Research On The Influence Of Oil-immersed Transformer Load On Winding Hot Spots

In the power system,oil-immersed transformer is an important part of it.The reliable operation of the equipment will directly affect the security and stability of the power system.When transformer runs for a long time,the winding will generate a lot of heat,and then the temperature inside the transformer will rise.The hot spot temperature of transformer winding is the key factor to limit the overload capacity of transformer.At present,few people consider the influence of load on the hot spot location when studying the hot spot temperature and hot spot location.Therefore,the relationship between hot spot location of transformer winding and load needs to be studied comprehensively and deeply.This paper mainly studies from the following aspects:(1)In order to calculate the heat transfer of transformer SFZ11-10000/35,the heat generation and heat transfer of large oil-immersed transformer are analyzed.In order to obtain the relevant temperature parameters of transformer,a temperature measuring platform for transformer is built.Fiber Bragg Grating temperature sensor is installed in the key position of large oil-immersed transformer.The oil temperature and winding temperature of transformer are tested.The heat transfer amount of transformer under rated load is calculated by using the measured temperature data,the internal thermophysical parameters of transformer under rated load are calculated.The results show that the thermal conductivity,thermal conductivity and oil density of transformer are mainly affected by temperature.At rated load,the thermal conductivity,thermal conductivity and oil density of transformer are 0.120(w/m?K)?0.117 m?K and 877kg/m~3 respectively,and the heat capacity of transformer winding is 390 J/(kg?K).(2)By analyzing the principle of thermoelectric analogy,a simulation model of transformer temperature field based on thermoelectric analogy is established.The simulation results show that the hot spot position of the winding is not fixed and will change with the change of load.The hot spot locations occur at 85.88%of the winding height at rated load,79.85%of the winding height at 1.3 times rated load,and 75.66%of the winding height at 1.48 times rated load.The curve fitting shows that the relationship between load and winding hot spot location is Y=-69.55757X~2+143.29236X+14.09207.(3)Through the study of transformer structure and the analysis of transformer heat generation and heat conduction,a transformer temperature field simulation device is developed,and a test platform is built on the simulation device.The test results show that when the winding of transformer simulator is connected with 1.20 A current,the hot spot locates at 86.48%higher than the winding;when the winding of transformer simulator is connected with 1.37 A current,the hot spot locates at 81.66%higher than the winding;and when the winding of transformer simulator is connected with 1.46 A current,the hot spot locates at 75.03%higher than the winding.The curve fitting shows that the relationship between load and winding hot spot location is Y=-68.46898X~2+144.52242 X+11.73863.