Composite insulator’s shed and sheath are be made of high temperature vulcanizing (HTV) type silicone rubber, having silicone polymer content by weight 30% minimum. Alumina Tri hydrate (ATH) is used as filler. The filler is properly mixed with silicone compound to ensure the uniform distribution. Thickness of sheath shall be minimum 3 mm and shall have excellent hydrophobic and anti-tracking properties.
The material shall conform to the tests specified in IEC or other technical standard equivalent. The material preferably shall be such that it should not attract birds or other rodents at storage location or on the line. In some country, like India, the thickness of shed at edge should not be less than 2.5mm to minimize the external damage. The strength of shed to sheath interface shall be greater than the tearing strength of polymer. And cleaning methods of silicon rubber sheds shall be paid attention to.
To test material property of composite insulator, professional testing machines and device are needed to ensure accuracy. These are testers often used for insulator tests and test of its materials: