1,720,959 research outputs found
Influence of contamination on the electrical performance of power transformer oil
No full textTransformer failure statistics from all over the world showed that almost 30% of them were due to insulation. Large amount of those failures were due to particles in transformer oil. Main focus of this research is to effects of contamination on electrical performance of transformer oil. A literature review of major causes of transformer failure, breakdown mechanisms of transformer oil has been conducted. The experimental setup and results from the pressboard-dust-contaminated transformer mineral oil test are also discussed. Several experiments have been carried out with cellulose particle contaminated transformer mineral oil. The experiments of bridge formation are conducted under the influence of DC, AC, and DC biased AC voltages. Samples with several levels of contaminant are tested under different voltage levels. The influence of different electrode systems is also tested i.e. bare electrode, covered electrode, bare electrodes with paper barrier, spherical and needle – plane electrodes. These experiments revealed that the bridges are always formed under the influence of DC voltages. The particles are attracted towards high electric field due to Dielectrophoretic (DEP) force and become charged once in contact with the electrode surface. Long fiber particles were attached to the electrodes and aligned parallel to electric field towards the other electrode. More particles attached to the initial fibers and the process continued until a full bridge formed between the electrodes. The conduction current increased with contamination levels as the bridge thickened with increment of contaminations.There is no complete bridge formed under AC electric field. The particles were attracted to the high electric field and attached to the electrodes but the particles are not been able to charge before the polarity of AC electric field alters with spherical electrodes. The current for AC remained unchanged with the increment of particle contamination levels as there is no bridge formed. However, when the DC biased AC signal is applied, the bridge is formed for all the three voltage levels tested. DC and AC breakdown tests were also conducted for several contamination levels.Experiments with kraft paper covered spherical electrodes confirmed that a tightly bonded cover does not stop the bridge; only a loose bonded cover stopped the bridging. Another test with a paper barrier between bare electrodes also did not stop the bridging. Partial discharge (PD) and breakdown test of the contaminated transformer oil is also measured but the results were not conclusive.An initial mathematical model of pressboard dust accumulation using Finite Element Analysis (FEA) software, COMSOL multiphysics has been conducted. The result of the simulation model for charging-discharging and bridging showed similar trend as experimental results. There are a number of changes that can result in improved simulations. There are several variables affecting the simulation i.e. the pressboard dust particle shape, size, conductivity of impregnated pressboard fiber etc
Numerical simulation of charging and discharging of particles in contaminated transformer oil
No full textExperiments were carried out on transformer oil contaminated by cellulose fibre. After the high voltage was applied to the electrodes, the pressboard particles started to accumulate charge from one electrode and discharge to the other electrode. We have developed a mathematical model to simulate the charging and discharging dynamics. The dielectrophoretic, coulomb and drag forces are considered for simulation of the particles motion. The predicted particle movement path and the velocity between the electrodes showed similar trend to the experimental results. The model is a successful means of predicting particle movement phenomenon compared with the experimental data.</p
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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