Refined Modeling and Compensation of Current Transformers Behavior for Line Parameters Estimation Based on Synchronized Measurements

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

Outage severity analysis and RAM evaluation of italian overhead transmission lines from a regional perspective

Power transmission lines represent the core of the High Voltage Network since they are responsible for the transport of the electrical energy from the generation power plants to the electrical substations. In this paper, an analysis of the outages occurred to the Italian Overhead Transmission Lines (OHTLs) from 2008 to 2015 is carried out. A new simple and effective reliability index, namely the Severity Factor, is introduced with the aim to drive the prioritization of the failure causes and the enhancement of the maintenance activities. The analysis has been performed focusing on the geographical distribution of the OHTLs. For each analyzed region, the voltage levels more prone to failure have been determined. The proposed methodology, thanks to the introduction of the Severity Factor, is a useful and effective tool for the identification of the transmission network criticalities and the enhancement of the related maintenance activities. Finally, an evaluation of the reliability, availability, safety and maintainability (RAMS) of the Italian OHTL network has been performed from a regional point of view.</p

Improving Harmonic Measurements with Instrument Transformers: a Comparison Among Two Techniques

The measurement of harmonics is essential in modern power systems in order to perform distortion level assessment, disturbances source detection and mitigation, etc. In this context, the role of Instrument Transformers (ITs) is crucial, as they are key elements in every power systems measuring instrument. However, inductive ITs, which are still the most widely used, suffer from both a filtering behavior due to their dynamics and from nonlinear effects due to their iron core. The target of this paper is to deeply analyze the performance of two digital signal processing techniques, recently proposed in literature, aimed at mitigating their nonlinear behavior: they are SINDICOMP and the compensation of harmonic distortion through polynomial modeling in the frequency domain. Their performance in improving the measurement of voltage harmonics are analyzed through numerical simulations, by adopting waveforms that can be typically encountered in power systems during normal operating conditions

L’informazione in emergenza. I canali informativi e l’affidabilità delle fonti istituzionali

Il contributo analizza il ruolo dell'informazione (e della disinformazione) durante le prima fase dell'emergenza sanitaria emersa a seguito della diffusione in Italia del Covid-19 ponendo particolare attenzione alle fonti e ai canali informativi utilizzati

A cosa serve una bella campagna?

il volume analizza le ragioni che hanno portato alla sconfitta delle sinistre nelle elezioni del 2008. In particolare, il contributo analizza la campagna elettorale di Veltroni e della Sinistra Arcobalen

Outage severity analysis on Italian overhead transmission lines from a regional perspective

Power transmission lines represent the core of the High Voltage Network since they are responsible for the transport of the electrical energy from the generation power plants to the electrical substations. In this paper, an analysis of the outages occurred to the Italian Overhead Transmission Lines (OHTLs) from 2008 to 2015 is carried out. A new simple and effective reliability index, namely the Severity Factor, is introduced in order to prioritize the most relevant outage causes. The analysis has been performed focusing on the geographical distribution of the OHTLs. The obtained results have shown that the impact of the different outage causes on the OHTLs reliability is generally not uniform across the country but depends on the considered region. Further, for each analyzed region, the voltage levels more prone to failure have been determined. It can be concluded that the proposed methodology, thanks to the introduction of the Severity Factor, is a useful and effective tool for the identification of the transmission network criticalities and the enhance of the related maintenance activities

A Simple Method for Compensating Harmonic Distortion in Current Transformers: Experimental Validation

Conventional current transformers (CTs) suffer from nonlinearities due to their ferromagnetic cores. On one hand, it is well-known that severe core saturation may occur because of large overcurrents or unidirectional transient components: this may substantially impact the operation of relays. On the other hand, weaker nonlinear effects are also present during regular working conditions. In particular, the spectral content of typical current waveforms is characterized by a strong fundamental term responsible for harmonic distortion affecting the frequency components at the secondary side. In turn, this has a significant impact on the accuracy that can be reached as long as current harmonics must be monitored. The target of this work is implementing a simple signal processing technique that allows compensating for this effect. The method, characterized by extremely low computational complexity, is first introduced and validated using numerical simulations. After this, it was tested experimentally to improve the harmonic measurement capability of inductive CTs. The achieved results highlight a noticeable reduction of errors at low-order harmonics over a wide range of primary current amplitudes. It is worth noting that the black-box approach makes the technique suitable also for compensating nonlinearities introduced by current transducers based on different operating principles. Thanks to this peculiarity and to the low computational complexity, the proposed method is suitable to be employed in power quality analyzers and merging units. In this way, high-accuracy monitoring of current harmonics in power systems can be achieved, opening the way to advanced power quality management and to the location of disturbing users

A cosa serve una bella campagna?

il volume analizza le ragioni che hanno portato alla sconfitta delle sinistre nelle elezioni del 2008. In particolare, il contributo analizza la campagna elettorale di Veltroni e della Sinistra Arcobalen

Outage severity analysis and RAM evaluation of Italian overhead transmission lines from a regional perspective

Power transmission lines represent the core of the High Voltage Network since they are responsible for the transport of the electrical energy from the generation power plants to the electrical substations. In this paper, an analysis of the outages occurred to the Italian Overhead Transmission Lines (OHTLs) from 2008 to 2015 is carried out. A new simple and effective reliability index, namely the Severity Factor, is introduced with the aim to drive the prioritization of the failure causes and the enhancement of the maintenance activities. The analysis has been performed focusing on the geographical distribution of the OHTLs. For each analyzed region, the voltage levels more prone to failure have been determined. The proposed methodology, thanks to the introduction of the Severity Factor, is a useful and effective tool for the identification of the transmission network criticalities and the enhancement of the related maintenance activities. Finally, an evaluation of the reliability, availability, safety and maintainability (RAMS) of the Italian OHTL network has been performed from a regional point of view

Behavioral Representation of a Bridge Rectifier Using Simplified Volterra Models

Studying the propagation of harmonics in power grids represents a very important task nowadays. However, this demands for nonlinear models of power system devices representing a critical tradeoff between the accuracy and the computational cost. Simplified Volterra models with quasi-sinusoidal excitation have been recently proposed and they appear to be particularly suitable for the purpose. In this paper, these models have been applied to predict, for a given input voltage, the current harmonics of a full-bridge rectifier feeding an ohmic-capacitive load. Accuracy has been evaluated by means of both numerical simulations and experiments. Robustness has also been assessed by considering a set of realistic voltage waveforms different from those employed for the identification. Results highlight the remarkable accuracy of the proposed models in spite of the relatively small set of coefficients to be identified. This feature is extremely important when models have to be employed in frequency-domain simulations of large networks