Modelling and Simulations of Corona Discharge Currents in a Large Scale Coaxial Geometry with a Dielectric Barrier due to Low Frequency Triangular Voltages

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Master Thesis
Title: Modelling and Simulations of Corona Discharge Currents in a Large Scale Coaxial Geometry with a Dielectric Barrier due to Low Frequency Triangular Voltages
Authors: Macken, Martin
Abstract: When a high voltage is applied to electrodes immersed in air and provides a strongly non-uniform electric field, charged species such as free electrons and positive and negative ions can be created in gas due to corona discharge. Charged species will drift in the field from one electrode to another and eventually will be collected on dielectric surfaces if solid insulating elements are present in the discharge volume. The accumulated surface charges may strongly alter the electric field distribution in the entire system intensifying insulation ageing and increasing risk for flashovers. Such charge accumulation is an inherent phenomenon for DC applications and is also essential in cases of varying voltages when the dimension of the air gap is smaller than the travelling distances of the charged species. Recently, experiments have been carried out at ABB Corporate Research in Västerås (Sweden), where a large scale coaxial electrode arrangement was used to measure the level of the corona discharge current when triangular voltages of different frequencies were applied. The experiments were carried out both for free air and when a dielectric barrier was introduced in the discharge gap. In the thesis, the experimental results obtained for the case of coronas with dielectric barrier are analyzed by means of computer simulations. A model was developed that couples partial differential equations describing drift and diffusion of charged species with Poisson’s equation for computing space charge controlled electric field. The model accounts for field dependent generation and loss of free charges in gas and their accumulation of solid surfaces. The model was implemented in COMSOL Multiphysics. Simulations were conducted for conditions as close as possible to those used in the experiments including electrode system geometry, environmental parameters (temperature, pressure) and shapes of the applied voltages. Special attentions was paid to correct representations of boundary conditions that was found to be a key for reproducing experimental results for voltages of low frequencies when the travelling length of ions was large. The results obtained from the performed simulations are in agreement with the experimental corona characteristics acquired by ABB. The performed computational study allows for analyzing experimental data and provides insight on physical mechanisms leading to experimentally observed phenomena.
Keywords: Energi;Elektroteknik;Elektrofysik;Energy;Electrical engineering;Electrophysics
Issue Date: 2014
Publisher: Chalmers tekniska högskola / Institutionen för material- och tillverkningsteknik
Chalmers University of Technology / Department of Materials and Manufacturing Technology
Series/Report no.: Diploma work - Department of Materials and Manufacturing Technology, Chalmers University of Technology : 135/2014
Collection:Examensarbeten för masterexamen // Master Theses (IMS)

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