توسعه پوشش های ضد انعقاد مورد استفاده در عایق ها در چین Development of Anti-icing Coatings Applied to Insulators in China

Ice accretion on insulators can drastically reduce the effectiveness of electrical insulation, leading to flashovers and outages. The irregular shape of insulators makes it difficult to develop devices for automatic de-icing. Consequently, most efforts to eliminate ice on insulator strings have focused on passive methods, such as modification of the insulator surface characteristics. The use of hydrophobic materials on insulators cannot prevent the formation of ice, but it can reduce the adhesion of ice on insulators. As the adhesion is weak, ice will tend to slide off the surface by gravity. An alternative approach is the use of “super-hydrophobic” coatings or surfaces in which the contact angle of water is greater than 150°. For such surfaces water droplets will easily roll or slide off the surface and are unlikely to stay in one place long enough to freeze or to adhere to the surface when they do freeze. To this end, considerable effort has been expended on improving the hydrophobicity of surfaces [11]–[۱۵]. Conventionally, two approaches have been used to produce super-hydrophobic surfaces. The first is to create a nanostructured surface on a surface that is already hydrophobic (contact angle >90°), and the second is to modify the surface of materials already having low values of surface free energy [16]. Figure 1(a) shows water droplets on the surface of a lotus leaf, a naturally occurring super-hydrophobic surface, whereas Figure 1(b) shows water droplets on the surface of a biomimetic silicone rubber coating with a contact angle of more than 140°, fabricated in the Tsinghua University laboratory [17]. The white traces seen in Figure 1(b) are of the droplets sliding off the surface. J. Yang et al. fabricated a super-hydrophobic surface that can be used on HV outdoor insulators [18]. The super-hydrophobic surface was obtained by combining CaCO3/SiO2 mulberry-like composite particles and self-assembly of polydimethylsiloxane (PDMS); the measured water contact angle and sliding angle of the surface was about 164° and 5°, respectively [18]. The excellent hydrophobicity is attributed to the synergistic effect of the micron-scale roughness of the composite particles and the low surface energy of the PDMS. Chongqing University developed a novel PDMS/nanosilica hybrid super-hydrophobic coating for anti-icing on insulators [19]. This super-hydrophobic coating has a surface with micron/ nanometer dual-size structure having an average value of contact angle of 161°. In the icing experiment, icicles on the PDMS/nanosilica-coated insulator strings are short and sparse, in comparison with the ones on the untreated insulator string [20]. Furthermore, the flashover voltages of the insulators with the super-hydrophobic coating were found to be greater than for both the uncoated string and one where the insulators had a room-temperature vulcanizing (RTV) silicone rubber coating [11]. Xi’an Jiaotong University reported a simple method of producing a super-hydrophobic surface on silicone rubber by preparing moulds with surfaces of varying degrees of roughness [21]. A microstructure similar to that of a lotus leaf is formed on the silicone rubber surface and when the roughness of the surface was 6.33 μm, the static contact angle had a maximum value of 154°, and the sliding angle was 8°. However, testing of these surfaces applied to insulators, under icing conditions, has not yet been reported.