Calculation On Short-Circuit Strength And Electromagnetic Force Of Transformer Windings Under Multiple Short-Circuit Conditions

As grid capacity and coverage increase,short-circuit faults occur from time to time.The transformer is located in the necessary part of power transmission,and the ability of the transformer to withstand short circuit is closely related to the stability of the power grid.Although the ability of the transformer to withstand short circuits has improved a lot with the advancement of technology,it has also caused problems.The original qualified transformer products have insufficient ability to withstand short circuits after being subjected to multiple short circuits.In order to improve the ability of the transformer to resist multiple short circuits,this paper analyzes the process of multiple short circuit of the transformer.The main research contents of this theirs are: the calculation of short-circuit current of transformer under different connection modes;the influence of transformer phase-to-phase magnetic field on the stress of transformer winding;the calculation of short-circuit current of reclosing after transformer short-circuit;the change process of winding after multiple short-circuit accumulation of transformer.The accumulation process of transformers involves many disciplines such as electromagnetics,structural mechanics,and materials science.The calculation process is extremely complicated.Similarly,accurately calculating the multiple short-circuit mechanism of transformers is of great significance to the economic and stable operation of the power grid.Considering the multiple short circuit formation process,this theirs first calculates the short-circuit current of the transformer under different connection modes in a single short circuit,and then compares the short-circuit current with time under different conditions,analyze the effects of transformers under different short circuits.The system impedance is ignored when calculating the short-circuit current.The calculation result can reflect the worst case of short circuit and provide calculation ideas for calculating the short circuit of the transformer.The finite element model of the actual transformer was established by using the finite element analysis software of electromagnetic field.The leakage field and the force of the winding were calculated by the transient field.The rated current analysis is used to calculate the change of the transformer winding under the influence of the phase-to-phase magnetic field.The moment when the maximum short-circuit current occurs is not the moment when the maximum force of the winding occurs,and the maximum force position of each line cake changes with the change of the three-phase current.The rationality and practicability of the analytical methods used were confirmed.This method is thus applied to a transformer model of three-phase short-circuit current loads.When analyzing the multiple short circuit conditions of a transformer,the problem of transformer reclosing in the presence of a short circuit fault must be considered.In this paper,the simulink transformer reclosing model is used to analyze the reclosing of the transformer on the first and second sides in the presence of short circuit faults,and the application of the reclosing current in multiple short circuits is determined.Under the above factors,the stress and residual deformation of the winding under multiple short circuits are analyzed to provide recommendations for transformer stability.