Which is the Most Suitable for Anti-pollution Flashover of Transmission Lines, Porcelain Insulators

The insulator is the main body of the transmission line insulation. Its function is to suspend the wire and keep the wire insulated from the tower and the earth. Insulators should withstand working voltage and overvoltage, and bear the vertical load, horizontal load, and wire tension of the wire. Therefore, insulators must have good insulating properties and sufficient mechanical properties.

There are many types of insulators for transmission lines, which can be classified according to their structural type, insulating medium, connection method, and bearing capacity. According to the structure type, insulators can be divided into disc insulators and rod insulators. According to the insulating medium, there are porcelain insulators, glass insulators, semiconductor glazes, and composite insulators. According to the connection method, there are two types: ball type and groove type. According to the bearing capacity, they are divided into 40, 60, 70, 100, 160, 210, 300kN, 420kN, 550kN, and other grades. Each insulator has various types such as ordinary type, pollution-resistant type, aerodynamic type, and spherical type.

1. Porcelain insulators are still the most widely used insulators in power systems

High-strength porcelain for high-voltage insulators is made of quartz, feldspar, clay, and alumina. Porcelain is a brittle material and its compressive strength is much greater than its tensile strength. In order to make the electric porcelain have high mechanical strength, the design should make the porcelain bear compressive stress as much as possible. The surface of porcelain pieces is usually covered with enamel to improve its mechanical strength, waterproof infiltration, and increase surface smoothness. In order to improve the pollution flashover resistance of porcelain insulators, an insulator covered with semiconductor glaze has also been developed. When the leakage current on the surface of the insulator increases, the glaze heats up and evaporates the water on the surface, thereby preventing the generation and development of local arcs on the surface and preventing the occurrence of pollution flashover.

2. Composite insulators are generally composed of umbrella skirt sheath, glass fiber reinforced plastic mandrel, and end fittings

The shed sheath is generally made of organic synthetic materials such as high-temperature vulcanized silicone rubber and ethylene propylene rubber. The mandrel is generally a glass fiber reinforced plastic composite material with glass fiber as the reinforcing material and epoxy resin as the matrix. The end fittings are generally carbon cast steel or carbon structural steel with hot-dip galvanized coating on the outer surface. The mandrel and the shed sheath bear the mechanical and electrical loads respectively, thus combining the advantages of the superior atmospheric aging resistance of the shed sheath material and the good tensile mechanical properties of the mandrel material. Silicone rubber is currently the best material for composite insulator umbrella group sheaths, and its unique hydrophobic migration performance is the key to the successful use of silicone rubber in polluted areas.