1,721,019 research outputs found
MV/LV parallel transformers. An experimental study on circulating currents
No full textWhen a high value load is to be supplied and greater system reliability is required, the medium voltage power supply is generally used with a low voltage conversion by means of two or more MV/LV transformers. This configuration is also more suitable for maintenance or resilience aspects. In Europe, in case of use of these distribution transformers, the windings configuration is Delta (primary winding) and Star (secondary winding). To obtain a common ground reference for the three phases and neutral system, the star point is grounded. In case of parallel transformers, this ground point is common. Furthermore, when using transformers in parallel, a proportional reduction of the short-circuit impedance is obtained with the consequent increase in the short-circuit current during faults and the need to adopt cables and protections that consider this aspect. From the other hands, the use of parallel transformers may introduce an increasing of the no load losses. In transformers parallel configuration system, if the transformation ratios are not identical, a circulation current is generated. This current is proportional to the voltage difference divided by the sum of the impedances along the path comprising windings and ground connections of the star centers. In a distribution substation with two parallel transformers of identical characteristics, the circulating currents in each transformer are of equal amplitude and in opposite directions. Few studies have investigated what happens at the connection points between the star centers of the transformers and the earth bar of the secondary substations. This paper gives a contribution on the evaluation of the circulating currents based both on theoretical considerations and experimental measurements
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
Probability of damage of apparatus powered by an HV/LV transformer due to lightning to a structure protected by a lightning protection system
No full textThe paper deals with the probability of damage of circuits and apparatus connected to an HV overhead power line through an HV/LV transformer due to direct lightning to a structure protected by a Lightning Protection System (LPS) where such circuits are installed. An approach is proposed to evaluate such probability and guidance is given for dimensioning a surge protective device (SPD) able to protect LV apparatus against lightning surges with a given probability. Two conditions are analyzed, namely where the earthing system of LPS may be assumed as equipotential or not equipotential
Towards the textile transistor: Assembly and characterization of an organic field effect transistor with a cylindrical geometry
No full textQuesto lavoro è stato selezionato per la pubblicazione nel volume del 16/10/2006 del Virtual Journal of Nanoscale Science & Technology, pubblicato dall’American Institute of Physics e dall’American Physical Societ
Power distribution network configuration applying the corridor method
No full textIn this paper, an optimization scheme based on the Corridor Method (CM) matheuristic is proposed for power distribution network configuration with the objective of client balancing between feeders. The problem is formulated as a mixed integer optimization problem (MIP) referring to a variant of the constrained spanning forest problem on a network. The problem is classified as NP-complete in its decision version, and the proposed matheuristic optimization approach is aimed to find high quality solutions in a short computational time on large real instances. According to the characteristics of the power distribution networks, suitable modeling solutions are adopted to retain a radial structure, satisfy power flow and voltage constraints, and reduce the reconfiguration efforts requiring a limited number of maneuvers on the electrical network. Computational experiments on different instances related to a real network have been conducted. The results demonstrated the soundness and the effectiveness of the proposed solution with respect to a baseline represented by a MIP formulation solved by a state-of-the-art commercial solver: the scalability towards large-size cases has been also considered. These results show that the proposed configuration method can effectively and efficiently solve the considered problem giving adequate support to the decision-makers
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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