Effect Of Insulating Oil On External Insulation Of HTV

In recent years,HTV has been favored by the power system for its excellent hydrophobicity,hydrophobicity migration,resistance to electric corrosion,and other advantages,and gradually applied to insulators,arresters,bushing,and other insulating equipment.However different from general insulation equipment,the oil-immersed composite bushing may cause oil leak due to overheating,equipment defects or other reasons.In the case of oil leakage,the oil covers the surface of HTV in the form of an oil film and gradually penetrates into the interior of the HTV,severely affects the migration characteristics of HTV and increasing the risk of pollution flashover of the equipment.Therefore,it is of great significance to study the change of external insulation properties of HTV after insulation oil leakage to ensure the safety operation of power system.This paper firstly get aging HTV through aging test,and studies the change of HTV hydrophobicity and oil resistance before and after aging.Then its change mechanism has been analyzed by FTIR and SEM.The study found that: after aging,methyl of the HTV molecules' side chains oxidative cleavage,polar silicon-oxygen bond breakthroughs,surface polarity increases,which makes the HTV hydrophobic properties decline.The sample showed defects such as holes and cracks,the structure became loose,as a result the oil resistance of HTV was severely reduced.After the HTV is immersed in the insulating oil,the hydrophobicity of the HTV decreases and the recovery rate becomes slower.With the increase of the amount of oil immersion,the initial recovery speeds up first and then slows down,and sample that immersed in oil for 10 hours recovers fastest.Hydrophobic migration characteristics of HTV are greatly affected after oil immersion,and the migration speed of LMW and steady state hydrophobicity are greatly reduced.The presence of surface oil pollution impedes the hydrophobic migration characteristics of HTV: during the initial migration phase,the surface smear layer is like a layer of dense oil film covering the surface of the sample,hindering the migration of LMW,so the initial hydrophobic migration is slowly;as the migration proceeds,the dense oil film becomes loose and the migration channel recovers,and the water repellency changes faster;finally it reaches a steady state,and the steady-state hydrophobicity is less than that of the general contamination sample.Experiments show that the larger the ESDD is,the better the steady-state hydrophobicity,and the larger the NSDD is,the better the initial hydrophobicity is,but the worse the steady-state hydrophobicity is.After the HTV surface is covered by oil pollution,the pollution flashover voltage is reduced.As the migration progresses,the surface hydrophobicity gradually recovers and the flashover voltage increases.The experimental results show that the pollution voltage is positively correlated with the surface hydrophobicity.The effects of ESDD and NSDD on the pollution flashover voltage are relatively independent.The impact of ESDD on pollution flash voltage is due to the increase of the ion concentration of the pollution,which increases the conductivity and reduces the flashover voltage;There are two original effects of NSDD on the pollution flash voltage:(1)The more the NESS,the stronger the ability to absorb water,which is conducive to the dissolution of the electrolyte,which increases the conductivity of the pollution and reduces the flashover voltage;(2)The more the NESS,the thicker the pollution,the poorer the hydrophobicity of the surface,and the surface is easy to form a continuous water film,the leakage current increases.As a result the flashover voltage reducing.