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The regularly published statistics about the European energy mix and imports from Eurostat 1 shows, that the mix in 2020 consisted of 34.5% of oil and petroleum products, 23.7% of natural gas, 12.7% of nuclear energy, 10.5% of solid fossil fuels and only 17.4% of renewables. The EU's dependence on energy imports is declining, but is still very high at 57.5%. The Ukraine war demonstrates how critical such a great dependence from untrustworthy and unreliable suppliers is. It should be clear by now that the expansion of locally produced renewable energy serves not only to protect the environment and the global climate, but also to ensure security of supply and political sovereignty. It is no longer a prediction of the International Energy Agency that locally produced renewable energies have to grow significantly, but also a political and economic demand to realize this change now and on a large scale. Such considerable changes represent a significant reduction in CO2 emissions. At the same time, however, fossil fuels that are easy to store are being replaced by renewable energy sources that are at best rather inflexible and geographically as well as temporally unevenly available. This reorientation generates new and more complex requirements to keep the existing electric power system stable, and requires a new level of capacity and flexibility, both short-term and seasonal, at regional, national and international levels. From July 4-5, 2022, around 60 experts from industry, government and academia gathered for the sixth time the impact, perspectives and solutions of grid services for a changing power system. With 11 scientific papers and 13 invited presentations, the symposium addressed future market developments, international cooperation, operation and new enabling technologies and flexibility-creating solutions. The full program of invited and scientific contributions can be downloaded at www.GridServiceMarket.com. The scientific contributions were, among others: Different electricity market designs; Flexibility shares in low voltage grids; Market attractiveness of fuel cell CHPs; Grid services with electrolysers; Systemic market view, Support for grids with battery vehicles, smart grids and additional flexibility; Real-time pricing; … see all in the table of contents. Since Corona has influenced the way people met, the symposium was a hybrid event, with physical present attendees networking traditionally and virtual attendees with remote access. All the presentations are streamed and on-demand available on www.GridServiceMarket.com/MemberZone. Below you will find the proceedings of the scientific contributions of GSM 2022 , which we kindly invite you to read. &nbsp

In its World Energy Outlook 2020, the International Energy Agency predicts that renewable energy will more than double by 2030 for achieving global net zero emissions by 2050. Renewable energy is about to replace a significant proportion of fossil fuels, which are expected to decline by more than 35% compared to 2019. Under the same scenario, it is expected that 58% of car and light truck sales will be electric- and fuel cell-driven by 2030. Such developments would represent a significant reduction in CO2 emissions, while at the same time easily stored carriers become replaced with inflexible and geographically as well as temporally unevenly available alternatives. Such a transformation puts the existing electrical energy system under stress and requires an increasing degree of capacity and flexibility, both short-term and seasonal, at regional, national and international levels. From October 19 to 20 2020, 78 experts from industry, administration and academia discussed for the fourth time the effects, prospects and solutions of grid services for a transforming electricity system. With 15 scientific papers and 17 invited presentations, the symposium dealt with market developments, international cooperation, operation and enabling technologies, virtual power plants and flexibility providing technologies. The European perspective on energy transition and the flexibility roadmap were delved into along with national perspectives for the implementation of harmonized grid services markets, where their orientation and implementation also took account of national circumstances. Expanding flexibility products, digitalization, risk hedging and advanced market design were pointed out as ways of increasing market liquidity. Crucially as important, improved weather and load forecasting algorithms for reducing the balancing gap was covered. With Corona influencing the way people met, the symposium had to be transferred to a virtual space at short notice. Although questions to the speakers had to be asked in the live chat room, no quality and quantity compared to previous years was lost. The discussions between the participants took place in break-out sessions, where personal contacts could be made. Despite travel restrictions, a very diverse and valuable exchange between experts from industry, administration and science could ultimately still take place. This gives the base and the motivation to reorganise the growing Grid Service Market symposium. Due to the shift of GSM 2020 in to autumn, the GSM 2021 will be a shorter, attractive reunion of the experts also in autumn. However, GSM 2022 is planned to be a fully physical networking and exchange event in summer in Lucerne again. Naturally the virtual attendance will be one of the new features allowing participating from all over the world, when travelling is restricted due to any reason. Enjoy now the proceedings of GSM 2020 and seek for upcoming releases.

In its World Energy Outlook 2020, the International Energy Agency predicts that renewable energy will more than double by 2030 for achieving global net zero emissions by 2050. Renewable energy is about to replace a significant proportion of fossil fuels, which are expected to decline by more than 35% compared to 2019. Under the same scenario, it is expected that 58% of car and light truck sales will be electric- and fuel cell-driven by 2030. Such developments would represent a significant reduction in CO2 emissions, while at the same time easily stored carriers become replaced with inflexible and geographically as well as temporally unevenly available alternatives. Such a transformation puts the existing electrical energy system under stress and requires an increasing degree of capacity and flexibility, both short-term and seasonal, at regional, national and international levels. From October 19 to 20 2020, 78 experts from industry, administration and academia discussed for the fourth time the effects, prospects and solutions of grid services for a transforming electricity system. With 15 scientific papers and 17 invited presentations, the symposium dealt with market developments, international cooperation, operation and enabling technologies, virtual power plants and flexibility providing technologies. The European perspective on energy transition and the flexibility roadmap were delved into along with national perspectives for the implementation of harmonized grid services markets, where their orientation and implementation also took account of national circumstances. Expanding flexibility products, digitalization, risk hedging and advanced market design were pointed out as ways of increasing market liquidity. Crucially as important, improved weather and load forecasting algorithms for reducing the balancing gap was covered. With Corona influencing the way people met, the symposium had to be transferred to a virtual space at short notice. Although questions to the speakers had to be asked in the live chat room, no quality and quantity compared to previous years was lost. The discussions between the participants took place in break-out sessions, where personal contacts could be made. Despite travel restrictions, a very diverse and valuable exchange between experts from industry, administration and science could ultimately still take place. This gives the base and the motivation to reorganise the growing Grid Service Market symposium. Due to the shift of GSM 2020 in to autumn, the GSM 2021 will be a shorter, attractive reunion of the experts also in autumn. However, GSM 2022 is planned to be a fully physical networking and exchange event in summer in Lucerne again. Naturally the virtual attendance will be one of the new features allowing participating from all over the world, when travelling is restricted due to any reason. Enjoy now the proceedings of GSM 2020 and seek for upcoming releases.

Electrical grid services refer to a range of services required by transmission and distribution system operators to maintain a reliable and balanced electrical power system. The diffusion of intermittent renewables and distributed energy resources is increasing, meaning the demand for grid services is likely to grow. GSM 2019 was the third edition of the international Grid Service Markets symposium. From July 3 to 4, 2019, 80 experts from different areas of the power market shared their knowledge and experience in the field of grid services. The topics presented and discussed were wide-ranging and included international collaboration, technologies, operations, market developments and business potential. The proceedings contain contributions from scientists all over Europe. M. Stabile et al. consider recent changes in the Italian ancillary services market, which is opening up to Virtual Qualified Units consisting of smaller scale generators, storage systems and loads. The authors present the simulation tool MODIS and the impact on the ancillary services market resulting from a new transmission infrastructure, storage systems or new Virtual Qualified Units. E. Crespi et al. discuss the modelling and optimization of a flexible PEM fuel cell power plant providing grid balancing as one of the results of the EU project GRASSHOPPER. Different layouts for a pilot plant are simulated and compared. In a second report on GRASSHOPPER, the authors report on the goal of building a MW-sized PEM fuel cell power plant and a 100 kW pilot project in Delfzijl (NL), which is integrated into a demand side management program. P. Marocco et al. analyse the techno-economic impacts of a hydrogen-based storage system suitable for micro-grid and off-grid applications as part of their work for the EU project REMOTE. The authors consider four different European sites, including solar, wind, biomass and hydro as renewable energy sources, where excess energy is fed into an electrolyzer. M. Alkämper, S. Stypka, B. Oberschachtsiek and A. Heinzel report on test results of PEM, alkaline and solid oxide electrolysis systems, measuring reaction time, stack stability, durability of the balance of plant components and maintenance effort in dynamic operation, as performed for the Carbon2Chem project. X. Zhang and B. S. Oh investigate a hydrogen power generation system that provides a zero-emission renewable energy solution for energy independent islands, such as Gageodo Island, South Korea. K. Poplavskaya, F. Ocker and K.-M. Ehrhart analyze the effects of the sequence and timing of different marketplaces on the bidding behavior of market participants, including balancing markets. The authors develop a theoretical bidding calculus for participants in multiple markets based on decision theory. I. Kockar et al. report on the European SmartNet project, in which they investigate new market architectures to enable the participation of distributed energy resources in energy and ancillary service markets. V. Klemenz, T. M. Mbavarira and C. Imboden analyse the effects of participation in balancing markets on hydrogen production costs. J. Bagemihl et al. propose a novel market-based approach for the use of dynamic load management in the medium-voltage grid to avoid grid extensions as carried out in the EU Power Alliance project. S. Parella et al. propose a hierarchical clustering method for the offers accepted in the electricity market and assess the affordability of energy storage systems capable of providing ancillary services in different market areas. R. Reissner et al. report on the FCH JU QualyGridS project, which aims to establish standardized test protocols for electrolysers to provide electricity grid services. Finally, J. Kučica reports on the Core CCR project, which implements the methodology of flow based capacity calculation. The GSM 2019 is supported with funds from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract No 17.00009 and the Fuel Cells and Hydrogen 2 Joint Undertaking under agreements No 735485 and 700339.

Electrical grid services refer to a range of services required by transmission and distribution system operators to maintain a reliable and balanced electrical power system. The diffusion of intermittent renewables and distributed energy resources is increasing, meaning the demand for grid services is likely to grow. GSM 2019 was the third edition of the international Grid Service Markets symposium. From July 3 to 4, 2019, 80 experts from different areas of the power market shared their knowledge and experience in the field of grid services. The topics presented and discussed were wide-ranging and included international collaboration, technologies, operations, market developments and business potential. The proceedings contain contributions from scientists all over Europe. M. Stabile et al. consider recent changes in the Italian ancillary services market, which is opening up to Virtual Qualified Units consisting of smaller scale generators, storage systems and loads. The authors present the simulation tool MODIS and the impact on the ancillary services market resulting from a new transmission infrastructure, storage systems or new Virtual Qualified Units. E. Crespi et al. discuss the modelling and optimization of a flexible PEM fuel cell power plant providing grid balancing as one of the results of the EU project GRASSHOPPER. Different layouts for a pilot plant are simulated and compared. In a second report on GRASSHOPPER, the authors report on the goal of building a MW-sized PEM fuel cell power plant and a 100 kW pilot project in Delfzijl (NL), which is integrated into a demand side management program. P. Marocco et al. analyse the techno-economic impacts of a hydrogen-based storage system suitable for micro-grid and off-grid applications as part of their work for the EU project REMOTE. The authors consider four different European sites, including solar, wind, biomass and hydro as renewable energy sources, where excess energy is fed into an electrolyzer. M. Alkämper, S. Stypka, B. Oberschachtsiek and A. Heinzel report on test results of PEM, alkaline and solid oxide electrolysis systems, measuring reaction time, stack stability, durability of the balance of plant components and maintenance effort in dynamic operation, as performed for the Carbon2Chem project. X. Zhang and B. S. Oh investigate a hydrogen power generation system that provides a zero-emission renewable energy solution for energy independent islands, such as Gageodo Island, South Korea. K. Poplavskaya, F. Ocker and K.-M. Ehrhart analyze the effects of the sequence and timing of different marketplaces on the bidding behavior of market participants, including balancing markets. The authors develop a theoretical bidding calculus for participants in multiple markets based on decision theory. I. Kockar et al. report on the European SmartNet project, in which they investigate new market architectures to enable the participation of distributed energy resources in energy and ancillary service markets. V. Klemenz, T. M. Mbavarira and C. Imboden analyse the effects of participation in balancing markets on hydrogen production costs. J. Bagemihl et al. propose a novel market-based approach for the use of dynamic load management in the medium-voltage grid to avoid grid extensions as carried out in the EU Power Alliance project. S. Parella et al. propose a hierarchical clustering method for the offers accepted in the electricity market and assess the affordability of energy storage systems capable of providing ancillary services in different market areas. R. Reissner et al. report on the FCH JU QualyGridS project, which aims to establish standardized test protocols for electrolysers to provide electricity grid services. Finally, J. Kučica reports on the Core CCR project, which implements the methodology of flow based capacity calculation. The GSM 2019 is supported with funds from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract No 17.00009 and the Fuel Cells and Hydrogen 2 Joint Undertaking under agreements No 735485 and 700339.

To successfully accomplish electro-mobility integration into city traffic, plans for the installation of adequate public charging infrastructures are of utmost importance. The assessment of the effects of the transients caused by the concurrent charging of a large number of electric vehicles to the operating conditions of the power network is part of such a planning development. The paper summarizes some of the work carried out in the authors’ laboratories to accomplish such an assessment. In particular it describes the co-simulation platform integrating a) a mobility simulator suitably adapted to reproduce e-mobility in a typical middle-size Italian city center with b) a dynamic simulator of the power distribution network and with c) a simulator of a UMTS communication network, which has been developed to this purpose. The platform is shown to be able to support the development and performance test of specific countermeasures against power components overload, voltage variations and unbalances.

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.

Several accidents that occurred in the last decades evidenced that the impact of natural events in industrial plants may trigger accidental scenarios involving the release of relevant quantities of hazardous substances. Severe scenarios typical of the process industry, as fires, explosions, toxic releases, and water pollution were reported as the consequence of natural events in industrial areas. The specific features of technological accidents triggered by natural events were recently recognized, and these scenarios are now indicated as NaTech (natural-technological) accidents. The screening of past accident databases points out that NaTech scenarios are quite common in industrial facilities. Past accident analysis evidences that lightning is one of the most common initiator event for fires in oil refineries and tank farms. In most facilities, simple lightning protection measures, such as grounding or lighting rods, are implemented to reduce the risk due to lightning strikes. However, several accidents suggest that these measures may not be sufficient to retain the structural integrity of the equipment. In the present study a procedure for the determination of the mitigation effect due to lightning rods on storage tank farms is proposed. A statistical method was developed to evaluate the failure frequency of tanks due to lightning strikes. The model includes both the assessment of lightning impact probability and of tank damage conditional probability given the lightning impact. The method then considers the effect of lightning rods placed at given distances from the equipment items and calculates the reduction of the failure frequency due to attraction competition between the rods and the equipment. The procedure was implemented in a GIS-based software tool for the calculation of individual and societal risk. The method allows the assessment of the effect of lightning protection in terms of individual risk reduction.

We present a method for the evaluation of the sea return impedance term to be employed in the construction of the per-unit-length parameter matrix which is required to describe submarine cables in Electromagnetic Transient software. We evaluate the sea return impedance using the quasi Monte Carlo technique, and an adapted sequence of pseudo-random variables to get a faster convergence. In the calculation of the impedance integral we employ a change of variable in order to reduce its oscillatory behavior and allow it to converge. We also introduce the stochastic collocation technique in order to analyze the impact of uncertainties on the knowledge of the input parameters. This technique is well adapted to numerical calculations; it gives results similar to those obtained with a standard Monte Carlo method, but requires a minor number of computations, some units, instead of the thousands needed with the Monte Carlo method; this is an advantage because the computation time with the latter method would be too long. Furthermore this technique is non intrusive and thus does not necessitate a modification of the function. We show that for the evaluation of the sea return impedance a certain inaccuracy in the knowledge of the cables laying configuration and of the conductivities of the soil can be tolerated in some cases.

Various parameters of lightning discharges will be reviewed. Both common negative and less frequent but potentially more destructive positive and bipolar flashes will be covered. Direct lightning current measurements on instrumented towers will be discussed. Properties of first and subsequent strokes will be compared. The average number of strokes per flash and multiple channel terminations on ground will be considered. Parameters of subsequent strokes in natural lightning will be compared to their counterparts in rocket-triggered lightning. New insights into the lightning processes gained from triggered-lightning experiments will be discussed.

The improvement of the reliability and power quality levels of electric systems is a matter of increasing concern because today’s equipment are much more susceptible to power quality issues than was equipment used in the past. Distribution networks are often located in areas with high ground flash densities, being therefore subject to lightning-caused power interruptions. As a significant number of line faults and equipment damages, as well as malfunction of customer electronic systems, is lightning-associated, many studies have been carried out, especially on medium voltage (MV) lines, aiming at obtaining a better understanding of the characteristics of the lightning overvoltages. More recently, special attention has been drawn to the transients on low voltage (LV) networks. Due to their much lower withstand capabilities in comparison with those of MV lines, LV networks are more prone to lightning electromagnetic interferences.

The aim of this document is to provide an extended description and application guide of methods belonging to the so-called Numerical Electromagnetic Analysis (NEA) applied to the calculation of electromagnetic transients in power systems. As known, the accurate computation of electromagnetic transients is a fundamental requirement of several studies in the area of power systems. Lightning and switching studies are, for instance, typical subjects where the accuracy of transient’s computation has a direct influence to the proper sizing of components like insulators and breakers. Traditional approaches adopted since now were based on the combination of circuit and transmission lines theories. These approaches, analytically and numerically validated by numerous contributions to the literature, rely on specific assumptions that are inherently relaxed by NEA methods. Indeed, NEA methods mostly rely on the numerical solution of the full-wave Maxwell’s equations and, in this respect, the assessment of their accuracy, as well as the description of the various numerical methodologies, have motivated the preparation of this Technical Brochure.

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.

Le celle a combustibile (Fuel Cells - FCs) a bassa temperatura sono potenzialmente utilizzabili per applicazioni cogenerative, sia nel settore residenziale sia nel terziario. L’energia elettrica prodotta può essere utilizzata o accumulata ed è possibile recuperare la potenza termica fornita durante il funzionamento di tali sistemi. Dal 2003 è condotto un programma di ricerca in collaborazione fra i dipartimenti DIEM e DIE dell’Università di Bologna sulle FCs e sulle applicazioni cogenerative delle stesse. Sulla base dei risultati ottenuti anche mediante la realizzazione di un sistema prototipale della taglia di alcuni kW si vuole ora proseguire tale studio mediante lo sviluppo del progetto di ricerca “stazione di prova per sistemi a cella a combustibile” presso il Tecnopolo di Ravenna, nell’ambito del CIRI Energia e Ambiente. La finalità del progetto è la caratterizzazione completa di un sistema energetico complesso basato su FCs e accumuli. Nel presente articolo si illustrano le caratteristiche del banco prova che si intende sviluppare per il progetto.

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.

Overvoltages due to direct and indirect lightning events depend on several factors and are characterized by complex wave shapes. For this reason numerical codes have been developed, aiming at the evaluation of the lightning overvoltages on realistic distribution line configurations. These tools are of fundamental help in the protection scheme design and the insulation coordination of actual distribution systems, as well as in evaluating the overvoltages transferred through distribution transformers to the low voltage part of the system. The basic information for designers of lightning protection of MV and LV networks has been presented in the part 1 of this guide. This second part presents an application of the basic information to the lightning protection of MV networks containing overhead lines3. This part of the guide applies primarily to MV networks with system voltage in the range from 1 kV to 36 kV. It is relevant for higher system voltages as well, but it becomes gradually less relevant when the system voltage increases. It is thus not possible to specify an upper limit for the system voltage, but the guide should not be used for system voltages above 50 kV.

This lecture focuses on lightning performance of transmission and distribution lines. Modeling procedures and source data recommended by CIGRE and IEEE are reviewed and compared. Emphasis is given to differences, when present, between procedures proposed in the two frameworks. First, transmission lines performance is covered, with special attention to statistical distribution of lightning current amplitude, to the attachment process, and to the assessment of the shielding failure and backflashover rates. Distribution lines performance is then dealt with, with special attention to electromagnetic coupling models, to statistical procedures to evaluate the line lightning performance, and to the influence of the distribution line configuration on the final results. Joint CIGRE-CIRED WGs have produced relevant documents that this lecture is in part aimed at summarizing and at comparing with what accomplished on the same subject within the IEEE framework. The need for re-assessment of data and modeling procedures is emphasized, and reference to new initiatives in this respect is also made.

An extended analysis of past accident data indicated that lightning events may cause significant damage to process equipment handling dangerous substances, often leading to an extended loss of containment followed by fires, explosions or toxic releases. Data reported in the literature show that lightning caused 150 out of 480 tank fires reported in industrial accident databases between 1951 and 2003. The industrial accident databases indicate that lightning impacting on chemical plants is among the most important causes of the technological accidents triggered by natural events that are usually referred to as NaTech accidents. Considering specifically storage and processing activities, lightning events account for 61% of the accidents initiated by natural events. Moreover, due to the increasing frequency and intensity of severe storms, the frequency of such accidents may grow in the future. Nevertheless, a limited work has been dedicated to the development of quantified assessment procedures for the industrial risk generated by lightning phenomena in sites were relevant quantities of hazardous substances are present. The present study focused on the assessment of the lightning hazard and on the development of a detailed methodology for the quantitative assessment of the industrial risk due to loss of containment events triggered by lightning in the chemical and process industry. The procedure takes advantage of the progress made in recent years in the assessment of the expected frequency due to lightning. The methodology was developed within a common framework for the quantitative assessment of risk due to external hazard factors in chemical and process plants.

Monitoring units for the measurement of high frequencyvoltage transients have been in operation at three different busses of an Italian medium voltage (MV) distribution feeder, mainly composed by overhead lines, in March 2007 – August 2008. The feeder is located in a region characterized by a high ground flash density value (4 flashes/km2/yr); many of the recorded voltage transients may be correlated with the lightning events detected for the same region by the Lightning Location System (LLS) CESISIRF. The paper presents some experimental results obtained using the monitoring units and their comparison with computer results obtained using a LIOV-EMTP model of the considered MV feeder. A procedure aimed at achieving the best fit between measurements and calculations, which takes into account the uncertainties associated with LLS data, is also presented.

The evaluation of electromagnetic field coupling to transmission lines is an important problem in electromagnetic compatibility. The use of the transmission line (TL) approximation theory has permitted the solution of a large range of problems (e. g. lightning and EMP interaction with power lines). However, the continual increase in operating frequency of products and higher-frequency sources of disturbances (such as UWB systems) makes TL basic assumptions no longer acceptable for a certain number of applications. In the last decade or so, the generalization of classical TL theory to take into account high frequency effects has emerged as an important topic of study in electromagnetic compatibility. This effort resulted in the elaboration of the so-called "generalized" or "full-wave" TL theory, which incorporates high frequency radiation effects, while keeping the relative simplicity of TL equations.

In this paper, the developed formulation, which we shall call the ‘‘reference’’ one, is used to assess the validity of the most popular simplified approach for the calculation of the lightning electromagnetic field over a conducting earth, namely, the Cooray-Rubinstein (CR) approximation. This formula provides a simple method to evaluate the radial component of the electric field which is the component most affected by the finite ground conductivity and which plays an important role within the Agrawal et al. (1980) field-to-transmission line-coupling model. Several configurations are examined, with different values for the ground conductivity and different field observation points. A thorough analysis of all the simulated field components is carried out and comparisons are also made with the ‘‘ideal’’ field, namely, the field that would be present under the assumption of perfectly conducting ground. It is shown that for channel base current typical of subsequent strokes and for very low conductivities, the CR formula exhibits some deviations from the reference one but it still represents a conservative estimation of the radial field component, since it behaves as un upper bound for the exact curve. The developed algorithm is characterized by fast performances in terms of CPU time, lending itself to be used for several applications, including a coupling code for lightning induced overvoltages calculations.

For the accurate statistical assessment of the lightning performance of distribution lines one needs to take into account the presence of protection devices such as surge arresters and shielding wire/neutral groundings. Indeed, the presence of those devices can significantly modify the indirect lightning response of the overhead line and, therefore, the relevant lightning performance. In particular, this paper aims at investigating the impact of the presence of surge arresters on the indirect lightning performance of overhead distribution lines having realistic configuration. Specifically, reference is made to typical Italian distribution lines. The investigation is performed with the help of a statistical procedure developed by the authors – based on the Monte Carlo method and of the use of an accurate modelling/calculation tool for the induced surges – that has been recently compared with one proposed in the IEEE 1410 Std for the same purpose, and shown to be more complete and suitable for the problem of interest. The paper also aims at investigating the influence of the presence of surge arresters on the indirect lightning surges transferred through power transformers. Such an additional investigation is performed by means of a suitable high-frequency power transformer mode integrated with the lightning-induced computation tool.

Study Committee C4 was one of the new study committees created as a result of the restructuring of CIGRE in 2002. It has a relatively broad mandate, and is responsible for facilitating and promoting progress in the development of methods and tools for analysis of power system performance related to the following five fields: - Power Quality - Electromagnetic Compatibility - Insulation Coordination - Lightning - Power System Security SC C4 is essentially a merger of significant parts of three former study committees: SC 33 «Insulation Coor dination»; SC 36 «Power System Electromagnetic Com patibility”; Comp atibility”; and SC 38 «Power System Analysis and Techn iques”. It brings together all activities related to the power system “technical” performance under one study committee, thus providing for the coordination and integration of these activities. In addition, it leads to “broadbased” expertise essential for effectively dealing with complex technical issues of present-day power systems. In carrying out studies and other work necessary to meet its objectives, SC C4 takes into account a number of external factors: technological evolution of the electri cal power industry; environmental impact considerations; impact of socio-economic, sociopolitical and ownership changes on power systems; and the changing needs for developing standards and recommended practices at national and international levels. Co-operation with other CIGRE committees and with external organizations is a key factor in this regard. SC C4 has established strong ties to CIRED and IEC, particularly in the activities related to Power Quality and Electromagnetic Compatibility. Cooperative relationships have also been established with IEEE PES, UIE, ITU-T and EURELECTRIC. A key focus of the planned activities of SC C4 is on technical challenges related to power system physical performance that need to be addressed by system planners, equipment suppliers, network operators. The technical activities of SC C4 have been organized in terms of the five distinct areas related to power system performance. Advisory Groups have been set up to assist in the planning and steering of the activities in each of the five areas. The following are the current and future planned activities in each area.

To appropriately infer the correlation between lightning events and flashovers/voltage dips on real distribution networks, data coming from lightning location systems are certainly needed, but need to complemented on the one hand by data coming from distributed measurement systems able to record both protection manoeuvres and lightning-originated transients, and on the other hand by accurate calculation results. Additionally, the analysis needs to be performed on a statistical basis. The paper illustrates the main concepts used in developing a procedure aimed at inferring the above mentioned correlation, which is based on the integrated use of experimental data obtained from the Italian lightning location system CESI-SIRF, a monitoring system of relay operation, a distributed monitoring system of lightning-induced transients and of calculations performed using the LIOV-EMTP code. The application of the procedure to the portion of a real distribution network located in Italy in a high level keraunic area is presented by making use of some CESI-SIRF-detected events.

Contributions to SC C6 Session on Paper C6-304 – Preferential Subject 3 - Innovative distribution systems facilitating widespread deployment of DER

The introduction of generators in distribution grids, possibly together with storage systems, could cause a substantial change in grid operational practice: currently a rising idea proposes to treat generators and even loads as distributed resources that are able to supply services to the grid and accept on-line requests. To emphasise the advantages of Distributed Generation (DG) it is necessary to face the problem with a system approach. In this work both services coming from each generator and deriving from the co-ordination of different resources have been investigated. A complex master-slave configuration has been discarded in order to avoid the necessity of fast communication and control actions. Instead a model based on a centralised dispatcher and plug-and-play functionality for generators has been chosen. For that purpose, a distinction is made between fast transient dynamics, due to uncontrollable load changes, and slow modifications of the system conditions, due to increase/decrease of loads during a day, a week or a month. Individual generators have been requested to give response to fast and unpredictable transient dynamics, i.e. to participate to voltage and frequency regulations, harmonic compensations and phase balancing, while the central dispatcher has been requested to deliver proper set-points in order to allow each generator to offer its services in an appropriate way, either for the actual and the foreseen grid conditions. To realise voltage and frequency regulations, a droop control algorithm has been designed and implemented on board of some generators coupled to the grid by inverter technology. In that scenario each machine, working in parallel with the others, takes on part of the regulation according to its possibilities. The focus of the paper is on the architecture of the system and on the modules that a centralised dispatcher has to incorporate. The main topics are: the short-term forecasts of the power produced by renewable energy, the short-term forecasts of uncontrollable low voltage distribution loads, the state estimation of LV grid, the use of load flow, the definition of objective functions for economical optimisation, the sub-grid regulation and the Test Facility set up in CESI, where some experiments have been done. The conclusion of the activity is that the high penetration of DG could become an opportunity rather than be considered as a problem. The distributed resources could be used to control the voltage profiles, the power flows, the separations from the main distribution grid and islanding operations. The activities was supported by a National Research Project named GENDIS 21- Distributed Generation for the Improvement of Power Quality and Environment.

La prima parte della memoria riporta i risultati di un’analisi della capacità complessiva del parco di produzione elettrica italiano, nella sua composizione attuale, a reagire a squilibri di potenza. Viene fatto riferimento ad alcune situazioni reali d’esercizio verificatesi di recente. La seconda parte è motivata dal previsto rapido diffondersi delle unità operanti in ciclo combinato gas-vapore. E’ illustrato un modello di un impianto di produzione a ciclo combinato, implementato in ambiente Matlab-Simulink, che consente lo studio preliminare del comportamento di tale tipo d’unità in occasione di variazioni di frequenza improvvise e severe. I risultati ottenuti mostrano l’importanza delle prescrizioni tecniche attinenti alla connessione dei generatori alla rete elettrica, al fine di garantire in maniera durevole la capacità del sistema di reagire adeguatamente agli squilibri di potenza.

This brochure presents basic information and principles related to lightning protection of Medium Voltage (MV) and (LV) networks. The present material constitutes the first part of a 3-part guide. Parts 2 and 3, to be published later, will deal specifically with the application to MV (Part 2) and LV (Part 3) networks. This part provides first a survey of different sources of overvoltages, as well as a review of the most widely accepted and well established methods of evaluating the expected rate of direct lightning strokes and induced lightning overvoltages. The document describes in addition the characteristics of lightning overvoltages, general characteristics of surge protective devices, and earthing systems.

The paper deals with the stresses of cable insulations due to lightning induced overvoltages for the case of distribution networks composed by MV overhead lines and buried cables. We are here interested only in the conditional probability of the cable breakdown in absence of line flashovers, which means that flashovers along the overhead line are disregarded. We illustrate a procedure based on the application of the Monte Carlo method and on a simulation tool for the accurate computation of lightning-induced voltages on an overhead line, namely the LIOV code. A frequency dependent parameter cable model is used for the calculation of the overvoltages stressing the cable insulation, which is assumed not to be illuminated by LEMP. We associate to each calculated overvoltage a breakdown probability for the cable, by using experimentally obtained probabilistic distributions of the breakdown voltages of the cable insulation for different families of voltage wave shapes. These probabilities, together with the expected number and characteristics of the lightning events, allow us to infer the yearly number of expected failure events in the above assumptions. The breakdown behavior of extruded cable insulation is represented by a 2-parameter Weibull distribution obtained from experimental tests on cable models, manufactured with the same materials and same technologies of real cables, by applying the well-known statistical “enlargement law”.

The aim of this paper is to analyze and compare the lightning performances of different configuration of overhead distribution lines. The results are obtained within the partnership among AES Sul Utility Company, Federal University of Itajubá and University of Bologna. The resultant performance is presented in terms of expected faults for 100 km of line for a density of discharges to the ground (GDF) of 1 discharge/km²/year. Commentaries on the relative performance and comparisons are presented

Methods aimed at locating the position where a fault is occurred can be seen as part of a complex measurement system oriented at more general power quality purposes. This paper faces the comparison between two methods recently proposed in literature for fault-location in distribution networks, based on a distributed and on a single-ended measurement system, respectively. By assuming a common distribution system topology, the two methods are applied in order to compare their performances as well as the obtained results. On the basis of the different drawbacks and advantages shown by the two methods, potential improvements are eventually taken into account, and a possible integration of the two approaches is investigated and discussed.

Con riferimento al problema dell'instabilità delle tensioni delle reti di trasmissione, viene proposta una soluzione protettiva di grandi aree di rete, molto efficace, capace di mantenere ai valori alti desiderati le tensioni, anche durante i transitori di disalimentazione dei carichi, annullando il rischio di black-out. La soluzione proposta, che ha caratteristiche di estrema semplicità funzionale e realizzativa, si avvale della presenza operativa del sistema gerarchico di controllo delle tensioni di rete che realizza le regolazioni Secondaria e Terziaria di tensione.

We investigate the effect of the finite conductivity of the ground on the amplitude and waveshape of electromagnetic fields radiated by lightning return strokes to tall towers. The study is based on the engineering return stroke models extended to take into account the presence of a vertically-extended strike object. The propagation along a finitely-conducting ground is taken into account using Cooray’s approach. Simulations are presented for a homogeneous ground and considering three cases: (1) a return stroke initiated at ground level, (2) a return stroke to a 168-m tall tower corresponding to the Peissenberg tower, and (3) a return stroke to a 553-m tall tower corresponding to the CN Tower. It is shown that the propagation along an imperfectly conducting ground causes the amplitude of the field to decrease and its risetime to increase with decreasing ground conductivity. In addition, it was found that some of the fine structure of the electromagnetic field associated with transient processes along the struck tower vanishes due to propagation effects.

The role that can be played by thermo electrical power plants in the restoration procedure after blackout events, is discussed in the paper, with particular reference to steam thermoelectric plants repowered by gas turbines (GT) that are provided with bypass valve of the GT exhaust flow. The reassessment of restoration plans, which is taking place in several countries as a consequence of the liberalization of the electrical energy market, renders the above issue of utmost interest. Some results of an investigation carried out in cooperation between University of Bologna and ENEL-CESI are reported. The black start up capability of gas turbines can be exploited by implementing adequate procedures and automatic control devices that would render it possible also for the combined cycle power plant to autonomously start up and contribute to the restoration process after black out.

Contributions to SC C4 Session on Paper C4-303 – PREFERENTIAL SUBJECT 3 - Lightning performance of MV systems.

Recent power quality studies have been focused on the source-identification of voltage disturbances at distribution network busses. This paper describes a method aimed at correlating indirect-lightning events with power systems relay operations, associated with voltage dips. The proposed method, based on the coordinated use of the Italian lightning location system CESI-SIRF, the Italian monitoring system of protection manoeuvres CESI-SAM, and the availability of an advanced simulation tool for the accurate simulation of lightning-induced voltages on complex power networks, namely the LIOV-EMTP code, is applied to the real case of an Italian distribution system. The LIOV-EMTP code is also employed along with a statistical procedure based on the Monte Carlo method to carry out a statistical analysis aimed at assessing the lightning performance of a typical Italian distribution line.

Measures for improving the lightning protection performance of schemes applied to overhead power distribution lines are discussed in this guide.