Simulation Study On Current And Remanence Of Power Transformer Under Short Circuit And Reclosing Conditions

Power transformers play a very important role in the power system and directly affect the safety and reliability of power grid operation.With the continuous development of the power system,the capacity and voltage level of power transformers are also constantly improving,and short-circuit faults occur from time to time.Therefore,the analysis of power transformers under different short-circuit operating conditions is of great significance.The main content of this study includes three parts:Firstly,the calculation method of short-circuit current of power transformer under different operating conditions is studied.In this paper,the field-circuit coupling method based on the finite element is used to calculate the current of the transformer under different short-circuit conditions.At the same time,the traditional analytical method is used to calculate the shortcircuit current of the power transformer under different operating conditions.Finally,the fieldcircuit coupling method is calculated to obtain The short-circuit current calculated by the traditional analytical method is compared with the short-circuit current calculated by the traditional analytical method.The calculation results show that the current calculation of the power transformer under different short-circuit conditions is more reasonable and the calculation accuracy is improved.Secondly,the residual magnetism of the iron core after the initial short-circuit of the power transformer is estimated,and the short-circuit impulse current after the reclosing is calculated and analyzed.In this paper,the voltage integral method is used to calculate and analyze the residual magnetism of the transformer core after the initial short circuit,and the finite element simulation analysis method is used to calculate and analyze the residual magnetism of the transformer after the initial short circuit.As a result,the rationality of the method was verified.The residual magnetization curve of the iron core with different opening phase angles is obtained,which provides a basis for the subsequent analysis of the short-circuit current of the reclosing winding.In addition,on the basis of considering the residual magnetism and the initial phase angle of reclosing,the short-circuit impulse current suffered by the windings after the reclosing of the power transformer is calculated and analyzed,which provides excitation conditions for analyzing the electromagnetic force and short-circuit strength of the windings after the reclosing of the transformer.Finally,the calculation and analysis of the short-circuit leakage magnetic field,electromagnetic force and winding strength of the power transformer after initial short-circuit and reclosing are carried out.In this paper,the method of electromagnetic-structural coupling is used to analyze the leakage magnetic field and electromagnetic force of the windings when the initial short-circuit and short-circuit inrush current of the power transformer is at its maximum after reclosing,and the calculated electromagnetic force results are imported into the structural field calculation model.The transient dynamic analysis of the winding pie displacement and stress change under different short-circuit conditions provides a certain reference for the analysis of the winding strength of the power transformer under this operating condition.The effectiveness of this method is verified by experiments.