W.L.A. Neves

• Federal University of Campina Grande

A propósito de comparação de desempenho, três metaheurísticas são aplicadas para localização ótima de geradores distribuídos com o objetivo de minimizar as perdas totais de potência em um sistema de distribuição. Os critérios de esforço computacional, menor valor encontrado para a função objetivo e dispersão das soluções são as métricas utilizadas....

O despacho econômico de geradores tem como objetivo a minimização do custo de produção de energia, o que se dá por meio da melhor distribuição de carga entre as unidades geradoras disponíveis e da minimização das perdas na transmissão mediante algumas restrições. Vários métodos de otimização podem ser utilizados para a resolução de problemas de des...

Propõe-se realizar um estudo comparativo entre os métodos de detecção de faltas em linhas de transmissão de corrente contínua. Os métodos selecionados para o estudo comparativo pertencem ao grupo dos métodos baseados na teoria de ondas viajantes. Foram utilizados métodos que se baseiam na transformada wavelet discreta redundante e um método que se...

A new controlled switching method for purely series compensated transmission lines is proposed here. The main idea is based on the estimation of trapped charges using a recursive digital filter for correction of the secondary voltage of the capacitive voltage transformer (CVT). Several operating conditions of series capacitor banks (SCB) are taken...

Anti-aliasing filters are used in cascade with instrument transformers (IT) as part of protective relay data acquisition systems for providing input signals to fault locators. Due to IT and anti-aliasing filters transient responses, the fault locators input data may not be replicas of the power network voltage and current waveforms, and incorrect i...

A new method to numerically estimate the primary voltage waveform of coupling capacitor voltage transformers is presented. The outcome is a simple digital filter suitable for the frequency range from 10 to 60 Hz, enabling to recover the transformer primary voltage waveform from its secondary voltage waveform. Unlike the techniques reported in the l...

Most existing controlled switching techniques applied on transmission lines were developed for shunt reactor compensated lines. In this work, the effect of series compensation on the controlled switching of transmission lines is evaluated. The assessment is based on simulations on a 500 kV transmission line using ATP (Alternative Transients Program...

In this work Recursive Digital Filters (RDF) are used to correct the inaccuracies of the Capacitive Voltage Transformers (CVT) transient response to properly estimate the DC line voltage polarity and make controlled reclosing strategies applicable to uncompensated lines. The details of the filter design as well as the controlled reclosing strategie...

In this paper, a fault detector (FD) based on Park's transformation (TDQ) for digital power system relaying application is presented. It detects faults by identifying decaying DC components and phase unbalance in current signals and, therefore, it does not require high sampling rates. To improve the FD reliability, a self-adaptive threshold is used...

In this paper, the influence of the frequency response of coupling capacitor voltage transformers (CCVT) on traveling wave-based fault locators is analyzed, highlighting the benefits of the CCVT secondary voltage compensation when only voltage measurements are available. In order to do so, the frequency response of a well-known 230 kV CCVT model is...

This paper presents a new methodology for evaluation of digital filter techniques, whose main goal is to improve the insight about the advantages and disadvantages of the half- and one-cycle phasor estimation performance during transients. The voltage and current phasor estimation during transients affects the distance relay performance. With the a...

An approach for controlled reclosing of transmission lines with shunt reactive compensation is proposed here to reduce switching surge overvoltages. It consists of applying Karrenbauer's transformation as a matrix operator for the analysis of voltage signals required to control switching operations. The procedure also determines the arc extinction...

In this paper, a new two-terminal traveling-wave-based fault-location algorithm is proposed. Its main advantage over similar two-terminal algorithms lies in the fact it does not require the data from both line terminals to be synchronized. In order to do so, the algorithm is applied in real time, and a communication system is used, whose data-trans...

A novel algorithm for transient detection based on Park's transformation is proposed. It is very simple, self-adapts to electrical noise and phase imbalances, and is appropriate to be used in connection with traveling-wave fault location (TWFL) methods. The proposed technique is evaluated through Electromagnetic Transients Program simulations. A 23...

With the continued growth of power systems, it is possible that Transient Recovery Voltage (TRV) requirements lead circuit breakers to failure. In the medium voltage networks, studies have been made to evaluate the design and performance of a device which can reduce TRV peaks. The basic cell and its structure are presented and modeled in an Electro...

This paper presents a transient based approach to diagnose high impedance faults (HIFs) on smart distribution grids. The algorithm does not require the knowledge of the feeder parameters and uses the discrete wavelet transform (DWT) to monitor fault-induced transients at strategic points of the power system, taking advantages of available Smart Gri...

This paper presents a high impedance fault (HIF) location method in distribution systems. The estimation of the HIF location is carried out by using an artificial neural network (ANN). The ANN inputs are both three phase currents and its energy of the Wavelet Coefficients obtained during the HIF. The Wavelet mother function used was Daubechies 48....

A sampling frequency evaluation used in digital fault recorders for fault locations was implemented. A chained structure of artificial neural networks (ANN) was adopted to locate the faults. The ATP (Alternative Transient Program) software was used in the building of the database for training, testing and validation of the ANN, with different sampl...

Among various algorithms used to diagnose electrical disturbances, the transient detection is considered one of the most important functions. The objective of this paper is to present the Park's transformation (Tdq0) as a simple and efficient tool to detect transients in EHV transmission lines. The evaluation of such technique is performed with act...

This paper describes an adaptive fault location method for distribution and transmission networks based on the travelling waves' theory. The algorithm is self-adaptive to the unbalance of the electrical system and performs the transient detection through the Park's transformation application. The method is able to calculate automatically the fault...

This paper summarizes the main results about design and evaluation of a device to reduce Transient Recovery Voltage (TRV) magnitude in medium voltage switching equipments. Zinc Oxide (ZnO) devices are modeled in an Electromagnetic Transients Program (EMTP), being applied as an alternative to limit TRV peaks in circuit breakers and reclosers of 15 k...

This paper presents a novel phasor estimation algorithm, which combines the filtering characteristics of the maximal overlap discrete wavelet transform (MODWT) and the least error square (LES) algorithm. Time and frequency response of the designed filters are compared to the ones of traditional discrete Fourier transform (DFT) filters. The obtained...

In this work, an accurate coupling capacitor voltage transformer (CCVT) model for electromagnetic transient studies is presented. The model takes into account linear and nonlinear elements. A support routine was developed to compute the linear 230kV CCVT parameters (resistances, inductances and capacitances) from frequency response data. The magnet...

Digital protection schemes have been around for decades. Although there are many relay schemes reported in the literature, the protection engineer may gain more insight on how schemes work properly if well known cases are previously simulated with the EMTP to evaluate relay algorithms. Here, a very simple case study is presented in which the EMTP i...

In this work, measurements were carried out for a 230 kV coupling capacitor voltage transformer (CCVT) in a high voltage laboratory. In order to obtain the frequency response data to be used as input data to a routine developed to compute the CCVT parameters, frequency response measurements, for magnitude and phase, were carried out for the CCVT. T...

An algorithm for finding the steady state solution of systems containing linear, nonlinear elements and/or periodic switching power electronic devices is presented. The method is suitable to be used in connection with programs like the EMTP to determine the network initial conditions. Linear elements are represented as pure conductance matrices: fo...

This paper presents a novel method to estimate transformer saturation characteristics that extend to the 'deep' saturation region. The basic idea of the method is to use recorded inrush voltage and current waveforms to estimate the saturation characteristics. Accurate representation of a transformer's 'deep' saturation region is important for study...

This work presents a general and simple method to obtain a single multiphase equivalent pi-circuit, suitable for power flow studies that takes the coupling effects into account for any line transposition scheme. The resulting circuit, suitable for use in connection with multiphase power flow programs is obtained from node reduction of all cascaded...

This work presents a methodology for deriving a sparse network equivalent representation in the phase-domain based on time-domain fitting. The proposed formulation corresponds to a Norton Equivalent (admittance in parallel with a steady state current source) for three-phase system representations. The equivalent admittance is a polynomial matrix in...

In this work, laboratory tests of ferroresonance and circuit breaker switching were carried out for a 230 kV coupling capacitor voltage transformer (CCVT). The magnetic core and surge arrester nonlinear characteristics were taken into account in the model in order to improve the transient response to overvoltages. Digital simulations were performed...

A case study of fault classification in transmission lines using artificial neural networks (ANN) is presented. The database is built from current and voltage waveform samples obtained from fault simulations with the ATP. Utility companies usually have digital fault recorders with different sampling rates, so it is important to evaluate how good th...

Artificial neural networks have been used to develop software applied to fault identification and classification in transmission lines with satisfactory results. The input data to the neural network are the sampled values of voltage and current waveforms. The values proceed from the digital fault recorders, which monitor the transmission lines and...

This work presents a methodology for deriving a sparse two-phase transmission line representation in the phase-domain based on time-domain fitting. The resulting model is described by a polynomial matrix in the z-domain. The robustness of the representation, i.e. stability and passivity, is attained by imbedding a set of constraints in the fitting...

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...

Summary form only given. In this work, sensitivity studies were performed using EMTP-type programs in order to show how shunt conductance values affect the characteristic impedance and the propagation function of overhead transmission lines. Time domain simulations were carried out using modal and phase-domain line models. It is shown that, in some...

In this work, sensitivity studies were performed using electromagnetic transients program (EMTP)-type programs in order to show how shunt conductance values affect the characteristic impedance and the propagation function of overhead transmission lines. Time-domain simulations were carried out using modal and phase-domain line models. It is shown t...

When modeling overhead multiphase transmission lines in modal or phase domain, transformation matrices derived from eigenvalue/eigenvector theory are needed to obtain the characteristic admittance Y_c(ω) and the propagation function A(ω). Although these matrices are complex and frequency-dependent, electromagnetic transients programs (EMT...

In this work, a coupling capacitor voltage trans-former (CCVT) model to be used in connection with the EMTP (Electromagnetic Transients Program) is presented. A support routine was developed to compute the linear 230 kV CCVT parameters (resistances, inductances and capacitances) from the magnitude and phase of the CCVT voltage ratio measured in lab...

When modelling overhead multi-phase transmission lines in modal or phase-domain, transformation matrices derived from eigenvalue/eigenvector theory are needed to obtain the characteristic admittance Y_c(ω) and the propagation function A(ω). Although these matrices are complex and frequency-dependent, electromagnetic transients programs (E...

A method to obtain the coupling capacitor voltage transformer (CCVT) model parameters from frequency response curves is presented. Frequency response measurements of magnitude and phase, in the range from 10 Hz to 10 kHz, were carried out for a 230 kV CCVT at our high voltage laboratory and used as input data to a full Newton-type fitting routine t...

Resumo – Um estudo de sobretensões transitórias resultantes da energização e desenergização de bancos de capacitores de alta tensão é apresentado. Um programa tipo EMTP (Electromagnetic Transients Program) é utilizado para realizar as simulações digitais. Estudos de análise de sensibilidade foram realizados para avaliar o efeito da representação da...

An algorithm is described for the computation of the saturation characteristics of three-phase delta-connected transformers from measured V_rms-I_rms curves and no-load losses at rated frequency. For these transformers, positive sequence excitation tests are usually carried out with the delta connection closed. While triplen har...

Transformer models for distribution network harmonic studies based on rated parameters are presented. Results from simulations and measurements on power transformers are compared. Sensitivity studies are carried out to show how the total harmonic distortion of current and voltage behaves as a parameter of the transformer change. A field test involv...

An algorithm is presented for the computation of the saturation characteristics of transformer iron cores based on supplied conventional V _rms- I _rms curves and no-load losses at rated frequency. Laboratory measurements on a steel sample were carried out. It is shown that the iron core losses are a nonlinear function of the ap...

Resumo – Materiais Elétricos é uma disciplina de formação profissional essencial nos cursos de graduação em Engenharia Elétrica. Seu objetivo na UFPB é o entendimento das propriedades físicas de dielétricos, materiais magnéticos, materiais condutores e semicondutores, visando suas aplicações em Engenharia Elétrica. O conteúdo é muito abrangente e e...

Resumo – Neste trabalho é apresentado um modelo de transformador de potencial capacitivo (TPC) para ser utilizado em conjunto com o EMTP (Electromagnetic Transients Program). Uma rotina computacional foi desenvolvida para a obtenção dos parâmetros lineares do modelo a partir de medições, em laboratório, das curvas de amplitude e fase da relação de...

Circuit breakers can fail to interrupt three-phase fault currents when power systems have Transient Recovery Voltage (TRV) characteristics, which exceed their ratings. This paper is the outcome of a study for the reevaluation of three 15 kV breakers at the CHESF (Companhia Hidroelétrica do São Francisco) Angelim substation, located in the northeast...