Benemar Alencar de Souza

Multiobjective Optimization and Fuzzy Logic Applied to Planning of the Volt/Var Problem in Distributions Systems

This paper deals with integrated voltage and reactive power control (volt/var) for radial distribution feeders in planning issues, by means of the application of automatic voltage regulators (AVRs) banks and capacitors. A multiobjective genetic algorithm (SPEA2) improved using fuzzy logic is presented to solve the volt/var problem, since it is a combinatorial multiobjective optimization problem. The expert knowledge is taken into account via fuzzy logic in order to reduce the search space using voltage regulators in standard units. According to the multiobjective optimization fundamentals, an optimal solution ensemble is obtained, which concomitantly represents the solutions to both objectives, in such way that the operational restrictions of systems are satisfied. The algorithm is evaluated for a known 69-bus feeder in the literature of the subject. The obtained results demonstrate that the proposed method provides good concordance between the obtained solution and the Pareto front.

Optimal Placement of Distributed Generators Networks Using Evolutionary Programming

An algorithm is presented for the allocation and sizing of generators in radial distribution networks in order to maximize the reduction on the load supply costs. In addition, it is given the operational schedule for each installed generator for all feeder load levels. The evolutionary programming is used as the optimization technique. The applicability of the method was evaluated using a feeder with high losses index and the proposed allocation provided a considerable reduction on total costs.

Real-Time Detection of Transients Induced by High-Impedance Faults Based on the Boundary Wavelet Transform

The development of modern protection functions is a challenge in the emerging environment of smart grids because the current protection system technology still has several limitations, such as the reliable high-impedance fault (HIF) detection in multigrounded distribution networks, which poses a danger to the public when the protection system fails. This paper presents the wavelet coefficient energy with border distortions of a one-cycle sliding window designed for the real-time detection of transients induced by HIFs. By using the border distortions, the proposed wavelet-based methodology presents a reliable detection of transients generated by HIFs with no time delay and energy peaks scarcely affected by the choice of the mother wavelet. The signatures of different HIFs are presented in both time and wavelet domains. The performance of the proposed wavelet-based method was assessed with compact and long mother wavelets by using data from staged HIFs on an actual energized power system, taking into account different fault surfaces, as well as simulated HIFs. The proposed method presented a more reliable and accurate performance than other evaluated wavelet-based algorithms.

Mitigation of switching overvoltages in transmission lines via controlled switching

The goal of this work is to present a controlled switching strategy to reduce overvoltages due to transmission line closing and re-closing. Controlled closing and re-closing of transmission lines eliminates the need of pre-insertion resistors, reducing in this way the costs of transmission line circuit breakers. The switching strategy consists on finding a suitable circuit breaker making instant, i. e., the time in which the voltage across the circuit breaker contacts is zero and the time span between the closing instant of the first and the last pole is as small as possible, minimizing in this way, the effect of the electromagnetic coupling between transmission line phases. The method is based on a very simple zero crossing algorithm with constraints and is implemented in the Alternative Transients Program (ATP) using the MODELS language. Data from the North-Northeast Brazilian Power System Grid, planned to be in service by 2009, are used to produce a few case studies. Some line switching events are analyzed: line closing and re-closing taking into account trapped charges and shunt compensation effects. The controlled switching performance is compared to the pre-insertion resistorpsilas method. The simulations attest the efficiency of the method, limiting switching overvoltages to nearly 1.55 per unit for shunt compensated transmission lines. In addition, controlled switching provides an increase of power apparatus life time, improvement on power quality and possibly the elimination of impositions that makes prohibitive some switching operations.

Optimal capacitor allocation in electrical distribution systems based on typical load profiles

This paper presents a genetic algorithm for the solution of capacitor allocation and control problems in electrical distribution systems. From the typical load profiles the proposed technique finds optimal locations for fixed and switched shunt capacitors. The objective function variables are the energy loss at distribution feeders and the costs of the capacitor banks including installation and the voltage constraints. A simple iterative method is used to compute the power flow. The results obtained for the 282-branch test system is showed. The results indicate the efficiency of the proposed method.

Real-time classification of transmission line faults based on Maximal Overlap Discrete Wavelet Transform

The analysis of fault-induced transients in three-phase overhead transmission lines can provide extensive information about the fault type, detection, location, direction, and sustained time in satisfactory agreement with real application in protective relays. In this paper, the wavelet coefficient energies of the Maximal Overlap Discrete Wavelet Transform regarding the fault-induced transients were used for real-time fault classification in transmission lines. The performance of the real-time fault classification was evaluated by means of the Real Time Digital Simulator (RTDS) and good results were obtained. The performance of the method was also off-line evaluated with actual oscillographic records of a Brazilian Power System Utility and good results were also obtained.

A wavelet-based algorithm to analyze oscillographic data with single and multiple disturbances

This paper presents a discrete wavelet transform approach to recognize disturbances by the analysis of electromagnetic transients in transmission lines using oscillographic data. It is usual that different types of disturbances simultaneously exist in an oscillographic record supplied by a monitoring device in a transmission line. However, most of the existing methods treat the events as a single type. Thus, the performance of these methods might be limited and impracticable for real applications in power systems. In this framework, the proposed approach overcome this problem by the ability to analyze single and multiple disturbances in actual oscillographic records. Other distinctive feature of the proposed method is that it can recognize faults, some events related to power quality and normal maintenance operation in transmission lines. Sliding data windows of the detail spectral energy with length equivalent to one cycle of the fundamental power frequency are used to achieve wavelet-based information for detection and classification tasks. The performance of the method was evaluated for actual data and excellent results have been obtained.

Comparison between backpropagation and RPROP algorithms applied to fault classification in transmission lines

The computed results from implemented artificial intelligence algorithms, used to identify and classify faults in transmission lines, are discussed in this paper. The proposed methodology uses sampled data of voltage and current waveforms obtained from analog channels of digital fault recorders (DFRs) installed in the field to monitor transmission lines. The performances of resilient propagation (RPROP) and backpropagation algorithms, implemented in batch mode, are addressed for single, double and three-phase fault types.

Haar Wavelet-Based Method for Fast Fault Classification in Transmission Lines

The application of Haar wavelet transform for fault classification in transmission lines is proposed. The faulted phases identification is carried out by the analysis of the energy of the detail coefficients of the phase currents. In addition, by the analysis of the smooth coefficients of the neutral current, the ground faults can be distinguished from phase to phase ones. The algorithm was evaluated with EMTP-simulated faults. The obtained results reveal that the proposed method can accurately identify transmission line faults from a wide variety of power system operating conditions, within the first half-cycle after the beginning of the fault

Harmonic passive filter planning in radial distribution systems using microgenetic algorithms

The harmonic filter planning in distribution systems is presented as a combinatorial optimization problem, which is solved using microgenetic algorithms. The optimization of filter sizes and localizations on radial system with distributed linear and nonlinear loads has been considered. The minimization of voltage total harmonic distortion and active power losses has been used as an objective function. The harmonic levels of system are obtained by current injections method and the load flow is solved by the iterative method of power sum, which is suitable for the accuracy requirements of this type of study. It is shown that total voltage harmonic distortion and active power losses are minimized simultaneously. The simulation results for a 15 bus radial system show that the proposed method is efficient for solving the presented problem.