Study On Short Circuit Withstand Ability Of Amorphous Alloy Distribution Transformer

With the emergence of global energy shortages and the popularization of energy-saving economic and social system,amorphous alloy distribution transformers with good energy-saving characteristics have been put into power grid in recent years,which become an indispensable part of the power system.However,due to their poor short-circuit withstand ability,transformer accidents occur frequently,which affects the normal operation of the power grid.Therefore,it is imperative to study and analyze the short-circuit withstand ability of amorphous alloys distribution transformers.Firstly,this paper summarizes the experiments of amorphous alloy distribution in short circuit test in recent years,analyses the fault modes caused by the insufficient short circuit withstand ability of amorphous alloy distribution transformers,and compares the differences in material properties,physical properties and structure between amorphous alloy distribution transformers and silicon steel distribution.Duing to the original calculation method of short-circuit impedance of circular winding is not suitable for rectangular winding structure of amorphous alloy distribution transformers,this paper proposes a calculation method of short-circuit impedance based on "magnetic circuit method".Comparing with the existing "energy method",it is easy to get more accurate short-circuit current,which results in more reliable short-circuit withstand ability analysis results.Secondly,in the analysis of the radial stability,the simplified three-dimensional solid model of the amorphous alloy distribution transformer is established by ANSYS simulation software.After the "magnetic-structure" multiphysics coupling calculation,the leakage magnetic field distribution and winding stress distribution of the winding are obtained.Due to the uneven stress distribution of the rectangular winding structure(the stress at the winding rounding is greater than the two straight sides),the radial stress optimization model is proposed in this paper.By optimizing the stress at the fillet,the forces in the windings are more evenly distributed.The optimized transformer and the unoptimized transformer are compared and analyzed by experiments.Finally,the windings and spacers are considered as spring-quality systems in the axial stability analysis.Due to the special structure of the small distribution transformer(there is no wire cake between the windings),its structure is different from that of a large power transformer with many layer cakes.Therefore,the mass-spring system is simplified and a three-dimensional model of amorphous alloy distribution is established.The relationship between natural frequencies,which is simulated by ANSYS software,and pre-compressionforce is studied.The above research can prevent resonance phenomenon and avoid more damage to transformer caused by resonance phenomenon.