Study On Temperature Field And Temperature Rise Characteristics Of Natural Ester Transformer Winding

As one of the important equipment for power transmission in the power system,oilimmersed transformers are developing in the direction of ultra-high voltage,intelligence,energy saving,environmental protection,safety and reliability.Transformer oil plays the role of insulation and cooling.At present,mineral insulating oil is widely used in large oilimmersed power transformers.However,in recent years,as the requirements for green power equipment and fire and explosion-proof at home and abroad have increased,natural ester insulating oil has gradually become a new green transformer favorite.The temperature rise characteristic of transformers is one of the most important indicators of the operating condition and health of transformers.Natural ester insulating oil has different physical and chemical characteristics than mineral insulating oil,for example,the kinematic viscosity is3 to 4 times higher than mineral insulating oil.This will have a great impact on the temperature rise characteristics of the winding of natural ester insulating oil transformers,especially for power transformers of 110 k V and above,because of the complex internal insulation structure and the extremely uneven distribution of eddy current loss generated by the winding leakage field,therefore,it is easy to cause the local overheating problem of the winding,and the research on the temperature field and temperature rise characteristics of the winding of natural ester insulating oil power transformers has important Theoretical guidance and engineering value.The temperature rise of a transformer is caused by the losses generated during its internal operation.In this paper,the eddy current losses of each line cake of the winding are calculated based on the finite element principle using MF2 D,a special software for leakage field calculation.Due to the specificity of the location of the regulating winding of the transformer studied in this paper,the eddy current losses of the high and low voltage winding have asymmetric characteristics.This provides data support for the heat source calculation in the temperature field simulation.The temperature rise characteristics of natural ester insulating oil and mineral insulating oil power transformer winding were calculated,compared and analyzed by building a two-dimensional finite volume method fluid-solid coupling model for 110 k V power transformers.In order to make the simulation results more accurate,the winding heat source is programmed.The results show that: the winding temperature rise of natural ester insulating oil transformer is slightly higher than the corresponding value of mineral insulating oil transformer,but considering that natural ester insulating oil can improve the transformer temperature rise limit,the winding temperature rise characteristics of natural ester insulating oil transformer are better than mineral insulating oil transformer;meanwhile,the winding overload characteristics of the two types of insulating oil transformers are compared and analyzed.It is found that the overload capacity of natural ester transformers is better than that of mineral insulating oil transformers,and the difference between the overload performance of natural ester transformers and mineral insulating oil transformers is further enlarged as the overload factor increases.In addition,by analyzing the factors influencing the temperature field of natural ester transformers,three measures to reduce the hot spot temperature of natural ester power transformer winding were proposed and adopted by the 110 k V natural ester transformer product design.According to the characteristics of the product structure,a three-dimensional fluidsolid coupling calculation model is established.By simulating the three-dimensional steady-state temperature field of the transformer,the relationship between the temperature rise of the high-voltage and low-voltage three-phase winding is analyzed.In addition,the transient simulation of winding temperature field of natural ester insulating oil power transformer and mineral insulating oil power transformer was carried out to obtain the characteristics of winding temperature field of natural ester insulating oil transformer and top layer oil temperature of both types of insulating oil transformers with time.Finally,the accuracy of the two-dimensional and three-dimensional winding temperature field calculation methods in this paper is verified by temperature rise tests.