Study On Short Circuit Stability Of Transformer Based On Finite Element Simulation

The safe and stable operation of the power transformer is very important to the power system.The short circuit damage is the main cause of transformer damage.Transformer sudden short circuit,short circuit current surge,leakage magnetic field increases,the interaction between the short-circuit current and the leakage magnetic field,winding under short-circuit force big,winding short-circuit force in case of displacement and deformation,will cause serious damage of transformer.The short circuit current of the transformer is directly determined by the short circuit impedance of the transformer,and the inductance component in the short circuit impedance is closely related to the winding structure.Therefore,in the short circuit impact,winding short-circuit force and large displacement and deformation,will cause the change of shortcircuit impedance of transformer,thereby affecting the short-circuit current,which have influences on the stress of the leakage magnetic field distribution and winding.In this paper,variation of the short-circuit impedance of transformer is analyzed,under which,the shortcircuit current,magnetic field distribution,winding force,short-circuit stability are studied.Firstly,the short circuit damage mode of transformer is investigated.The checking method of transformer short circuit stability and the calculation method of short circuit current based on equivalent circuit is introduced.The influence factors of short circuit current and the changing trend of the resistance and reactance component of short circuit impedance is analyzed.Secondly,a variety of winding inductance on the calculation methods were compared,verified the validity of the finite element method;and set different winding structures(turns,wire spacing,winding radius),compared the inductance change trend,study on the relationship between the structure and the size of the winding inductance: the winding turns,winding to feel the effects of the larger radius.Then,establish the actual transformer two-dimensional axisymmetric model,finite element simulation,the displacement and deformation in the process of winding short circuit coupled to the electromagnetic field,the magnetic field distribution in the transformer shortcircuit calculation under the impact of the short circuit,short circuit impedance under the impact of changes,and based on the fault current of short circuit impedance;short circuit in the impact process in the winding displacement and deformation,short-circuit impedance of transformer is time varying,with respect to the design value of short circuit impedance,realtime short-circuit impedance decreases;short circuit short circuit impedance changes the flow based on the short-circuit current in the fixed impedance calculation increases accordingly.Finally,the actual transformer,establish corresponding three-dimensional model,calculated the short-circuit impedance of fixed short circuit impedance and change the magnetic field distribution,based on the winding force;and the comparative analysis of the changes of two cases of winding maximum magnetic induction intensity,maximum force and other parameters.The results show:(1)The transformer leakage flux distribution is symmetric,large leakage flux concentrated in the empty position of middle high and low voltage winding,and the low-voltage winding of the inner side and the lateral distribution of less high voltage winding;winding leakage magnetic field took place in the second half cycle in the short circuit reaches the maximum;the axial magnetic induction intensity is higher than radial,axial end winding along the winding.The magnetic induction intensity is higher than the middle;along the winding direction,high and low voltage winding hollow road magnetic induction maximum.(2)Along the axial end of the transformer,the low voltage winding stress was higher than that in the middle,is short circuit accident prone position;the radial force winding is higher than along the radial,axial,radial compression force by the low voltage winding,and low voltage winding outside stress is higher than the inside,should strengthen the low voltage winding radial support.In the middle of the high and low voltage winding of the transformer,the magnetic induction intensity is high and the winding force is large.(3)Fixed short-circuit impedance based on radial axial strength meet the verification requirements;short circuit impedance changes meet the axial strength check based on the requirements of the radial strength is slightly higher than the check limit;based on checking the short-circuit impedance of transformer short circuit changes on the stability of more stringent.