Study On The Leakage Magnetic Field And Axial Stability Of Large Transformer

How to enhance the capacity of transformer short-circuit impact resistance,is one of hot issues on the research of the transformer in recent years. The transformer axial vibration stability analysis plays an important role in research in enhancing the transformer short-circuit impact resistance.Large power transformer will get a short-circuit force impact when short circuit occurs, when winding mechanical strength is insufficient, the result will be a short circuit accident of transformer.In this paper, according to a 120 MVA / 220 k V with off-circuit tap changing transformer,we do something on the short-circuit electrodynamic force of static analysis and dynamic analysis. The so-called static analysis, is to use the Mag Net finite element software, to use the method of field- road coupling to analys when the low voltage winding outlet three-phase symmetrical short-circuit occurs the leakage magnetic field model of the transformer.First of all, in order to improve the accuracy of the transformer winding short-circuit electrodynamic force calculation.Finite element model is established by using 3d models, including core, iron yoke and tank.Model considers the imbalance of ampere turns,nonlinear ferromagnetic materials and oil duct size on the effects of transformer leakage magnetic field. Comparatively analyzed the differences between winding leakage magnetic field nearby inside and outside the core window.Then, we can get short circuit electric power of different taps in preparation for the subsequent calculation of axial dynamic vibration system.The so-called dynamic analysis, is to use the ANSYS finite element software,through the establishment of spring quality model to analyze the axial dynamic response of the winding.First of all, because of the winding axial dynamic response is mainly affected by the natural frequency of the model. So when the spring mass model is setting up,we need to consider the influencefactors such as bread quality, the block size, pre-tightening force and so on. Through the modal analysis, we can get the winding model inherent frequency under different pre-tightening force.Secondly, use each wire quality center for the load point.By using each wire bread wire static force changing with time and winding’s own gravity for the exciting force. Calculate the vibration displacement change rule of different wire breads of the multi-degree of freedom, different load points,changing load vibration system. We get the conclusion that only the elastic force can match the force, the inertia force and the damping force will be complicated fluctuates up and down.Based on the research of the transformer leakage magnetic field inside and outside, we can get the differences on the end of the windings,so we need to enhance the transformer short-circuit impact resistance there. Through the analysis of the axial stability of transformer winding, we can calculate the vibration system to get the inertia force, elastic force, damping force of different wire breads,and provide some basis for the research behind.