. F. ARAÚJO, FABRÍCIO J. B. BARROS, ADRIANO PARANHOS SEGUNDO, RONALDO F. ZAMPOLO, WELLINGTON FONSECA, VICTOR DMITRIEV, FERNANDO S. BRASIL