1,721,016 research outputs found
Lightning - Induced voltages on distribution systems: influence of ground resistivity and system topology
No full textMost of the work on lightning-induced voltages makes reference to single or multi-conductor lines above a perfectly conducting ground. Distribution systems are, however, of different and more complex topology, as they generally consist of one or more main feeder and several laterals, and are situated above a lossy ground. The paper is aimed at showing whether the above simplifications are appropriate for the problem of interest. To accomplish that, first the explanation of the mechanism of lightning-induced voltages for the case of a lossless and of a lossy ground is summarized; then a sensitivity analysis on a H-shaped network is presented, aimed at showing the influence of the presence of the network branches on the calculated lightning-induced voltages
On the Comparison Between Experimental Results and Calculations of Lightning-Induced Voltages on Distribution Systems - Effect Of The Distribution Network Topology
No full textThis paper deals with the comparison between measurements of lightning–induced voltages in distribution networks having complex topology, and numerical calculations. We make reference to a distribution system located in Colombia within a region with high ground-flash density. The numerical simulations are made by means of the LIOV-EMTP-code. The topological complexity of the experimental network requires the analysis of the influence of the network topology on the lightning-induced voltages. We discuss different methods that can be used to build equivalent LEMP-illuminated networks, with simpler topology than the original one. These methods are based on the appropriate placement of either surge impedances or non-illuminated lines
Lightning Protection of Medium Voltage Networks
No full textThis paper presents some of results relevant to the activities carried out within the Joint CIRED/CIGRE Working Group 05 "Protection of MV and LV networks against lightning", with particular attention to the points that are been discussed nowadays.
Typical overvoltage waveshapes due to direct strokes and induced by nearby strikes are presented. The main design aspects intended to improve the lightning performance of distribution lines are commented. General principles for the protection of equipments are enunciated and the comparison between estimated and specified line lightning performance level is discussed
Propagation Effects on the Electromagnetic Field Radiated by Lightnining to Tall Towers
No full textWe 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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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