Influence Of Transformer Oil On Corona Aging Characteristics Of High-temperature Vulcanized Silicone Rubber

As the main material of the external insulation of the transformer composite casing,the insulation performance of the high-temperature vulcanized silicone rubber is directly related to the operating condition of the transformer.During the operation of the composite casing,the effect of insulation oil on the external insulation performance gradually appears.Diffusion of oil will affect the insulation performance of silicone rubber and affect the safe and reliable operation of high-voltage electrical equipment.This paper studies the diffusion process of insulating oil in silicone rubber,then conducts corona aging test of silicone rubber under the action of insulating oil,and analyzes the effect of insulating oil on the electrical properties and physical and chemical properties of silicone rubber after corona aging.It is of great significance to understand the deterioration of composite insulation jackets of transformer substations and other transformation equipment,and to improve the operating life and reliability of substations using composite insulated substations.A multi-needles corona electrode system recommended by CIGRE was employed to ensure the corona discharge to form a uniform electric field on the surface of silicone rubber samples.After that,a high-temperature curing silicone rubber corona aging test platform was built in the laboratory.The related parameters such as the distance between the needle plate electrode and the test voltage in the corona aging test were determined according to the ANSYS simulation results and experimental test results.In order to study the diffusion characteristics of insulating oil in high-temperature vulcanized silicone rubber and the effect of diffusion on the performance of silicone rubber,the weight gain curve of the sample when the insulating oil diffused in the silicone rubber sample was obtained by weighing test.The influence of temperature on this diffusion process was analyzed.And using Fick's law of diffusion to fit the diffusion process of insulating oil.The results show that the increase of temperature will accelerate the diffusion rate of insulating oil in the silicone rubber sample and increase the saturated oil absorption of the sample.It is found that the results of the gravimetric method are in good agreement with the mathematical description of the Fick diffusion model and FTIR analysis showed that the diffusion of insulating oil did not change the internal chemical structure of high temperature vulcanized silicone rubber.So the diffusion of oil in high temperature vulcanized silicone rubber conforms to the classical Fick diffusion model.After that,the effects of insulating oil diffusion on the hydrophobic properties and flashover voltage of high-temperature vulcanized silicone rubber were studied.The results show that the increase of the oil absorption rate will reduce the hydrophobicity of the high-temperature vulcanized silicone rubber and increase the time required for the recovery of the hydrophobicity of the silicone rubber.In the dry environment,the diffusion of insulating oil has little effect on the surface flashover voltage of high-temperature vulcanized silicone rubber.SEM analysis,FTIR test,hydrophobic and flashover voltage were taken to analyze the performance change of silicone rubber after corona aging under the effect of insulating oil.The test results show that corona aging will produce black aging products on the surface of silicone rubber and destroy the physical and chemical structure of the surface layer,and will also affect the hydrophobicity and flashover voltage of silicone rubber samples.The diffusion of insulating oil will accelerate the aging of high temperature vulcanized silicone rubber by corona discharge.After corona aging for the same period of time,the absorption peak corresponding to the original chemical group of the silicone rubber sample containing the insulating oil is more reduced,and the micro cracks and holes on its surface are also increased.At the same time,its hydrophobic recovery characteristics will slow down and the flashover voltage will decrease.The diffusion of insulating oil aggravates the occurrence of chemical defects and physical defects in silicone rubber during corona aging,and further affects the macroscopic electrical and physical properties of high-temperature vulcanized silicone rubber.