Analysis Of The Short-Circuit Withstand Capability Of Distribution Transformers And Improvement Measures

With the continuous progress of science and technology and the improvement of people’s living standard,people have higher and higher requirements for power supply reliability and power quality.As the core of power distribution and voltage level transformation,distribution transformer is one of the most important equipment in distribution network.Whether it can ensure its safety,reliability and economic operation plays a vital role in the reliability of power supply of distribution network.Amorphous alloy distribution transformer can effectively reduce the no-load current and no-load loss of the transformer,but its unique rectangular winding structure is more likely to cause deformation and insulation burnout under the action of short-circuit fault than circular winding.Therefore,this paper mainly studies the rectangular winding,analyzes its dynamic and thermal stability,and puts forward some measures to improve its short-circuit resistance,which is of great significance.In this dissertation,the circuit model of transformer short-circuit fault was established.Firstly,the short-circuit fault type of distribution transformer was analyzed,and the peak short-circuit current was calculated and deduced.Secondly,the magnetic field distribution inside the transformer was analyzed,the model of the true amorphous alloy distribution transformer was established by COMSOL finite element simulation software,and the magnetic flux leakage distribution in the unique rectangular winding of the amorphous alloy distribution transformer was analyzed.Then,according to the left hand rule,the short-circuit electromotive force of the winding was judged,and the stress distribution of the rectangular winding was studied by combining the finite element simulation software.The deformation condition of the rectangular winding was obtained.Aiming at the weak anti-short circuit ability,the measures such as changing the radius of the rectangular winding fillet and the number of braces are proposed to improve the dynamic stability.At the same time,due to a large number of losses caused by short-circuit fault,the heat generation and heat dissipation mechanism of the winding was analyzed,and the winding temperature was calculated when the transformer is short-circuited.The temperature distribution map of the rectangular winding was drawn by finite element software,and the temperature position of the winding hot spot was found,and the optimization measures to improve the thermal stability of the winding were given.The research shows that when the amorphous alloy distribution transformer occurs short circuit fault,the axial force of the rectangular winding is large at both ends of the axial direction and small in the middle.The radial force of the rectangular winding is large in the middle of the axial direction and small at both ends.The radial force along the circumferential direction shows that the long axis angle of the winding is much larger than that of the other parts of the winding,and the long axis angle of the winding is easier to deform under the action of short circuit electric power.The dynamic stability can be effectively improved by increasing the fillet radius of rectangular winding,and the placement of braces can improve a certain dynamic stability,but the influence of the number of braces on the thermal stability needs to be comprehensively considered.The short circuit temperature distribution of rectangular winding shows a trend of high in the middle and low at both ends along the axis direction.The average temperature of low voltage winding is higher than that of high voltage winding,and the hot spot temperature appears at the long axis angle of low voltage winding.The research content of this dissertation can provide certain engineering practical value for further studying amorphous alloy distribution transformers and improving their short-circuit resistance.