Research On Boundary Conditions Of Thermal Circuit Model With Distributed Parameters Of Oil-immersed Transformers

Oil immersed transformer is the key equipment to ensure the normal operation of the power system.Its hot spot temperature is a standard for measuring the load capacity and operating life of the transformer.In order to ensure the normal operation and reliable operation of the transformer,the transformer hot spot temperature must be accurately obtained,and the internal winding temperature of the transformer Difficult to measure directly.In this paper,by analyzing the relationship between the externally available temperature measurement point temperature and the oil temperature around the winding,a distributed thermal circuit model with external temperature measurement points as boundary conditions is established to solve the hot spot temperature.The temperature of the transformer is measured by a temperature sensor,and the solution results of the thermal circuit model under different boundary conditions are compared with the measured temperature to optimize the boundary conditions.The main work of this paper is:1)By using the finite element analysis method in numerical calculation,based on the actual size,internal structural characteristics,heat source,and heat dissipation method of the oil-immersed transformer,a fluid-structure coupling model is established,and the transformer temperature and oil flow results at different power are calculated.Using the finite element calculation results,the relationship between the current easy-to-monitor temperature of the oil-immersed transformer and the distribution of oil temperature around the winding is analyzed one by one,and the feasible boundary conditions that can be used as a hot circuit model to solve the hot spot temperature are obtained,and further utilized The temperature field data calculated by the finite element method determines three feasible boundary conditions to solve the relationship of oil temperature around the winding,which will help to further solve the winding hot spot temperature in the next chapter.2)Using the hot-spot analogy method,transform the transformer's thermal circuit transfer process into a circuit theorem,establish a distributed parameter thermal circuit model between the winding and the oil,and calculate the oil temperaturearound the winding based on the three boundary conditions obtained to calculate the winding temperature Surrounding oil temperature,finally substitute the surrounding oil temperature of the winding into the established thermal circuit model,set the relevant parameters,and use Multisim software to simulate and calculate the distributed parameter thermal circuit model.Based on the top oil temperature,the bottom oil temperature,and the top layer,Combining the oil temperature and the bottom oil temperature as the boundary conditions,the winding hot spot temperature results of 1.0 times the rated power and 1.3 times the rated power in the three cases.3)In the temperature rise experiment,install and arrange the fiber Bragg grating temperature sensor to measure the transformer temperature,compare the winding temperature monitored by the temperature sensor in real time with the calculation results of different types of boundary conditions,and select the boundary conditions with small calculation errors.The main factors that cause errors are analyzed and optimized.The optimized calculation results are compared with the measured winding temperature results again,and it is verified that the optimized errors are reduced,the accuracy is higher,and the hot spot position prediction is more accurate.It is proved that the boundary conditions obtained in this study,the calculation results can more accurately reflect the temperature distribution of the transformer windings,and can provide a better basis for the transformer's overload capacity and insulation life assessment.