Power line insulators are subject to electric arc phenomena caused by the deposition of inorganic and organic contaminants on their surfaces. In order to mitigate this problem, insulators are covered with hydrophobic vulcanized rubber, which can keep the surface relatively dry even in the presence of humidity and facilitate the washing away of deposits when it rains. While being effective and widely used, these coatings tend to degrade over time. Furthermore, erosive phenomena lead to the formation of rougher surfaces, which can collect greater quantities of contaminants and, in the long run, cause the formation of fissures and cracks in the coating itself. For these reasons, despite the good results already achieved at an industrial level, it is appropriate to try to improve both the durability and the self-cleaning properties of the insulator surfaces.
This report explains the theoretical bases necessary to define the wettability of the surface and describes how coatings can keep a clean surface, depending on their hydrophobic or hydrophilic properties. Furthermore, the mechanism by which photocatalytic materials act is presented.
With specific reference to the creation of coatings, the following topics are illustrated:
➢ the synthesis of multilayer coatings – a first layer adhering to the glass is subsequently functionalized with hydrophilic, hydrophobic, superhydrophobic coatings;
➢ the synthesis of superhydrophobic nanoparticles that can be used in the formation of a superhydrophobic bi-layer coating;
➢ the synthesis of photocatalytic coatings based on TiO2 or polydimethylsiloxane (PDMS) which have different wettability properties, depending on the proposed formulation.
All synthesized coatings were characterized in terms of wettability, adhesion and aging, through exposure to open air for 30 days. Many samples demonstrated excellent adhesive capabilities. The most promising samples were tested in a climatic chamber, through accelerated aging tests: some of these, in particular those based on PDMS, showed excellent resistance. As far as self-cleaning properties are concerned, two indoor test procedures were defined: one to evaluate the photocatalytic properties and the other to evaluate the self-cleaning capabilities with respect to contaminants. Specifically, the analytical characterization method was developed and validated for indoor contamination tests. Some samples were then tested and all showed good self-cleaning capabilities; some PDMS-based coatings show up to 30 times better self-cleaning capabilities than bare glass.
Finally, the work carried out for the start of field tests is presented; in the prospect of these tests the size of the Contisola test facility located in RSE headquarters in Milan was doubled: now it can house two strings of insulators and a new dry chamber for sampling contaminants from airborne deposition. A string made up of 6 insulators coated with a low-adhesion coating will be exhibited at Contisola and their self-cleaning capacity will be evaluated in 2022 through quarterly sampling and analyses. Furthermore, an isolating disk housed inside the dry chamber allows for the sampling of the contaminant deposited on its surface and the evaluation of the aging of the coating, net of solar radiation and precipitation.