Rodrigo Salim

Extended Fault-Location Formulation for Power Distribution Systems

In this paper, an extended impedance-based fault-location formulation for generalized distribution systems is presented. The majority of distribution feeders are characterized by having several laterals, nonsymmetrical lines, highly unbalanced operation, and time-varying loads. These characteristics compromise traditional fault-location methods performance. The proposed method uses only local voltages and currents as input data. The current load profile is obtained through these measurements. The formulation considers load variation effects and different fault types. Results are obtained from numerical simulations by using a real distribution system from the Electrical Energy Distribution State Company of Rio Grande do Sul (CEEE-D), Southern Brazil. Comparative results show the technique robustness with respect to fault type and traditional fault-location problems, such as fault distance, resistance, inception angle, and load variation. The formulation was implemented as embedded software and is currently used at CEEE-Ds distribution operation center.

Hybrid Fault Diagnosis Scheme Implementation for Power Distribution Systems Automation

Power distribution automation and control are important tools in the current restructured electricity markets. Unfortunately, due to its stochastic nature, distribution systems faults are hardly avoidable. This paper proposes a novel fault diagnosis scheme for power distribution systems, composed by three different processes: fault detection and classification, fault location, and fault section determination. The fault detection and classification technique is wavelet based. The fault-location technique is impedance based and uses local voltage and current fundamental phasors. The fault section determination method is artificial neural network based and uses the local current and voltage signals to estimate the faulted section. The proposed hybrid scheme was validated through Alternate Transient Program/Electromagnetic Transients Program simulations and was implemented as embedded software. It is currently used as a fault diagnosis tool in a Southern Brazilian power distribution company.

Ground Distance Relaying With Fault-Resistance Compensation for Unbalanced Systems

Fault resistance is a critical variable in distance relaying. If not considered due to underreaching phenomenon, it may cause the misoperation of ground distance relays for internal faults. Still, as a consequence of the overreaching phenomenon, the unbalanced nature of loads and asymmetry of lines can affect the distance protection operation efficiency. Mainly due to these aspects, there is low precision in protection zone limits of ground distance relays. In this paper, a new algorithm is proposed to increase the precision of these limits, improving efficiency in the distance protection process. The proposed method is based in phase coordinates and uses a fault resistance estimate to develop the trip decision procedure. The results show that the algorithm is suitable for online applications, and that it has an independent performance from the fault resistance magnitude, the fault location, and the line asymmetry.

Fault Location in Unbalanced DG Systems using the Positive Sequence Apparent Impedance

The fault location techniques for power distribution systems (PDS) in use nowadays assume that the system has a radial power flow. Since new technologies in development, such as the distributed generation (DG), change this characteristic, it is necessary to adjust the already existing methods for fault location, since they show to be inefficient. Moreover, the unbalance between phases due to different loading at laterals is another issue that interferes in the fault location methodologies. In this paper, it is presented a new fault location method based on positive sequence apparent impedance. Computational simulations were made and the method was tested in two systems and compared with other existing fault location techniques in order to validate it. The basic characteristics of the method, the new algorithm and a variety of case studies are presented in the paper in order to illustrate its efficiency in unbalanced distribution systems with DG

A Model-Based Approach for Small-Signal Stability Assessment of Unbalanced Power Systems

In this paper, a modeling technique for small-signal stability assessment of unbalanced power systems is presented. Since power distribution systems are inherently unbalanced, due to its lines and loads characteristics, and the penetration of distributed generation into these systems is increasing nowadays, such a tool is needed in order to ensure a secure and reliable operation of these systems. The main contribution of this paper is the development of a phasor-based model for the study of dynamic phenomena in unbalanced power systems. Using an assumption on the net torque of the generator, it is possible to precisely define an equilibrium point for the phasor model of the system, thus enabling its linearization around this point, and, consequently, its eigenvalue/eigenvector analysis for small-signal stability assessment. The modeling technique presented here was compared to the dynamic behavior observed in ATP simulations and the results show that, for the generator and controller models used, the proposed modeling approach is adequate and yields reliable and precise results.

A Novel High Impedance Fault Location for Distribution Systems Considering Distributed Generation

In this paper it is proposed a novel high impedance fault detection and location scheme for power distribution feeders with distributed generation. The proposed scheme is capable to obtain precise fault location estimations for both linear low impedance and non-linear high impedance faults. This last class of faults represents an important subject for the power distribution utilities because they can be difficult to detect and locate by the protection devices commonly used in todays electric distribution systems. The proposed scheme uses real time data which are processed in a way that the fault detection and location can be estimated by a set of characteristics extracted from the voltage and current signals measured at the substation. This characteristic set is classified by an artificial neural network based scheme whose output results in a fault detection and location. The scheme is based on the calculation of the symmetrical components of the current signal harmonics at the relay point. Other traditional fault detection and location methodologies were also implemented, making possible to obtain comparative results. The scheme was applied in two simulated feeders. The results of this work shows, that the proposed methodology is worthy of continued research objecting real time applications

Analysis of the small signal dynamic performance of synchronous generators under unbalanced operating conditions

This work presents a thorough study about the effects of load unbalance in the dynamics of a power system that can be modeled as a single machine (synchronous generator) connected to an infinite bus. The main motivation for such a study is to better understand the behavior of power distribution systems when distributed synchronous generators with such typical topology are present, which is common in several countries around the world, including Brazil. The focus of this paper is the dynamic behavior of the system after small perturbations, as characterized by the system eigenvalues, focusing on the electromechanical oscillation frequencies and damping ratios, as affected by the load unbalance. In this work, other typical characteristics are also analyzed, such as the AVR and PSS gains, when well- or poorly-tuned. All the analysis is done through the estimation of these eigenvalues via a rotational invariant technique (ESPRIT method) from nonlinear simulations performed on ATP.

Unbalanced Underground Distribution Systems Fault Detection and Section Estimation

This paper presents a novel fault detection and section estimation method for unbalanced underground distribution systems (UDS). The method proposed is based on artificial neural networks (ANNs) and wavelet transforms (WTs). The majority of UDS are characterized by having several single/double phase laterals and non-symmetrical lines. Also, Digital Fourier Transforms (DFT), used in the majority of traditional protection relays, supplies a low level of robustness to the fault diagnosis process due to its inversely proportional time-frequency characteristic. These characteristics compromise the traditional fault diagnosis methods performance. ANNs are capable of learning and generalizing, whereas WTs are robust tools capable of evaluating a signals frequency range that can characterize the fault phenomenon. This paper describes the proposed diagnosis method and discusses the results obtained from simulated implementation. The obtained results demonstrate the capability and robustness of the technique indicating its potential for on-line applications.

Diagnostic performance of 3D TSE MRI versus 2D TSE MRI of the knee at 1.5 T, with prompt arthroscopic correlation, in the detection of meniscal and cruciate ligament tears.

Objective To compare the diagnostic performance of the three-dimensional turbo spin-echo (3D TSE) magnetic resonance imaging (MRI) technique with the performance of the standard two-dimensional turbo spin-echo (2D TSE) protocol at 1.5 T, in the detection of meniscal and ligament tears. Materials and Methods Thirty-eight patients were imaged twice, first with a standard multiplanar 2D TSE MR technique, and then with a 3D TSE technique, both in the same 1.5 T MRI scanner. The patients underwent knee arthroscopy within the first three days after the MRI. Using arthroscopy as the reference standard, we determined the diagnostic performance and agreement. Results For detecting anterior cruciate ligament tears, the 3D TSE and routine 2D TSE techniques showed similar values for sensitivity (93% and 93%, respectively) and specificity (80% and 85%, respectively). For detecting medial meniscal tears, the two techniques also had similar sensitivity (85% and 83%, respectively) and specificity (68% and 71%, respectively). In addition, for detecting lateral meniscal tears, the two techniques had similar sensitivity (58% and 54%, respectively) and specificity (82% and 92%, respectively). There was a substantial to almost perfect intraobserver and interobserver agreement when comparing the readings for both techniques. Conclusion The 3D TSE technique has a diagnostic performance similar to that of the routine 2D TSE protocol for detecting meniscal and anterior cruciate ligament tears at 1.5 T, with the advantage of faster acquisition.

Analyzing the effect of the type of terminal voltage feedback on the small signal dynamic performance of synchronous generators

This work presents a thorough study about the effects of the type of terminal voltage feedback in the dynamics of a power system that can be modeled as a single machine (synchronous generator) connected to an infinite bus. As is presented in this paper, the type of terminal voltage feedback employed directly affects the dynamic performance of power systems when they are subjected to load unbalance, and hence, if the terminal voltage is not correctly defined, the behavior of the system can be completely different than the one predicted by the linear or nonlinear analysis. The main motivation for such a study is to better understand the behavior of power distribution systems with typical topology when distributed synchronous generators are present, which is common in several countries around the world. The focus of this paper is the dynamic behavior of the system after small perturbations, as characterized by the system eigenvalues representing the electromechanical oscillations. All the analyses are carried out through the estimation of these eigenvalues via a rotational invariant technique (ESPRIT method) from nonlinear simulations performed using the Alternative Transients Program.