Lightning Induced Voltages on Overhead Lines above Non-Uniform and Non-Homogeneous Ground

Abstract: lightning induced voltages are one of the most common sources of failures on distribution networks operating in high lightning activity regions. Traditionally, the selection of insulation levels and protecting devices are carried out using statistical analysis based on typical values of resistivity and assuming a homogeneous ground for the whole network. In calculating lightning induced voltages, the effect of the topography and non-homogeneities of the ground have been traditionally neglected. In rural distribution lines, non-homogeneous and non-uniform ground is a common feature. In literature, induced voltages calculations are mainly calculated based on several assumptions that are not valid when more realistic conditions are taken into account. In order to allow a better selection of protective devices and hence contributing to the improvement of some power quality indicators of rural distribution networks, the calculation of lightning induced voltages for distribution lines must be performed including the effects of the non-homogeneous and nonuniform ground. Most of the theoretical approaches proposed for calculating the propagation path effects on the radiated electromagnetic fields for a current dipole above ground, are valid only in the far-field region even when considering irregular and inhomogeneous terrain. Despite some authors have demonstrated the validity of those approaches for flat ground in the near field range calculations, there are valid for some specific cases and geometric symmetry that in some practical cases cannot be assumed. In order to overcome this problem, this thesis presents an extensive application of a full wave solution obtained from the implementation of the Finite Difference Time Domain (FDTD) method including a non-regular mesh. This method is applied to the calculation of lightning induced voltages on an overhead single wire when different ground features such as: homogeneity, inhomogeneity and non-uniformity are present all simultaneously in a simulation scenario. In order to validate the FDTD implementation, some numerical comparisons were made with previous results presented in the literature. The aim of this thesis is to provide new elements related to the effects on lighting induced voltages on overhead lines when different electric and geometric parameters of the surrounding ground are considered. Along this thesis, the lightning induced voltage problem has been analyzed taking into account three involved aspects individually: the return-stroke model, the propagation of the electromagnetic field produced by it, and the resulting induced voltages on the overhead lines once all their models are included into an FDTD simulation. This document has been divided into eight sections. The first section presents a discussion about lightning induced voltages and how they have been addressed in the literature. Throughout this iii section all the involved elements into the lighting induced problem have been addressed and a short discussion about their previous results and conclusions is also presented. In section 2 the scope of the thesis is defined in order to give the reader a brief summary about the objectives that were established in the master thesis proposal. Section 3 presents the FDTD method. In this section most of the theoretical background is presented related to: sources, lumped elements and thin-wire modeling techniques. Next, the FDTD method is formulated for a non-regular mesh and a general formulation for an automatic meshing algorithm is proposed. Finally, a comparison between the FDTD method implementation used in this thesis and some experimental data from a two horizontal wires cross-talk problem is presented. Section 4 deals with the calculation of radiated fields when different propagation paths are present. Homogeneous ground effects on radiated fields were obtained by using the Norton’s approach and the surface impedance concept. Inhomogeneities of the ground conductivity for flat grounds were also analyzed by using the surface impedance concept and the Wait´s formula derived from the compensation theorem; the Wait´s formulas for a mixed-path of two and three section were implemented and compared with some results presented before in literature. Finally,the terrain non-uniformity was addressed by means of the Ott’s integral approach. Despite all of these implemented approaches allow the analysis of radiated fields, they are derived under several assumptions and are valid only for the far field region and a cylindrical symmetry regarding geometry. Then, a comparison between these and the results obtained by means of the FDTD method were performed for different simulation scenarios in order to analyze their validity. In section 5 the lightning return-stroke is modeled by means of an implementation of engineering and electromagnetic models. A discussion about the current distribution along the cannel depending on the return-stroke model is also presented. Besides, a comparison between the antenna theory and the series RL-loaded thin-wire model included into the FDTD method was carried out taking into account the characteristics of apparent propagation velocity and current wave shape along the channel. In section 6 the lightning radiated fields are calculated for different propagation path conditions such as: perfectly conducting ground, homogeneous finitely conductive ground and inhomogeneous conducting ground. For those propagation paths a set of comparisons between the FDTD method and the approximated formulas discussed in section 5 were performed. Lightning induced voltages are analyzed in section 7. In this section the lightning channel and the overhead line are included into the FDTD method. A set of simulations scenarios were proposed in order to evaluate the influence of different ground features on the induced voltages on a single overhead-wire. Important influences on induced voltage waveforms were determined for inhomogeneous and irregular terrains, resulting in changes on polarity and higher induced peak voltages values when compared to those obtained from a flat homogeneous ground. iv In section 8 concluding remarks about the analyzed cases and most critical situations are presented. There is also a future work proposed by the author based on the obtained resultsMaestrí

The 1991 International Aerospace and Ground Conference on Lightning and Static Electricity, volume 1

The proceedings of the 1991 International Aerospace and Ground Conference on Lightning and Static Electricity are reported. Some of the topics covered include: lightning, lightning suppression, aerospace vehicles, aircraft safety, flight safety, aviation meteorology, thunderstorms, atmospheric electricity, warning systems, weather forecasting, electromagnetic coupling, electrical measurement, electrostatics, aircraft hazards, flight hazards, meteorological parameters, cloud (meteorology), ground effect, electric currents, lightning equipment, electric fields, measuring instruments, electrical grounding, and aircraft instruments

Locating transient disturbance sources and modelling their interaction with transmission lines:use of electromagnetic time reversal and asymptotic theory

This thesis deals with the application of electromagnetic time reversal to locating transient disturbance sources and the use of the asymptotic theory for the modelling of their interaction with transmission lines. We demonstrate that the time-of-arrival, which is one of the most commonly used methods to locate lightning discharges, can be seen as a special case of time reversal. The problem of a lossy ground that affects the propagation of electromagnetic transient fields generated by a lightning strike is addressed by proposing three different back-propagation models and comparing their performances in terms of location accuracy. Two sets of simulations are carried out to evaluate the accuracy of the proposed approaches. The first set of simulations is performed using numerically-generated fields and the proposed algorithm is shown to yield very good results even if the soil is not perfectly conducting. In particular, it is shown that considering a model in which losses are inverted in the back-propagation yields theoretically exact results for the source location. We also show that a lack of access to the complete recorded waveforms may lead to higher location errors, although the computed errors are found to be within the range of performance of the present LLSs. A second set of simulations is performed using the sensor data reported by the Austrian Lightning Location System (ALDIS). The locations obtained by way of the EMTR method using only the available sensor data (amplitude, arrival time and time-to-peak), are observed to be within a few kilometres of the locations supplied by the LLS. The possible sources of this discrepancy are discussed in the thesis. The second part of this document deals with the computation of the current induced in a line due to an external electromagnetic field. We derive high-frequency expressions for the current induced along a multiconductor line by an external plane wave, in which the effects of the terminals of the line are modelled by matrices of scattering and reflection coefficients. Different approaches are proposed to compute the coefficients that feed the analytical expression for the current induced along the line. Using an iterative method, mathematical expressions are derived, for the particular case of open-circuit lines. For the general case of arbitrary line terminations, an approach using auxiliary short lines, solved with a numerical solver is proposed. At low frequencies, the proposed three-term formulation can be adapted to lossy lines and analytical expressions for the coefficients, providing a new and elegant formulation for the classical transmission line theory. The proposed theory is validated through numerical simulations and experiments and is found to be much more effective than the traditional full-wave approaches in terms of memory requirements and computational times. The asymptotic theory is also applied to a lumped source excitation, according to a procedure analogous to the one for a plane wave excitation. A method for the determination of matrices of coefficients is also presented

Lightning Modeling and Its Effects on Electric Infrastructures

When it comes to dealing with high voltages or issues of high electric currents, infrastructure security and people’s safety are of paramount importance. These kinds of phenomena have dangerous consequences, therefore studies concerning the effects of lightning are crucial. The normal operation of transmission and distribution systems is greatly affected by lightning, which is one of the major causes of power interruptions: direct or nearby indirect strikes can cause flashovers in overhead transmission and distribution lines, resulting in over voltages on the line conductors. Contributions to this Special Issue have mainly focused on modelling lightning activity, investigating physical causes, and discussing and testing mathematical models for the electromagnetic fields associated with lighting phenomena. In this framework, two main topics have emerged: 1) the interaction between lightning phenomena and electrical infrastructures, such as wind turbines and overhead lines; and 2) the computation of lightning electromagnetic fields in the case of particular configuration, considering a negatively charged artificial thunderstorm or considering a complex terrain with arbitrary topograph

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

Advanced Automation for Space Missions

The feasibility of using machine intelligence, including automation and robotics, in future space missions was studied

Princeton Advanced Satellite Study Final Report, 8 Mar. 1965 - 15 May 1966

Development of large aperture spaceborne telescope and high resolution ultraviolet photometry for orbiting astronomical satellit

Development of a composite CAD package to predict and reduce EM radiation from a PCB

A composite CAD package to predict and reduce radiation from a printed circuit board (PCB) is presented in this thesis. The composite CAD package is implemented using an electromagnetic (EM) computation tool linked with other circuit design packages (CDPs) such as ORCAD (a schematic design package), PSPICE (a circuit simulation package) and Boardmaker (a board layout tool). Software is developed to link all the packages so that one can incorporate EMC verification in the design process of an electronic product. The well-known Numerical Electromagnetic Code (NEC) version 2 is used as an EM computation tool. In using NEC-2 to predict PCB radiation, the PCB is simulated as a loaded thin wire structure just above (but not contacting) the surface of an imperfect ground. An algorithm is developed and implemented to automate the geometrical modelling of a wire structure for NEC-2. The data required by NEC-2 ( geometrical, load and electrical) for prediction of PCB radiation can be obtained from various CDPs. The development and implementation of data extraction algorithms are presented in this thesis. Single and double sided PCBs can be accommodated and the work can be extended to handle multilayer PCBs. The use of NEC-2 for this type of application has been validated experimentally and theoretically (by comparing NEC-2 predicted radiation with that obtained where the EM radiation from a pair of parallel PCB tracks running between two components/devices is computed using transmission line modelling-TLM). Both methods of evaluation are described in detail in this thesis and results showing good agreement are presented. TLM is employed by considering, (i) the effective dielectric constant of the medium (air and substrate) surrounding the PCB tracks and (ii) the displacement current between the two PCB tracks. The effect of displacement current in near field radiation is highlighted. The use of TLM for prediction of PCB radiation is verified experimentally. Measured radiation is in good agreement with prediction. In the developed composite CAD package, one can compare the predicted radiation with the mandatory EMC requirement laid down by the regulating bodies and "close the loop" to modify the design where these requirements have not been met. Various techniques to reduce radiation can also be employed. Reduction of radiation by providing shielding in some section of the circuit is proposed. An algorithm is developed and implemented to find the section of the circuit where shielding is necessary. The optimum layout (track separation to width ratio) that can minimise radiation is found theoretically. An optimum layout is also determined experimentally and compared with the theoretical value. A good agreement is found in this comparison. Thus a guideline to choose optimum layout for minimum radiation is provided

Annual Review of Progress in Applied Computational Electromagnetics

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