1,721,026 research outputs found
Partial discharge phenomena within an artificial void in cable insulation geometry: experimental validation and simulation
No full textIn the presence of void in cable insulation, repetition of partial discharge (PD) occurrences is one of the main sources of insulation degradation, which may lead to complete breakdown. Therefore, it is important to monitor the condition of cable insulation through PD measurement. Replicating PD measurement on a test object with the presence of a void within cable insulation may help a better understanding of PD characteristics within cable insulation to be achieved. Therefore, in this work, test samples of cable insulation geometry containing an artificial void were prepared in the laboratory for PD experiment. The PD measurements were done as a function of void size and applied voltage. A physical model of PD activities within an artificial void in cable insulation geometry was also designed using finite element analysis method. The model was developed by considering PD occurrences within non-uniform electric field distribution in the void and charge movement along the void surface. The model was applied for simulation of PDs within the void in cable insulation geometry to increase the understanding on PD physical phenomena. This includes the impact of distribution of void surface charge on the distribution of the electric field within the void through comparison with the captured measurement results
Experiment and modeling of void discharges within dielectric insulation material under impulse voltage
No full textThe presence of cavity in motor insulation fed by variable speed drive is one of the sources of partial discharge (PD) occurrence, especially under impulse voltage. This is a serious problem as PD can accelerate degradation of the motor insulation. Therefore, it is important to prevent void discharges from occurring in motor insulation under impulse voltage. In this work, the characteristics of void discharges within dielectric insulation material under impulse voltage were investigated through experiment and modeling. The test object consists of a rectangular void within a polyethylene material. The test object was stressed with different peak magnitude, front time and tail time of the applied impulse voltage. The experimental results were reproduced by simulation results from a void discharge model in insulation material. From the model that was developed, a better understanding on physical parameters that influence the characteristics of void discharges within dielectric material under impulse voltage can be attaine
Determination of partial discharge time lag in void using physical model approach
No full textRepetition of partial discharge (PD) activities within a dielectric insulation of high voltage equipment may lead to dielectric breakdown, eventually resulting in failure of the whole equipment. Thus, PD measurement is essential in high voltage insulation system. Modeling of PD activity may increase an understanding of PD phenomenon. One of the parameters which can be determined from PD modeling is the statistical time lag. In this work, a physical model of PD using finite element analysis (FEA) method has been developed to determine the relationship of statistical time lag with different applied stresses; these include different applied voltage, frequency and temperature. The statistical time lag as a function of different applied stresses was determined through comparison between measurement and simulation results. The proposed experimental-modeling approach may increase an understanding on the physical explanation about the statistical time la
Partial discharges within two spherical voids in an epoxy resin
No full textA void in a dielectric insulation material may exist due to imperfection in the insulation manufacturing or long term stressing. Voids have been identified as one of the common sources of partial discharge (PD) activity within an insulation system, such as in cable insulation and power transformers. Therefore, it is important to study PD phenomenon within void cavities in insulation. In this work, a model of PD activity within two spherical voids in a homogeneous dielectric material has been developed using finite element analysis software to study the parameters affecting PD behaviour. The parameters that have been taken into account are the void surface conductivity, electron generation rate and the inception and extinction fields. Measurements of PD activity within two spherical voids in an epoxy resin under ac sinusoidal applied voltage have also been performed. The simulation results have been compared with the measurement data to validate the model and to identify the parameters affecting PD behaviour. Comparison between measurements of PD activity within single and two voids in a dielectric material have also been made to observe the difference of the results under both conditions
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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