Research On Castable Of Dry-type Transformer With High Thermal Conduction And Flame Retardant

With the rapid development of society and economy in recent decades,there are more and more occasions that need fire prevention,and the safety of transformers has been taken seriously.The dry-type transformer is not easy to burn because of its insulation.Even if the transformer breaks down in operation and causes a fire,the scope of the fire will not be expanded in a short time.In addition,the dry-type transformer does not need oil conservator,safety airway,accelerator and other components.There is not sealing problem,so it can reduce the workload of maintenance and repair.However,with the increasing capacity of dry-type transformer,the following thermal problems are highlighted.Overheating of transformer winding will accelerate the aging of insulation and shorten the service life of dry-type transformer.The data shows that the service life of power equipment such as transformer and motor will be shortened by half when the winding temperature increases about 7?.The thermal conductivity of epoxy resin is very low,which seriously limits the cooling capacity of dry-type transformer.In this paper,a kind of heat conductive and flame retardant epoxy resin for insulation of dry-type transformer is manufactured by studying the optimal modification temperature of silane coupling agent and the optimal ratio of flame retardant filler with heat conductive filler.Secondly,the thermal conductivity,flame retardancy,electrical properties and viscosity of the filled resin are tested.Finally,the improvement effect of the temperature field of the thermal conductivity and flame retardant dry-type transformer is studied by using ANSYS finite element software.The research on the optimum modification temperature of silane coupling agent shows that the best modification temperature of coupling agent to Si O₂is 90?.When the Si O₂filler is treated with JFCA-1 coupling agent at 30?,50?,70?,90?,the viscosity of the four composite materials?72 wt%?is 3797,3537,3187,2806m Pa?s at80?.With the increase of temperature,the viscosity decreasing effect of the coupling agent becomes better.The thermal conductivity of the four composites is 1.6547?1.5421?1.5412?1.4505W/?m·K?.The thermal conductivity of the composite increases with the increase of modification temperature.The flame retardant experiment shows that Si O₂with the same particle size of20?m is used to mix with aluminum hydroxide according to four ratios of 1:0,1:1,2:3and 1:4,and the mass fraction of 2.5%JFCA-1 silane coupling agent is used to conduct surface modification at 90oC to prepare the composite material.Among them,the flame retardant grade of the composite material with the mass ratio of 1:4 reaches UL94 V-0.The volume resistivities of the four materials are 3.11×10¹⁴,2.11×10¹⁴,2.08×10¹⁴,1.18×10¹⁴?·m,all of which are maintained at the order of 10¹⁴?·m.The values of relative permittivity and dielectric loss tangent of the four materials are similar and the trend of change with temperature is the same.The AC breakdown field strength of the four materials are maintained at about 20k V/mm.The thermal conductivity of the four materials are 1.6547,1.5421,1.5412,1.4505W/?m·K?.The thermal conductivity of the composite decrease with the increase of the content of aluminum hydroxide.The finite element simulation of dry-type transformer shows that the heat dissipation in the transformer can be effectively improved by using the epoxy resin with the flame-retardant grade of UL94 V-0 and the thermal conductivity of 1.4505W/?m·K?.The longitudinal temperature of the core and the winding decrease significantly,among which the temperature at the bottom is the most obvious,the temperature at the bottom of the core decreases by 2.7K,the bottom of the low-voltage winding decreases by 4.5K,and the bottom of the low-voltage winding decreases by 6.9K.The transverse temperature at the bottom of the core decreases by a maximum of 0.36K,the low-voltage winding decreases by a maximum of 0.9K,and the high-voltage winding decreases by a maximum of 1.55K.In addition,it can be seen that the transverse temperature change of each part becomes gentle after using the modified high thermal conductivity epoxy resin,which is of great significance for improving the thermal stability of dry-type transformer.