Research On Mechanical Strength And Stability Of Transformer Windings Under Multiple Short-circuit Conditions

In this paper,based on fully and thoroughly summarizing the current research status of mechanical strength and stability of transformer windings under short-circuit condition,the finite element method is used to analyze multiphysical fields coupling of transformer short-circuit test model.The distribution characteristics of electromagnetic field,electromagnetic force,and deformation of transformer windings are known.Accumulative deformation and critical buckling load of windings under multiple short-circuit conditions are solved while the mechanical strength and stability of transformer windings under multiple short-circuit conditions had been simulated by ANSYS.The influences of the short-circuit currents and the radial spacers on transformer windings mechanical strength are further discussed.The stresses of the end rings of windings are calculated by mechanical field analysis.On the basis,the natural frequencies of windings are further caculated by modal analysis under multiple short-circuit conditions.Moreover,the effects of axial spacers preloading on natural frequencies of windings are analyzed in detial.First of all,based on the basic principles of electromagnetic analysis and structural analysis,the multiphysics problem including the electromagnetic field and mechanical field on the mechanical strength and stability of transformer windings,are analyzed firstly using the transformer short-circuit test model.The equations of the stress and motion of windings are deduced and electromagnetic field is analyzed intensively using the simplified model.The 3D mesh model,based on the transformer short-circuit test model,is built and solved as a example for using ANSYS multiphysical field coupling.Secondly,the reason and process of accumulative deformation are elaborated comprehensively and a method is proposed to analyze radial mechanical strength of transformer windings under multiple short-circuit conditions.The validity and reliability of the finite element method are identified through the comparsion of analytical values and experimental values.The effects of number of times and peak duration of short-circuit currents on accumulative deformation are explored in different short-circuit peak currents.According to the characteristics of transformer windings radial spacers,radial deformation performances are researched in different number and width of radial spacers.Futher more,based on the elastic beam model,the radial stability of transformer windings is analyzed under multiple short-circuit conditions and the effects of radial accumulative deformation on critical buckling load of windings are studied.Finally,based on the basic principle of axial vibration of transformer windings,the "force-spring model" is used to analyze the mechanical field of the transformer windings.The stresses distribution of every cake and the end rings in the winding are solved.After the modal analysis,the first six modes of the winding before and after short-circuit conditions are compared and analyzed,and the natural frequencies of the winding are also calculated before and after the short-circuit conditions.The natural frequencies of the winding are measured by transient excitation method with spectrum analysis method,and the validity and reliability of the finite element method are also verified.At the last,the effects of the axial spacers preloading on the natural frequencies of the winding are explored mainly.