Study On Dynamic And Thermal Stability Of Power Transformer Based On Multi-physical Fields Coupling

Power transformer is an important primary equipment in the power system,whose operational reliability is directly related to the effective and safe operation of the relevant power grid.In recent years,short-circuit operation of power transformer has become the primary cause of power transformer accident.In order to reduce the accident of power transformer,it is necessary to improve the dynamic and thermal stability of power transformer under short-circuit operation.Therefore,the ability to study the short-circuit dynamic and thermal stability of power transformers has important reference value for improving the ability of power transformers to resist short-circuit.Based on this,this article focuses on the dynamic and thermal stability of power transformers.Firstly,the short-circuit current in three-phase and three-winding power transformer under various short-circuit fault conditions is theoretically deduced through impedance network and numerical calculation methods.Then the power transformer of the model SFPSZ7-150000KVA/220 kV is used as an example.The operation of the power transformer at rated current and three-phase short-circuit is simulated by ANSYS Maxwell software,and the leakage magnetic field of the two-dimensional model and the three-dimensional model of the power transformer in the rated current operation and short-circuit operation of the power transformer is calculated,and the leakage magnetic field distribution of the two-dimensional model and the three-dimensional model are compared in these two cases.On this basis,a two-dimensional axisymmetric pie winding model of power transformer with multi-physical fields coupling is established.The transient stress of these pie windings is analyzed with the upper and lower ends of each winding and the middle part of the windings as the research object.The variation of the transient stress curves and the difference between the maximum transient stress values between them are compared,at the same time,the corresponding transient stress of the winding was checked.The results show that the adopted power transformer passed the test of the dynamic stability of the short-circuit and left a certain safety margin.Finally,a multi-physical fields coupling oil-immersed type three-dimensional power transformer model is established to calculate the temperature field distribution of the high,middle,and low voltage windings of each phase of the power transformer after short-circuit of 2 seconds by using Fluent software.The distribution of temperature field of each winding is obtained.Then the distribution of temperature field of the winding is summarized and the short-circuit thermal stability of the winding of the power transformer is checked.From the results of the verification,it can be known that the power transformer adopted in this paper not only passes the verification of the short-circuit thermal stability but also left a certain safety margin.