37 research outputs found

    Locating Multiple Soft Faults in Wire Networks Using An Alternative DORT Implementation

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    International audienceDecomposition of the time reversal operator (DORT) was recently applied to the problem of detection and location of soft faults in wire networks and proved effectual when dealing with a single fault, even in the case of complex network configurations. In this paper, the case of location of multiple faults is addressed, first proving that the standard DORT formulation does not allow to take a clear decision about the individual position of each fault. An alternative version of the DORT, based on an updating procedure, is presented and demonstrated to enable accurate and selective location of multiple soft faults. The proposed procedure is also shown to allow estimating the reflection coefficient of each fault, thus giving access to their severity

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

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    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

    The 1991 International Aerospace and Ground Conference on Lightning and Static Electricity, volume 2

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    The proceedings of the conference are reported. The conference focussed on lightning protection, detection, and forecasting. The conference was divided into 26 sessions based on research in lightning, static electricity, modeling, and mapping. These sessions spanned the spectrum from basic science to engineering, concentrating on lightning prediction and detection and on safety for ground facilities, aircraft, and aerospace vehicles

    Aeronautical engineering: A continuing bibliography with indexes (supplement 217)

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    This bibliography lists 450 reports, articles, and other documents introduced into the NASA scientific and technical information system in August, 1987

    Situation Awareness for Smart Distribution Systems

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    In recent years, the global climate has become variable due to intensification of the greenhouse effect, and natural disasters are frequently occurring, which poses challenges to the situation awareness of intelligent distribution networks. Aside from the continuous grid connection of distributed generation, energy storage and new energy generation not only reduces the power supply pressure of distribution network to a certain extent but also brings new consumption pressure and load impact. Situation awareness is a technology based on the overall dynamic insight of environment and covering perception, understanding, and prediction. Such means have been widely used in security, intelligence, justice, intelligent transportation, and other fields and gradually become the research direction of digitization and informatization in the future. We hope this Special Issue represents a useful contribution. We present 10 interesting papers that cover a wide range of topics all focused on problems and solutions related to situation awareness for smart distribution systems. We sincerely hope the papers included in this Special Issue will inspire more researchers to further develop situation awareness for smart distribution systems. We strongly believe that there is a need for more work to be carried out, and we hope this issue provides a useful open-access platform for the dissemination of new ideas

    Bibliography of Lewis Research Center technical publications announced in 1993

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    This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1993. All the publications were announced in the 1993 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

    Aeronautical engineering: A continuing bibliography with indexes (supplement 212)

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    This bibliography lists 493 reports, articles and other documents introduced into the NASA scientific and technical information system in March, 1987

    Aeronautical engineering, a continuing bibliography with indexes

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    This bibliography lists 419 reports, articles and other documents introduced into the NASA scientific and technical information system in March 1985

    Abstracts on Radio Direction Finding (1899 - 1995)

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    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

    A Noniterative Method for Locating Soft Faults in Complex Wire Networks

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    International audienceReflectometry-based methods are the standard choice for fault detection techniques in wire networks. While effective when dealing with simple networks and relatively hard faults, their results can be of more difficult interpretation if a network presents more than two branches. In this paper we propose the use of an alternative technique based on a coherent multi-port characterization of a network under test. The data thus collected are used to define excitation signals that will be focusing over the position of a fault, following a method already successfully applied in geophysical prospection techniques and non-destructive testing, namely the DORT method, based on the synthesis of time-reversed signals. It is shown that a direct transposition of this technique to wire networks is not possible, due to the guided nature of wave propagation in wire networks, leading to the impossibility of assuming a dominant direction of propagation, as opposed to the case of propagation in open media. A differential version of the DORT method is introduced, enabling an accurate identification of the original position of faults. Numerical and experimental results are presented to demonstrate the feasibility of this approach
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