Study On The Effect Factors Of Moisture Invading Into Composite Insulator

In recent years,heating phenomena and fracture phenomena of composite insulator happened in transmission lines have been found in China.Moisture might be the main factor causing these problems.Therefore,this paper studies the influence of different factors on moisture invading into composite insulator through moisture absorption test and water vapor permeation test.Weighing method is employed to study the effect of formula,aging on the moisture absorption behavior of silicone rubber and FRP rod material,and temperature,humidity and electric field on the moisture absorption behavior of silicone rubber.On this basis,this paper explores the impact of interfacial bonding strength and interface air gap condition on the water vapor permeability of composite insulator,and studies the differences of water vapor permeability along the string of composite insulators.Moisture absorption test results show that formula has significant influence on the moisture absorption property of the material.When the relative amount of Al(OH)3(ATH)ranges from ATH0~ATH200,the saturated weight gain of silicone rubber increases at first and then decreases.When the ATH amount is 100(namely the filler content of ATH in composite insulator silicone rubber),the saturated weight gain rate of silicone rubber reaches its peak.Silica has similar effect to that of ATH on the moisture absorption property of silicone rubber.The saturated weight gain rate of silicone rubber reaches its peak when the silica amount is 100(namely the filler content of silica in composite insulator silicone rubber).The saturated weight gain rate of red silicone rubber processed with iron oxide stain is higher than that of gray silicone rubber.Differences exist in the moisture absorption property of new FRP rods produced by different manufacturers.Aging has obvious destructive function on silicone rubber material and has significant effect on the weight gain rate of material caused by moisture absorption.The saturated weight gain rate of silicone rubber samples after corona aging is far higher than that of new samples.This is because that electron bombardment causes a great number of holes and cracks,which increases the absorption area on the silicone rubber of water molecule.Meanwhile,the hydrophilic groups in silicone rubber material are increasing.These two factors lead to the rise in moisture absorption of silicone rubber.The saturated weight gain rate rises exponentially with the increasing of aging time.The weight gain rate of FRP rods after hydrothermal aging is much higher than that of new samples.One possible reason is that the swelling and hydrolyzing of epoxy resin matrix cause the interfacial debonding of glass fiber,which promotes the forming of moisture diffusion channel.Environmental factors effect the moisture absorption behavior of material by altering the intensity of diffusion conditions.When the temperature is constant at 25℃,the saturated weight gain rate of silicone rubber increases with the rising of environment humidity.When the humidity is constant at 75%,the moisture absorption property of silicone rubber weakens with the rising of temperature.Because the silicone rubber will give out heat in the moisture absorption process,and rising temperature will decrease the solubility of water molecule in silicone rubber.2.6k V/cm AC electric field has no significant influence on the moisture absorption property of silicone rubber materials,but 2.6k V/cm DC electric field has certain inhibitory effect on the moisture absorption property of silicone rubber material.Water vapor permeation test results show that moisture in the air could reach the interior of FRP rods after successively permeating the silicone rubber material,the interface of silicone rubber and FRP rod,and the FRP rod material.Interfacial bonding strength has no obvious correlation with the water vapor permeability of composite insulator.Interfacial air gap caused by physical damage has limited influence on the water vapor permeability of composite insulator.Different composite insulators along the string on the same branch has different water vapor permeability.The water vapor permeation rate from high to low in order is high voltage end,low voltage end,middle voltage.