Attenuation of very fast transients in Sf6 insulated high voltage busducts. theoretical and experimental considerations of the effect of a ferromagnetic coating applied to busbars.

[摘要] Particularly at the higher system voltages, certain faults have been attributed to VFTs. This workpresents a full frequency domain mathematical model of the effects likely to be introduced bythe application of a thin ferromagnetic coating to the surfaces of the busbars as a means ofattenuating these transients. Experimental verification shows the model to perform accuratelyas an analysis tool for a continuous coated co-axial system. While comparison between themodel developed here (based on a planar conductor) and the very accurate Bessel functionsolution is presented, it must be remembered that it is not feasible to include the effects ofcoatings in the latter solution. Hence it is used merely as a bench-mark for improvements to thegeneral model. Consideration is also given to the transient skin effect, and this is shown to resultin an increased attenuation of VFTs. detectable during high voltage experimentation. The frequencydomain model is extended to that of a full travelling wave model for VFTs in GIS. TheFourier technique is used to move between the frequency and time domains. Laboratory resultsobtained at high voltage.show that this technique will introduce both risetime increase and peakmagnitude attenuation of VFTs. As the most frequent faults directly attributable to disconnectoroperation are known to be faults to earth at the switch, it is noted that the technique proposedin this work is uniquely suited for use in a design strategy that requires totally robust disconnectorsat the expense of more severe VFTs in the GIS. The model is used to determine a rangeof physical characteristics of materials suitable for use in this application. While thecharacteristics of the most suitable materials have therefore been established, it is concludedthat extensive metallurgical experimentation remains before this technique may be economicallyapplied.

[发布机构] University of the Witwatersrand