Study Of Oil Flow Distribution And Winding Temperature Field In Large Power Transformers

With the development of power industry, the rated capacity of EHV, UHV large powertransformer is increasing, the losses and temperature rise of transformer has become one ofthe hot issues studied in the field of international electricity. Load losses is one of the mainperformance parameters of the transformer, which includes the various loss components isthe heat source in research of the transformer temperature rise, its value and distributionaffects the hot-spot and temperature rise analysis of transformer directly. Due to thedimeasion restrictions during the transportation, the specific losses is higher and heatradiating is difficulty, the accurate calculation and analysis of load losses, cooling systemand winding temperature rise are the key issues in design.This article focuses on the calculation and analysis of the decomposition of variousloss components which include reducing problems load loss, the inherent characteristics ofoil flow cooling system and working state analysis, winding temperature rise are carriedout in-depth theoretical calculation and analysis and experimental research. The maincontents are as follows:(1)3D nonlinear time-harmonic field analysis method is taken to calculate themagnetic leakage flux of transformer, and some of the calculation results are comparedwith the measured values. The relative error of calculation results and test value ofmagnetic leakage flux in specified location is within5%. This meets the engineeringrequirements and the validity of the calculation method is varified.(2) Establish the3D finite element time-harmonic eddy current calculation andanalysis model to consider material anisotropy and different forms of shielding structurefor large power transformer; analyze the loss and loss distribution in transformer structureparts. Through the analysis of18units’ transformer in different structure forms anddifferent ultimate tapping position, the comparision between the load loss and test values iscarried out and the various loss components of load loss is determined. This calculationmethod is applied to new product development. (3) Based on the weight coefficient method the mathematical model of transformerwinding stray loss is established, the stray loss of transformer winding is calculatedaccurately. Experiments are performed for wire in different structure, the load lossnumerical simulation results are compared with the experimental results and analyzed, theweight coefficient of this methodis has been determined; increase the calculation accuracyof winding stray loss is increased. This calculation method has been adopted in evoluationof new products.(4) According to fluid mechanics, fluid dynamics and mechanics of viscous fluidsknowledge, the inherent characteristics of transformer oil flow cooling system is analyzedand the wording status of the oil flow cooling system is determined, FVM-FLIC couplingmethod is brought forward, the numerical analysis model of large power transformer influid domain is established in order to calculate and analyze the cooling system of alltransformer oil flow cooling system. Through the research of the oil flow cooling systeminherent characteristics the pump operating point of the cooling system power source isdetermined, thus the working state of transformer oil flow cooling system also. The dataobtained from the calculation results are applied to the calculation of the windingtemperature rise.(5) Based on multi-field coupling and fluid-solid coupling method of electromagneticfield, fluid field and temperature field, the winding temperature rise calculation model isestablished, the temperature rise distribution in winding is analyzed. Firs, through theresearch and analysis of electromagnetic field, the loss and loss distribution of winding iscalculated to obtain the heat source of winding; second, the calculation and analysis towhole transformer oil flow cooling system is done, the operating point and working state isdetermined to obtain the boundary conditions for calculating winding temperature field;finally, through of the multi-field coupling and fluid-solid coupling method calculation andanalysis of the transformer winding area, the temperature rise and distribution of windingregion is obtained. Through fiber optic temperature measurement test, the calculationresults and test values are compared to correct the calculating method, and theeffectiveness and practicability of this temperature calculation method are verified also inthe meantime.(6) The calculation method used in this paper has been applied to the optimizeddesign and analysis calculations for one UHV, large power transformer. Based on thedecomposition calculation of transformer load loss, analysis of oil flow cooling system and calculation of winding temperature rise, improving the winding area loss distributionapproach is put forward and an efficient, energy saving oil flow cooling system oftransformer is established, the cooling structure is simplized, the transformer windingtemperature rise is improved, and the designed product has been passed the test checking.