1,720,974 research outputs found
The pilot projects for the development of Smart Grids [I progetti pilota per lo sviluppo delle Smart Grids]
No full textLumped-parameter and finite element models of overhead power line conductors for dynamic thermal rating purposes
No full textThe steady-state approaches traditionally used to assess the capacity of overhead transmission power lines are being progressively replaced by procedures that consider the real and extremely variable weather conditions that are present along the path of the line under analysis (Dynamic Thermal Rating). Dynamic Thermal Rating (DTR) does not just estimate the temperature of the conductor in the different spans of the line, but also some mechanical quantities like their tension and sag, in order to appreciate the limitations imposed by the constraint of the minimum ground clearance. Modern DTR procedures need, therefore, proper mechanical models of the lines, in order to assess what happens both in normal and fault conditions. This paper proposes a comparison between a Finite Element Method (FEM) and a novel lumped-parameter model implemented through the Modelica language. Different realistic scenarios have been considered, like gusts of wind and the presence of ice. The outcomes of the two dynamic models have been compared to identify a trade-off between the accuracy of results and the computational time, as well as the dependency on the number of lumped masses used to model the line
Topological Considerations on the Use of Batteries to Enhance the Reliability of HV-Grids
Full text linkThe large amount of renewable energy sources (RESs) recently integrated within the electric power systems across the world poses new challenges for their operation. Among several viable solutions, energy storage systems are the most promising to increase reliability and flexibility. This paper proposes a novel topological and probabilistic approach to find the optimal capacity and siting of energy storage devices, in order to increase the system reliability and the hosting capacity of renewables. Wind and solar productions, generators availability, and real-time demand are modeled with proper distribution functions, and the yearly expected energy not supplied is estimated using a sequential Monte Carlo technique. Four siting policies are applied and compared to place the optimal storage capacity on eight grids with different topological characteristics. Power flows are linearized and the optimization of resources is formulated as a linear programming problem. The results show that large-scale batteries operated by the Transmission System Operator can significantly improve system reliability and exploitation of RESs. The presence of energy-hubs and small-world properties strongly increase the transmission effectiveness of weakly- and well-meshed grids. A siting policy based on the Power Transfer Distribution Factors matrix of the grid turns out to be particularly successful
Use of VSC-HVDC links for power system restoration
No full textThis paper shows how a VSC-HVDC system can be profitably used as a black start unit to restart a thermal power plant, as well as to help it to follow the constrained power ramping up to its technical minimum. A frequency vs real power and voltage vs reactive power droop control is proposed for the receiving end converter of the link, including a Local Frequency Integrator function which enables the system to be easily reconnected with other units
Black-start of remote areas through SCR-based HVDC Links
No full textThis paper analyses the possibility to black-start a remote area using an existing Line Commutated Converter HVDC link.To do this, a relatively small size Voltage Sourced Converter must be installed at the link receiving-end. The black start takes place using the existing receiving end network and line commutated converters, and the DC line. The paper shows that the black start operation can take place fast and effectively
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
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