Analysis Of Wave Process And Thermo-electric Field Of Transformer

Transformer is extremely important equipment in the power system,which must guarantee its reliable operation.The primary condition for the safe and reliable operation of transformer in power system is to have good insulation ability.According to the existing statistical results and research reports,the fault of transformer was mainly caused by insulation damage,and lightning impulse overvoltage was the most important factor causing insulation damage of transformer in operation.Therefore,it is of engineering value to analyze the wave process of transformer under lightning impulse overvoltage and the distribution of thermo-electric field for transformer structure design and safe operation.In this paper,dry-type transformer which type was DG-500-220/12 was taken as the object to investigate the process of lightning impulse overvoltage and the distribution of electric heating field.In order to analyze the wave process of transformer under lightning impulse voltage,firstly,the simple wave process was simulated and tested.The matching impedance was solved through finite element simulation,and the test platform was built based on the simulation results,which laid the foundation for the study of transformer wave process;Secondly,the equivalent circuit of transformer winding was theoretically analyzed and its parameters were solved,and the influence of different winding forms and neutral grounding state on winding wave process was discussed through MATLAB modeling and simulation.Finally,on the basis of theoretical analysis and modeling simulation results,the self-developed impulse voltage generator was used to conduct wave process test research on the winding model,and the voltage and potential gradient distribution of different types of windings were obtained,and the insulation weak points were found out,which provided a theoretical basis for the insulation design optimization of transformer.When the transformer was invaded by lightning,the electric field intensity was large or the distribution was uneven,which was easy to cause the insulation breakdown damage of the transformer;in addition,the heat could not be dissipated in time during the operation of the transformer,which might lead to the insulation damage due to high temperature.Therefore,in order to evaluate the distribution of thermo-electric field of transformer,the finite element simulation calculation was carried out.The two-dimensional electric field calculation model of transformer was established to obtain the voltage distribution of each winding and the influence of different insulation structure on the electric field distribution;on the basis of this,the three-dimensional electric field calculation model was established to obtain the electric field intensity distribution of each part of transformer;the two-dimensional and three-dimensional temperature field calculation model of transformer were established to obtain the temperature field and distribution law of each part.The simulation results showed that the maximum electric field strength of the transformer was,which was located at the junction between the insulation cylinder and the air,and the highest temperature was 90.2 ℃,which was located at 1/3 of the top.The results provided reference for insulation design optimization and fault state detection of transformer.