Study On Dynamic Model Of Non-Spillover Icing Growth On Insulator Surface

In recent years,due to the sustained impact of the La Ni(?)a effect,winter temperatures in the Northern Hemisphere have generally decreased.Frequent extreme weather events such as freezing rain and snow pose a serious threat to the safe and reliable operation of power systems.Insulator,as the widely used basic electrical equipment in power systems,has received high attention from domestic and foreign scholars for its ice-covered insulation problems.The research of flashover on ice-covered insulator has achieved fruitful results.However,there has been little research conducted on building the ice-covered insulator model.This study combined theoretical analysis,numerical simulation and experimental validation to establish a three-dimensional model of ice accretion on insulator and explored the mechanism of insulation covering growth.The study facilitates the advancement of icing research from experimental to numerical simulation,while providing a scientific basis for the establishment of an early warning mechanism for transmission line icing.This has significant engineering application value.The main contributions of this paper are as follows:Firstly,based on the principles of fluid mechanics and control equations for airflow and droplet motion,the external gas-liquid two-phase flow model for two typical insulators of LXY-160 and FXBW-35/70 were established.By simulating and observing the movement trajectories,transport characteristics,and collision distribution patterns of water droplets under different particle sizes and wind speeds,local collision coefficients on insulator surfaces were calculated.The impact mechanism of various environmental conditions on local collision coefficients was also analyzed in depth.The research findings indicate that under high wind speed conditions,water droplets tend to move horizontally due to the greater air drag force,and larger droplets are more easily captured by insulators.Under low wind speed conditions,the effect of gravity becomes apparent and there is an increased tendency for vertical movement of water droplets.This leads to an increased probability of water droplet deposition on the insulator surface.Additionally,the local collision coefficient presents a symmetrical distribution on insulator surface,with the highest value at the central stationary point and gradually decreasing towards both sides.Different wind speeds and particle sizes can cause changes in water droplet movement patterns,leading to alterations in the local collision coefficients.Secondly,a thermodynamic model of insulator surface was constructed based on the principles of mass conservation and thermal equilibrium equations.The freezing characteristics of water droplets were investigated by analyzing the effects of environmental conditions such as wind speed,particle size,liquid water content and temperature on convective heat transfer coefficients and freezing coefficients at the surface of insulator icing.A three-dimensional numerical calculation model for non-spillover icing growth on insulator surfaces was established according to the modeling method from “point-line-surface-solid”.Simulation results show that the freezing coefficient is influenced by temperature,median volume diameter of water droplets and liquid water content;while convective heat transfer coefficient has a direct correlation with wind speed distribution on insulator surface but is almost unaffected by changes in temperature.Dry and wet icing growth characteristics without spillover on the insulator have significant differences that the icing with dry growth mainly grows in opposite direction along the collision direction between water droplets,while the icing with wet growth mainly grows along normal direction to insulator surfaces.Furthermore,the icing on the insulator surface increases the equivalent area of the shed,which leads to the shielding effect that affects the icing morphology of the rod or steel cap.As a result,a special shape of icing is exhibited in these areas with a wide bottom and gradually narrowing towards the top.Finally,the effectiveness of the three-dimensional icing model for two typical suspension insulators was validated through natural icing experiments.Comparative analysis shows that the average error between the icing mass,length and thickness of the insulator obtained by the numerical calculation model and those measured in experiments is found to be less than 15%,which confirms the capability of the icing model to effectively simulate non-spillover icing growth characteristics on insulator surfaces.