1,720,957 research outputs found
Identification of Cascading Failure Propagation Under Extreme Weather Conditions
Get PDFAs a fundamental infrastructure, power systems play a vital role in modern society, but it can be damaged by different adverse events e.g. natural, accidental, and malicious, of which the adverse natural events, especially extreme weathers, with huge destructive force can bring tremendous damages and economic losses. The high exposure and comprehensive geographical coverage of the power system make it highly vulnerable to extreme weathers, resulting in equipment damage which leads to cascading failures and blackouts.
Traditional methods only focus on modeling and analysing the reliability of the power system under extreme weathers, without focusing on the propagation of the cascades. In this thesis, innovative methods of studying the cascading failure were proposed, and further extend to collectively consider the impact of extreme weathers on the transmission networks. The proposed models were further validated by applying them to a study system (IEEE-30 bus system) and a real system (Italian transmission network).
A so called normal failure model based on probabilistic graphs was proposed to describe how a cascading failure propagates under a contingency analysis. This model employed Monte Carlo simulation to consider most of the possible operating conditions to establish directed probabilistic graphs to identify the cascading propa-gation by tripping all branches one by one under each operating condition. Obviously, the results of the model can clearly and legibly show the main cascading path of a given network without considering the initial operating condition and the triggering contingency. Further, an index based on branch vulnerability was designed to select the triggering event to increase the effectiveness of the failure in the simulation.
Furthermore, by integrating a probabilistic model of extreme weather impact into the normal failure model, the extreme weather model was proposed based on failure networks, which maps a physical electricity network into a graph in the cascading propagation dimensions. Based on the generated failure networks, a new method based on clustering techniques was proposed to fast track the cascading failure path from any initial contingencies without recalculating the cascading failure in the physical network. The high similarity of the simulation results on the IEEE 30 bus system from the two proposed models indicates the validity of the models.
Further, to demonstrate the extreme weather model, we selected a winter storm, which could happen in Northwest of Italy as an example. The data of snowfall on the Alps was collected and modeled by probability density function and probability mass function. By applying the proposed extreme weather model, the propagation paths can be predicted.
The values of the study provide two powerful tools which can 1) clearly present the inherent characteristic of any one given network, i.e. main propagation paths exist regardless of the initial network and failure condition; 2) fast and reasonably predict the cascading paths in a network under extreme weather conditions
ANALYSIS AND VISUALIZATION OF NATURAL THREATS AGAINST THE SECURITY OF ELECTRICITY TRANSMISSION SYSTEM
Get PDFElectricity is one of the crucial energies of modern society, but it is greatly threatened by various kinds of menaces, especially natural hazards. Although they rarely happen, their occurrence may hugely affect the operation of power system. In this paper, we firstly, according the impact on power systems, classify natural threats into two categories (natural disasters and extreme weather conditions) and several subcategories (geological, hydrological, meteorological and climatological). Then the changes in natural threats to power systems and their trends during recent decades are discussed, along with a review of events that pose natural threats to the power system. Finally, the georeferenced model based on the Italy transmission system for natural threats analysis is presented
Electricity independence of the Baltic States: Present and future perspectives
No full textDue to historical and geographical reasons, the Baltic States are strongly interconnected to power transmission grids of Russia and Belarus. Current energy security policies and electricity interconnection targets in the EU trigger the need for studying and implementing alternative electricity supply options and power system configuration schemes for the Baltic countries.
In order to provide a supporting analysis for the energy policy making, with a special focus on electricity, a framework with methodologies is proposed in this paper to assess the electricity independence of the Baltic States. To comprehensively assess the electricity independence, we provided three indices: “adequacy”, “security” and “economic factor”. The proposed framework and methodologies are applied for assessing the electricity independence of the Baltic States in the present (2014) and future scenarios: mid-term (2020), and long-term (2030) time frame.
The analysis results show that the planned generation capacities are adequate to cover future electricity demand in the Baltic States in 2020 and 2030. Under the current electricity grid planning, power distribution in some local areas is limited in the future scenarios. Additional grid investments are necessary to keep high security level of power supply in 2020/30
Integration of the Baltic States into the EU electricity system: A technical and economic analysis
No full text
The Baltic Power System Between East And West Interconnections
No full textDue to historical and geographical reasons, the Baltic States are strongly connected to the power (electricity) transmission grids of Russia and Belarus. Current energy security and energy independence targets in the EU trigger seeking for alternative power sources for the Baltic. Knowing that, a power system model of the Baltic States has been developed and validated with the purpose of providing comparative options for a reliable and secure development of the Baltic electricity system. The analysis of horizon 2020 and 2030 showed that the dependency of Baltic States on the outside resources is fairly low, provided that the expansion of the electricity system goes as planned
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
- …
