1,720,964 research outputs found
A comprehensive study on performance of YD transformer in ac electrified railway systems
No full textThe selection of appropriate traction transformers decreases power quality problems and critical impacts of Electrified Railway System (ERS) on the power grid. Using the Yd transformer in ERSs is not common and popular like the power systems. In this paper, the performance of Yd transformer in a Traction Power Substation (TPS) is investigated and its superiority against single-phase, V/V and Scott transformer is ascertained. The evaluation and analysis is based on electrical performance, power quality parameters and economics issues. The analysis is studied under unbalanced and balanced conditions considering Railway Power Quality Compensator (RPQC) as the auxiliary compensator is TPS. The simulation results validate correctness of theoretical analysis
Regenerative Braking Energy and Power Quality Analysis in 2x2 kV High-Speed Railway Lines Operating with 4QC Locomotives
No full textThe AC 2× 25 kV feeding system is considered as a wide applicated existing power supply system for high speed and high capacity railway lines all around the world. Multiconductor overhead catenary system (OCS), high-power four-quadrant converter (4QC) based trains and a large number of elements have made the power flow and power quality (PQ) analysis complex in such a system. In this paper, an accurate simulation of 4QCs along with traction motors and eight-conductor based OCS have been implemented for the 114 km double-track railway line with realistic information. The PQ analysis together with regenerative braking energy (RBE) assessment are carried out based on extracted voltage and currents waveforms. The proposed methodology is executed in MATLAB software taking into account train movement equations, speed profile and various modes of operation
A new robust dynamic control method for Railway Power Quality Compensator
No full textIn this paper, a fast and robust control method for Railway Power Quality Compensator (RPQC) is proposed. A new extraction method based on modified instantaneous reactive power (p-q) theory is presented to keep the RPQC performance, efficient and suitable for different kinds of transformers used in Traction Power supply Substation (TPS). Due to the fast dynamicity of traction loads, a novel controller based on Variable Forgetting Factor Recursive Least Squares (VFF-RLS) is adopted. Independency on the harmonic components of the load currents, fast, dynamic and high accuracy response are the advantages of the proposed controller. The performance of the proposed control strategy is verified by a precise simulation study using MATLAB/SIMULINK program
Impacts of traction transformers on power rating of Railway Power Quality Compensator
No full textDifferent types of transformers (i.e. Single-phase, V/V, Wye-Delta (Yd), Scott) are used in AC electrical railway systems. The selection of reasonable type of these transformers will decrease power quality problems and critical impacts of electrified railway system on the power grid. In this paper, the performance of popular traction transformers in the presence of Railway Power Quality Compensator (RPQC) as the auxiliary compensator in a Traction Power Substation (TPS) is investigated. The evaluation and analysis is based on electrical performance, power quality parameters and economics issues. Finally, the impacts of these parameters on RPQC performance and its capacity have been studied. The simulation results validate the correctness of the mathematical models and theoretical analysis
Capacity diminution of railway power conditioner using a new smart control system
No full textIn order to overcome the power quality problems in AC electrical railway networks, the Railway Power Quality Compensator system (RPQC) is proposed and used effectively in a Traction Substation (TSS). The power rating of RPQC installed in every TSS is considerably large. In this paper, a RPQC capacity is studied and a compensation strategy with the aim of reducing installed capacity of RPQC is proposed. This method is implemented using of phase rotation in connections of Yd transformer and the Steinmetz-based Intelligent Control System (SICS). The proposed control method can significantly reduce the RPQC converters capacity and installation costs. The simulation results validate the proposed compensation strategy
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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