Silicone Rubber for Composite Insulators
What is silicone rubber for composite insulators?
The housing (sheds and sheath) of composite insulators are made of silicone rubber, but it’s not a kind pure material. It's a kind of composite (polymeric) material consists of long-chain polysiloxanes, aluminium hydroxide (Al(OH)3) and various filler additives.
Classification of silicone rubber
Silicone Rubber are converted into silicone elastomers by vulcanization and are classified according to the curing method, the viscosity of the base polymer, and whether they cure at high or room temperature. Usually there are 2 kinds of silicone rubber for composite insulators:
- HTV (High Temperature Vulcanized – solid silicone rubber): The core of the Solid silicone rubbers are cured at elevated temperature (200 ºC approx), either by means of organic peroxides or with platinum catalyst. The cured rubber is compounded with reinforcing fillers to give it its mechanical strength.
- LSR (Liquid Silicone Rubber): Liquid silicone rubbers are also members of the group of high-temperature-vulcanizing rubbers (100 – 200 ºC). This kind of silicone rubbers are characterized by a low viscosity compared to solid silicone rubbers (HTV). Liquid silicone rubbers are two-part compounds mixed to be vulcanized.
How is the silicone rubber made into insulator sheds?
The core of the composite insulator is completely covered by a continuous housing consisting of a waterproof and insulating coating. The housing of the insulators, i.e. sheds and core rod sheath, is a one-piece with only one internal interface throughout the whole insulator, namely the boundary interface between the housing and the FRP core rod.
Molding manufacturing process:
The molding process (silicone- rubber injected into a mold) is carried out in an enclosed system to avoid contact with the air and ensure that the silicone-rubber does not contain bubbles. The surface of the silicone-rubber is free of burrs, even on the edge of the weathersheds the maximum admitted burr must be shorter than 3 mm. The thickness of molding weather shed and sheds should be more than 3 mm. And if the system voltage is over 220KV, the thickness of molding weather shed and sheds should be more than 4.5 mm.
Assembly manufacturing process:
Composite insulators may be also manufactured by assembling their different elements. Prefabricated sheds are installed and glued over a HTV-coated FPR rod. These sheds have to be vulcanized in order to get a one-piece housing.