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.