Study On Formation Mechanism And Model Of Snow Accretion On Suspension Insulators

In recent years,extreme disasters such as raining,snowing and freezing have occurred frequently in some regions of China,which seriously threaten the stable operation of power grid,especially the stability of green energy power supply.Extensive research has been done on the flashover characteristics of snow-accreted insulator at home and abroad,and deeply analyzed the influence of various factors on the insulation performance of snow-accreted insulator.Due to the complex structure of the insulator,the growth of snow accumulation lack of systematic analysis,which restricts the research on the formation mechanism of snow accretion on insulator and its subsequent discharge process.Therefore,the establishment of numerical model of snow-covered insulator and the realization of three-dimensional visual simulation of snow-covered insulator have important engineering application value on promoting the development of the research on the insulator snowing from experiment to numerical simulation.In this paper,the process of snow accretion on insulator was studied by three methods: theoretical analysis,numerical simulation and experiment verification.The main work and achievements of this paper are as follows:Firstly,based on computational fluid dynamics,combined with the control equations of airflow and snow particles motion,the gas-liquid two-phase flow model was established.Then the flow field characteristics and particle motion at different positions on the surface of insulator were numerically simulated and theoretically analyzed.The results show that there are two opposite processes during flow around an insulator,namely,the pressure decreasing accompanied by the increase of the velocity and the increase of the pressure with the velocity decreasing.Because of the viscous effect of the airflow,the trajectories of the particles are consistent with the streamlines when they are far away from the insulator.As the particles move near the insulator,some deviate from the streamlines and collide with the insulator due to the large molecular mass and inertial effect.Affected by the complex structure of the insulator,the flow field characteristics at different positions are different.As a result,the force acting on the particles is not consistent,which in turn affect collision characteristics of particle.Secondly,the local collision coefficients of snow particle were calculated.According to the equations of mass balance and energy conservation,a three-dimensional numerical model for snow accretion on the insulator was elaborated.The effects of wind velocity,liquid water content and median volume diameter of the particle were studied,and compared with the results of snowing test.Local collision coefficient on the windward side of the insulator gradually decreases along the steel cap of the porcelain insulator and the rod of the composite insulator or the both sheds from stagnation point to both sides.The coefficient at the edge of the shed and the steel cap(or rod)of the windward side of the insulator is much higher than other positions.Snow amount on the insulator influenced by the wind velocity,particle diameter and liquid water content through factors such as the diameter,kinetic energy and inertia of snow particles.The overall trend is that snow amount on the insulator increases with the increment of the wind velocity,particle diameter and liquid water content.The difference between numerical simulation and artificial tests of the XP-70 insulator is within 16.3%,which of the FXBW-35/110 composite insulator is less than 18.79%,indicating the validity of the numerical model.Finally,based on the three-dimensional numerical simulation of snow accretion on the insulator,the influence of structural parameters such as the tilt angle of shed,rod diameter and sheds spacing on snow mass was analyzed,and the optimal shed structure suitable for the snow-covered area was proposed.The composite insulator should choose a smaller upper tilt angle under the requirements of mechanical strength;the lower tilt angle should be 0°;the rod diameter should choose a small size under the requirements of mechanical strength;under the requirements of creepage distance,smaller sheds spacing and sheds ratio should be selected.The shed structure should adopt a combination of one large shed and two small sheds.