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In turn, this requires the ability to clear overhead line faults, either by means of circuit breakers tailored for HVDC applications, providing adequate breaking current ratings at line voltage [[2]], or by adopting converter topologies intrinsically able to interrupt DC fault currents [[3]], i.e., full-bridge or similar. In [[11]], a different DC breaker architecture based on the superconductive elements' double quench is modeled in the software PSCAD/EMTDC, and the fault current interruption is analyzed for two scenarios, i.e., "larger" and "lower" fault current values. Multiterminal DC (MTDC) systems fault analysis and protection is discussed in several papers, either from the perspective of the system or of its components (i.e., DC breakers) [[5]]. Lacking operational DC circuit breakers, DC cables are the only option for HVDC-VSC transmission, but in some cases, cables might be preferred to overhead lines due to their reduced environmental impact and the rather intricate authorization processes which discourage the realization of new overhead power lines. [Extracted from the article]

Rapidly convergent series are derived to efficiently evaluate a class of integrals involving the product of spherical Bessel functions of the first kind occurring in acoustic and electromagnetic scattering from circular disks and apertures. Depending on the involved parameters, the series can be further reduced to closed-form expressions in terms of generalized hypergeometric functions or Meijer G-functions, which can immediately be evaluated through current mathematical toolboxes. Numerical results are provided showing that the accuracy of the series representation can easily be controlled and that the proposed solutions are at least 1000 times faster than specific quadrature schemes which, in general, have to deal with irregularly oscillating and slowly decaying functions. • Efficient evaluation of improper integrals involving the product of spherical Bessel functions. • Efficient expressions in terms of rapidly convergent series and/or in terms of special functions. • Speed-up factor larger than 1000 with respect to the most updated quadrature routines. • Detailed numerical comparisons shows the accuracy and the efficiency. • Possibility to extend the approach to other integrals occurring in different field of physics. [ABSTRACT FROM AUTHOR]

The twenty-four papers in this special section focus on electromagnetic shielding and absorbers. [ABSTRACT FROM AUTHOR]

During transients involving multiconductor lines, the importance of the ground finite conductivity is well known and various techniques and expressions have been presented in literature for the inclusion of its contribution into the per unit length parameters. The direct time domain approach based on the introduction of the transient parameters and on the numerical solution of the telegrapher's equations demonstrated to be accurate and efficient for the analysis of typical transients. In this letter, the expressions for the ground transient resistance for underground cables, based on the closed-form inverse Laplace transform of the classical Pollaczek expressions (valid for the low-frequency-range), are presented and discussed. [ABSTRACT FROM AUTHOR]

The shielding performance of different buildings in presence of indirect lightning return strokes are investigated directly in the time domain. To this end, a sensitivity analysis is conducted by varying the channel geometrical characteristics and considering three different buildings. The performance is evaluated by adopting the time-domain shielding parameters recently proposed, which appear to be suitable for shielding studies in presence of lightning electromagnetic pulses. The results confirm the usefulness of introducing different parameters to fully characterize the shielding behavior of buildings exposed to lightning electromagnetic fields. [ABSTRACT FROM PUBLISHER]

The assessment of the shielding effectiveness of enclosures under transient conditions calls for an accurate analysis of fundamental aspects. Stemming from a correct understanding of the coupling mechanism and from a victim point of view, new shielding parameters are proposed as figures of merit to designate the actual effectiveness of an electromagnetic enclosure. Their suitability is tested in different configurations excited by typical transient electromagnetic threats. [ABSTRACT FROM PUBLISHER]

The aim of this work is to design an innovative exposure system that enables accurate reproduction of various high-frequency exposure environments for the experiments. Attention is given to the solution of the general problem concerning the design of an antenna system, given a set of constraints on the field components profiles. Special reference is made to the replication of the field distribution due to radio base (RB) stations for mobile communications, but the procedure may be applied to other sources as well, without significant modifications. The sources adopted for this purpose are microstrip antennas. The field profiles obtained by means of the realized source system have been measured and compared favorably with the design specifications. The root means square (rms) value and the polarization and spatial variations are replicated. [ABSTRACT FROM AUTHOR]

This paper describes a versatile exposure system for the reproduction of static and extremely low-frequency (ELF) magnetic fields. The system can be used for in vitro and in vivo experiments. The exposure setup consists of six circular loops, each placed on the face of a cubical box and suitably fed. The paper shows, by means of a genetic-algorithm approach to optimize the degrees of freedom of the system, that such a configuration allows a given magnetic field to be reproduced, with great accuracy, in amplitude, phase, and polarization, on a specific surface of interest. The paper provides details of the design procedure and presents extensive numerical simulations that confirm the validity of the proposed design procedure. [ABSTRACT FROM AUTHOR]

Presents a method for the analysis of ferro-magnetic shields under low-frequency excitation conditions. Demonstration of the validity of the analysis; Orientation of current loops and multiconductor lines; Solution to relevant equations in the time domain by adopting a finite element procedure.

Studies the shielding performance of planar shields against near field sources. Background on shielding theory; Shield characteristics; Types of source frequencies; Time domain modeling of the electromagnetic field propagation through the shield.

In high-voltage transmission lines, the continuity of shield wires is often broken to reduce losses. The accurate simulation of the effects of this practice on power line communications in multiconductor transmission lines is performed in order to put in evidence the relevant channel features and the consequences on the radiated electromagnetic fields. [ABSTRACT FROM PUBLISHER]

The analysis of the shielding performance is conducted on the basis of the classical IEEE Standard 299, which is typically a local and frequency-domain approach, may be not sufficient for the thorough appraisal of protection levels achievable through actual enclosures in the presence of transient electromagnetic fields. Stemming from a victim point of view, a new, global approach is proposed for the assessment of average and minimum guaranteed shielding performance directly in the time domain, in the presence of either near fields or plane waves. The method is suitable for the analysis of all the typical transient EMI phenomena and recommended for the analysis of protection levels of mission-critical devices or systems. An elementary statistical analysis of performance data is also presented. [ABSTRACT FROM PUBLISHER]

The magnetic shielding effectiveness of a single planar screen of infinite extent against a parallel current loop source is evaluated through an analytic closed-form expression which is valid for arbitrarily thick screens and for any source-observation distance. The only assumption in the formulation consists in considering small loops having a constant current. The resulting formula can be expressed in terms of only elementary functions and is believed to represent the most general closed-form expression for the magnetic shielding effectiveness of a planar screen in the presence of a parallel loop. Numerical results are provided to show the generality and the validity of the proposed formula. [ABSTRACT FROM AUTHOR]

The field penetration through a circular aperture in an infinite plane with a nonzero surface impedance excited by an axially symmetric source is analytically investigated. The problem is formulated in terms of an original dual-integral-equation approach and solved through the method of moments in the Hankel spectral domain. The proposed formulation is applied to the calculation of the axial magnetic field when the source is a current loop of finite radius coaxial with the aperture and it is shown that it is possible to separate the contributions of the aperture and of the nonzero impedance plate to the transmitted field. In the case of low frequencies and small apertures, closed-form expressions are also derived. Moreover, the approach is also applied to the case of a perfectly conducting plane giving rise to results that coincide with those recently presented in the literature. Finally, the accuracy of the proposed approach is validated through full-wave calculations. [ABSTRACT FROM AUTHOR]

Day-ahead PV production forecasting can be crucial not only for energy allocation in the day-ahead market, allowing the direct participation in markets of PV power plants and aggregated systems, but also for predictive maintenance. This means that if the correlation between environmental factors and PV degradation rates is known, these can be estimated for any location worldwide, even before PV systems are operational. The number of field data to analyze increases as PV systems become larger, making manual PV monitoring more and more challenging. In [[20]], the authors use long short-term (LSTM) neural networks on a multivariate set of input data: they use publicly available weather reports and measured PV power output. [Extracted from the article]

The shielding effectiveness of artificial periodic screens is investigated with reference to high-frequency high-impedance near fields produced by arbitrarily oriented electric dipoles. The screens are formed by metallic objects of arbitrary shape displaced in a 2-D lattice. The problem is first studied through a full-wave approach, using the array scanning method in conjunction with a periodic method of moments in the spatial domain. Next, the shielding problem is solved analytically in some characteristic electromagnetic compatibility configurations through the use of approximate low-frequency homogeneous models together with a classical analysis in the spectral domain. Finally, the solutions are compared with those deriving from the use of the so-called transmission-line approximation. The provided results show the suitability of the analytical approaches in dealing with finite sources different from standard plane-wave excitations and give a useful tool for the design of periodic shields. [ABSTRACT FROM PUBLISHER]

The shielding performance of a planar metamaterial wire-medium (WM) screen under plane-wave illumination is studied. The screen consists of a finite number of periodic layers of thin conducting cylinders embedded in a dielectric matrix; in the low-frequency limit and for waves with the electric field polarized along the wire direction, such a screen can be modeled as a homogeneous slab with a plasma-like dispersive permittivity. In particular, well below the plasma frequency, the effective relative permittivity is negative and very large in absolute value, giving rise to high values of the shielding effectiveness. A comparison with a conventional planar metal screen is reported, showing how the proposed structure can be designed to be advantageous in terms of low density and weight saving. In order to be effective against arbitrarily polarized waves, the original structure is modified, adding a second WM screen with wires orthogonally oriented with respect to the first one. Numerical results are provided that illustrate the validity of the homogenized model in predicting field levels both near to and far from the screen and show the shielding performance attainable with the proposed metamaterial screen in both single. and double-layer configurations at normal incidence. [ABSTRACT FROM AUTHOR]

A novel wavelet-based technique is presented for the extraction of two-port equivalents of common printed circuit board (PCB) discontinuities. The wavelet-transformed scattering parameters of the discontinuity can be included in a wavelet equivalent of TEM wave propagation paths along the PCB in order to obtain an overall equivalent of the whole structure under analysis. The wavelet representation. minimizes the CPU time and computer storage requirements while maintaining excellent accuracy, thus, it proves to be a very useful modeling tool, especially in the design stage. [ABSTRACT FROM AUTHOR]

Research on corona discharge, shared by physics, chemistry and electrical engineering, has not arrested yet. As a dissipative process, the development of corona increases the resistive losses of transmission lines and enhances the line capacitance locally. Introducing additional losses and propagation delay, along the line, non-linearity and non-uniformity of the line parameters; therefore, corona should not be neglected. The present work is meant to provide the reader with comprehensive information on the corona macroscopic phenomenology and development, referring to the most relevant contributions in the literature on this subject. The models proposed in the literature for the simulation of the corona development are reviewed in detail, and sensitivity curves are provided to highlight their dependence on the input parameters. [ABSTRACT FROM AUTHOR]

The transmission of an electromagnetic field produced by a current loop of finite radius through a coaxial circular aperture in a perfectly conducting plate is evaluated through a rapidly convergent formulation in an exact form. By applying the equivalence principle, the problem is first formulated in the Hankel transform domain, obtaining a set of dual integral equations in which the equivalent surface magnetic current density defined on the aperture is not known. The set of dual integral equations is regularised in a second‐kind Fredholm integral equation by applying the Abel integral‐transform technique. The solution is achieved by expanding the unknown in a set of orthogonal basis functions that correctly reproduce the behaviour of the equivalent magnetic current at the edge of the aperture. Finally, under particular assumptions, a low‐frequency solution is extracted in a closed form. Numerical results are reported to validate the accuracy and efficiency of the proposed formulations. [ABSTRACT FROM AUTHOR]

The transmission of an electromagnetic field produced by a current loop of finite radius through a coaxial circular aperture in a perfectly conducting plate is evaluated through a rapidly convergent formulation in an exact form. By applying the equivalence principle, the problem is first formulated in the Hankel transform domain, obtaining a set of dual integral equations in which the equivalent surface magnetic current density defined on the aperture is not known. The set of dual integral equations is regularised in a second‐kind Fredholm integral equation by applying the Abel integral‐transform technique. The solution is achieved by expanding the unknown in a set of orthogonal basis functions that correctly reproduce the behaviour of the equivalent magnetic current at the edge of the aperture. Finally, under particular assumptions, a low‐frequency solution is extracted in a closed form. Numerical results are reported to validate the accuracy and efficiency of the proposed formulations. [ABSTRACT FROM AUTHOR]

This paper presents experimental results of high-current impulse tests on six ground electrode configurations. A high impulse current generator is employed to inject different magnitudes of current into these rod electrodes, under both positive and negative impulse polarities. The effect of increasing the number of rod electrodes, hence the resistance at DC or steady-state (RDC), on the impulse response of ground electrodes is analysed. From the analysis of the results, it was found that the larger the size of rod electrodes, the less current-dependent Zimpulse becomes. The percentage of reduction of impulse impedance, Zimpulse from its steady state, and RDC values are found to be independent of impulse polarity. However, as the voltage magnitudes were increased, an occurrence of breakdown was seen, with higher breakdown voltage seen in negative impulse polarity in comparison to positive impulse polarity. Relatively, the higher the breakdown voltage is, seen in the ground electrodes subjected to negative polarity, the faster the time to breakdown is. [ABSTRACT FROM AUTHOR]

In this article, the low-frequency magnetic shielding effectiveness of a planar screen with magnetic and conductive properties in a coplanar-loops configuration (as required in the IEEE Standard 299) is evaluated through a new closed-form formula under the thin-sheet and small-loop approximations. The formulation clearly shows the separate contribution of the permeability and the conductivity of the screen to the shielding performance. The results obtained with the proposed closed-form formulas are compared with the exact ones derived through numerical integrations to assess the relevant accuracy and limits of validity. [ABSTRACT FROM AUTHOR]

This article shows the advantages provided by implicit time stepping schemes for the study of multiconductor transmission lines. Implicit schemes allow for choosing time and space steps independently by attending only to resolution criteria, without the limitation imposed by the Courant–Friedrich–Levy stability condition. Hence, they behave favorably whenever a large time step would be preferable, for instance when a massive number of simulations is required for sensitivity analyses. We focus our attention on two common schemes in electromagnetics, Crank-Nicolson and Newmark-β methods, that are shown to have the same accuracy and to lead to the same solving-equation structure. We illustrate how to include frequency-dependent losses in the algorithms, and we show the influence of dispersion on fast transients. Results show that implicit formulations can be favorably compared with the classical explicit leap-frog scheme. [ABSTRACT FROM AUTHOR]

A recent analytical formulation for the low-frequency magnetic shielding effectiveness of a thin metal screen against a circular loop source is extended to the case of a screen exhibiting both magnetic and conductive properties. The presence of magnetic properties introduces a series impedance in the equivalent network of the structure, in addition to the shunt admittance associated with the screen conductivity. However, the fields scattered by the two elements do not interact and hence can be treated independently; furthermore, the series impedance gives rise to integrals akin to those stemming from the shunt admittance. A generalized analytical formulation for a combined magnetic and conductive screen is thus obtained, that is favorably compared with both classical approximate formulations and exact results. [ABSTRACT FROM AUTHOR]

The magnetic shielding effectiveness of a planar metallic screen of infinite extent against a circular loop field source is analytically evaluated in a new closed-form formula under the thin sheet and small-loop approximations. The results obtained with the proposed formulation are compared with the exact ones derived numerically and with those obtained through classical approximate formulations. It is thus shown that the proposed formula is the most accurate closed-form expression proposed so far and the frequency range where a percentage relative error less than $\text{1}\%$ is obtained is clearly identified. [ABSTRACT FROM AUTHOR]

The improvement of the lightning performance of overhead distribution lines, hit by direct strokes, is investigated considering the use of additional shield wires beneath the phase conductors. The frequency-domain theory of multiconductor transmission lines with periodical grounding is adopted permitting a rigorous evaluation of the phase and shield wire currents and of the overvoltages across insulators. These can be minimized by careful positioning of the underbuilt shield wires. A sensitivity analysis on the overvoltages is conducted by varying either the position of the underbuilt shield wires and the grounding impedance. [ABSTRACT FROM AUTHOR]

The electromagnetic problem of calculating the pulsed radiation from a horizontal magnetic dipole in the presence of a planar thin conductive screen is solved analytically in the time domain via a modified Cagniard-de Hoop approach. The components of the relevant time-domain electric and magnetic dyadic Green's functions are expressed by simple one-dimensional integrals over a finite integration domain. Expressions for the transient electromagnetic fields can thus easily be obtained and numerical results are provided that illustrate the main time-domain shielding characteristics. [ABSTRACT FROM AUTHOR]

The classical problem represented by a planar thin conductive shield in the presence of vertical dipole field sources (electric or magnetic) is solved analytically in the time domain via the Cagniard-de Hoop technique. Comparisons with numerical solutions carried out by means of efficient integration algorithms are provided and discussed. [ABSTRACT FROM AUTHOR]

The 3-D time-domain Green’s function (GF) for the vector potential excited by a transient vertical electric dipole in the presence of a thin sheet with high-contrast dielectric and conductive properties is derived using a modified Cagniard–de Hoop approach. The resulting expression involves the numerical evaluation of a 2-D integral over a finite integration domain, computationally much less expensive than the direct numerical evaluation of the inverse Laplace/Hankel transform of the relevant spectral-domain GF. Expressions for the transient electromagnetic fields can thus be obtained, and numerical results are provided, which illustrate their salient features and validate the proposed formulation. [ABSTRACT FROM AUTHOR]

Nano-scale devices based on zinc oxide (ZnO) are expected to be widely used as building-blocks of future innovative sensors due to outstanding properties of this semiconductive material including presence of a direct bandgap, piezoelectricity, pyroelectricity, biocompatibility. Zinc oxide nanostructures can be also conceived as ultra-high efficiency nanogenerators to harvest electrical energy from the strain vibrational energy in order to drive an array of nanosensors. In fact most applications are based on the cooperative and average response of a large number of ZnO elongated micro/nanostructures, such as wires, rods and pillars. In order to assess the quality of the materials and their performance it is fundamental to characterize and then accurately model the specific electrical and piezoelectric properties of single ZnO structures, in an integrated manner. In this paper, we report on the brittle-to-ductile transition that occurs when reducing the size down to the nanoscale, which has been rarely documented. Then we report on focused ion beam machined of high aspect ratio nanowires and pillars and their mechanical and electrical (by means of conductive atomic force microscopy) characterization. Finally, we present new simulation results concerning ZnO nanowires under lateral bending obtained through the classical approach and the finite element method. Here we use a new power-law design concepts to accurately model the relevant electrical and mechanical size-effects whose existence has been emphasized in recent reviews. [ABSTRACT FROM AUTHOR]

Grounding systems (GSs) must be tested periodically in order to maintain the touch voltage (TV) and step voltage (SV) below a safe value in all of the zones of the installation. Measurements of the ground resistance and of the TV and SV are typically done by the fall-of-potential (FoP) method, locating the auxiliary current electrode at remote distance to test the effective behavior of the GS. In urban areas, it could be very complicated or impossible to install the auxiliary current electrode as required, not having area around with sufficient accessibility. At this aim, this paper describes a methodology of using multiple current electrodes at short distances, modifying the classic FoP practice, so that the measurements of TV and SV are always conservative. The adequacy of a GS is verified if the values of the TV and SV, tested inside and in the vicinity of the GS, are below the permissible limits, regardless if they are true or conservatively increased. Thus, the measured TV and SV by the suggested method, always conservative, allow verifying the adequacy of GSs, in the cases where it is impossible to locate the remote auxiliary electrode. [ABSTRACT FROM AUTHOR]

Micro- and nano-scale materials and systems based on zinc oxide are expected to explode in their applications in the electronics and photonics, including nano-arrays of addressable optoelectronic devices and sensors, due to their outstanding properties, including semiconductivity and the presence of a direct bandgap, piezoelectricity, pyroelectricity and biocompatibility. Most applications are based on the cooperative and average response of a large number of ZnO micro/nanostructures. However, in order to assess the quality of the materials and their performance, it is fundamental to characterize and then accurately model the specific electrical and piezoelectric properties of single ZnO structures. In this paper, we report on focused ion beam machined high aspect ratio nanowires and their mechanical and electrical (by means of conductive atomic force microscopy) characterization. Then, we investigate the suitability of new power-law design concepts to accurately model the relevant electrical and mechanical size-effects, whose existence has been emphasized in recent reviews. [ABSTRACT FROM AUTHOR]

Ionisation can occur in the soil when high impulse currents are subjected to grounding systems. This occurrence is generated by a difference in the dielectric strength value between the soil and air voids. Several published works investigating the ionisation process in soil have seen that the degree of ionisation is dependent on several factors, among them soil resistivity, ground electrode size and impulse polarity. The effects on soil resistivity, such as the moisture content in soil, soil grain size, type of soil and its temperature, have been studied; however, the effect of the size of air voids in soil has not been extensively presented. This study considered four rod electrodes—a conventional rod electrode, conventional electrode with porous concrete (PC), conventional electrode with concrete mixed with a foaming agent (FC) and conventional electrode with concrete (NC)—to provide variations in the size of air voids. Resistance values, RDC, were measured for all these electrodes, and we found that the conventional rod electrode had the lowest value. A detailed evaluation of these rod electrodes under high impulse conditions revealed that similar current rise and discharge times were seen in all electrodes; however, PC, with the largest size of air voids, had the lowest impulse impedance (Zimp value) for the current magnitudes below 2 kA. [ABSTRACT FROM AUTHOR]

Current measurement is a key part of the monitoring system for power transmission lines. Compared with the conventional current sensor, the distributed, self-powered and contactless current sensor has great advantages of safety and reliability. By integrating the current sensing function and the energy harvesting function of current transformer (CT), a time-multiplexed self-powered wireless sensor that can measure the power transmission line current is presented in this paper. Two operating modes of CT, including current sensing mode and energy harvesting mode, are analyzed in detail. Through the design of mode-switching circuit, harvesting circuit and measurement circuit are isolated using only one CT secondary coil, which eliminates the interference between energy harvesting and current measurement. Thus, the accurate measurement in the current sensing mode and the maximum energy collection in the energy harvesting mode are both realized, all of which simplify the online power transmission line monitoring. The designed time-multiplexed working mode allows the sensor to work at a lower transmission line current, at the expense of a lower working frequency. Finally, the proposed sensor is verified by experiments. [ABSTRACT FROM AUTHOR]

Surge arresters may represent an efficient choice for limiting lightning surge effects, significantly reducing the outage rate of power lines. The present work firstly presents an efficient numerical approach suitable for insulation coordination studies based on an implicit Crank–Nicolson finite difference time domain method; then, the IEEE recommended surge arrester model is reviewed and implemented by means of a local implicit scheme, based on a set of non-linear equations, that are recast in a suitable form for efficient solution. The model is proven to ensure robustness and second-order accuracy. The implementation of the arrester model in the implicit Crank–Nicolson scheme represents the added value brought by the present study. Indeed, its preserved stability for larger time steps allows reducing running time by more than 60 % compared to the well-known finite difference time domain method based on the explicit leap-frog scheme. The reduced computation time allows faster repeated solutions, which need to be looked for on assessing the lightning performance (randomly changing, parameters such as peak current, rise time, tail time, location of the vertical leader channel, phase conductor voltages, footing resistance, insulator strength, etc. would need to be changed thousands of times). [ABSTRACT FROM AUTHOR]

A general numerical method for calculating the time‐domain characteristics of the electromagnetic field generated by a pulsed dipole in the presence of a planar multilayered screen is presented. The method involves the efficient evaluation of classical Sommerfeld integrals and an inverse Fourier transform to recover the time‐domain field from the frequency‐domain field. For sufficiently thin screens with highly conductive properties, an analytical method, based on a modified Cagniard–de Hoop approach, is also presented to validate the results. [ABSTRACT FROM AUTHOR]