1,720,975 research outputs found
Risk-Based Security and Control Framework for Power System Operation Under Significant Amounts of HVDC-connected Wind Power Generation
No full textIn the context of power system operation, probabilistic techniques can provide a deeper insight into security aspects compared to deterministic approaches, by quantitatively considering power system uncertainties and contingency impact. Moreover, they can be helpful to identify and suggest operators the most adequate control actions to reduce the operational risk. This paper proposes an original framework for risk-based assessment and control of operational security in High-Voltage Alternating Current (HVAC) power systems connected to Multi-Terminal High-Voltage Direct Current (MTDC) networks like those envisaged for the integration of future, large off-shore wind farms. After the presentation of a security assessment methodology based on the concept of risk, the paper investigates three possible preventive control strategies to reduce the risk of high current by exploiting control resources available in the system (specifically, generating units and power injections from MTDC grids). Results of the methodology applied to a test system and to a realistic power system (adapted from the Italian transmission network) are presented and discussed
Dynamic models for Distributed Energy Resources in a Microgrid environment
No full textSecurity assessment issues on modern power systems become more and more important also because of the growing penetration of DG (Distributed Generation) sources on the electric power systems. Today their penetration is still marginal with respect to the overall system load, but in the future they can cover a significant part of the consumptions, which means that research on power system security assessment has to investigate the possible impacts of such a phenomenon on security issues. Moreover, these models are essential for Microgrid studies and evaluation of their performances. In order to assess the actual impacts of DG sources on operational security it is necessary to have adequate dynamic models of the sources themselves. This paper presents the dynamic models of several renewable and fossil fuel based Distributed Energy Resources (DER) implemented in a well-known time domain simulator for power systems. Some simulation results are discussed
An innovative platform integrating deterministic and probabilistic tools for power system security assessment within a unified approach
No full textPower system security assessment for off-line operational planning and on line operation applications requires various analysis methods aimed to highlight different phenomena (steady-state violations, angle stability, voltage stability, etc.), overall providing an exhaustive vision of the problems. However, carrying out the different analyses in an integrated way is not an easy task. Different types of results come from both conventional deterministic and more advanced risk-based probabilistic assessment tools. Moreover, operators are more and more interested in practical information like the time at their disposal before instability occurs, to deploy adequate control actions. To provide a comprehensive security assessment framework, this paper proposes a methodology and a platform, which integrates the outcomes from probabilistic and deterministic security assessment tools within a unified approach to system security
A Gas Turbine Model for Studies on Distributed Generation Penetration Into Distribution Networks
No full textThe paper proposes a detailed model of a gas turbine for a combined heat and power (CHP) plant. The prime mover is endowed with several controls: first of all, a speed control which can be either droop type or isochronous type according to the status of connection to the distribution grid. An acceleration limiter and an exhaust gases temperature limiter intervene to cut the fuel request, respectively, in case of an excessive rotor acceleration and of a too high temperature of the exhaust gases. A further control regulates inlet guide vanes (IGV) in order to keep the exhaust temperature almost constant. This is important in a cogeneration plant where the heat recovery from the exhaust gases is used to satisfy the demand of the thermal load. Some validation simulations on a model of cogeneration plant connected to a MV distribution grid are carried out and commente
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
Controllo dei carichi termostatici per la sicurezza del sistema elettrico
No full textIl potenziale contributo dei carichi termostatici alla regolazione primaria di frequenza è analizzato rispetto alla disponibilità della risorsa nel tempo e all’efficacia dell’intervento, considerando anche le condizioni alle quali questo servizio potrebbe essere applicato
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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