Mariana Resener

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.

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.

Extended impedance-based fault location formulation for unbalanced underground distribution systems

Underground distribution systems are commonly exposed to permanent faults. Due to specific construction characteristics, visual inspection for fault location cannot be performed. To overcome this limitation, accurate fault location techniques must be applied. In this paper, an extended impedance-based fault location formulation for unbalanced underground distribution systems is described considering single line-to-ground faults. The technique uses only local voltages and currents as input data. An iterative algorithm for cable capacitive current compensation in the fault location formulation is proposed. The formulation focuses an easily practical implementation and is based on typical available systempsilas data, as lines impedance and admittance matrices, and also system loads. Test simulations on a real data underground distribution system demonstrate the proposed extensions improvements. The algorithm performance presents negligible fault resistance, distance, and inception angle variation effects.

Computational model for the analysis of distributed generation in systems including smart grids

This work presents a simplified computational model for the analysis and the optimization of distribution networks considering the presence of smart grids. The determination of bus voltages and branch currents is based on a linear approximation, which allows to evaluate the impact on the network resulting from the connection of different distributed generation sources (DG). One of the main advantages of the proposed model is the convergence for any operation condition. Furthermore, it is possible to apply the model to problems concerning the operation and expansion of smarts grids. Finally, to test and validate the model, it was applied to an existing distribution network composed of 135 buses and with distributed generation. The main results are presented and discussed.

Impacts of excitation control modes of distributed generators on distribution systems transient stability: A case study

This paper focuses on analyzing the impact of the excitation control mode of synchronous generators when operating connected to power distribution systems, through the study of a system derived from a real distribution feeder from a Brazilian utility. The number of connections of distributed generation has increased over the last years, bringing new technical issues when planning and operating a distribution system. In Brazil, the major part of the distributed resources applications is composed by synchronous generators directly connected to the distribution system. The objective of this paper is to contribute to the stability analysis of these systems, as there is still no consensus among the electric energy companies about the best control mode of synchronous generators in the context of distributed generation.