Study On 3D Numerical Modeling Of Dry-growth Icing On Suspension Insulators

In the icing environment,the insulation decline of insulator string of transmission lines is one of the important reasons leading to power grid accidents.Many scholars have done a lot of research on icing flashover characteristics of insulator,and the results show that:insulator icing mass and shape are the key factors affecting flashover characteristics.Insulator icing is a complex natural phenomenon involving multiple disciplines such as hydrodynamics,thermodynamics,meteorology and so on.Because of the complex structure,the variety of icing form and type,and various influence factors,it’s difficult to simulate the process of insulator icing.Therefore,it is of great significance to build a numerical calculation model of insulator icing model,which would help predict insulator icing mass and shape and benefit the establishment of prediction and early warning system of insulator icing flashover.Environmental parameters of insulator icing are obtained by using rotating multi-cylinder method,and the characteristics of water droplet collision and freezing on the rotating multiple cylinders are simulated.Then,an improved three-parameter particle swarm optimization（PSO）inverse model is established to predict the four icing environmental parameters,i.e.wind speed,temperature,liquid water content in air and median diameter of water droplets,with an lower average error of 4.07%.In the verification icing tests on Xuefeng mountain,the traditional rotating multi-circular conductor device is improved to realize the continuous measurement of icing weight.The test results show that the overall prediction error by using the device and the inverse model in this paper is about 4.8%-17.4%,which meets the requirements of insulator icing simulation.In this paper,based on the basic physical process,the dry-growth icing of insulators is systematically studied by combining model building,simulation analysis and natural icing test.Firstly,boundary element method is taken as the basic method of modeling and the movement and collision process of water droplets in the external flow field are studied.Secondly,the flow and freezing process of water film on insulator surface are studied,based on which,three different insulator icing types are classified and parameterized.Thirdly,the measuring device and predicting model icing environment parameters are studied.Fourthly,considering the time-varying characteristics of icing shape and parameters,a 3D dry-growth icing model of insulator is constructed.The main work and achievements of this paper are as follows:Instead of using finite element method to calculate icing flow filed,a numerical calculation model of the external flow field of insulators based on boundary element method is established,which avoids the complex three-dimensional meshes and greatly improves the calculation efficiency.The results of model calculation show that the smooth airflow trajectory with high accuracy can be obtained by optimizing the time step and the mesh size of insulator surface while ensuring a good computational efficiency.A mathematical model of water droplet’s movement is established,which describes the process of water droplets moving along wind and colliding with insulator surface.The simulation results show that the main collision areas are insulator steel cap and insulator shed edge.The wind speed and the median diameter of water droplets are the main environmental factors affecting the collision area and the number of captured water droplets.Secondly,A triangular-area method is innovatively proposed to calculate the local collision coefficientβ₁ distribution on the insulator surface.Insulator icing are divided into dry-growth icing,wet-growth icing with icicles and wet-growth icing without icicles.Based on heat balance and basic mechanics,a numerical calculation model of water film flow and freezing is established,according to which,the accretion coefficientβ₃ and the distribution of overflow water M_out under different conditions are obtained,the critical models of three icing types are established,and the environment conditions required for dry-growth icing are determined.Based on the characteristics of insulator dry-growth icing,the reconstruction algorithm of insulator ice growth is determined.By integrating the water droplet impact model,water film flow model,freezing model and icing environment parameters inverse model,a three-dimensional insulator dry-growth icing model is established,and the time-varying characteristics of various icing parameters are obtained.Four kinds of insulators were tested on Xuefengshan mountain.Through simulation and comparison,it is found that the numerical calculation errors of the icing weight and thickness on insulators are both less than 15%.