Artigos em Revistas

The efficient protection of electric power distribution networks against lightning discharges is a crucial problem for distribution electric utilities. To solve this problem, the great challenge is to find a solution for the installation of surge arresters at specific points in the electrical grid and in a sufficient quantity that can ensure an adequate level of equipment protection and be within the utility’s budget. As a solution to this problem of using ATP (Alternative Transient Program), this paper presents a methodology for optimized surge arrester allocation based on genetic algorithm (GA), with a fitness function that maximizes the number of protected equipment according to the financial availability for investment in surge arresters. As ATP may demand too much processing time when running large distribution grids, an innovative procedure is implemented to obtain an overvoltage severity description of the grid and select only the most critical electric nodes for the incidence of lightning discharges, in the GA allocation procedure. The results obtained for the IEEE-123 bus electric feeder indicate a great reduction of flashover occurrence, thus increasing the equipment protection level

GABRIEL VIANNA SOARES ROCHA, RAPHAEL PABLO DE SOUZA BARRADAS, JOÃO RODRIGO SILVA MUNIZ, UBIRATAN HOLANDA BEZERRA, IGOR MEIRELES DE ARAÚJO, DANIEL DE SOUZA AVELAR DA COSTA, ABNER CARDOSO DA SILVA, MARCUS VINÍCIUS ALVES NUNES, JUCILENO SILVA E SILVA

The efficient protection of electric power distribution networks against lightning discharges is a crucial problem for distribution electric utilities. To solve this problem, the great challenge is to find a solution for the installation of surge arresters at specific points in the electrical grid and in a sufficient quantity that can ensure an adequate level of equipment protection and be within the utility’s budget. As a solution to this problem of using ATP (Alternative Transient Program), this paper presents a methodology for optimized surge arrester allocation based on genetic algorithm (GA), with a fitness function that maximizes the number of protected equipment according to the financial availability for investment in surge arresters. As ATP may demand too much processing time when running large distribution grids, an innovative procedure is implemented to obtain an overvoltage severity description of the grid and select only the most critical electric nodes for the incidence of lightning discharges, in the GA allocation procedure. The results obtained for the IEEE-123 bus electric feeder indicate a great reduction of flashover occurrence, thus increasing the equipment protection level.

GABRIEL VIANNA SOARES ROCHA, RAPHAEL PABLO DE SOUZA BARRADAS, JOÃO RODRIGO SILVA MUNIZ, UBIRATAN HOLANDA BEZERRA, IGOR MEIRELES DE ARAÚJO, DANIEL DE SOUZA AVELAR DA COSTA, ABNER CARDOSO DA SILVA, MARCUS VINÍCIUS ALVES NUNES, JUCILENO SILVA E SILVA

Computer Numerical Control (CNC) is a technology made up of several blocks. Among these, lies the Trajectory Planning block, responsible for reference profile generation that are fed to position control loops. The need for Trajectory Planning arises from the mechanical constraints inherent to every plant to which CNC technology is applied. The machine’s operational limits myst be respected, in order to avoid several issues, such as: loss of precision, early wear of machine’s parts and excessive vibration. This paper proposes a novel smooth real-time trajectory generation setup based on an embedded system platform. A real-time snap and jerk bounded control algorithm is proposed, to achieve continuous and smooth feed motion in traditional Numeric Control code file, dealing both with straight lines and arcs. A local motion blending algorithm, applicable to the proposed method, is also presented. The developed algorithm was deployed to a BeagleBone Black, an embedded System-on-Chip, single board computer and tested in a prototype router machine. A comparison between the proposed method against the seven segments and trapezoidal acceleration methods is presented, both in terms of performance and of real-time computing viability. Simulation and Experimental results demonstrate the effectiveness of the proposed method to generate velocity, acceleration, jerk and snap bounded three dimensional trajectories, reducing the RMS error in up to 8.2% and 22.38% when compared to the Seven Segments and to Trapezoidal Acceleration methods, respectively. Assessing the error area on straight angles, the proposed method produced error areas 24% and 80% smaller when compared to the Seven Segments and to Trapezoidal Acceleration methods, respectively.

PAULO AUGUSTO SHERRING DA ROCHA, WERBESTON DOUGLAS DE OLIVEIRA, MARIA EMÍLIA DE LIMA TOSTES

This study presents a method to place, size, coordinate and adequate protection systems in distribution networks (DNs) with directly-coupled distributed generation (DG). DG penetration increase in DNs is beneficial to the operation of these grids. However, since the majority of DN is already consolidated, with protective devices sized for certain current levels and directionality, adding DG to these systems may cause issues. This study introduces a method to determine protective devices placement, their coordination and sizing, depending on DG location. Direct-coupled DG is considered since DG connected to DNs through power electronics limit the fault current to the network. Firstly, recloser allocation is treated in a multiobjective approach, reducing reliability indices. To solve this problem, particle swarm optimization is applied. Fuse cutouts allocation is determined by a set of rules, developed considering feeder particularities. After, DG is considered and its effects on the protection coordination are evaluated. To adapt DN to receive DG, fault current limiters are placed to avoid recloser – fuse miscoordination. Finally, recloser operation is analyzed to determine the operational philosophy to avoid misoperation in the presence of DG. Graphical and numerical results are presented for test systems to show the functionality and performance of the proposed method.

FERNANDO GUILHERME KAEHLER GUARDA, GHENDY CARDOSO JR., UBIRATAN HOLANDA BEZERRA, JOAO PAULO ABREU VIEIRA

This paper proposes the development of a three-phase state estimation algorithm, which ensures complete observability for the electric network and a low investment cost for application in typical electric power distribution systems, which usually exhibit low levels of supervision facilities and measurement redundancy. Using the customers´ energy bills to calculate average demands, a three-phase load flow algorithm is run to generate pseudo-measurements of voltage magnitudes, active and reactive power injections, as well as current injections which are used to ensure the electrical network is full-observable, even with measurements available at only one point, the substation-feeder coupling point. The estimation process begins with a load flow solution for the customers´ average demand and uses an adjustment mechanism to track the real-time operating state to calculate the pseudo-measurements successively. Besides estimating the real-time operation state the proposed methodology also generates nontechnical losses estimation for each operation state. The effectiveness of the state estimation procedure is demonstrated by simulation results obtained for the IEEE 13-bus test network and for a real urban feeder.

THIAGO MOTA SOARES, UBIRATAN HOLANDA BEZERRA, MARIA EMÍLIA DE LIMA TOSTES

This study presents an approach to calculate average technical losses (TLoss) and non-technical losses (NTLoss) in distribution grids using an equivalent operational impedance (EOI) calculated from a load flow solution for the transformers’ average loads, obtained from customers’ electric bills. If transformers are supervised, i.e. have available active and reactive power injections measurements or estimates from a state estimator program, the transformers’ average technical and non-technical losses can be calculated by running a load flow for the grid supplied by the transformer and using the definition of EOI presented in this study. For unsupervised transformers, i.e. no measurements or estimates are available, pseudo measurements of average active and reactive power injections can be obtained by a procedure that uses active and reactive power measurements at the feeder substation. The use of this methodology by electric utilities allows the calculation of technical and non-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 and an urban real distribution grid are presented to demonstrate the effectiveness of the proposed methodology.

ALLAN R.A. MANITO, ALLAN R.A. MANITO, UBIRATAN H. BEZERRA,, THIAGO M. SOARES, JOÃO P.A. VIEIRA, MARCUS V.A. NUNES, MARIA E.L. TOSTES, RAFAEL C. DE OLIVEIRA

Computer Numerical Control is a technology made up of several blocks. The single most important of these blocks is the Control Unit, responsible for performing security checks, user interface, coordinating the motion, file handling and coordinating several peripherals usually used on CNC applications. Over the course of last years, embedded systems presented a huge improvement in processing power as well as easiness of use and application, given the advances in the open source and open hardware development community. The present paper presents the development process of a high-end embedded system based CNC controller, capable of operating including motion constraints up to the fourth order time derivative of position for each of the individual Cartesian axis.

PAULO ROCHA, EMÍLIA TOSTES

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