Development of a Numerical Model for High-Temperature Shape Memory Alloys

A thermomechanical hysteresis model for a high-temperature shape memory alloy (HTSMA) actuator material is presented. The model is capable of predicting strain output of a tensile-loaded HTSMA when excited by arbitrary temperature-stress inputs for the purpose of actuator and controls design. Common quasi-static generalized Preisach hysteresis models available in the literature require large sets of experimental data for model identification at a particular operating point, and substantially more data for multiple operating points. The novel algorithm introduced here proposes an alternate approach to Preisach methods that is better suited for research-stage alloys, such as recently-developed HTSMAs, for which a complete database is not yet available. A detailed description of the minor loop hysteresis model is presented in this paper, as well as a methodology for determination of model parameters. The model is then qualitatively evaluated with respect to well-established Preisach properties and against a set of low-temperature cycled loading data using a modified form of the one-dimensional Brinson constitutive equation. The computationally efficient algorithm demonstrates adherence to Preisach properties and excellent agreement to the validation data set

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Estudio de saturación de transformadores de corriente: análisis y simulación / Current transformer saturation study: analysis and simulation

Este artigo descreve o estudo da saturação do transformador de corrente durante uma falta transitória, quando causará distorção da corrente secundária. Quando ocorre a saturação, a corrente secundária não será linearmente proporcional à corrente primária, o que pode causar um mau funcionamento dos dispositivos de proteção. A metodologia é baseada na pesquisa documental, que apresenta os princípios teóricos, causas e efeitos desse fenômeno. Um tipo de medição TC de 2000/5 A, 25 VA nominal, é usado na análise e é testado para condições de falha normais e transitórias usando o software MATLAB-Simulink. Nos resultados da simulação, as formas de onda da corrente secundária são registradas para diferentes valores de corrente de falta no lado primário. Todas as formas de onda atuais são comparadas para analisar o comportamento do TC durante uma falta transitória. O objetivo deste estudo é apresentar uma investigação sobre a modelagem da saturação por TC em software de computador. 

Contribution for the Study of Inductive Fault Current Limiters in Electrical Distribution Grids

Inductive type fault current limiters with superconducting tapes are emerging devices that provide technology for the advent of modern electrical grids, helping to mitigate operational problems that such grids can experience as well as preventing the often-costly upgrade of power equipment, namely protections. The development of such limiters leads to several design challenges regarding the constitutive parts of those devices, namely the magnetic core, primary winding and superconducting secondary. Fault current limiters are required to operate at overcurrents during a certain amount of time. The operation at such currents can lead to harmful effects due to mechanical, electromagnetic and thermal stresses, especially in the superconducting tape. Since the operation principle of fault current limiters envisaged in this thesis is based on the superconducting-normal transition of superconducting materials, the study of its transient behaviour is an important research subject. In this work, an electromagnetic methodology based on the characteristics of the constitutive parts of the limiters, previously developed and compared to finite element modelling simulations with very similar results, is simulated and validated with experimental results. Furthermore, the current in the superconducting tape is modelled from experimental results with the purpose of predicting the temperature of the material during normal and fault operation conditions, by employing a thermal-electrical analogy. These results are also compared to experimental measurements. A fast simulation tool, with computation times in the order of minutes, is also developed in Simulink, from Matlab environment. With the developed simulation tool, it is possible to quickly predict the transient electromagnetic-thermal behaviour of an inductive type fault current limiter operating in electrical grids, namely the line current and primary linked flux, as well as current and temperature in the superconducting tape

Nouvelle approche de modélisation de la branche de magnétisation pour la simulation des transitoires électromagnétiques

Trajectoires du phénomène d'hystérésis avec saturation -- Modèle de Preisach -- Modèle de Stoner et Wolhfarth -- Modèle de Jiles et Atherton -- Revue des modèles numériques actuels -- Modèle type 96 -- Modèle type 92 -- Modèle de Preisach modifié -- Modèle de MATLAB/Power system blockset -- Modèle de résistance de magnétisation instantannée -- Nouveau modèle -- Boucle majeure -- Boucles mineures -- Courbe de première magnétisation -- Contexte de programmation -- Domaine du temps -- Domaine fréquentiel et régime permanent -- Initialisation -- Gestion de la pile des extrema -- Méthode de modification d'estimation de flux -- Méthode de la bissection et oscillations numériques -- Méthode d'itération panique -- Régresseur non-linéaire -- Scénarios de simulation