Ready to Generate - Wacker Chemie AG

Ready to Generate

Pronounced Hydrophobicity

A 145-kilovolt TE “Axicom” hollow-core insulator from TE Connectivity in front of a high-voltage mast.

Unlike a porcelain surface, a silicone surface is permanently hydrophobic or water-repellent. It is even capable of transferring its water-repellency to adhering particles of dirt. This is a huge advantage for silicone composite hollow-core insulators in areas of high airborne pollution, in intensively farmed regions and in coastal areas, says Dr. Hans-Jörg Winter, who has been in charge of an applied laboratory for the transmission and distribution market segment at WACKER SILICONES for over 20 years. “Rainwater and dew simply roll off the silicone sheds in beads,” adds Winter. “Even if the sheds are exposed to the elements for years outdoors, there is no risk of pollution flashovers, because a continuous, electrically conducting moisture film cannot form.” Silicone composite hollow-core insulators are unbreakable, earthquake-proof and weigh much less than their porcelain counterparts. They can withstand high internal pressure – up to 100 times atmospheric pressure – and will not shatter at higher internal pressures, i.e. they are explosion-proof.

Furthermore, composite insulators can be made much faster than porcelain insulators. Equipment makers, energy providers and grid operators are keen to exploit these advantages and are therefore turning more and more to composite hollow-core insulators, especially for high voltage levels. “Originally, silicone composite hollow-core insulators were mainly used at 220 kilovolts and above. They were too expensive for the lower voltage levels,” reports Rainer Röder. They have since been used more and more at the 72 kilovolt level. “The trend is clearly in favor of composite insulators,” says Röder, confidently.

Hollow-core insulators for high-voltage technology can assume vast dimensions. The higher the voltage level, the longer the insulator is, with every 100 kilovolts adding one meter to the length. Dimensions of this kind are not exactly conducive to cost-effective maximum-quality production, especially as the insulators are produced to order and each order is generally composed of just a few units.

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 weigh only one third as much. This lower weight makes itself apparent during assembly, transport and installation of the electrical equipment in the plant. By virtue of their design, composite hollow-core insulators are explosion-proof and earthquake-proof and cannot break during transport. Thanks to their pronounced water repellency and ability to impart water-repellency to dirt deposits, silicone composite hollow-core insulators do not have to be cleaned in situ. 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. Finally, composite hollow-core insulators can be made in a much shorter time than porcelain models.

Silicone composite hollow-core insulators have been commercially available since the 1980s. “Back then, custom solutions involving tailored shed shapes were all the rage. Dedicated production methods were set up for these and this made them expensive,” recalls Röder. “That has changed over time. Nowadays, equipment makers are willing to tailor their designs to a portfolio of specified shed shapes and diameters.” This has paved the way for more efficient and thus more cost-effective industrial production methods.

Low-pressure diecasting at atmospheric pressure has since proved to be the best-practice method for industrial shielding with silicone. Although it is very similar to conventional injection molding, the mold-filling pressure is much lower. The principle is simple: Basically, the GRP pipe to be sheathed is inserted into a two-part negative mold of the shielding. After the mold has been closed, a pourable, liquid silicone rubber is automatically introduced into it and cured at elevated temperatures.