1,721,052 research outputs found
Il codice modulare Lego per la simulazione dei sistemi dinamici
No full textII lavoro tratta dei codici ingegneristici di simulazione "modulari" ed in particolare del codice Lego, sviluppato presso il Centro Ricerca di Automatica dell'ENEL per la simulazione dei processi termoidraulici delle centrali termoelettriche. Di esso vengono descritti la struttura, gli aspetti algoritmici, il metodo di integrazione impiegato ed i campi di applicazione. Parti fondamentali del codice sono il programma generale ed una libreria di modelli elementari rappresentanti le diverse parti del sistema dinamico, i "moduli". Il programma si presta anche all'applicazione ai sistemi elettrici, la libreria potendo essere ampliata mediante l'aggiunta di nuovi moduli, e ciò senza alterare il programma generale. Risultano quindi possibili per lo stesso componente modellizzazioni diverse. Alcuni esempi chiariscono la formazione del modello complessivo dell'impianto da simulare. Le caratteristiche del metodo numerico di integrazione rendono il codice particolarmente adatto al trattamento di problemi "stiff"
Lagrangian Heuristics Based on Disaggregated Bundle Methods for Hydrothermal Unit Commitment
No full textThe paper presents a simple and effective Lagrangian relaxation approach for the solution of the optimal short-term unit commitment problem in hydrothermal power-generation systems. The proposed approach, based on a disaggregated Bundle method for the solution of the dual problem, with a new warm-starting procedure, achieves accurate solutions in few iterations. The adoption of a disaggregated Bundle method not only improves the convergence of the proposed approach but also provides information that are suitably exploited for generating a feasible solution of the primal problem and for obtaining an optimal hydro scheduling. A comparison between the proposed Lagrangian approach and other ones, based on subgradient and Bundle methods, is presented for a simple yet reasonable formulation of the Hydrothermal Unit Commitment problem
The role of dynamic loads representation in dynamic analyses
No full textAppropriate modelling of dynamic loads is of primary importance in voltage stability studies. The paper deals with the modelling of a load consisting of a static load plus an aggregate of induction motors. Three simplified models for such a load configuration are compared with a more complex one, considered as ‘reference’: i) a pair of static exponential models representing the static load and the induction motor respectively, ii) a static exponential load plus a dynamic Ist-order model for the induction motors, iii) a generic non-linear dynamic model of the 1st-order as proposed by Karlsson and Hill. The reference load model consists of one static exponential model for the static load plus one dynamic 3rd-order model for the induction motors. A power system with a longitudinal structure is chosen as case-study. It is shown that for specific cases only a dynamic model for the induction motors predicts the voltage collapse al the load bus. Discussion of the results is given
On dynamic load models for voltage stability studies
No full textAppropriate modelling of dynamic loads is of primary importance in voltage stability studies. The paper deals with the modelling of a load consisting of a static load plus an aggregate of induction motors. The behavior of three simplified models for such a load configuration is compared. The three models are (A) a generic nonlinear dynamic model of the first order as proposed by Karlsson and Hill, (B) a static exponential load plus a dynamic first-order model for the induction motors, and (C) a static exponential load plus a dynamic third-order model for the induction motors. A power system with a longitudinal structure is chosen as the case-study. It is shown that for the same perturbation (tripping of one of two high-voltage parallel lines) the simulation results are quite different from each other and, in certain cases, only the third-order dynamic model correctly predicts the voltage collapse phenomena at the load bus. An interpretation of the different behavior of the various models is give
Inferring the Correlation Between Lightning Events and Voltage Dips in Distribution Networks
No full textAbstract – To appropriately infer the correlation between lightning events and flashovers/voltage dips on real distribution networks, data coming from lightning location systems are certainly needed, but need to complemented on the one hand by data coming from distributed measurement systems able to record both protection manoeuvres and lightning-originated transients, and on the other hand by accurate calculation results. Additionally, the analysis needs to be performed on a statistical basis. The paper illustrates the main concepts used in developing a procedure aimed at inferring the above mentioned correlation, which is based on the integrated use of experimental data obtained from the Italian lightning location system CESI-SIRF, a monitoring system of relay operation, a distributed monitoring system of lightning-induced transients and of calculations performed using the LIOV-EMTP code. The application of the procedure to the portion of a real distribution network located in Italy in a high level keraunic area is presented by making use of some CESI-SIRF-detected events.
Generic dynamic load models in long-term voltage stability studies
No full textThe aim of this paper is to examine up to what extent the so-called generic non-linear dynamic (GNLD) loadmodels can replace a more detailed representation of aggregate load, including induction motors, thermostatically controlled and static loads, in long-termvoltagestability simulations. In the first part of the paper the main characteristics of the GNLD models are compared with those of more detailed models considered as ‘reference’. It is concluded that the long-term instability phenomena are closely reproduced, in most cases, by using the GNLD model. The accuracy of the GNLD reproduction depends on the load characteristics, the type of phenomena that have to be reproduced and the position of the load in the network. Short-term instability phenomena solely due to induction motor dynamics might not be reproduced with adequate accuracy by GNLD models that are characterised by an inherent de-coupling of active and reactive power. Further, the possibility of including on load tap changer transformer into GNLD models is investigated and accomplished. These considerations are illustrated by adopting as case study a network often used in the literature
An automatic system to locate phase-to-ground faults in medium voltage cable networks based on the wavelet analysis of high-frequency signals
No full textThe paper presents a microcontroller-based automatic system that applies the continuous wavelet analysis to the measured fault-originated electromagnetic transients in order to locate phase-to-ground faults in power distribution networks composed by coaxial cables. The paper describes the numerical procedure conceived to: (i) detect the presence of fault-originated transients superimposed to steady-state voltage waveforms, (ii) identify the faulted phase-conductor and (iii) identify the part of the fault transient that can be used to build a specific mother wavelet so to improve the fault location accuracy. The paper also describes the implementation of the procedure into an embedded microcontroller as well as its experimental validation carried out by means of analog real-time generated fault waveforms obtained from EMTP simulations. © 2011 IEEE.DESLDepartment of Electrical Engineering, University of Bologna, Bologna, Italy, Conference code: 86744, Export Date: 25 April 2012, Source: Scopus, Art. No.: 6019280, doi: 10.1109/PTC.2011.6019280, Language of Original Document: English, Correspondence Address: Paolone, M.; Department of Electrical Engineering, University of Bologna, Bologna, Italy; email: [email protected], References: Radial distribution test feeders (1991) IEEE Trans. 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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
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