Effect Of Nano-Micro Structure Of Coating Surface On Condensation And Flashover Characteristics

Condensation is a common gas-liquid phase change behavior that occurs at the gas-solid interface and is commonly seen on cold surfaces exposed to moist air.Condensation is common on the surface and even inside of power equipment in our country,and condensation will damage the mechanical strength and insulation performance of power equipment,so as to greatly improve the possibility of power accidents.Therefore,it is very important and urgent to study the moisture-proof measures of power equipment and solve the condensation problem of equipment.At present,hydrophobic materials have been widely concerned as an effective means to prevent condensation.Scholars have prepared a variety of hydrophobic materials and tried to apply them to the surface of power equipment to avoid condensation flashover accidents.However,there are few researches on how to construct hydrophobic coatings with different nano-micro structures in a controllable way,and the influence of surface structure on condensation behavior and flashover characteristics,and condensation and flashover experiments have not been organically combined.Therefore,starting from the surface structure,the key influencing factor of material surface hydrophobicity,it is of great significance to prepare anti-moisture and anti-flash materials and study their condensation law and flashover characteristics for the development of anti-condensation coatings for power equipment with practical application prospect.In this paper,SiO₂ particles with different particle sizes were used to stably construct four hydrophobic coatings with different surface structures,and their physical and chemical structures were characterized by SEM,AFM and FTIR to analyze the root cause of the difference in hydrophobicity of coating samples.Then different hydrophobic coatings were subjected to surface flashover experiment and electrochemical impedance test under wetting conditions to study the effect of coating surface structure on insulation and water resistance.Finally,the condensation experiment under certain temperature and humidity conditions was simulated and the condensation flashover test was carried out in the self-made condensation flashover box,and the condensation law of different surface structures and its influence on the flashover were analyzed and concluded.Firstly,in this paper,SiO₂ nanoparticles were used as inorganic filler and silicone resin as reinforcement,and stable coatings with different static contact angles were constructed by controlling the mixing ratio of SiO₂ with different particle sizes and optimizing the dosage ratio of inorganic filler/organic resin.（a）The results show that the static contact angles of pure resin and the coatings with 2μm,300 nm,20 nm/300nm and 20 nm SiO₂ are 94°,110°,125°,136°and 152°,respectively.The stability of coatings with different surface structures can be achieved by controlling the particle size of the filler.（b）Four surface structures of SiO₂ with different particle sizes were constructed.The R_q of pure resin coating with the worst hydrophobicity was 30.4 nm,and the surface height span z was 229.9 nm,while the R_q of SiO₂ with 20 nm increased to 81.9 nm,z increases to 544.1 nm,and the static contact angle increases to 152°due to the connection of the aggregates to form a mesh porous structure.The coating prepared by this method has good acid and alkali resistance（p H:1-13）,heat resistance up to 250℃,and still maintains good hydrophobicity after sandpaper friction.Secondly,the surface flashover characteristics of different nano-micro structure coatings are systematically studied,and the water-resistance performance of the coatings is tested.（a）The flashover test shows that the wet flashover voltage of the 20nm SiO₂ coating is 15.7 k V,twice that of the ordinary resin coating,and the wet flashover voltage of the 5 mg/L Na Cl solution is 15 k V,1.5 times that of the 2μm SiO₂ coating,indicating that the superhydrophobic structure can effectively reduce the risk of partial discharge.The experimental results show that the higher static contact angle,larger droplet spacing and smaller droplet volume on the surface of the wet coating can significantly reduce the distortion of the surrounding electric field,which is beneficial to maintain a higher wet flash and pollution lightning pressure.（b）EIS results show that the 2μm and 300 nm SiO₂ composite coatings lose water resistance rapidly after a short immersion due to the large surface microscopic pore size,and can not effectively prevent the infiltration of water molecules;However,the 20 nm SiO₂composite coating has a good water-resistance performance because of the small size effect caused by the stacked network structure,which makes the electrolyte solution unable to penetrate into the dense pores blocked by nanoparticles.Thirdly,in this paper,condensation simulation experiments were carried out on the surface of different nano-micro structure coatings,and analysis was carried out combined with theoretical calculation.Meanwhile,the flashover of the coatings under condensation conditions was investigated.（a）Condensation results show that condensation occurs within 8 s for pure resin coating withθ94°,and the nucleation time of droplet can be extended to 1 min whenθis 152°;This results in that 90%of the condensation size of the coating surface withθangle of 152°is smaller than that of the ordinary hydrophobic coating.The maximum flashover voltage is 10.3 k V,which is 0.63 and 1.53 times of that of 2μm SiO₂ coating,respectively.This indicates that the superhydrophobic coating has the best anti-condensation effect,and thus has good insulation performance.Based on the above research,this paper summarizes the law of condensation growth and flashover occurrence of coatings with different surface structures in the humid electric field environment,providing theoretical basis and technical guidance for the formulation design and application of anti-condensation coating on the surface of power equipment.