Analysis On Characteristics Of Leakage Magnetic Field And Short Circuit Impedance Under Power Transformer Winding Fault

With the construction and development of my country’s energy infrastructure,the UHV grid is an indispensable part of my country’s power transmission network.As a key equipment in the UHV network,power transformers will inevitably experience short-circuit faults during operation,and their resistance to short-circuits Capability is related to the safety and continuity of the operation of the entire grid system.The winding of power transformers will deform and fail under the impact of multiple short-circuit currents.This is a comprehensive problem involving multiple disciplines.It requires comprehensive consideration of the knowledge involved in electromagnetic,mechanics,and materials,and summarizes the resistance applied to transformers.The short-circuit capability is being calculated.Therefore,perfecting the calculation and analysis of the leakage magnetic field and short-circuit impedance when a short circuit fault occurs in a power transformer winding has important practical significance for engineering design.The research content of this topic includes three parts:First of all,this article summarizes the domestic and foreign power transformer short-circuit current calculation,leakage of magnetic field characteristics,and winding deformation of the research status.Introduces the transformer leakage magnetic field and short-circuit current calculation method,calculation and analysis power transformer short-circuit fault in different forms of maximum short-circuit current,and to determine the maximum short-circuit current,short circuit calculation results can reflect the worst type,It provides idea for the calculation and analysis of the main air channel leakage magnetic field of the winding.Secondly,for the three-phase three-leg power transformer studied in this paper,a model suitable for the direct coupling calculation of "electromagnetic field-structure field" is established,and a model for the radial deformation of the medium voltage winding is established.Under the impact of short-circuit current peaks on medium voltage winding of different phases,the transient field of the finite element model is used to calculate the axial and radial magnetic leakage in the main air passage of the transformer winding,and the distribution law is summarized.In the case that the transformer winding has undergone instability deformation and is subject to short-circuit impact again,calculate the axial and radial magnetic flux leakage of the main air passage of the winding,and focus on the analysis of the leakage magnetic field of the radially deformed winding to its main air passage.The impact of distribution.Quantitatively analyze the weakest position of the winding under rated conditions and when radial deformation has occurred,and evaluate its short-circuit resistance ability to provide experience for future designers.Finally,Based on the basic laws of the magnetic circuit,a formula for calculating the short-circuit impedance is derived.Analyzing the change of short-circuit impedance to determine the winding state is an important method for transformer fault detection.In order to explore the influence of winding deformation on the short-circuit impedance of the transformer,it is established that the transformer winding are radially deformed at different positions and the medium-voltage winding are equivalently reduced.In the model,in the case of these kinds of deformation faults in the winding,the values of the short-circuit resistance are calculated respectively,and the quantitative analysis is performed to summarize the change law.The electromagnetic load on the rated winding and the deformed winding at the moment of the maximum short-circuit impulse current is calculated and analyzed,and the calculation results under several winding deformation conditions are compared,and the key positions of the winding that may be further damaged are determined.According to the above analysis,the measures that can improve the short circuit resistance of power transformer are put forward,the research in this article provides certain experience and value for the design and stability verification of transformers in the future.