The Analysis Of Transient Simulation On Electromagnetic Field And Thermal Field Of Three-phase Oil-immersed Power Transformer

This paper studies the simulation of three-phase oil-immersed power transformer ofS7-10kV level below, the rated capacity of630kVA, which core and winding in theprocess of transient start in every peak phase moment of the electromagnetic fielddistribution and the resulting loss as a heat source, to simulate the thermal field distributionof iron core and winding. For now domestic and foreign scholars only study for transformerelectromagnetic field and temperature field alone, or only given the transformer windingcurrent density to simulate the temperature rise. Based on the simulation in the process ofthe normal operation of power transformer in transformer of the loss to be converted intoheat source, so as to analyze the distribution of the thermal field, so that we can verify theexperimental results more accurately, and explore the fundamental factors that affect thetransformer temperature rise.This article is through the finite element analysis software of ANSOFT Maxwelll andTransient Thermal of ANSYS Workbench14.0to simulate the distribution ofelectromagnetic field and temperature field of iron core and winding in every peak phasemoment. First respectively simulate the electromagnetic field of transformer for no-load,load factor0.5, and load factor1, three different load operation conditions, analysis of thechange of the induced voltage and load current in the transient start-up process,and themagnetic induction (B), the magnetic field distribution (H), the current density distribution(J) of the core and winding in each phase peak time. Then the results are integrated into theTransient Therma to calculate the loss of the core and winding, and simulated thedistribution of the temperature field from the distribution of transient to steady state,and thechange characteristics of maximum temperature difference of the core and winding. By means of simulation on the electromagnetic field of the transformer in no-load, loadfactor0.5, load factor1condition,it is demonstrated that the voltage ratio for three phaseone side voltage compared with the secondary side was25.Under no-load and minus oneload coefficient conditions,it showed that the no-load current is far less than5%~8%ofprimary rated current and the no-load condition will produce magnetizing inrush currentphenomenon whose the highest current can reach as6~8times as the steady one. And thecurrent of large-volume transformer can reach dozens of times as the steady one. Accordingto the above simulations, we can come to the conclusion that the results of simulationconform with actual situation, satisfying the requirement of transformer simulation.Analysis of electromagnetic field on the core and winding magnetic fields under thecondition of peak times, the variation range of the magnetic field intensity of the middlephase B is less than phase A and C. In the meantime,the change of winding magnetic fieldvector is A cone-shaped distribution. During the simulation, the maximum magnetic fieldintensity is at the intersection between horizontal and vertical;with the increase of loadfactor, winding magnetic field intensity would be multiplied with it. The magneticinduction distributions under the three kinds of phases were uniform while average loadfactors were different. The variation of the magnetic induction and maximum on thesurface of iron core was little which means load factor has no effect on surface of themagnetic induction intensity.Core loss has nothing to do with the size of the load factor, but along with the rising ofthe transformer load factor, core temperature will increase.The reason is because of the loadfactor increases after winding temperature rise sharply, the heat generated quickly passed tothe core by transformer oil,So that its temperature rising is nonlinear with time;Thetemperature of secondary winding is greater than the primary winding as a whole,this isdue to the secondary winding loss density is greater than the primary,therefore the calorificvalue of the secondary winding will be greater than the primary winding.Another part ofthe reason is due to the secondary winding in the inside of the primary winding,oil flowconnectivity contact with transformer is poorer, heat dissipation of primary winding isbetter than the secondary winding;Along with the increase of winding load factor, the overall winding temperature rise, under steady state temperature difference value willincrease.Through the above analysis,transformer heat production is due to the loss of core andwinding,reduce the current density to control the degree of loss to reduce the maximumtemperature inside;On the other hand enhance the efficiency of transformer cooling toreduce the maximum temperature.in this paper, the research provides a reliable referencefor transformer design personnel, at the same time in order to further improve thetransformer cooling cooling measures laid the foundation.