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Modeling and Simulation of Varistors

Denz, Frank (2014):
Modeling and Simulation of Varistors.
Darmstadt, TU Darmstadt, [Online-Edition: http://tuprints.ulb.tu-darmstadt.de/4197],
[Ph.D. Thesis]

Abstract

This thesis treats various problems that arise in the context of varistors and microvaristors, which are are used for the suppression of transient overvoltages, due to their extraordinary nonlinear electrical conductivity. The present work is mainly motivated by the desire to simulate the behavior of high-voltage surge arresters used for lightning protection on the one hand and of microvaristors as materials for future applications in nonlinear resistive stress control on the other hand.

The analysis of surge arresters requires the numerical calculation of mutually-dependent electric and thermal fields, whereby the principal difficulty resides in the extreme nonlinearity of the electric problem. For this purpose, the electro-quasistatics equation is solved in time domain by means of the finite-element method. The calculation of the thermally stationary state of a surge arrester and the evaluation of an envelope equation model for simulating the heating and cooling behavior of arresters are discussed in more detail.

These simulations depend on sufficiently accurate models that describe the material properties. The estimation of nonlinear conductivity and permittivity of varistor materials is an inherent part of this thesis.

Furthermore, nonlinear capacitance and conductance matrices are introduced. The presented approach is based on an equivalent circuit model. Its parameters are determined from field-simulation results.

Item Type: Ph.D. Thesis
Erschienen: 2014
Creators: Denz, Frank
Title: Modeling and Simulation of Varistors
Language: English
Abstract:

This thesis treats various problems that arise in the context of varistors and microvaristors, which are are used for the suppression of transient overvoltages, due to their extraordinary nonlinear electrical conductivity. The present work is mainly motivated by the desire to simulate the behavior of high-voltage surge arresters used for lightning protection on the one hand and of microvaristors as materials for future applications in nonlinear resistive stress control on the other hand.

The analysis of surge arresters requires the numerical calculation of mutually-dependent electric and thermal fields, whereby the principal difficulty resides in the extreme nonlinearity of the electric problem. For this purpose, the electro-quasistatics equation is solved in time domain by means of the finite-element method. The calculation of the thermally stationary state of a surge arrester and the evaluation of an envelope equation model for simulating the heating and cooling behavior of arresters are discussed in more detail.

These simulations depend on sufficiently accurate models that describe the material properties. The estimation of nonlinear conductivity and permittivity of varistor materials is an inherent part of this thesis.

Furthermore, nonlinear capacitance and conductance matrices are introduced. The presented approach is based on an equivalent circuit model. Its parameters are determined from field-simulation results.

Place of Publication: Darmstadt
Divisions: 18 Department of Electrical Engineering and Information Technology
18 Department of Electrical Engineering and Information Technology > Institute of Electromagnetic Field Theory (from 01.01.2019 renamed Institute for Accelerator Science and Electromagnetic Fields)
Date Deposited: 02 Nov 2014 20:55
Official URL: http://tuprints.ulb.tu-darmstadt.de/4197
URN: urn:nbn:de:tuda-tuprints-41971
Referees: Weiland, Prof. Thomas and Hinrichsen, Prof. Volker
Refereed / Verteidigung / mdl. Prüfung: 8 September 2014
Alternative Abstract:
Alternative abstract Language
Diese Arbeit befasst sich mit verschiedenen Problemen im Zusammenhang mit Varistoren und Mikrovaristoren, welche dank ihrer außergewöhnlichen, nichtlinearen elektrischen Leitfähigkeit zur Unterdrückung transienter Überspannungen eingesetzt werden. Diese Arbeit ist vor allem dadurch motiviert, dass man zum einen das Verhalten von Überspannungsableitern im Hochspannungsbereich simulieren möchte, zum anderen dasjenige von Mikrovaristoren für zukünftige Einsatzmöglichkeiten bei der nichtlinearen resistiven Feldsteuerung. Die Untersuchung der Überspannungsableiter erfordert die numerische Berechnung wechselseitig gekoppelter elektrischer und thermischer Felder, wobei die Hauptschwierigkeit in der extremen Nichtlinearität des elektrischen Teilproblems zu finden ist. Zu diesem Zweck wird die Elektroquasistatik-Gleichung mittels der Finite-Elemente-Methode im Zeitbereich gelöst. Auf die Berechnung des thermisch-stationären Zustandes eines Überspannungsableiters und die Untersuchung eines Enveloppengleichungsmodells zur Simulation des Erwärmungs- und Kühlverhaltens von Ableitern wird näher eingegangen. Diese Simulationen sind abhängig von hinreichend genauen Modellen zur Beschreibung der Materialeigenschaften. Die Schätzung der nichtlinearen Leitfähigkeit und Permittivität von Varistormaterialien ist ein essenzieller Bestandteil dieser Arbeit. Des Weiteren werden nichtlineare Kapazitäts- und Leitfähigkeitsmatrizen eingeführt. Der hier vorgestellte Ansatz beruht auf einem Ersatzschaltungsmodell, dessen Parameter mithilfe von Feldsimulationsergebnissen bestimmt werden.German
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