Composite insulators are usually composed of mandrel, silicone rubber umbrella sleeve and end fittings. They have the characteristics of small volume, light weight, strong pollution resistance and smaill maintenance. Nanjing Electric is one of the earliest manufacturers to develop composite insulators in China. It has both AC and DC series, with voltage level from 10kV to 1000kV and strength grade from 40kN to 550kN. The product performance has reached the domestic advanced level.