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In the usual practice, the evaluation of overvoltages due to direct lightning strikes to overhead power lines is focused on the representation of the effects of the lightning current injection, whilst the effects of the coupling between the conductors and the lightning electromagnetic pulse (LEMP) is disregarded. Motivated by recent results obtained for the case of a medium voltage line configuration with a shield wire, this paper extends the analysis to assess the contribution of the LEMP on the lightning performance of an overhead distribution line with and without periodically grounded wires and surge arresters. Moreover, the paper deals with the LEMP effect on the occurrence probability of flashovers on different phases, which is an important information on the service continuity of networks with isolated or compensated neutral earthing. A validation of the results is obtained by comparing the overvoltages calculated by the electromagnetic transient program including the model of the line illuminated by the LEMP and those obtained by a three-dimensional finite difference time-domain approach.

In medium-voltage distribution lines, lightning outages associated with indirect strokes are less frequent when surge arresters are installed at close intervals. In this case, the lightning performance is mainly determined by the line response due to direct strikes, usually assessed disregarding the effect of the lightning electromagnetic pulse (LEMP). This paper examines the influence of such an electromagnetic effect on the voltages across the line insulators caused by direct lightnings. The presence of both surge arresters and a shield wire is considered. By means of adequate modeling and numerical calculations, we show that the flashover rate due to the direct strikes is increased by the LEMP. The obtained results indicate that in the statistical assessment of the direct lightning performance of lines equipped by surge arresters and shield wires, the LEMP effect is not negligible and its accurate evaluation is hence required.

The state estimation of distribution networks has long been considered a challenging task for the reduced availability of real-time measures with respect to the transmission network case. This issue is expected to be improved by the deployment of modern smart meters that can be polled at relatively short time intervals. On the other hand, the management of the information coming from many heterogeneous meters still poses major issues. If low-voltage distribution systems are of interest, a three-phase formulation should be employed for the state estimation due to the typical load imbalance. Moreover, smart meter data may not be perfectly synchronized. This paper presents the implementation of a three-phase state estimation algorithm of a real portion of a low-voltage distribution network with distributed generation equipped with smart meters. The paper compares the typical state estimation algorithm that implements the weighted least squares method with an algorithm based on an iterated Kalman filter. The influence of nonsynchronicity of measurements and of delays in communication and processing is analyzed for both approaches.

New legal arrangements for the aggregation of distributed generation and demand are required for the future electricity grid so as to increase flexibility, resilience, citizens’ participation and also alleviate energy poverty. To promote the transitioning to a low carbon society, countries are reforming their legal framework to enable broad civic engagement in the energy markets. This work analyses the process of reform of the legal framework of the electric sector with focus on energy communities, using two study cases, one in Brazil and another in Italy. The research performed is applied, qualitative, descriptive and exploratory. The work uses multiple research methods, blending case studies, semi-structured interviews and a systematic literature review for data collection and the functional method of comparative law, discourse analysis and triangulation for data analysis. The findings suggest greater consideration of the energy poverty nexus in the policy design of the electricity sector and they also reveal the important role of specialized technical bodies and governmental institutions for the take-off and success of an energy community endeavour, highlighting crucial aspects for an energy transition aligned with the Paris Agreement and the goals of Agenda 2030.

Battery-based Energy Storage Transportation (BEST) is the transportation of modular battery storage systems via train cars or trucks representing an innovative solution for a) enhancing Variable Renewable Energy (VRE) utilization and load shifting, and b) providing a potential alternative for managing transmission congestions. This paper focuses on point b) and proposes a long-term transmission-planning model coordinated with both stationary and mobile storage units. The planning-problem objective function minimizes the total system cost, i.e., the sum of i) the investment cost of candidate transmission lines, stationary and mobile storage systems, and ii) the operation cost, including conventional generating units fuel consumption, load shedding penalty and BEST transportation costs. An alternative approach for BEST vehicle scheduling problem is implemented. The contribution lies in the accomplishment of the spatial-temporal scheduling of the mobile storage units by including the Number-of-nonzero mathematical function in the optimization model set of constraints instead of using additional binary variables as generally accomplished. The identification of either storage systems optimal location, or both optimal location and size of storage systems is also allowed. BEST usefulness is analyzed and discussed for a test-system emulating a reals system in China-Northwestern-grid with high VRE penetration divided in five regional areas, of which the most promising one for BEST implementation is identified.

This chapter provides the background required to understand the main aspects of power systems analysis and operation under steady-state and transient or dynamic conditions. It is intended for senior undergraduate or graduate students of electrical engineering as well as practitioners, so readers are assumed to have asolid background knowledge of electrical engineering. The main technical issues associated with power systems analysis are addressed, focusing in particular on alternating current (alternating current (AC)) transmission lines, networks, load-flow and short-circuit calculations, stability analysis, frequency control, and electromagnetic transient appraisal. The chapter also references the most important and popular model frameworks and calculation/modeling tools that have been developed by researchers and engineers working within the electric power systems area in the last few decades. It is emphasized in this chapter that an understanding of the issues dealt with here is required to comprehend other chapters of this handbook devoted to distributed generation and smart grids, and this knowledge will also be needed to be able to operate upcoming power systems. The chapter is divided into sections focusing on the following topics: 1.Power systems evolution, from the origins to the traditional structure2.Transmission lines in steady state, transmitted active and reactive power3.Power flow analysis (load-flow equations and resolution methods)4.Short-circuit calculations for unbalanced faults (symmetrical components, fault equations, and sequence networks)5.Stability (states of operation, classification, P-delta curves, rotor angle stability, equal area criterion, multi-machine stabilty and voltage stability)6.Generators reserve and dynamics, frequency dependence of the load, control structure for frequency control7.Traveling waves in alossless line, reflection and transmission coefficients, multiple reflections in aline of fine length; electromagnetic transients (classification of transients, electromagnetic transient (EMTP))8.Power systems in the future (why we need asmart(er) grid, microgrids and energy communities) Additional information and supplementary exercises for this chapter are available online.

This paper deals with the protection against earth faults in distribution networks with unearthed or compensated neutral. A transient-based protection system is proposed and assessed through electromagnetic transient program (EMTP) simulations. The fault detection algorithm is based on the estimation of the angle between the zero-sequence voltage and current phasors. The estimation is carried out at the dominant transient frequency of the network response within the first milliseconds after the fault. The implementation of an improved filter and a zero-padding process allows for the identification of high resistance faults with a relatively low sampling frequency. An operation zone is proposed and assessed, also for unbalanced or mixed bare and cable line networks. The performances of the protection system are evaluated for a distribution network in both the cases of unearthed and compensated neutral through a Monte Carlo method that considers the fault resistance, incidence angle and fault location variations as random variables in the EMTP simulations.

In medium-voltage distribution lines, lightning outages associated with indirect strokes are less frequent if these lines are equipped with a grounded shield wire and surge arresters are installed at close intervals. Thus, for this case, the lightning performance is mainly associated with the line response due to direct events. Recent analysis concerning medium voltage line equipped with a shield wire shows that the electromagnetic pulse radiated from the channel may enhance the overvoltage across insulators during direct strikes. This paper extends the analysis to lines over lossy soils, assuming different values of ground conductivity. The results indicate that the effect of the electromagnetic pulse needs indeed to be considered for an accurate lightning performance assessment of distribution lines with shield wire. On the one hand, the voltages across insulators increase as the soil conductivity decreases; on the other hand, it is shown that for direct strikes the difference between the voltage amplitudes calculated considering or not the LEMP contribution increases with the ground conductivity. Thus, appropriate modelling and relevant calculation tools availability is fundamental for the problem of interest.

Lightning insulation coordination is based on statistical approaches. This allows to correlate the electrical stress caused by lightning and the electrical strength of the insulations, both having probabilistic nature. This chapter provides an example of lightning insulation coordination. Specifically, it deals with the statistical appraisal of the so-called lightning performance of distribution systems, carried out by means of Monte Carlo (MC) simulations. The relevant application to both the cases of direct and indirect lightning events, considering the correlation between the probability distributions of the lightning current parameters, is described and discussed. In particular, the application to the indirect events is based on the definition of a surface around the power line and on the calculation of the induced voltages along the line caused by indirect events having stroke location uniformly distributed within such a surface. The result obtained through the MC simulations is fmally scaled taking into account the annual number of fl ashes per square kilometer expected in the region of interest. In order to obtain significant results, two aspects need to be considered: the surface around the power line should be large enough in order to collect all the events that may endanger the insulation, and the density of the stroke locations should be sufficiently high. Therefore, for medium voltage systems, or even more for the case of low voltage ones, the area can reach a large value indeed, and the number of events to be considered can be consequently huge. The chapter also describes the application of the stratified sampling technique able to reduce the computation effort typical to this type of calculation.

This chapter describes two of the most adopted software tools for the evaluation of the lightning performance of transmission and distribution lines, namely FLASH and LIOV-EMTP (Lightning Induced OverVoltage - ElectroMagnetic Transient Program), together with some application examples. The FLASH program has been developed by IEEE Working Groups. LIOV-EMTP is the result of the integration between the EMTP and the LIOV code, developed by Alma Mater Studiorum - University of Bologna (Italy), Ecole Polytechnique Federale de Lausanne - EPFL (Switzerland), with the support of University of Rome `La Sapienza' and of Centro Elettrotecnico Sperimentale Italiano `G. Motta' CESI S.p.A. (Italy).

This paper deals with the assessment of the lightning performance of a medium voltage (MV) power line sharing the same poles of a high voltage (HV) line. We focus on the case of a 15-kV line with compact configuration that is supported by the concrete poles of a 69-kV or a 138-kV transmission line. Due to the taller HV pylons and conductors, the number of direct events to the multi-circuit line is higher than for a MV line alone. The presence of the HV conductors and of the overhead ground wire reduces the amplitudes of the induced overvoltages in the MV conductors due to indirect lightning events. For the considered configurations, with a compact MV line, the number of flashovers per year expected in the double-circuit line due to both direct and indirect flashes is lower than in a MV line alone. It is shown that such a number depends mainly on the line withstand voltage, on the grounding resistance and on the number of surge arresters. The dependence is quantitatively discussed in the paper. The analysis of the overvoltages transferred on the LV side of the distribution transformers is also performed.

To address the decreasing power system inertia challenges due to the increasing penetration of Renewable Energy Sources (RESs), this paper proposes a Fast Frequency Response (FFR) technique for wind turbines equipped with Doubly Fed Induction Generators (DFIG). The DC-link of a DFIG unit can be controlled to partially exchange energy in case of frequency transients, thus providing FFR that in turn helps maintain grid stability. This control is achieved by levelling up or down the DC-link voltage. Supercapacitor units connected to the DC-link provide the required energy for FFR services. We perform a detailed analysis to achieve the expressions of the minimum DC-link voltage required for the proper operation of the grid side converter and the factors affecting its value. We then propose a procedure to estimate the optimal value for FFR controller gain and a DC-link protection scheme that decouples the FFR controller design from the grid characteristics. The method can be applied to any RES using converter with sufficient energy buffer in order to provide FFR service.

Distribution lines located in areas with high ground flash densities are prone to lightning-caused power interruptions. Lightning overvoltages can be produced on medium-voltage (MV) systems when lightning hits either the line conductors (direct strokes) or a point in the vicinity of the distribution network (indirect strokes). The evaluation of the lightning electromagnetic environment is essential to mitigate its effects and improve the power system quality. This chapter presents initially, using the concepts given in Chapter 5 of Volume 1, a procedure for the estimation of the mean annual number of direct lightning strikes to a given overhead distribution line. Then, the basic features of the lightning overvoltages are discussed. Although some typical characteristics can be identified, the analysis of the overvoltages depends on various parameters relevant to the adopted model of the lightning return stroke, soil and power network. The influences of the most important ones are discussed in this chapter, with examples of measured and calculated voltage waveshapes. Then, the main protective measures that can be applied to improve the lightning performance of MV distribution lines, namely the increase of the line insulation withstand capability, the use of periodically grounded shield wires and the installation of surge arresters along the line, are addressed. The analysis of the effectiveness of each measure as a function of the type of phenomenon (direct or indirect strikes) and of various parameters, such as the soil resistivity, ground resistance and grounding spacing, is performed. After that, the procedure presented in Chapter 1 of this volume for estimating the mean annual number of line flashovers that an overhead MV line can experience, is applied to the case of lines with different protective measures and the relevant performances are compared. The case of urban lines, whose performance is affected by the presence of buildings in their vicinity, is also dealt with, as well as the case of hybrid configurations, in which MV and high voltage (HV) lines share the same structures.

This special issue brings together recent international research on one of the most challenging and multidisciplinary subjects of present and future engineering, architectural, medical, economic, information, and social sciences: the smart city paradigm.

Renewable energy has a crucial role in facing climate change. One promising strategy is the creation of energy communities that require active involvement from a bottom-up perspective. Their implementation is difficult, as they currently rely on local policies, community readiness, and technological availability. The objective of this paper is to provide a qualitative overview of energy community concepts and strategies at the European level. The aim is to identify common approaches that are framing the development of energy communities, and to understand the most successful steps leading to their creation and growth. To achieve this objective, a threefold methodology is provided: (1) an updated review on policies dealing with energy communities at the European and Italian level; (2) a qualitative overview of European-funded projects under the Horizon 2020 work program; and (3) a qualitative overview of some of the most successful existing energy communities in Europe. The results outline a series of considerations and lessons learned that are useful for implementing this transition pathway in a real case, which is also presented in the paper. The conclusions will identify some future directions of this research, particularly in relation to the results coming from the implementation of actions in the real case.

The paper compares the effect that the shield wire, underbuilt grounded conductor, and surge arresters have on the direct and indirect lightning performance of medium voltage overhead lines and provides its quantitative assessment. The paper focuses on a line configuration characterized by the presence of both shield wire and underbuilt neutral wire. The presence of the grounded shield wire significantly reduces the voltages induced across the insulators. In case surge arresters are installed, the effect of the shield wire is shown to have a lower impact. The environmental shielding on the overall lightning performance is also accounted for by considering the effect of the buildings close to the line that reduce the frequency of direct events and increase the frequency of indirect ones.

This paper focuses on the analysis of the dynamic behavior of an AC microgrid including rotating and stationary loads and battery energy storage systems during unplanned islanding transitions. The signal necessary to switch from grid-connected to standalone control mode is not instantaneous. The delay might be so long to result in frequency and voltage transients that could lead to the instability of the microgrid. The aim of this paper is to assess the potential benefits resulting from the implementation of an active and reactive power control scheme able to allow, starting from a grid-connected operation, a successful transition to island. The influence of different percentages of rotating load connected to the microgrid is analyzed by using EMTP-RV and time domain simulations of a modified version of the IEEE 34-bus test distribution system in which two battery energy storage systems are connected to two different buses.

The analysis of lightning-originated flashovers occurring on a multi-circuit high voltage (HV)-medium voltage (MV) overhead line, from indirect and direct lightning, is presented in the paper. We focus on the protection of a 15-kV line with compact configuration that shares the same concrete poles of a 69-kV transmission line. For the indirect lightning performance analysis, the electromagnetic coupling between the lightning electromagnetic field and the multi conductor system is calculated using a version of the LIOV-EMTP-RV tool adapted for the non-conventional line configuration. The HV line increases the incidence of direct strikes but the prevailing effect, as thoroughly discussed in the paper, is the shielding of the MV line by the above HV line. Lightning-originated voltages from both direct and indirect events are presented in the time domain for each conductor of the n-conductor line, with particular focus on the occurring flashover phenomena. The analysis of the overvoltages transferred to the LV systems through distribution transformers is presented too.

The proper insulation coordination of power apparatuses requires the knowledge of the withstand capability of the insulation against overvoltages stressing the given apparatus. By using a multivariate Monte Carlo procedure and the parameter probability distributions of the Cigré waveforms of the lightning current at the channel base, we provide a characterization of the parameter distributions of the induced voltage waveforms in a single conductor overhead line. A simplified formula is proposed to reproduce the curve that represents the expected annual number of lightning that induce voltages larger than the insulation level of the line in case insulators flashovers are not considered in the appraisal. The results for the case of an ideal insulation level are compared to those obtained by considering the flashovers in medium voltage insulators represented by means of the disruptive effect (DE) criterion. The parameters of the DE model are estimated by using the voltage-time-to-breakdown curve inferred from laboratory test results.

This paper analyzes the influence of the radial electric field radiated by return strokes on the lightning performance of an overhead distribution line. The calculation of the lightning electromagnetic pulse (LEMP) over a finitely conducting ground is performed by solving the Sommerfeld integral for the radial component of the electric field. The proposed method uses a trapezoidal scheme in which nodes are equidistant in logarithmic scale. The method is implemented in the LIOV-EMTP (lightning induced overvoltages-electromagnetic transient program) code that solves the field-to-multiconductor line coupling equations and calculates the lightning induced voltages in distribution networks having complex and realistic configuration. The results obtained by the proposed method for the LEMP calculation are compared with those obtained by using the Cooray-Rubinstein formula, which is the most commonly adopted approximation. Finally, the peak-amplitude probability distributions of the induced voltages obtained by using the two approaches are presented. It is shown that for ground conductivity values larger than 0.001 S/m, the Cooray-Rubinstein formula provides results in agreement with the accurate solution, while it significantly underestimates the lightning performance for lower conductivities and for lines with a high insulation level.

Microgrids (MGs) are characterized by faster dynamics than conventional grid-connected distributions systems. This is in part due to the lack of inertia of inverter-interfaced distributed energy resources such as photovoltaic and energy storage systems. In this context, load dynamics considerably affects the transient stability performance of MGs, especially if disconnected from the main grid. The aim of the paper is to analyze the influence of the load modeling and the load composition in the transient stability assessment of a medium voltage MG during islanding transition. The MG we analyze consists of a photovoltaic power plant, two battery energy storage systems, a synchronous generator and different classes and types of load, which we consider representative for the problem of interest. The system is implemented in the EMTP-RV simulation environment. The importance of appropriate load modeling for the adequate analysis of the transient response of an islanding microgrid is also addressed and discussed.

The aim of the paper is to present an efficient procedure for the accurate assessment of the frequency of lightning-originated faults in low voltage distribution lines. The advantage of the proposed procedure lies in the application of the stratified sampling technique, which allows to reduce the computational effort required by the Monte Carlo method. Indeed, such a sampling technique is particularly effective when the collecting area is very large, as in the lightning performance analysis of low voltage lines. The paper shows the results for the case of an overhead cable line and similar results have been obtained for a line with bare conductors. The procedure is also applied for the selection of surge protective devices through the assessment of the statistical distribution of their absorbed charges.

A communication-supported system for the earth fault protection in medium voltage loop and meshed networks with unearthed neutral, is proposed and assessed. The system is based on directional relays installed at both ends of each line, which communicate with each other. The directional relays implement an innovative transient fault detection technique that determines the directionality of the fault by calculating the angle between the earth mode voltage and the current at the dominant transient frequency. The performance of the protection system in response to cross-country faults, is assessed by using a specifically developed software tool that interfaces EMTP-RV with Matlab. The influence of the communication network limitations, i.e. latency and complete loss of communication, on the protection system performance and the effect of the sampling frequency on the operation zones are also analyzed.

This paper deals with the assessment of the lightning performance of a double-circuit HV-MV overhead line. We focus on the protection of the 15-kV line with compact configuration that shares the same concrete poles of a 69-kV or 138-kV transmission line. Due to the presence of the HV conductors, the number of direct events to the multi-circuit line is higher than the one of a typical MV line alone in open terrain. The presence of the HV conductors and of the overhead ground wire reduces the induced overvoltages in the MV conductors due to indirect lightning events. For the considered configurations, the number of flashovers per year expected in the double-circuit line is lower than in a compact MV line in open terrain. It is shown that such a number depends mainly on the line withstand voltage, on the grounding resistance and on the presence of surge arresters, along with their location along the line. Such a dependence is quantitatively discussed in the paper.

An accurate evaluation of the lightning performance of overhead power distribution lines, that is, the evaluation of the expected number of annual flashovers, can be obtained by the application of the Monte Carlo method. In order to reduce the computational effort, a simplified waveform of the channel base current is generally assumed, for example, a linearly rising current with flat top. This paper proposes a Monte Carlo approach able to take into account the typical functions adopted to represent the waveform of the lightning current at the channel base (i.e., the Heidler function and the CIGŔE function). Moreover, this paper analyzes the effects of different current waveforms on the lightning performance of distribution lines for both direct and indirect strokes.

The impact of the increasing connection of distributed generation to medium voltage (MV) distribution feeders, with particular reference to photovoltaic (PV) units, justifies the application of an adaptive control of voltages and reactive power flows. This paper describes the analysis of a voltage/var control (VVC) structure that includes the cooperative control of the reactive power regulators of the PV inverters over a third generation cellular network, namely a Universal Mobile Telecommunications System (UMTS). The control structure integrates the regulation of transformers equipped with on-load tap changers. The characteristics and performances of the this VVC structure, with particular reference to the multi agent system constituted by the decentralized and networked reactive power controllers, are illustrated and analyzed by using a specifically developed ICT-power co-simulation platform.

When assessing the lightning performance of distribution lines, major attention is in general devoted to the induced voltages from nearby strikes rather than to direct events hitting the line, as the latter are always expected to cause a fault in the line. This paper proposes a Monte Carlo procedure capable to make it possible the evaluation of the overvoltage probability due to both indirect and direct strokes. The results are presented making reference to specific nodes of medium voltage overhead distribution networks, namely the locations of MV/LV transformers connections. The problem is of interest when a major upgrade of surge arresters is required, for instance when the neutral grounding practice needs to be changed (e.g. from grounded to resonant).

In the past decades the impact of natural events in industrial plants have triggered a number of technological accidents. Accidents may be followed by the release of relevant quantities of hazardous substances, with relevant consequences for the population and for the environment. Technological accidents triggered by natural events are very common in the industrial facilities, although only recently their specificity was recognized and they are now indicated as Natech (natural-technological) events. In particular, lightning strikes are a recognized hazard that causes the loss of large quantities of product and compromise the safety for chemical and oil industries. Past accident analysis evidenced that the most vulnerable installations to lightning strike are oil tank terminals of oil refineries. Since there is general agreement that a total protection from lighting hazard is impossible, quantitative risk assessment is needed to assess the possibility of technological accidents caused by lightning strike. The aim of the present study was the development of a dedicated methodology for the quantitative assessment of risk due to technological accidents triggered by lightning strikes in chemical and process industries. In particular the accidental scenarios have been identified and the frequencies for every scenario have been calculated. The method developed was applied to assess the risk reduction that can be achieved by the installation of air terminals to protect storage tanks in lightning prone zones. Different solutions are compared in order to select the best protection system for different storage tanks and lay-outs. © Copyright 2014, AIDIC Servizi S.r.l.

The specification of the withstand voltage of apparatuses as well as the location and characteristics of overvoltage limiting devices to be installed to protect them, requires a careful estimation of the fast front over-voltages, which might potentially exist on the system. This is usually done using an EMTP-like software program. The components of the electrical system located in the vicinity of the apparatuses under consideration are modeled to represent their high-frequency behavior. The precision on the results provided by this approach is limited by the uncertainty in the knowledge we have of key-parameters like, for instance, the value of the grounding resistance of towers or the value of the stray capacitance of some elements. We propose in this paper to examine the consequence of these uncertainties upon the precision of the final results provided by EMTP-like software program’s simulations, using stochastic collocation on a practical case of lightning study.

The paper presents a Mixed Integer Linear Programming (MILP) model for the solution of the three-phase volt/var optimization (VVO) of medium voltage unbalanced distribution feeders. The VVO of a distribution feeder is aimed at calculating the most efficient operating conditions by means of the scheduling of transformers equipped with an on-load tap changer and distributed reactive power resources (such as embedded generators and switchable capacitors banks). The proposed model allows the representation of feeders composed by three-phase, two-phase, and single-phase lines, by transformers with different winding connections, by unbalanced wye- and delta-connected loads, by three-phase and single phase capacitor banks and embedded generators. The accuracy of the results is verified by using IEEE test feeders.

AES Sul, a Brazilian electric distribution utility, has recently started a project focused on the installation of neutral resonant grounding devices at the medium voltage side of some substation transformers previously operated with solid grounded neutral. As a consequence of the expected increase of the voltage in the sound conductors during phase to ground faults, all the surge arresters must be replaced with ones with increased rating. In order to minimize the number of required surge arresters, a procedure has been developed for the estimation of the annual number of lightning events causing concomitant faults in more than one phase conductor. The paper describes the procedure, which takes into account all the main factors that have a significant influence on line insulation flashovers caused by lightning, and presents results obtained for the case of an overhead line with and without protection means.

The integration of distributed energy resources for the production of electrical energy is related to the evolution of future power distribution networks in order to achieve: flexibility (meeting final user's requirements); accessibility (allowing access to local generation and particularly to renewables); reliability (ensuring the highest possible security and power quality levels); economy (allowing an adequate management of energy in an efficient and competitive way).In this framework, the paper presents some results of a joint research project involving five Italian universities. The focus is on the proposition and development of the main functionalities implemented into a centralized Distribution Management System (DMS) for the operation and control of the energy resources connected to distribution networks (generation, storage and loads) and of the network itself (automation systems, protection, etc.). Architecture, hierarchical structure and relevant functions for the control, operation and management of the active distribution network, are illustrated.

The historical analysis of accidental scenarios triggered by lightning shows that the impact of a lightning on a process plant might be the initiating event of a severe accident. The analysis identifies the most common damages to the equipment as either immediate ignition of flammable atmospheres or structural damage with subsequent release. However, the available information on lighting damage to industrial equipment is fragmented and not very detailed. The aim of the present study is to define a failure model for reference equipment categories following lightning impact. Starting from the analysis of lightning damage, the possibility of equipment damage is assessed on the basis of lightning characteristics. The probability of failure is evaluated as the probability to find, in impacting lightning strikes, the minimum energy necessary to cause the loss of containment of the selected equipment. Probability distribution functions available for lightning characteristics, used together with the lightning capture frequency, allow the development of a failure probability model for reference equipment categories.

A new method for determining sheath currents as the consequence of electromagnetic coupling during line-to-ground short circuit is described in this article. This method is based on using both the current load factor and the current reduction factor. The model cables are selected to represent major constructions encountered in practice. The cable line consists of three single-core cables laid in trefoil formation and touching each other. Cable sheaths are grounded at both ends. Current load factor and current reduction factor are characteristic data of the analyzed cable line. The method presented in this paper is easy to use.

The paper deals with the dynamic behaviour of power systems when large active power imbalances occur. The influence of the response of thermoelectric units is examined using results obtained with a network simulator, taking into consideration a scenario similar to that of the Italian black-out of September 28, 2003. The importance of advanced tools for power systems dynamic simulation is stressed.