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To find a viable alternative to SF6 with growing climate change regulations, proper evaluation of alternatives such as compressed air ought to be done. For medium voltage applications, the withstand voltage is used as the dimensioning criteria and this is dependent on the initiation and propagation of streamers which are precursors to electrical breakdown. For design optimization, a thorough understanding of the initiation and propagation mechanisms of such electrical discharges under different stresses, pressure etc. ought to be studied experimentally and numerically also via a predictive model. Most of the numerical studies have so far been done via homemade codes as streamer models are not readily available in commercial software because of the complexity and non-linearity of such computations. Recently, with the increased robustness of the plasma module of the commercial finite element software, COMSOL(tm) Multiphysics, streamer discharge models can be developed with reasonable accuracy. In this paper, an implementation and validation approach is presented for streamer evolution in air for different voltage stresses. Results of simulations for short gaps ($\le$ 5 mm) under Standard Temperature and Pressure (STP) conditions have been presented, analyzed and compared with some classical papers to evaluate the suitability of such a model for further studies of non-thermal electrical discharges. Index Terms-medium voltage, streamer discharges, eco-friendly gas, numerical models.

International audience

International audience

International audience

International audience; In this article, a design methodology tooptimize IGBT gate drivers for high insulation voltage capability(up to 30kV) is proposed. A Pot core ferrite with circular coilstransformer is used for high insulation capabilities. Theinsulation voltage level is defined by the air gap length and thedielectric material. The pulse width modulation (PWM) signaltransmission and power transmission functions of IGBT gatedriver are studied and optimized. For both functions, theobjective of the studies is to optimize the geometric elements oftransformer and the associated electrical components by the helpof a virtual prototyping tool. Therefore, the optimization resultsare proposed under Pareto fronts: optimization objectives for aset of the barrier insulation thickness. Finally, the experimentalverifications are shown to validate the proposed methodology.

International audience; The measurement of ‘dark current’ in pressurized SF6 at high electric field is performed usingelectrodes with a coaxial geometry. To identify the main mechanisms involved in measuredcurrents, the influences of electrode roughness, gas pressure and relative humidity have beeninvestigated. The experimental results reveal that charge injection from the electrode constitutethe predominant process responsible for the dark current. The latter is nearly identicalin positive and negative polarities, and shows an exponential increase versus the relativehumidity and the electric field. The analysis of results shows that under high electric field,the emission of charged water clusters from the water films adsorbed on electrodes probablyconstitutes the main mechanism of charge emission.