Investigation On Magnetic Field And Temperature Field Characteristics Of Transformer Based On Field-circuit Coupling Method And Thermal-fluid-solid Coupling Method

Overheating fault is a multiple fault of transformer,which seriously threatens the service life and stable operation of transformer,rational design of transformer structure is very important to reduce the failure rate.The excessive concentration of eddy current losses in the transformer field,such as winding,clamping piece,iron core pulling plate,oil tank,etc.,as well as the effect of transformer cooling are two important causes of overheating fault.In order to study the causes of these two kinds of faults and to take reasonable preventive measures,on the one hand,it is necessary to calculate the leakage flux and its distribution reasonably,to explore the factors that affect the magnetic flux leakage,and to calculate the eddy current loss and distribution in the metal structure accurately;on the other hand,it is necessary to simulate the heating and cooling process of the transformer and calculate the temperature distribution,the temperature and the location of the temperature and the distribution of the oil velocity.However,for the traditional analytical formula method,it is difficult to consider the complexity of the internal structure,the time variation of the field,the nonlinearity of the material and the multi field coupling.In this paper,based on the finite element method,the numerical model of the transformer is established,and the related problems are calculated and analyzed.The model is helpful for the operator to analyze the cause of the fault,and it is convenient for the designer to improve the structure of the transformer.The main work and achievements are as follows:(1)A two-dimensional finite element model is established to analyze the distribution characteristics of the magnetic flux leakage inside and outside the core window,The characteristics of the magnetic flux density,the longitudinal and transverse components of the windings and the fuel tanks are studied,and the influence of the magnetic shield on the leakage flux distribution of the fuel tank is also studied,which provides a reference for the rational design of the transformer in the design process.In addition,the idea of adjusting the structure to reduce the wall loss is proposed.(2)The finite element method of magnetic field and eddy current is calculated based onTEAM problem 7,and the simulation results are compared with the experimental results.Based on the field circuit coupling method,a three-dimensional finite element model of the transformer is established,studied the distribution of magnetic flux density,surface induced current density and volume loss density,and the influence of the slot on the eddy current loss is investigated.(3)The basic form of heat dissipation is analyzed,established two dimensional heat flow coupling model of natural oil circulation pancake winding transformer.The size and distribution of transformer temperature and fluid velocity are calculated by using the damped Newton method,the average temperature rise,hot spot temperature and its position are obtained,and discussed the relationship between oil flow field and temperature distribution.In addition,based on the above model,the influence of viscosity on the temperature rise of the transformer is studied,and compared the result with mineral oil immersed transformer.And studied the influence of the oil baffle on the increase of oil flow rate and the improvement of the heat dissipation.