Study On Dynamic Contamination Depositing Characteristics Of Insulators Using Coupled DEM And CFD Methods

The contamination flashover of insulator is one of the main danger of the safe operation on the power system.Study on dynamic contamination depositing characteristics of insulators can help us to understand the mechanism of pollution on insulators,and it will let us know the contamination state under various environmental conditions.Then it can lead us to take measures to effectively reduce the contamination and the occurrence of flashover.The contamination depositing process is a dynamic process coupling of particles and fluid,then some particles may adhere to the insulator surface when the interaction between particles and insulator happens.While researchers at home and abroad have used many kinds of means to analyze the insulator pollution characteristics,but they did not combine the discrete element method(DEM)with computational fluid dynamics method(CFD)to do the researches.This paper introduces the discrete element technology and establish the dynamic contamination model to analyze the contamination characteristic,then the coupled DEM and CFD methods was used to simulate and calculate the pollution process of different types of bar insulators to realize the selection and installation based on influence of various factors,such as climatic conditions,terrain environment and pollution type.In this paper,the dynamic contamination process of insulator was analyzed firstly,then dynamic contamination model of insulator including the movement of particles in the external flow field,the contact and adhesion process was established.Through the calculation and analysis of the contamination model,the minimum horizontal wind speed required to remove the particles from the insulator surface is obtained.Then according to discrete element method and the method of computational fluid dynamics coupling technique,using simulation software EDEM and FLUENT,and selecting the appropriate coupling numerical method to simulate and calculate the air flow field with RNG k-? turbulence model in FLUENT.At the same time,the dynamic properties of particles and the contact characteristics between particles and insulator using JKR model in the coupling domain were analyzed in EDEM.The deposition process of particles on insulator surface was simulated considering the effects of turbulent fluctuation and surface energy on particle diffusion with Euler coupling method to obtain the contamination characteristics on insulator.On the basis of the external flow field and the depositing characteristics of particles on insulator surface,the influence of wind speed,coming angle,particle diameter and setting angle on the dynamic contamination characteristics of insulators was analyzed.The result shows that there is a quadratic function relationship between critical wind speed of gravity sedimentation and particle diameter;the minimum horizontal wind speed of particle detachment form insulator approximately exhibit a negative power distribution with the increasing of particle diameter;the smaller the particle is,the better the adsorbability will be,it will be easier for particles to adhered to surface;the rebound to desorption performance improves with the increasing of particle diameter.The collision incident angle between particles and upper surface is less than that between particles and lower surface,which causes a more serious pollution on lower surface.The hydrophilic property of insulator has the most significant effect on the adhesion of the particles,and the wettability of the particles is the least influential factor on the adhesion performance;and for the adhered particles the particles would be removed when the shear velocity is greater than 30.8m/s.the polluting area rate showed a linear increasing trend in a certain period of time.With the increase of wind speed,particle adhesion rate increased first,then decreased gradually,when the adhesion rate reaches the highest level,the wind speed is the most suitable for the contamination,the optimum wind speed decreases with the increase of particle size,and the reduction extent is getting smaller;When the coming angle is about 135 degree,the adhesion rate is maximum.With the change of the coming angle,the possibilities of secondary collision is increased between the particles and the lower surface,this behavior can increase the pollution of the lower surface.When the insulator axis,wind direction and gravity direction are not in the same plane and perpendicular to each other,the contamination rate is the biggest;however,the influence of the setting angle on the contamination rate is not significant.The setting angle mainly affects the insulators which the axial direction,the direction of wind and the direction of gravity are in the same plane.Therefore,the installation measures of insulators in different regions can be took based on contamination characteristics of insulator under different working conditions in order to reduce the surface contamination.And we can observe the pollution states of the insulator surface and then provide guidance for the visual cleaning on the insulator at the same time.