1,720,963 research outputs found
Sequence impedance computation by means of multiconductor method
No full textThe computation of sequence impedances is a very important topic for insulated cable systems chiefly in HV and EHV levels. Both in planning and operating activities, power flow and short circuit studies are always based on the knowledge of sequence impedances. Furthermore, the correct behaviour of network protection (mainly distance relays) is strictly depending upon their correct settings which are based on positive-negative and zero sequence impedances. Moreover in the planning phase of a new cable link power flow and short circuit studies are always based on the knowledge of sequence impedances. This highlights the importance of using reliable procedures in order to compute these impedances since, up to now, their computations are based on simplified formulae. One of the authors has already presented some papers [1, 2, 3] which allow studying cable systems by means of the multiconductor cell analysis (MCA). This method considers the cable system in its real asymmetry without simplified and approximated hypotheses. One of the advantages of the MCA is the possibility to supply the cable system with three sequence voltage phasors and to compute the ratios between voltage and current phasors for each phase
Sequence impedances of insulated cables: measurements versus computations
No full textThe computation of the sequence impedances is a very important topic for insulated cable systems chiefly in HV and EHV levels. This highlights the importance of using reliable procedures in order to compute these impedances since, up to now, their computations are based on simplified formulae. In this paper, results of some measurement campaigns have been compared with both simplified IEC formulae and advanced matrix procedures based on Multiconductor Cell Analysis (MCA) [1, 2, 3, 4]. MCA considers the cable system in its real asymmetry without simplified and approximated hypotheses. One of the advantages of the MCA is the possibility of supplying the cable system with three sequence voltage phasors and of computing the ratios between voltage and current phasors for each phase.
Both in planning and operating activities, power flow and short circuit studies are always based on the knowledge of the sequence impedances. Furthermore, the correct behaviour of network protection (mainly distance relays) is strictly depending upon their correct settings which are based on the positive-negative and zero sequence impedances. Moreover in the planning phase of a new underground cable (UGC) link the evaluation of its impact on the grid needs to know the sequence impedances.
It is worth remembering that the use of zero, positive-negative sequence impedances Z0, Z1, Z2, is only exact if the system is symmetric since the application of voltage phasors of a sequence causes the circulation of current phasors only of the same sequence so that it is possible to compute the ratios between voltage and current phasors. For cable lines, this assumption is only true if the insulated cables are cross-bonded (CB) with phase transpositions (PTs) or if they are cross-bonded in trefoil arrangement. In all the other cases, the use of the sequence impedances Z0, Z1, Z2 would be theoretically mistaken. Even if an insulated cable is cross-bonded with PTs (or in trefoil arrangement) there could be causes of asymmetry:
minor sections with different lengths, so that the induced currents in the screens are not zeroed;
the presence of joint chambers and terminals which introduce a flat arrangement and a consequent asymmetry;
crossings of possible interfering services or natural obstacles usually overcome by means of directional drillings which can introduce a great spacing between the cables.
If the line length is long enough, the presence of these installation differences can become less important but theoretically they would give always an asymmetric system. In this context, as already highlighted, it would not theoretically licit to refer to the sequence impedances
Linee miste aereo-cavo in altissima tensione
No full textNell'attuare il rafforzamento e l'ampliamento della rete di trasmissione, che si rendono tuttora necessari per soddisfare la crescente domanda di energia elettrica, sempre più spesso i pianificatori e gli esercenti devono ricorrere all'impiego di linee in cavo e linee miste, che possono in alcuni casi ridurre sensibilmente, in virtù della loro flessibilità, i problemi di tracciato. Infatti, le linee in cavo e le linee miste sono più facilmente adattabili a particolari vincoli del territorio e danno la possibilità di superare ostacoli sia di natura orografica (come grandi fiumi, montagne, laghi, collegamento di isole) sia ambientali (come aeroporti, aree urbane, zone industriali o aree estremamente sensibili all'impatto "paesaggistico"). È importante ricordare che alcune installazioni di linee miste sono già state realizzate da parecchi anni per consentire grossi flussi di potenza in grandi centri cittadini. Ancor più oggi, per gli aumentati problemi, gli operatori della rete devono affrontare l'analisi di questa tipologia di linea, per sfruttarne al massimo le prestazioni. In questa memoria si richiamano sinteticamente da [1] le procedure di carattere generale per linee composite a tre tronchi (areo-cavo-aereo) che consentono di costruire capability chart in grado di mostrare con evidenza le massime prestazioni dell'intera linea nel rispetto dei vincoli di ampacity e dei livelli di tensione. Le capability chart sono integrate da altri parametri utili per circostanziare maggiormente le condizioni di esercizio e per limitare con adeguata compensazione reattiva derivata le sovratensioni dovute all'energizzazione della linea mista. Viene inoltre considerato anche un caso concreto realizzato recentemente nella rete italiana e si riportano i criteri per le protezioni della linea e dei reattori di compensazione
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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