A Shield Against Flashover
For porcelain insulators to function flawlessly, they must be regularly cleansed of dirt and salt particles. Silicone coatings from WACKER provide protection for their surfaces. Locations in extreme climate zones can particularly benefit from such a coating since the insulators need to be cleaned much less often.
Covering an area of 8,502 km2, Lake Volta in the West African country of Ghana is the size of the island of Corsica – and the largest man-made reservoir on Earth. At its southernmost end, this enormous lake is harnessed by the Akosombo Dam. The hydroelectric power from the dam supplies the majority of Ghana’s electricity. From here, power is transmitted and distributed throughout the country on high- and medium-voltage power lines, covering hundreds of kilometers. Many of these lines are no longer state-of-the-art, however, and Ghana’s two major energy providers estimate that some 27 percent of all generated power is being lost as a result. By comparison, the loss is only two to three percent in Western Europe.
“The coatings are not just excellent insulators, they are also highly hydrophobic (i.e. water-repellent).”Dr. Georg Simson, Technical Marketing Manager, WACKER SILICONES
High Power Losses due to Conventional Insulators
Africa's energy sector has developed dynamically over the past few years. However, there are still millions of people without electricity access. After sunset, whole swathes of land are plunged into darkness, particularly south of the Sahara.
To reduce these losses, power lines must be kept in the best possible condition. “This mostly involves repair work on the existing porcelain insulators,” explains Dr. Georg Simson, technical manager at WACKER SILICONES in Burghausen, who is responsible for the coating project in Ghana. Throughout the electric transmission and distribution lines in the grid, there are components that control the transfer of energy – bushings, for example. These are the parts that link overhead power lines with electrical equipment such as transformers, act as bridges between different voltage levels, and transform the voltages themselves. They also ensure that electronic appliances are supplied with the correct operating voltage.
To enable safe operation of electricity grids, electrical bushings must be insulated, and the insulators are often still made of glass or porcelain. But these conventional materials have drawbacks. If the surface becomes moist, deposited dirt particles and the salts they contain form a conductive film. “This will sooner or later lead to partial discharges, which not only destroy the electrical components, but can also impair the performance of the power grids,” explains Simson. To avoid this scenario, the surfaces of porcelain and glass insulators must be cleaned regularly, which is complex and expensive. A more modern, more technically efficient alternative to glass and porcelain insulators would be to replace them with counterparts made of silicone rubber, but that would require removing the old parts completely and replacing them with the new ones.
“Since Energo Izotech decided in early 2012 to apply POWERSIL® coatings to the insulators, cleaning has been rendered unnecessary.”Alexey Amirkhanov, WACKER sales manager in Kiev
Silicone Coating Greatly Extends the Service Life
POWERSIL® silicone coating is a grade of silicone coatings for use in the T&D industry. Due to the silicone coating’s water repellency, conventional porcelain and glass insulators are imparted with beneficial electrical properties and become extremely dirt repellent.
Instead of completely replacing them, insulators can be refurbished using specially-formulated silicone coating solutions. These are sprayed onto the ceramic bodies as emulsions and then form a protective silicone film. “The coatings are not just excellent insulators, they are also highly hydrophobic (i.e. water-repellent),” explains WACKER expert Dr. Georg Simson. At the same time, they produce electrostatic charges in adhered dust particles, causing them to repel each other. As soon as rain touches the silicone surface it beads into separate droplets, and the potential formation of a conductive film is eliminated at the outset. The typical flashover scenario caused by a wet film layer is thus prevented. Moreover, the silicone coatings are highly resistant to tracking and arcing.
News of the capabilities of WACKER coatings has made its way to West Africa. For a year now, Emmanuel Gärtner from EGART Ventures and his team of ten have been making power lines fit for the future all over Ghana. “WACKER’s POWERSIL® coating is our material of choice,” says Gärtner. This is because many porcelain insulators in Ghana are of poor quality, and in the hot and humid Equatorial climate, they have to be replaced every two years. “With POWERSIL®, we can prolong the service life of these components to as many as ten years,” reports Gärtner. This has helped reduce costs substantially.
Hardly any cleaning necessary
Insulators must withstand numerous environmental influences. They are impacted by dirt pick-up, strong temperature fluctuations and salty sea air. POWERSIL® coatings provide long-term and extremely reliable protection for this sensitive equipment.
Building on his initial successes, Gärtner is now also traveling to neighboring countries such as Ivory Coast, Togo and Nigeria. It is precisely in these coastal areas where insulators suffer the most: in the worst cases, salts from the sea air can even attack the porcelain and promote corrosion. But insulators treated with POWERSIL® are far more resistant to this kind of pollution.
Some 6,000 kilometers to the north-east – in Donetsk, Ukraine, with its hot, dry summers and cold winters – silicone coatings are proving their worth as well. This is where the company Energo Izotech performs maintenance and repair work on power grids. “In the past, the company’s services were mostly concentrated on cleaning insulators,” explains Alexey Amirkhanov, WACKER sales manager in Kiev. That was because the Donetsk area is home to many coal mines and to a metal-processing industry, both of which cause a lot of air pollution. “To avoid power losses, cleaning operations had to be performed twice a year – that’s a major cost factor for grid operators,” says Amirkhanov. “Since Energo Izotech decided in early 2012 to apply POWERSIL® coatings to the insulators, there has been no more need for such cleaning work,” explains the WACKER expert.
Silicone Withstands Heat and Salts
Insulators in the Salt-Fog Test
Insulators coated with POWERSIL® 570 PLUS during the salt-fog test. WACKER’s new, tin- and solvent-free silicone coating is permanently erosion-resistant and thus suitable for outdoor use in the T&D sector. POWERSIL® 570 PLUS is the first insulator coating to stem from a patented silicone-in-water emulsion technology. The emulsion coating can be applied in a single spray cycle in the desired final layer thickness.
In Australia, it is the high temperatures – which frequently exceed 40 °C during the day in Central Australia – that have led WACKER to offer a water-based silicone coating for insulators Down Under: POWERSIL® 570 PLUS “Solvent-based products can be problematic in such heat, because they tend to be flammable,” explains Martin Bruetsch, WACKER sales manager in Sydney. “However, additional safety precautions are not required to transport the water-based POWERSIL®.”
Insulators undergoing the salt-fog test.
Another factor in favor of silicone coatings is that the Australian electricity grids are located primarily in coastal areas, where most of the population lives. That is also where exposure to salt water is greatest. Salt-fog tests have shown that porcelain insulators coated with silicone are considerably more resilient under these conditions than uncoated insulators.