Effects Of Water Droplets On The Creeping Discharge Of Composite Insulator

Composite insulators were widely used in power transmission lines,as its advantages of small volume,light weight,high strength,strong function of resistance to pollution flashover,convenient to maintenance,and so on.With the increases of operating time,composite insulators were in varying degree of aging,which greatly weakened its performance of hydrophobic and resistance to pollution flashover.Under the humid environment,the aging insulation surface easily congealed water droplets and formed conductive layer,which increased the conductivity and leakage current of insulator surface.It made the flashover voltage decrease significantly and posed a threat to the safe operation of power system.Therefore,it had an important significance to study the influence of water droplets in creeping discharge of composite insulator strings.The process of solving electrostatic field by finite element method(FEM)and Naiver-Stokes fluid dynamics control equation were given to solve the problem of E-Field numerical calculation and fluid dynamics of water droplets.A large number of hydrophobic classification experiments were conducted in laboratory to calculate out the regularities of distribution of water droplets.On this basis,some 3-D models of composite insulator were built to analyze the influence of water droplets on the E-Field distribution in detail.The calculation results showed that the existence of droplets distorted the E-Field of insulation surface,increasing its values at the triple junction of the water droplet,air,and the insulating material.The nearer was droplets to the high voltage electrode,the stronger was the E-Field effect and the greater was the rate of E-Field distortion.On the contrary,the weaker was both of them.Greater volume & distribution density or smaller spacing distribution of droplets made E-field distortion more powerful,and the rate of E-Field distortion of the droplets which under umbrella surface was larger than up umbrella surface's.The weaker was the hydrophobic of insulation surface,the easier to form the E-Field distortion channel,and more obvious was the E-Field effects between water droplets and films.Dielectric surface flashover test were carried out to study the movement characteristics of droplets under AC E-Field and the effects of droplets deformation on creeping discharge.The results showed that the droplets produced periodic vibration under certain power frequency E-Field whose period was 0.1 seconds.The greater was the volume of water droplets,the more complex was the vibration form,and the bigger was the inclination angle of insulation surface,the more complex was the vibration form.The greater was E-Field and conductivity,the larger was deformation variables of droplets;while the deformation variables was small as the umbrella surface was rough or had a low hydrophobic.The deformation of droplets had a certain influence on surface E-Field.The more serious was deformation,the more obvious was the E-Field distortion;and the bigger was the volume of droplet,the greater is the E-Field distortion rate.When multiple droplets spread over the specimen's surface,greater distribution density,volume and conductivity or smaller spacing distribution of droplets made flashover voltage along he surface lower.