Carlo Alberto Nucci - Academia.edu (original) (raw)

Papers by Carlo Alberto Nucci

The lightning discharges are one of the main causes of interruptions of medium voltage overhead d... more The lightning discharges are one of the main causes of interruptions of medium voltage overhead distribution lines, being the reason of great concern for the utility companies. Its destructive effects frequently extends to equipments and connected installations, with the possibility to cause personal injuries and material damages, beyond economic losses, due to out of income and the possibility of indemnities, penalties and fines. With the beginning of the deregulation of the electric energy supply, some actions were been taken by the utilities for the prevention and minimization of the damages associated to the lightning discharges. However, as the lightning discharges are random events, consequently, difficult to predict, the majority of these actions does not follow a study or a detailed analysis of the problem. By this way, in the majority of the cases the actions were taken based on the knowledge of the engineer in charge, or based in rules defined without any effective evidence, by means of studies or by laboratory tests. As a result, many of them besides of presenting high cost are not effective. Among others, the distribution network reliability depends directly on its exposition to the lightning discharges. To determine the exposition level of the line, the designer should know the number of discharges to the ground per unit of area per unit of time. The aim of this paper is to present the results of the performance study of medium voltage overhead distribution lines against lightning discharges, in the way to define methodologies to reduce the system failures. The results were obtained within the partnership among the High Voltage Laboratory of the Federal University of Itajubá, AES Sul Utility Company and the University of Bologna. Direct discharges and induced surges were simulated into real networks to identify the major factor of influence for network failures. Then commentaries on the relative performance and comparisons of different construction configurations of overhead lines are presented. Once that the atmospheric discharges phenomena are random, this work considers that the parameter generation of the discharges follows the statistical data proposed by Anderson and Eriksson. The Monte Carlo Method is used for the incidence distribution of the discharges and the Electro Geometrical Model for the interception point of the discharge.

A two-year experimental campaign on lightning-originated disturbances carried out in an Italian r... more A two-year experimental campaign on lightning-originated disturbances carried out in an Italian rural region characterized by a high ground flash density (4 flashes/km 2 /yr) has provided a set of voltage transient measurements in a medium voltage (MV) feeder that are clearly correlated with both specific events detected by the Italian lightning location system (LLS) CESI-SIRF and sequences of relay operations. The paper describes the sequence of relay events, reports the data of the correlated LLS-detected stroke and presents the corresponding voltage transients recorded at three different busses of the MV feeder.

ABSTRACT For the case of urban overhead lines, the presence of nearby buildings is expected to af... more ABSTRACT For the case of urban overhead lines, the presence of nearby buildings is expected to affect the overvoltages induced by nearby lightning return strokes. This effect until now has been seldom taken into account in the literature on the subject. The paper presents a 3D FEM model that calculates the lightning electromagnetic pulse (LEMP) taking into account the presence of building placed in proximity of the LEMP-coupled overhead line. As a first approximation, the building surfaces are assumed as perfect conductors. Also the finite ground conductivity is neglected. The calculated fields are then introduced in the Agrawal et al. coupling model for the calculation of the induced voltages. The preliminary results of a sensitivity analysis carried by varying the dimensions of the building, its distance to the line and the position of the lightning stroke location are presented and discussed.

IEEE Transactions on Electromagnetic Compatibility, 1993

The paper discusses a modeling procedure that permits calculation of lightning-induced voltages o... more The paper discusses a modeling procedure that permits calculation of lightning-induced voltages on overhead lines starting from the channel-base current. The procedure makes use of 1) a lightning return-stroke model proposed by the authors for the calculation of the lightning electromagnetic field; and 2) a coupling model already presented in the literature based on the transmission line theory for field-to-overhead line coupling calculations. Both models are discussed and tested with experimental results. The hypothesis of perfect conducting ground, generally adopted in studies on the subject, is discussed in order to better assess its validity limits. The procedure is applied for the analysis of the voltages induced on an overhead line by a nearby lightning return stroke with a striking point equidistant from the line terminations. The analysis shows that the vertical and horizontal components of the electric field are both to be taken into account in the coupling mechanism. The peak value and the maximum time derivative of the channel-base current are shown to affect both the peak value and the maximum front steepness of the induced voltages while, for the examined case, the returnstroke velocity affects practically only the front steepness of the induced voltages. A comparison with other models proposed for the same purpose is presented. Peak value and maximum front steepness of the induced voltages calculated using other lightning return-stroke models differ; these differences are of the same order of magnitude as those that would result from different sets of characteristic parameters of the lightning discharge. It is also shown that a different coupling model used in the power-lightning literature by several other authors may result in a less accurate estimation of the induced voltages.

IEEE Transactions on Electromagnetic Compatibility, May 1, 1997

ABSTRACT Voltage sags are one of major concerns in power quality, as they cause serious malfuncti... more ABSTRACT Voltage sags are one of major concerns in power quality, as they cause serious malfunction of a large number of apparatuses. There are a number of reasons for voltage sags in distribution networks: there is some evidence, however, that in electrical systems located in regions with high value of isokeraunic level, lightning can cause the majority of voltage sags. Data from lightning location systems, which provide an estimation of both lightning flash location and return-stroke current amplitude, can then be used to understand whether lightning is indeed the real cause of circuit breaker operation during thunderstorms-which means, in turn, of voltage sags-or not. Due to the complexity of the problem, the information coming from LLS (lighting location and estimate of lighting current amplitude) are, in general, not enough to infer the origin for voltage sags. It is necessary to suitably integrate them with data from system monitoring, e.g. relevant to the intervention of circuit breakers in primary substations, and with simulation results from of accurate models for computing lighting-induced voltages on complex power networks.

Electric Power Systems Research, 2018

Vacuum circuit breakers (VCBs) are widely used for medium voltage applications when low maintenan... more Vacuum circuit breakers (VCBs) are widely used for medium voltage applications when low maintenance, long operating life, and large number of allowable switching cycles are required. The accurate estimation of the transient recovery voltages (TRVs) associated with their switching operation is indispensable for both VCB sizing and insulation coordination studies of the components nearby the switching device. In this respect, their accurate modelling, which is the object of the paper, becomes crucial. In particular, the paper illustrates two applications of a VCB model, which show the model capabilities of simulating TRVs due to opening/closing operation, namely the switching of large electrical motors and the switching of cables collecting offshore wind farms (OWFs). Data from digital fault recorder (DFR) in a water-pumping plant and from a measurement campaign in an OWF using a high-bandwidth GPS-synchronised measurement system, respectively, are used for model validation. It is shown that the inclusion of detailed VCB models significantly improves the agreement between the measurements related to both pre-and restrikes and the corresponding simulation results obtained by using two well-known electromagnetic transient simulation environments, namely, EMTP-RV and PSCAD/EMTDC. The procedure adopted for the identification of the VCB model parameters is described.

2010 30th International Conference on Lightning Protection (ICLP), 2010

The paper aims at illustrating a procedure for the lightning risk assessment of industrial oil pr... more The paper aims at illustrating a procedure for the lightning risk assessment of industrial oil process plants. The procedure is based on the use of the Monte Carlo method and applies to each event both a lightning attachment criterion and a damage calculation model. In particular, for the case of oil tanks, the model calculates the expected annual number of damages associated to the metal melting due to direct lightning events. The paper also presents and discusses an application example of the proposed procedure.

Ownership of a CIGRE publication, whether in paper form or on electronic support only infers righ... more Ownership of a CIGRE publication, whether in paper form or on electronic support only infers right of use for personal purposes. Are prohibited, except if explicitly agreed by CIGRE, total or partial reproduction of the publication for use other than personal and transfer to a third party; hence circulation on any intranet or other company network is forbidden". Disclaimer notice "CIGRE gives no warranty or assurance about the contents of this publication, nor does it accept any responsibility, as to the accuracy or exhaustiveness of the information. All implied warranties and conditions are excluded to the maximum extent permitted by law".

Riassunto-La presente memoria descrive la struttura di un sistema automatico di esercizio ottimiz... more Riassunto-La presente memoria descrive la struttura di un sistema automatico di esercizio ottimizzato delle risorse di produzione/accumulo di energia e quelle di regolazione, disponibili in una rete di distribuzione. Tenendo conto delle difficoltà di previsione dei carichi e della produzione da fonte rinnovabile, il sistema automatico è organizzato su una struttura a due livelli: il primo, con orizzonte giornaliero, è dedicato all'applicazione di criteri di gestione economica; il secondo, con orizzonte temporale limitato al successivo quarto d'ora, è dedicato al raggiungimento degli obiettivi di qualità e sicurezza dell'esercizio della rete. Gli studi effettuati mostrano che la struttura proposta può consentire anche l'esercizio volontario in isola di carico, con riferimento sia a microreti di bassa tensione sia a parti di reti in media tensione. Parole chiave-Generazione distribuita, Micro-reti, Gestione automatica, Ottimizzazione.

In this paper, direct lightning current measurements obtained on the Säntis Tower from June 1st, ... more In this paper, direct lightning current measurements obtained on the Säntis Tower from June 1st, 2010 to May 31st, 2011 are used to evaluate the ability of the EUCLID lightning detection network to detect this type of lightning triggered by a tall tower in terms of detection efficiency, location accuracy and peak current estimates. The Säntis Tower is a 124-meter tall tower sitting on the top of the Säntis Mountain (2500 m) in Switzerland. The tower has been instrumented to measure waveforms of the lightning current and of its time derivative. In the considered period, 57 flashes were recorded at the Säntis Tower out of which 15 were of positive polarity. The data have been correlated to EUCLID data by comparing the time-stamps provided by the GPS time references. The flash detection efficiency for negative flashes is estimated to be 93%. The median value of the location error is 126 m. The EUCLID peak current estimates were on average significantly larger than the measured current. The measurements include four typical positive flashes, which were successfully detected by EUCLID. The location errors for the positive events ranged from 1 to 3 km, with a median of 959 m.

2005 IEEE Russia Power Tech, 2005

Abstract The paper focuses on bidding selection mechanisms based both on offer price and electric... more Abstract The paper focuses on bidding selection mechanisms based both on offer price and electricity-quantity strategies. The aim of the paper is to present a procedure that allows the use of both game theory and of detailed cost-based unit-commitment computer codes. The procedure is conceived in a way to be as much as possible independent of the specific market rules. The results of a preliminary analysis are shown, concerning simple test cases that incorporate some distinctive characteristics of electricity markets and power plants.

Journal of Electrostatics, 2007

The aim of this paper is to present an experimental validation of a frequency-domain approach to ... more The aim of this paper is to present an experimental validation of a frequency-domain approach to the solution of the lightning electromagnetic field-to-buried cable coupling equations. The coupling to the inner conductor is evaluated using the concept of cable transfer impedance. The theoretical model and relevant computer code are tested using experimental data on lightning-induced currents in buried cables carried out in 2002 and 2003 at the International Center for Lightning Research & Testing (ICLRT) at Camp Blanding, Florida where currents induced by triggered lightning events were measured at the ends of a buried coaxial cable, both in the shield and in the inner cable conductors. Reasonably good agreement has been found between numerical simulations and recorded waveforms. In particular, the early-time response of the cable and the peak value of the induced currents were generally well reproduced by the simulations.