Silicone rubber composite insulator is generally composed of two or more organic materials.Compared to electric porcelain insulator,it has the advantages of light weight, high strength (mandrel), impact resistance, high pollution lightning voltage, easy installation, no need to measure zero, lightning strike, pollution flash will not occur insulation breakdown, etc.Composite insulator is composed of mandrel, sheath, umbrella skirt, end fittings and accessories. It is the first choice for heavy pollution area.

The composite insulator is in the extremely uneven electric field in the ultra-high voltage line.There is only a short distance near the wire at the high field strength position,the long insulation string in the middle is located at a relatively low electric field, so it is necessary to install a corona ring on both ends to improve the distributed voltage of the insulator string, to protect the silicon rubber skirt from being burned by the arc in the case of over voltage short circuit and flash over, and to protect the connection of both ends of mandrels and metal fittings from the damage of sealing performance due to leakage marks and electrical erosion.The interface between the metal, the mandrel, the sheath and other materials is the most dangerous interface of the composite insulator.There are many kinds of materials at the interface, and the electric field intensity is high. The air at the interface is prone to ionization, which leads to dendritic discharge of silicone rubber and electric corrosion of silicone rubber sheath, resulting in direct contact with the atmosphere.

Under the action of electric field, corona is generated, which makes nitrogen in the air react with oxygen to produce nitrous anhydride, and then react with water vapor to generate nitrous acid, which corrodes the mandrel and causes brittle break of composite insulators, leading to major accidents of line dropping.In addition, corona discharge is easily generated near the metal port at high field intensity.It can make the sheath with silicone rubber as the main material undergo corona ablation for a long time, and the hydrophobicity is weakened until it disappears.