1,720,963 research outputs found
Life estimation of MIND HVDC cables subjected to qualification tests conditions
No full textThis study aims at estimating for the first time the life in HVDC Mass-Impregnated Non-Draining MIND cables subjected to Prequalification Test (PQT) conditions according to CIGRÉ Technical Brochure 853-2021. A MATLAB simulation is carried out to calculate temperature and electric field distribution within MIND insulation during PQT Load Cycles, and to estimate cable insulation life under PQT conditions. The results show that
estimated life of MIND cables under PQT conditions is far longer than the duration of the PQT (360 days), as well as longer than that previously estimated under the same conditions for extruded cables
Parametric analysis of HVDC extruded cable reliability for different cable designs
No full textAfter former studies focused on pre-qualification test load cycles, focus is here on life fraction lost by HVDC XLPE insulated cables with rated voltage up to 500 kV subject to Type Test load cycles after CIGRÉ Technical Brochure 496. This study is carried out by refining a previously developed procedure - implemented in Matlab - for reliability estimation using both an iterative solution for transient electric field calculation and Eoll’s formula. A comparison with the results obtained by applying Eoll’s formula is performed to check the accuracy of its approximation at TT voltage
Broadening the Simulative Analysis of the Effects of Long Temporary Overvoltages on the Reliability of HVDC Cables
No full textLong Temporary Over-voltages (TOVs) due to pole-to-ground faults occur in HVDC cable transmission systems with VSC. Preliminary experimental and numerical studies of the possible adverse effects of these long TOVs on HVDC extruded insulation cables have been started by the authors, focusing on one single DC-XLPE insulated 320-kV case-study cable for the simulative analysis. This paper aims at broadening the simulations, by extending the previously-developed method for the estimation of the effects of long TOVs on HVDC cable reliability to other types of DC-XLPE insulated cables with the much higher rated voltage of 600 kV and larger conductor cross-section. The results obtained here for these new cable designs essentially confirm what already obtained for the 320-kV cable
Preliminary estimation of the effect of insulation losses on HVDC cable reliability
No full textInsulation losses in HVDC cables are mostly deemed negligible compared to conductor losses, but this might not always be the case, especially for innovative cable designs. This paper aims at a preliminary evaluation of the effect of insulation losses on the temperature rise in the insulation of HVDC XLPE-insulated cables subject to load cycles according to CIGRÉ Technical Brochure 496. The ultimate goal is finding the voltage values above which insulation losses lead to a non-negligible increase of insulation temperature, thereby affecting life and reliability of HVDC cables. The results show that the effect of insulation losses on the loss of life is deemed negligible. Thus, insulation losses can have an impact only on the thermal stability of cables, not on the loss of life itself
The Effect of Ambient Thermal Properties on Transient Electric Field Distribution and Life Estimation in HVDC Cable Insulation
No full textInnovative cable designs have recently achieved high rated temperatures. Cable environment properties are getting more attention to guarantee thermally stable operation and reduced loss-of-life of the HVDC cable at all possible weather conditions. This paper aims at studying the effect of different resistivities and seasonal temperatures of the laying environment on the electric field distribution inside the insulation of HVDC cables subjected to the type test load cycles according to CIGRÉ Technical Brochure 496. Five different conditions of the laying environment are considered, set according to IEC 60287, i.e., soil saturated with water, very moist, moist, partially dry, and dry; different temperatures of the laying environment are also taken accordingly. The results show that the greater the thermal resistivity and/or the temperature of the laying environment, the shorter the life of the cable insulation
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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