Un rivoluzionario comunista

1. Le “leggende” che hanno riguardato Gramsci negli ultimi decenni, soprattutto nel periodo successivo alla caduta del Muro di Berlino e al crollo dell’URSS, sono state certamente tante. La più ricorrente e diffusa mi pare tuttavia quella secondo cui sia i sovietici, sia il Partito italiano, ovvero Palmiro Togliatti, avrebbero agito per impedire che Gramsci uscisse dal carcere considerandolo ormai addirittura un “eretico”, estraneo al movimento comunista. In realtà, al di là degli stessi grav..

Characterization and Error Compensation of a Rogowski Coil in the Presence of Harmonics

This paper reports the results of an experimental study dealing with a commercial Rogowski coil current transducer (RCCT) in the presence of harmonic distortion. The RCCT was observed under two conditions: 1) sinusoidal excitation with frequencies from 50 to 750 Hz and 2) nonsinusoidal excitation using fundamental frequency and one harmonic, with adjustable amplitude and phase shift. The experimental results show only a weak dependence of the harmonic current ratio error and phase displacement on the amplitude and phase shift of the excitation harmonic. The phase displacement is also independent of the conductor position within the Rogowski coil window. An error compensation method, based on the frequency response, was implemented and tested with a distorted waveform. The compensation method allows one to obtain an improvement of the RCCT accuracy class from 1% and 1°, in the case of a sinusoidal signal at mains frequency, to 0.05% and 0.05°, both for the fundamental and the distorted signal harmonics

Measurement uncertainty impact on simplified load flow analysis in MV smart grids

This work is focused on the measurement uncertainty impact on load flow analysis in medium voltage (MV) distribution networks. In more detail, the paper presents the uncertainty evaluation of a simplified load flow algorithm, which is based on the load power measurements at each secondary substation and one voltage measurement at the slack bus (i.e. the voltage at the MV bus bars of the primary substation). To reduce the costs of the monitoring system, the load flow algorithm makes use of LV load power measurements for all the substations except those of MV users, where MV transducers are usually already installed. The uncertainties on the algorithm input quantities (load powers and slack bus voltage) are calculated, considering the actual values of the loads power factors and currents and the accuracy specifications of the measurement instruments installed in the distribution network. Starting from the input quantities uncertainties, the power flows uncertainties are obtained applying the Monte Carlo analysis. The analysis is carried out on a real test system, i.e. the distribution network of Favignana Island. The compatibility is also shown between the algorithm power flow estimations and the power measurements

Un approccio semplificato per il calcolo del load flow nelle smart grids basato su misure distribuite in bassa tensione

Gli autori hanno sviluppato un approccio semplificato per il calcolo del load flow per le reti radiali, basato sulle misure delle potenze in BT e su una sola misura di tensione sulle sbarre MT. L’algoritmo di load flow è di tipo “backward/ forward” a somme di potenze, che, rispetto al precedente approccio a somme di corrente, consente di ottenere una migliore efficienza computazionale, senza peggiorarne le caratteristiche di convergenza e accuratezza. Questo rappresenta un vantaggio dal punto di vista dell'implementazione dell'algoritmo, anche in sistemi SCADA con limitate capacità di calcolo. I risultati riportati nell'articolo, ottenuti per la rete di distribuzione dell’Isola di Favignana, mostrano l'efficacia della soluzione proposta in termini di compatibilità tra le stime dei flussi di potenza e le misure sul campo

Uncertainty evaluation in load flow analysis: real MV distribution networks case studies

This work investigates the measurement uncertainty impact on load flow analysis in medium voltage (MV) distribution networks. The considered algorithm is a simplified load flow algorithm (LFA), developed by authors, which is based on the load power measurements at each secondary substation and one voltage measurement at the slack bus (i.e. the voltage at the MV bus bars of the primary substation). In the viewpoint of a real implementation, to reduce monitoring system costs, the LFA makes use of low voltage (LV) load power measurements for all the substations except those of MV users, where MV transducers are usually already installed. The uncertainties on LFA input quantities (load powers and slack bus voltage) are calculated, considering actual values of loads powers and currents and the accuracy specifications of measurement instruments installed in distribution network. Starting from this, power flows uncertainties are obtained applying a Monte Carlo analysis. The analysis has been carried out for real case studies; i.e. the distribution networks of Favignana and Ustica Islands. The following results refer to the Favignana case

Rogowski coil current transducer compensation method for harmonic active power error

In the harmonic active power measurement, the highest uncertainties are generally introduced by the current and voltage transducers. In a previous paper, the authors showed that the current transformer (CT) can introduce significant errors in such measurement, especially if the phase shift between voltage and current is close to ±90°. In such condition the errors on harmonic power measurement are mainly due to the CT phase displacement. This paper shows that better results can be achieved with more linear transducers, such as the Rogowski coil current transducers (RCCTs), whose metrological performance in distorted condition can be improved, by means of a proper compensation method. The proposed method for RCCTs compensation is based on the frequency response and it allows to reduce the errors on harmonic power measurement, also for phase shift close to ±90°. The study is supported by several experimental tests

A New Solution for Low-Voltage Distributed Generation Interface Protection System

In this paper, a new solution is proposed for the remote monitoring and control of distributed generators (DGs) and energy storage systems (ESSs) connected to low-voltage distribution networks. The proposed system fulfills the in-force standard requirements for the connection of DGs to the utility grid. Moreover, it allows implementing some enhanced functions for the remote control of inverters of DGs and ESSs, not only in terms of disconnection but also in terms of voltage regulation and power shuttering. The proposed solution is based on a new interface protection system and a dedicated secondary substation concentrator, which allows the communication between the distributed system operator and the inverters of DGs or ESSs. The proposed system was tested on field in the electrical network of the island of Ustica. An experimental characterization was carried out to find the best communication conditions, i.e., the frequency band with the lowest noise and attenuation, considering the signal amplitude and signal-to-noise ratio constraints, as well as the desired transmission data rate and transfer time

Narrowband power line communications for medium voltage smart grids

The aim of the paper is to show how narrowband power line communications (NB-PLCs) can be a valid solution for medium voltage grids. Advantages and drawbacks of this solution are analyzed, starting from some experimental communication results, which were carried out on the medium power system networks of the islands of Ustica and Favignana, in the presence of the net voltage. Furthermore, some communication architectures and hardware prototypes based on NB-PLCs are proposed for different smart grids applications

On-field demonstration of distributed generation and storage systems monitoring and control in small Islands power systems

This work summarizes the final results of the I-SOLE project (“Smart grids per le Isole Minori”, co-financed by European Union under the framework of PO FESR Sicilia 2014-2020, Action 1.1.5, https://www.progettoisole.com/), which has been aimed at developing innovative solutions and devices for distributed generation and storage systems integration in small Islands power grids. For such networks, the increase of energy production from renewable sources is a strategic theme for the sustainability and energy independence goals; at the same time, it entails specific problems concerning the robustness of the distribution grids against instability, power flows inversions and other power quality (PQ) problems. The I-SOLE project partnership has involved the University of Palermo, two research institutes of the National Research Council (Institute of Marine Engineering and Advanced Energy Technology Institute) and five industrial partners (Layer Electronics Srl – project leader; STMicroelectronics; SEA – Società Elettrica di Favignana SpA; SOPES Srl – Ustica desalination plant management company; Elettromeccanica Mangano Sas). The on-field demonstrators on the Islands of Favignana, Ustica and Lipari have provided the opportunity to test different architectures of distributed measurement systems and new devices and equipment prototypes, allowing the industrial partners to develop new products for smart grids applications