Abnormal appearance of ice accretion on super-hydrophobic conductors:( at left) results from STRI test;( at right) taken from paper by Jiang Xingliang at IWAIS 2013 Plenary Session.
Schematic of ice screening test. at a significant icing rate. Moreover, this pattern continued even when the separated‘ islands’ of ice grew together. Chinese researchers apparently obtained similar results using their own super-hydrophobic conductors.
Based on this encouraging finding, a test program was organized to assess several desirable factors versus traditional conductors, including:
• Lower ice accumulation
• No significant increase in corona effects in the form of radio interference and audible noise
• Low ageing
• Comparable visually
• Offering hydrophobicity recovery
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Photos courtesy of STRI
Ice test performed in laboratory( left) and outdoors( right).
In principle, preventing ice accretion on overhead lines is feasible using coatings that have low adhesion against ice. Indeed, experiments years ago in Canada demonstrated reduced ice adhesion compared with fully hydrophilic surfaces. For example, silicone-based materials could theoretically have 3 to 5 times lower adhesion to ice than do the bare metallic conductors. To test this, a BLX conductor prototype impregnated with 5 % silicone was manufactured and tested at STRI about 10 years ago. Results, however, showed that there was no evidence that‘ standard’ hydrophobic materials result in lower ice adhesion than do those that are hydrophilic. At IWAIS( International Workshop on Atmospheric Icing of Structures) Conferences between 2009 and 2011, research groups presented results using super-hydrophobic materials( i. e. those characterized by a contact angle of about 150 ° and developed using nano-technology). Such materials apparently prevent
water drops from collecting on surfaces and thus impede ice forming on conductors and insulators. According to some reports, superhydrophobic coatings with small contact angle hysteresis were found to have from 5 to 6 times lower adhesion compared to reference samples made of polished aluminum.
With the support of power companies in Scandinavia, STRI carried out an ice-screening test of a superhydrophobic coating during which very specific behavior of the coating was obtained. On hydrophilic conductors tested as reference,( i. e. new, blasted, painted and acid treated), exposure to water spray resulted in radial growth of ice that within a short time led to a smooth surface and circular cross-section. Consequently, ice growth rates were almost identical on these conductors. Behavior of the super-hydrophobic conductor, however, proved to be different in as much as ice grew from frozen droplets on the surfaces and these remained separate even
Six different conductor & coating combinations were selected for the laboratory tests and the‘ original’ conductor samples were all Parrottype with 38.25 mm outer diameter. The six conductors tested were as follows:
1. New, never used conductor taken from a drum
2. Conductor with hydrophobic RTV silicone coating
3. Conductor with super-hydrophobic coating
4. Blasted conductor whose surface had been treated to make it less shiny
5. New conductor with standard paint for metal
6. Conductor treated with acid to reduce visual impact
Experiments on insulators with superhydrophobic coatings also took place.
A. Ice Accumulation To perform a simple screening test to compare the ability of different conductors to withstand ice accretion, samples were fixed in a rotating drum.
This principle was first developed in the laboratory( for glazed type of ice) and then outdoors( primarily for rime ice). Laboratory ice accretion tests were conducted inside a climate chamber where temperature was kept between-7 ° C and-4 ° C. Before testing, conductor samples were precooled to-7 ° C for a period of 24 h. Outdoor tests were then performed at about-10 ° C.