Porcelain insulators are mainly used in high-voltage overhead transmission and distribution lines to insulate and support conductors. Different types of insulators, such as ordinary and pollution-proof types, are selected according to different pollution areas. Moreover, insulator strings are formed according to different voltage levels. 

Porcelain insulators include high-voltage suspension porcelain insulators, high-voltage line post porcelain insulators, high-voltage line pin porcelain insulators, and high-voltage porcelain cross-arm insulators, with strength grades of 40kN, 70kN, 120kN, 160kN, 210kN, 300kN, 420kN, and 550kN. They are used in strings according to different voltage levels: 35kV uses 3 pieces per string, 110kV uses 7 pieces per string, 220kV uses 14 pieces per string, and 500kV uses 28 pieces per string. For insulator strings of 220kV and above voltage levels, suspension products with strength grades of 100kN and above are used. 

Porcelain insulators have a long history of use in China. They are safe, reliable, and not prone to aging. Their service life is generally over 30 years, and the annual deterioration rate is less than 0.01%.