Development Of VFTO Distribution Calculation Software For Large Power Transformer

With the rapid development of China's power grid,gas-insulated substations(GIS)have been widely used in power systems because of their advantages of high reliability,small size,long maintenance period and stable operation.GIS stations in the opening and closing of the switch,the contacts will be repeated breakdown and reignition occurred in the GIS multiple refraction and reflection,the final formation of very-fast transient overvoltage(VFTO).VFTO winding equipment is more harmful,when the VFTO into the transformer,may cause insulation damage,aging,or even breakdown.Transformer as an important power system equipment,its normal operation of the power system related to the stability.Therefore,the study of transformer winding VFTO distribution is of great significance.Based on this background,this paper developed the VFTO distribution calculation software for large-scale power transformers.First of all,the mechanism of VFTO generation,the suppression measures,the damage to transformers and the transformers caused by transformers are introduced.The research status of this subject at home and abroad are briefly summarized.Secondly,the multi-conductor transmission line model of transformer winding is established,and the capacitance parameters are calculated by finite element method.The inductance,resistance and conductance parameters are calculated by the formula method.Next,the finite element method is used to calculate the overvoltage distribution in the transformer windings.The structural characteristics of continuous,interweaved and entangled,common tangled,cross-section inner shielded,cross-section inner shielded and spiral are analyzed.And in order to facilitate the calculation of its turns on the renumbering,obtained the various types of winding boundary conditions.The influence of oil channel size and turn insulation thickness on the maximum oil gradient and the maximum inter-turn voltage is analyzed,providing a theoretical reference for the insulation design.Finally,the development of large-scale power transformer VFTO distribution calculation software in MATLAB,the software can calculate the continuous,flower arrangement tangled,ordinary entangled,four tangled,four-span inner shielded,span two inner shielded,spiral VFTO distribution in other winding,can well meet the practical application of the project.The actual large-scale transformers were calculated.