Research On Transient Electromagnetic Force Analysis And Optimization Technology Of Distribution Transformer

Distribution transformers are indispensable and important equipment in power systems,and their operational reliability is closely related to the safety of the distribution network.When an external short-circuit fault occurs in a distribution transformer,a relatively large short-circuit current flows through the windings,and its value is much higher than the rated current under normal conditions.Under the action of the leakage magnetic field,a huge short-circuit electromagnetic force will be generated on the windings,which will cause the winding deformation,through continuous accumulation,causes the relative displacement of the turns to cause insulation damage.With the continuous improvement of voltage levels,various accidents in the distribution network emerge in endlessly,especially the accidents caused by transformer short-circuit faults.Therefore,analyzing and studying the electromagnetic force distribution law in the distribution transformer windings under the short-circuit state has important engineering value.In the actual application of distribution transformers,circular windings have strong short-circuit resistance,so the research on leakage magnetic field and electromagnetic force is mostly focused on circular windings.However,considering factors such as increasing the duty cycle and reducing production costs during design and manufacturing,the windings of distribution transformers mostly adopt oblong structures,which have lower production costs,but often have poor short-circuit resistance.Therefore,this article mainly focused on the study of oblong windings,analyzed and compared the electromagnetic force distribution on the round and straight sides,found the weak points of the force,and provided a reference for the implementation of measures to improve the short-circuit resistance of distribution transformers.First of all,this article explained the theoretical basis of the calculation of the leakage magnetic field and electromagnetic force of the distribution transformer,and summarized the specific steps of the finite element simulation calculation;secondly,based on the specific structural parameters of a distribution transformer with a voltage level of 10 k V and a capacity of 400 k VA,a three-dimensional model was established using COMSOL finite element simulation software to simulate the leakage magnetic field and short-circuit electromagnetic force of the oblong winding.Through the analysis,the distribution law of electromagnetic force on the round side and the straight side was obtained and compared and analyzed,and the conclusion was that the force on the round side is slightly higher than that on the straight side;then the short-circuit electromagnetic force of the circular winding and elliptical winding distribution transformer was studied.The short-circuit electromagnetic force of the three windings of different structures was compared and analyzed.Summarized the influence of the winding structure on the force,and calculated and checked the stress on the oblong winding,which verified the stability of the winding;finally,changed the number of stays,the conductivity,density and other parameters of the winding wire material,analyzed and studied the influence of other factors on the winding force,and summarized the different influencing factors of the short-circuit resistance ability,and the optimization techniques and measures to improve the short-circuit resistance were proposed from the aspects of reducing short-circuit electromagnetic force,improving the dynamic and thermal stability of distribution transformers.The research in this paper shows that when a three-phase short-circuit fault occurs on the low-voltage side of a distribution transformer,the electromagnetic force on the high-voltage and low-voltage windings increases sharply,and reaches the maximum value in the half-cycle after the short-circuit.The short-circuit electromagnetic force of the oblong winding is greater than that of the circular winding,and the short-circuit electromotive force on the round side is relatively large and unbalanced,which is the position where the bearing force is relatively weak and the stability is poor,and it is easy to cause the deformation and damage of the coil in the event of a failure.Parameters such as the number of stays,the Young’s modulus and Poisson’s ratio of the wire material have a greater impact on the winding force.Measures such as strengthening the appropriate stays at the weak location and selecting appropriate materials can be taken to improve its short-circuit resistance.The research conclusions of this paper can provide practical reference for improving the short-circuit withstand capability of distribution transformers.