Effect Of Direct Fluorination On Thermal Oil Aging Properties Of Silicone Rubber

In recent years,composite insulated bushing has innate advantages in anti-explosion due to its unique physical characteristics and it is widely used in power system instead of ceramic bushing.HTV has excellent hydrophobicity,hydrophobicity migration,electrical corrosion resistance and flashover characteristics,but it is easy to aging under specific conditions,and its insulation performance decreases.Oil leakage and heating are easy to occur under the actual working conditions of composite insulating coat,which accelerates its aging process and endangers the safe and stable operation of power system.Direct fluorination technology can improve the electrical properties of materials without changing the original physical and chemical properties of materials.The application of direct fluorination technology to the modification of silicone rubber materials is of great significance to the study of improving the performance of insulating materials.In this paper,modified HTV was prepared by direct fluorination modification,and a thermal-oil aging platform was built to simulate the actual operating conditions.The effects of direct fluorination modification on thermal-oil aging properties of high temperature vulcanized silicone rubber were studied by testing the hydrophobicity,flashover characteristics and surface potential distribution characteristics of aging HTV samples.Meanwhile,the fluorination mechanism and thermal-oil aging mechanism of silicone rubber were analyzed by scanning electron microscopy and infrared spectroscopy.Firstly,the samples of fluorinated silicone rubber were prepared by direct fluorination reaction.The compatibility between silicone rubber and oil was tested.The oil absorption and hydrophobic recovery properties of HTV samples were tested.The fluorination mechanism was analyzed by SEM and FTIR.It was found that the surface morphology of HTV samples did not change significantly after fluorination.And a large number of C-F bonds were formed in surface molecules.The content of C-F bonds was proportional to the fluorination time.After direct fluorination modification,the oil absorption rate and saturated oil absorption rate of HTV samples decreased,and the hydrophobicity performance increased.At the same soaking time,the initial hydrophobicity angle and steady hydrophobicity angle of modified HTV samples were larger than those of non-fluorinated HTV samples,and the steady hydrophobicity angle increased with the increase of fluorination time.Fluorinated HTV samples and non-fluorinated HTV samples with different thermal-oil aging time were prepared by accelerated thermal-oil aging test.The hydrophobic recovery properties of the samples were tested.The thermal-oil aging mechanism of silicone rubber was analyzed by SEM and FTIR.It was found that there were defects such as pits,holes and cracks on the surface of the aged samples,breakage of molecular bonds on the surface of silicone rubber,and the content of C-H bonds,Si-O bonds,Si-C bonds,etc,decreased.After thermal-oil aging,the initial hydrophobicity angle of unmodified HTV is smaller,and the steady-state hydrophobicity angle decreases with aging time.After direct fluorination modification,the hydrophobicity of HTV samples is obviously improved.The initial hydrophobicity angle of HTV samples after thermal-oil aging is higher than that of unaged HTV samples.The steady-state hydrophobicity angle of HTV samples with the same aging degree increases with the increase of fluorination time.The influence of thermal-oil aging time on the flashover voltage of HTV specimens and the change of flashover characteristics of HTV specimens after direct fluorination were tested by flashover voltage testing system.It was found that the flashover voltage of unmodified HTV specimens decreased first and then stabilized with the increase of thermal-oil aging time.After direct fluorination modification,the flashover voltage of HTV samples increases obviously,and the longer the fluorination modification time is,the higher the flashover voltage of HTV samples is at different thermal-oil aging time points.Through the influence of direct fluorination on the hydrophobicity and flashover characteristics of HTV samples,it was found that direct fluorination can effectively improve the thermal-oil aging resistance of silicone rubber materials,and make them have better hydrophobicity and Flashover Properties in the thermal-oil environment.Through the influence of direct fluorination on the hydrophobicity and flashover characteristics of HTV samples,it was found that direct fluorination can effectively improve the thermal-oil aging resistance of silicone rubber materials,and make them have better hydrophobicity and Flashover Properties in the thermal-oil environment.However,with the aging of thermal-oil to a certain extent,the modification effect will gradually fail.The experimental results show that the longer the time of direct fluorination modification is,the better the aging effect of fluorination modification in thermal-oil environment is.The surface voltage attenuation curves of HTV specimens were measured by isothermal surface potential testing system,and the surface trap distribution was calculated.The change of surface trap distribution characteristics of silicone rubber during thermal-oil aging and the effect of direct fluorination modification on the trap distribution characteristics of HTV specimens were studied.The surface trap density and trap energy level of HTV samples first increase with the increase of thermal-oil aging time.After a period of time,the trap density tends to saturate and no new traps appear,and the trap energy level is limited by aging temperature.After direct fluorination modification,the trap density of HTV samples increases slightly with the increase of fluorination time,while the trap energy level decreases with the increase of fluorination time.Direct fluorination modification can significantly improve the trap properties of silicone rubber materials,but with the thermal-oil aging process,the fluorinated layer will be destroyed,and the modification effect will gradually fail.The longer the fluorinated modification time is,the thicker the fluorinated layer is,the better the modification effect of the modification in the thermal-oil aging process is.The relationship between surface trap distribution and flashover voltage of silicone rubber was studied.It was found that the flashover voltage of HTV sample was negatively correlated with the center of surface deep trap energy level.At the same deep trap energy level center,the flashover voltage of HTV samples modified by direct fluorination is higher.