Study On Effects Of Hydrophobic Coatings On The Glaze Icing And AC Flashover Characteristics Of Insulator

The superhydrophobic materials possess low surface energy and special microstructures.Water droplets are extremely difficult to attach to their surfaces.Therefore,this new material shows significant applicable potential in the anti-icing area.There have been researchers and organizations taking a lot of tests on the making and improvement of superhydrophobic materials,but the mechanism and application of antiicing in the power system are in lack of systematic research.In order to study the application characteristics and prospects of superhydrophobic materials in the anti-icing area of power system,and provide theoretical guidance for the research and development of this materials,it is necessary to further investigate and discussion.This paper aims at the potential demand of the anti-icing application in power systems,preparing four coatings with different hydrophobicity for the tests according to the current status of R&D and application of hydrophobic material.Simulting glaze ice condition in the artificial climate room,and the movement characteristics and the freezing characteristics of droplets on hydrophobic surface under glaze condition are experimented;Then,artificial icing and flashover tests for hydrophobic insulator strings are conducted in an artificial climate chamber.Through the above experiments,the following results are obtained:(1)The experimental investigation and anlysis on the motion characteristics of droplets on hydrophobic surface under glaze ice condition are performed in the article.Test results indicate that the hydrophobicity of the coating reduces the tension of droplets on the “solid-liquid" contact surface,which will change the collison process between water droplets and the solid surface.On stronger hydrophobic surface,the probability of the water droplets can stay after collison is lower.In the absence of wind,the water droplets stay on the hydrophobic surface will convergence increases until it rolls off.On stronger hydrophobic surface,the critical diameter required for droplets rolling is smaller.Under windy condition,the droplets with same volume on stronger hydrophobic surface will suffer greater force exerted by wind,which make the droplets easier to roll off the surface.(2)The influence of hydrophobicity on the crystallization mechansim and the cooling rate of droplets on the surface under glaze ice condition has been studied by experimental and simulation analyzing.Test results indicate that on the surface with bigger contact angle(CA),the difference of energy barrier between homogeneous nucleation and heterogeneous nucleation will be closer.The temperature difference between the location near the “solid–liquid” interface and the location near the “gas–liquid” interface is the key factor that affect the ice crystallization mechanism of water droplets.Under glaze icing condition without wind,the crystallization process of the continuously sprayed droplets on the superhydrophobic surface started with the homogeneous nucleation at “gas-liquid” interface.Under windy condition,the crystallization process of droplets on hydrophobic surface started with the heterogeneous nucleation at “solid-liquid” interface.Combine with the motion characteristics of droplets on hydrophobic surface,under glaze ice condition,the droplets cannot fix on the surface move until completely frozen.A thermodynamic model is established to analyze the freezing process of droplets on different hydrophobic surface under various wind speed.According to the simulation analysis,the shape feature of droplets with the same volume on stronger hydrophobic surface make the droplets have lower heat exchange efficiency during freezing,and longer the time required for complete freezing.In addition,the wind will accelerate the cooling rate of the droplets,but the wind speed has less impact on the cooling rate.It concludes that the hydrophobic surface can change the crystallization mechanism and reduce the cooling rate of droplets under glaze ice condition,and prolong the time required until the completely frozen of droplets appear.(3)The icing process on hydrophobic surface is experimented under glaze ice condition.And combined with the motion and freezing characteristics of droplets,analyze the influence mechanism of hydrophobic surface to the ice accretion characteristics.Test results indicate that the appearance of completely frozen droplets marks the formation of ice,and the ice accretion process on hydrophobic coatings can be divided into three characteristic stages: From the beginning before completely frozen droplets appear,from the appearace of completely frozen droplets before completely covered with ice,and after the surface is completely covered with ice.Under no-wind condition,the hydrophobic coatings can affect the rolling and freezing process of the droplets on the surface,and effectively delaying the appearance of totally frozen droplets and the time required for completely covered by ice on the hydrophobic surface.Under windy condition,the hydrophobic coatings cannot delay the appearance of frozen droplets.But the ice accumulation characteristics on different hydrophobic surface lead to the difference in ice morphology and make a higher hydrophobic surface to have a lower ice mass growth rate in the long period of icing tests.(4)Artificial icing and flashover tests for hydrophobic insulator strings under glaze ice condition are conducted in an artificial climate chamber.The difference of ice morphology,ice density,growth of ice weight,and AC flashover voltage under nonenergized and energized conditions are analyzed.Test results indicate that the hydrophobic coatings can change the icing characteristic on the insulator string,and the influence manchanism of hydrophobic coatings to the icing process will change with the icing stage.At the previous stage,the hydrophobic coatings will affect the movement and freezing characteristics of droplets on the surface,delay the appearance of frozen droplets and totally covered by ice on the insulator strings.And change the ice accumulating process and ice morphology on the insulator surface.After the insulator surface is covered by ice,the difference of ice accumulating forms on insulator strings with different hydrophobic coatings lead to different ice morphology characteristics on various hydrophobic surface.And result in lower ice mass growing rate on the stronger hydrophobic surface during long period icing tests.The stronger the hydrophobicity of the coatings is,the more granular the ice layer became.Ice density is lower on the insulator surface with SAR coatings than that on the insulator surface without coatings.After icing tests,the hydrophobic coatings change the ice characteristics on the insulator surface,make the water film on the insulator discontinuity during melting,and reduce the ice sewage parameter(ISP)of the insulator,which will lead to the rise of icing flashoer voltage.