Research On The Effects Of Short-circuit Electrodynamic Force On The Radial Stability Of Transformer Windings

Power transformer,which transfers electric energy and transforms voltage,is one of the most indispensable equipment in the power grid.With the development of social economy and the increasing demand of electricity consumption,the total capacity of power system and the capacity of single transformer are increasing as well,the problem of radial stability of winding,such as the transformer winding deformation caused by short-circuit power,are becoming more and more serious,and the winding deformation will accumulate until the winding is unstable radially.When the winding radial instability happens,the internal structure failure of the main transformer winding occurs,which needs replace the transformer to dismantle and inspect.The maintenance is difficult,the outage duration is long,and the influence is wide,these brings a huge economic losses.Therefore,in order to explore the mechanism of the radial instability of winding and the cumulative effect of winding deformation,a deep research on the main transformer is made.The main work is as follows:1)By the finite element method of "field circuit coupling",the simulation of three-phase symmetrical short circuit of the medium voltage side winding is carried out in the platform of ANSYS software,the short circuit current,the leakage magnetic field distribution and the leakage flux density distribution of the winding are deeply studied.By numerical analysis of short circuit electric power,the short circuit electric power is not only related to the short circuit time,but also to the position of the winding;the variation tendency of short circuit electric power of each position of the winding with time is similar to the change of short circuit current;at the same short circuit time,the short circuit electric power value near the middle of the winding is much larger than that at the end of the winding.2)The structural dynamic analysis model of transformer winding is improved to the multi-span model of the whole disc.The critical buckling value and radial critical displacement value of the disc are analyzed by the method of eigenvalue buckling analysis,so that the safety factor of winding can be determined;considering the initial defects of the winding when the transformer is installed and the nonlinear characteristics of the material,The nonlinear buckling analysis method is used to analyze the critical displacement value of the winding,and the result is compared with the results of buckling analysis.Finally,verify the correctness of the research by introducing deflection analysis method.The study also found that the winding temperature rise is small when the short circuit time is not more than 2s,which is little influence on the radial stability of the winding;The correlation between radial stability and radial width is high,while the correlation between radial stability and axial height of winding is low.3)The winding deformation will accumulate gradually.In this paper,it's studied from the point of elastic and plastic materials intensively,and calculate the winding deformation values when the main transformer is subjected to 1,15,30 short circuit impacts.It is found that,when subjected to short circuit shock,the winding will develop from the linear elastic stage,which can be restored,to the nonlinear elastic stage,until to the plastic stage which can't be restored,and the process is not continuous.At the end of the article,a relevant survey results of Failure Analysis Report of One#1 Main Transformer is used to verify the correctness of the content studied in this paper.