Grids That Communicate - Wacker Chemie AG

Grids That Communicate

An RPC employee testing an insulator.

In theory, a better insulating gas or insulating oil could be used, but this would introduce a high risk of leakage. The insulation medium could escape into the environment and, at the same time, air could enter the cavity. Thus, if a gaseous or liquid insulation medium were to be used, the system would have to be inspected and serviced regularly, which would be time-consuming and expensive for the operator. These problems do not exist with a solid insulation medium, such as a cured silicone gel. “With a silicone gel, a composite hollow-core insulator can be operated maintenance-free for decades,” says Merten.

Following extensive testing with different solid insulation media, Reinhausen Power Composites decided to go with WACKER’s POWERSIL® Gel C 670. This product is a pourable, addition-curing silicone rubber that, unlike conventional silicone rubber, doesn’t cure to form an elastomer, but a soft and highly tacky gel. “The cured rubber is loosely crosslinked, which makes it very compliant and flexible and allows it to snugly fit the form of solid surfaces,” says Glowacki. “In addition, POWERSIL® Gel C 670 is formulated with a special filler that makes the gel compressible and, at the same time, gives it a low density.” Added to this are the typical silicone advantages – the gel is aging resistant and highly electrically insulating, does not chemically attack other materials and has no known health risks.

Why Silicone Composite Hollow-Core Insulators?

For design and material reasons, silicone composite hollow-core insulators offer a number of advantages over their comparable porcelain counterparts. For one thing, they are one third lighter. This lower weight makes itself apparent during assembly, transport and installation of the electrical equipment in the plant. By virtue of their elasticity, composite hollow-core insulators are earthquake-proof and cannot break during transport or explode as a result of willful damage or under fire. Since silicone elastomers are highly hydrophobic, or water repellent, and because they are even able to impart water-repellency to dirt deposits, silicone composite hollow-core insulators do not have to be cleaned in situ. This minimizes maintenance. To which must be added the typical aging resistance of silicones. All these factors combine to endow composite hollow-core insulators with a long service life at minimum maintenance costs. Another advantage is that composite hollow-core insulators can be made in a shorter time than porcelain models.

Ideal Inherent Tack

The silicone gel’s property profile won over Reinhausen Power Composites, and head of development Merten is particularly impressed with the material’s inherent tack: “The silicone gel adheres incredibly well to the GRP pipe, the fiber-optic cables and the metal flanges. This is important for our application, because the gel must not detach from the other components, even if the materials differ in their thermal expansion.” If the filler were to detach, air bubbles would form – but high-voltage technicians try to avoid air bubbles like the plague. Merten explains why: “Partial discharges can occur on air bubbles, which increasingly damage the insulation medium and eventually cause the insulator to fail.”

Since the silicone gel is compressible, it counteracts its own thermal expansion in the sealed GRP pipe – it adjusts its volume to the given space during the expansion. This is important in practice, because the insulator is always exposed to daily and seasonal temperature fluctuations and, moreover, can heat up during operation. If the temperature rises, thanks to its compressibility, the gel, enclosed in the pipe, only expands so slightly that it doesn’t cause the pipe to burst. If the temperature falls, the gel practically doesn’t shrink, but again occupies the given volume without detaching from the other components – compressibility and adhesive properties harmonize perfectly here.