A primary requirement for the transmission system operator is an accurate knowledge of grid parameters. Moreover, the availability of effective and accurate monitoring tools allows the proper ...operation of power transmission grids. However, in spite of the now widespread possibility of having monitoring systems based on synchronized measurements, the monitoring applications can be affected not only by the inevitable uncertainty sources but also by the simplified or incomplete modeling of the network components. For this reason, the impact on power system monitoring and control applications of tap-changing transformer models is a key point. In this scenario, this article presents a method to estimate simultaneously line parameters, tap changer ratios, and systematic measurement errors associated with the instrument transformers. The method exploits a flexible model of the tap-changing transformer based on a parameter representing the ratio between the two winding impedances of the transformer. The proposal is based also on the suitable modeling of the measurement chain and on the constraints introduced by the equations of involved transmissions lines and transformers. The validation has been carried out by means of tests performed on the IEEE 14 Bus Test Case.
Nowadays, in modern management and control applications, line parameters need to be known more accurately than in the past to achieve a reliable operation of the distribution grids. Phasor ...measurement units (PMUs) may improve line parameter estimation processes, but the accuracy of the result is affected by all the elements of the PMU-based measurement chain, in particular by the instrument transformers. Current transformers (CTs) are nonlinear and, therefore, their behavior is not easily described: their models cannot be straightforwardly included in the estimation problem. In this regard, this article refines modeling and compensation of CT systematic errors in line parameter estimation processes, based on different methods to describe the transformer behavior under various operating conditions. As the main result, the systematic errors of CTs are remarkably identified and mitigated. Moreover, the estimation of shunt susceptance values is significantly improved.
The availability of accurate data is fundamental for several monitoring and control applications of modern power grids. Nevertheless, the knowledge of critical data, such as transmission line and ...transformer parameters, is often affected by uncertainty. This can lead to important problems in the correct management of the power systems. In spite of a monitoring infrastructure that is being renewed due to new generation devices providing synchronized measurements, the actual values of line parameters and tap changer ratios are still affected by uncertainty sources that need to be properly considered. The behavior of all the elements involved in the measurement chain must be duly modeled. This article proposes an improved method to carry out the simultaneous estimation of line parameters, tap changer ratios, and systematic measurement errors for a three-phase power system. The proposed method is based on the suitable modeling of the measurement chain and three-phase constraint equations (voltage drop and current balance) of all the components involved. Its effectiveness is confirmed by tests performed on an IEEE 14-bus test system reproduced as a three-phase system under different operative conditions.
Proposals have been presented in literature to estimate line parameters and monitor their changes. Synchrophasor measurements from phasor measurement units (PMUs) have appeared as a possible ...breakthrough for accurate estimation. However, few methods consider a realistic measurement chain including PMUs and instrument transformers and their systematic and random error contributions. This paper proposes an improved method to simultaneously estimate line parameters and systematic measurement errors on multiple network lines. The algorithm is designed to deal with realistic PMU measurement errors and, in particular, with phase-angle errors caused by common time-base errors on multiple PMU channels. The impact of PMU measurement errors is investigated to achieve a comprehensive view of the performance under realistic conditions. The results obtained on an IEEE test network prove the advantages of the proposed method with respect to other recent methods and its robustness in the presence of mismatches in the error model.
•Improved method, based on PMU measurements, for the simultaneous estimation of transmission line parameters and systematic measurement errors.•PMU errors composed of random and systematic contributions but also of possible phase-angle errors common to the channels.•Correlation related to the considered measurements evaluated and included at run-time within the estimation framework.•Robustness in the presence of a mismatch between the assumed PMU error model and actual instrument behavior.
Grid management undoubtedly benefits from an accurate monitoring of actual network operating conditions. Such monitoring can be obtained starting from a widespread presence of measurement points and ...different types of estimation techniques. To exploit all the possible measurements present on the network, data coming from the protection systems can be considered in addition to those from the measurement systems. In this scenario, however, accuracy should not be underestimated, because in the presence of dynamic signals it can be dramatically reduced. In this context, this paper presents an improved fault detection and location method based on synchronized measurements, estimation techniques and an appropriate accuracy modeling aimed at reducing the uncertainty in the fault analysis. The proposed approach is validated by simulations carried out by means of a Digital Real Time Simulator (DRTS) on the three-phase CIGRE European Medium Voltage distribution network.
Identifying the prevailing polluting sources would help the distribution system operators in acting directly on the cause of the problem, thus reducing the corresponding negative effects. Due to the ...limited availability of specific measurement devices, ad hoc methodologies must be considered. In this regard, compressive sensing (CS)-based solutions are perfect candidates. This mathematical technique allows recovering sparse signals when a limited number of measurements are available, thus overcoming the lack of power quality meters. In this article, a new formulation of the ℓ 1 -minimization algorithm for CS problems, with quadratic constraint, has been designed and investigated in the framework of the identification of the main polluting sources in smart grids. A novel whitening transformation is proposed for this context. This specific transformation allows the energy of the measurement errors to be appropriately estimated, and thus, better identification results are obtained. The validity of the proposal is proven by means of several simulations and tests performed on two distribution networks for which suitable measurement systems are considered along with a realistic quantification of the uncertainty sources.
Several monitoring, protection, and control applications designed for modern power grids are based on detailed grid models and thus require accurate knowledge of line parameters. A synchronized ...monitoring infrastructure based on phasor measurement units (PMUs) may be of great support to the task of line parameters estimation, but the accuracy of the estimated parameters may be largely affected by the uncertainty of all the elements of the PMU-based measurement chain. Thus, an accurate parameters estimation must appropriately consider the metrological behavior of all these elements, in particular that of instrument transformers (ITs). To address this challenge, this article proposes an enhanced multibranch method for accurate estimation of the line parameters and the systematic measurement errors introduced by the ITs when measurements for multiple operating conditions are considered. Indeed, multiple operating conditions are dealt with properly due to an in-depth analysis of the problem modeling within the framework of Tikhonov regularization. The validity of the proposed approach is confirmed by the results obtained on the IEEE 14-bus test system.
Accurate monitoring tools are fundamental for the proper operation of the transmission grids. In this context, an essential requirement for the transmission system operator is the availability of ...accurate knowledge on transmission line and transformer characteristics. Despite the high accuracy of the increasingly used Phasor Measurements Units (PMUs), there are still significant issues associated with the knowledge of the actual line parameters and on the actual tap changer ratio. In this regard, the paper proposes a method to estimate simultaneously the line parameters, the tap changer ratio, and the systematic measurement errors associated with the instrument transformers. With an appropriate model of the measurement chain, which includes the uncertainties associated with instrument transformers and PMUs, a linear formulation of the line and transformer constraint equations can be applied and accurate results can be obtained. The validity of the proposed method is confirmed by different types of tests performed on the IEEE 14-bus test system.
Fault detection and location algorithms require grid knowledge to be highly accurate. Possible deviations of actual line parameters with respect to the expected ones can affect the detection and ...location performance. To reduce fault analysis uncertainty, we propose the application of a simultaneous estimation of line parameters and systematic errors, along with a proper handling of the measurements chain, in a fault detection and location method. The validity of the proposed approach is confirmed by the simulations carried out by means of a Real Time Digital Simulator (RTDS) on the three-phase CIGRE European Medium Voltage distribution network.
Phasor Measurement Units (PMUs) may improve the line parameters estimation process, but the accuracy of the result suffers from all the elements of the PMU-based measurement chain. Systematic errors ...of instrument transformers can be included in the estimation model, but, in particular, current transformers are nonlinear and thus their modelling is not straightforward. In this regard, the paper analyzes the impact of current transformers on the line parameters estimation performance using a detailed description of the transformer behavior under different operating conditions.
