Roberto Chouhy Leborgne

Voltage Sag Source Location Methods Performance Under Symmetrical and Asymmetrical Fault Conditions

When several utilities operate interconnected power systems, a voltage sag generated in the grid of one utility may affect the loads connected to other utilities. From this point of view, it has become a crucial issue to identify the location of the source of a voltage sag. This paper describes and compares the methods for voltage sag source location. The methods are applied to locate the source of voltage sags considering symmetrical and asymmetrical faults. Radial and meshed areas are also analyzed. The results show that the available methods are not totally reliable and more research is needed to extend the location methods to meshed systems

Stochastic assessment of voltage dips (Sags): The method of fault positions versus a Monte Carlo simulation approach

Two methods for stochastic assessment of voltage dips (sags) are compared. The method of fault positions and a Monte Carlo simulation approach are utilized to stochastically describe the expected dip performance at some sites of a large transmission system. Fault scenarios are created and pseudo measurements are obtained in order to compare stochastic assessment with simulated measurements. It is shown that the method of fault positions cannot be used to predict the performance of a particular year, unless correcting factors are used to adjust the assessment. A Monte Carlo simulation approach is suggested to better describe the expected dip performance. Whereas the method of fault positions gives long- term mean values, the Monte Carlo approach provides the complete frequency distribution function of selected sag indices (SARFI-X).

Voltage sag source location at grid interconnections: a case study in the Zambian system

This paper describes a case study to find the location of the voltage sag source at a petroleum industrial facility where sags are causing undesired trips on critical loads. The network that supplies this industrial facility is operated by basically two transmission and distribution utilities. Therefore, finding the location of the disturbance source is a first step in mitigation and decisive in allocating responsibilities.

Differences in Voltage Dip Exposure Depending Upon Phase-to-Phase and Phase-to-Neutral Monitoring Connections

Voltage dip indices are estimated for a set of simulated and measured events. The simulated dips are obtained applying the method of fault positions on a large transmission network and the measured dips come from a one-year survey. The indices estimated to compare phase-to-phase and phase-to-neutral dips are SARFI-90, SARFI-70, SARFI-ITIC, and average voltage dip amplitude. Furthermore, the results are analyzed in terms of the cumulative distribution frequency of the voltage dip amplitude. The comparison of phase-to-phase and phase-to-neutral indices indicates that, at transmission level, phase-to-neutral dips are more frequent and more severe than phase-to-phase ones. However, these differences are reduced at the load connection level, where the phase and line voltages show similar performance for the monitored system

Analysis of voltage sag phasor dynamic

Voltage sag is one of the most expensive power- quality disturbances as a consequence of the huge increment of sensitive loads. Available standards recommend the characterisation of the voltage sag by means of two parameters: magnitude and duration. However, this approach fails to fully describe the vulnerability of three-phase loads because it does not consider the tolerance to phase-angle jumps and the response to the dynamic behaviour of the voltage phasors during the sag. A voltage sag characterisation based on the dynamic behaviour of the phasor is introduced. The fundamental voltage obtained by fast Fourier Transformation applied to the instantaneous voltage is employed to represent the voltage phasor. The dynamic behaviour of the phasor is studied by analysing the fundamental voltage plotted as a function of time. The voltage sag magnitude is estimated by the rms value of the fundamental voltage. The voltage-sag-phasor locus is represented in complex coordinates. Finally, voltage phasor snapshots are shown in multiple charts where the three-phase phasors are represented in different instants during the event. The most severe phasors are headlined. This methodology is applied to voltage sag measurements obtained from a power-quality monitoring-program at a Brazilian transmission grid and from a Swedish distribution grid.

Sensitivity analysis of stochastic assessment of voltage dips

This paper addresses the effect of different uncertainties on the stochastic assessment of voltage dip indices. This task is undertaken by introducing site and system indices and performing sensitivity analysis with regard to some uncertainties. Fault rate, fault-type distribution and fault location uncertainties are addressed in this work. Using a reduced model of the Brazilian power system, site and system indices are calculated for a selected number of buses. Relative variations on system and site indices are calculated in relation to a reference case. Results are presented in tables, graphs and figures.

Voltage Sag Source Location: Case Study in Zambian Grid

This paper describes a case study to find the location of the voltage sag source at a petroleum industry where sags are causing undesired trips on critical loads. The network that supplies this industry is operated by basically two transmission and distribution utilities. Therefore, finding the location of the disturbance source is a first step in mitigation and decisive in allocating responsibilities.

Methodology for Calculation and Management for Indicators of Power Quality Energy

This paper presents a methodology for calculus and manages of the indicators of power quality through the identification and quantification of electromagnetic disturbances. This methodology uses techniques of digital signal processing, enabling the detection of events and quantification of steady state disturbances. The main disturbance of the quality standards set by the ANEEL and ONS are quantified by a robust algorithm. The software has been tested using waveforms with known disturbances generated in the MatLab program to its validation. Were then analyzed waveforms obtained from field measurements to evaluate the strength of the algorithm against real disturbances.

Optimal Location of Substation Metallic Fences to Protect the Nearby Public Walking Through Numerical Evaluation

This paper shows one way to calculate grounding potentials in high voltage substation fences coupled by soil to a grounding grid in a two-layer soil. This problem is of special concern due to the presence of passers-by near metallic fences, whose potentials usually have not been evaluated, not directly connected to the grounding grid. In this context, the paper presents a general analytical formulation aiming to estimate the possible risk to human beings close to the substation. In order to do that the generated potentials originating from a short-circuit in the electric power system are calculated considering the coupling by soil between the main grounding system and the adjacent electrode (the metallic fence). Finally, the proposed methodology is tested and validated using different grounding topologies.

Harmonic Distortion in the Auxiliary Services of a Thermoelectric Power Plant

In this work the harmonic distortion in the auxiliary services of a coal fired power plant are assessed by simulation and measurements. The measurements are useful to validate the simulation method. Therefore, new operational conditions can be assessed, such as filters connection. The simulation of the electrical system is performed in the time domain and the software utilized is the ATP Draw. The results show the most critical and sensitive points for non-linear loads present in industrial plant.