Electric Field Simulation And Structure Optimization Of Main Insulation Of Power Transformer

Electric energy is an indispensable secondary energy in human life,and the power grid is an important transmission carrier to transport electric energy to thousands of households.With the increasing coverage of the power grid,the number of power transformers is also increasing.However,with the global energy shortage,the raw materials used to make transformers have been greatly increased in price,resulting in an increase in the cost of transformer manufacturing.Therefore,under the condition that the transformer conforms to the national standard,reducing the cost becomes a problem that transformer designers must face.Aiming at the problem of large volume and high cost of traditional oil-immersed power transformer,this paper takes the oil-immersed power transformer of 35 kV voltage grade as the research target.Through the traditional structural calculation,the corresponding model is established from the perspective of main insulation design at first,and the distribution of electric field is obtained by using finite element software simulation.The insulation properties were analyzed,and the parts with sufficient insulation margin and optimized space were found,which were: the distance between the main channel,the radius of curvature of the electrostatic ring,and the distance between the end of the winding and the iron yoke.Then,from the perspective of electromagnetic design,considering the distribution of ampere turns,and to establish model,connect the three-phase symmetrical short circuit as the external circuit of transformer,the transient analysis of electromagnetic field by finite element software,get the short circuit of transformer winding leakage magnetic field under the condition of axial component and electric power to the component distribution is approximately the same,the radial leakage magnetic field to the component to be about equal to the electrical power distribution of the axial component.Then,the model is refined.On the premise of ignoring the temperature,the supporting effect of bracing bar and cushion on the winding and the stress-strain curve of winding material are considered.The deformation and stress distribution of windings with short-circuit electric force and residual deformation and stress distribution of windings after unloading electric force are analyzed by coupling electromagnetic field with structure static field.Finally,the size of the transformer is optimized,the field strength and the wire stress are taken as the constraint conditions,and the minimum value of the total weight is obtained,so as to achieve the purpose of optimization.In this paper,the differential evolution algorithm is adopted,and the variables are rounded to avoid the algorithm falling into local optimization by making the crossover probability factor change with the number of iterations.The distribution of the winding stress and residual stress under each short-circuit condition is obtained by several short circuit current shocks before and after optimization.By comparing the main insulation strength and short-circuit resistance of the transformer before and after optimization,the results show that the optimized transformer can meet the requirements,and the total weight is lower,thus the cost is reduced.