Gabriel Olguin

An optimal monitoring program for obtaining Voltage sag system indexes

This paper presents a meter placement method for voltage sags monitoring in large transmission systems. An integer programming-based modeling is proposed for choosing the locations of power quality meters. A branch-and-bound-type algorithm is used to solve the optimization problem. A large transmission network is used to validate the method. Stochastic assessment of voltage sags is applied to the test network to obtain simulated monitoring results. Voltage sags system indexes are calculated from monitoring programs designed according to the optimization method. Comparisons with the system indexes obtained from a full monitoring program show the applicability of the method.

Identification of Critical Spans for Monitoring Systems in Dynamic Thermal Rating

Dynamic thermal rating (DTR) has been seen as an important tool for planning and operation of power systems, and recently, for smart-grid applications. To implement an effective DTR system, it is necessary to install monitoring stations along the studied lines, with a tradeoff between accurate estimations and equipment investments. In this paper, a novel heuristic is developed for identifying the number and locations of critical monitoring spans for the implementation of DTR. The heuristic is based on the use of historical-simulated weather data, obtained from a Mesoscale Weather Model, and the statistical analysis of the thermal capacities computed in each span along the line. The heuristic is applied to a line that is 325 km long in North Chile. Optimal monitoring sets, including the number and location of required monitoring stations, are determined for different confidence levels in all line segments. The results are compared to an equidistant monitoring strategy. The proposed heuristic shows robustness since it outperforms the equidistant monitoring strategy in all of the analyzed cases, especially for the longer line segments, which are subject to more complex weather patterns.

An Approach Based on Analytical Expressions for Optimal Location of Voltage Sags Monitors

This paper addresses the problem of identifying the optimal location for voltage sags monitors. The proposed approach is based on using a monitor reach matrix obtained from the solution of analytical expressions which are valid for any location of faults in the power system. This method provides the optimal number of monitoring devices and the best positions to place them in order to guarantee the observability of the whole system considering any type of fault (balanced or unbalanced). That is, the location of monitors obtained by means of the proposed algorithm ensures that any event leading to a voltage sag is captured by, at least, one voltage sag monitor. Several examples are provided showing the performance of the proposed formulation compared to other approaches.

Stochastic assessment of unbalanced voltage dips in large transmission systems

This paper focuses on the simulation of unbalanced voltage dips in a large transmission system. The theoretical background about symmetrical components and the impedance matrix is presented. Equations for during fault voltage are derived. Simulations of balanced and unbalanced dips are performed in a large transmission system taking into account the transformer effect. Results are presented in several ways including graphs and tables.

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).

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.