A device capable of withstanding voltage and mechanical stress that is mounted between conductors of different potentials or between conductors and ground members. Composite post insulators ‍ come in many varieties and shapes. Although the structure and shape of different types of insulators are quite different, they are composed of two major parts: insulation parts and connecting fittings. Insulator is a kind of special insulation control, which can play an important role in overhead transmission lines. In the early years, insulators were mostly used for telephone poles, and slowly developed in the high voltage wire connection tower with a lot of disk-like insulators.

According to the use of different voltage levels, can be divided into low voltage insulator and high voltage insulator; According to the different environmental conditions used, the antifouling insulators used in dirty areas are derived; According to the different types of voltage used, DC insulators are derived; There are a variety of special purpose insulators, such as insulation cross arm, semiconductor glaze insulators and power distribution tension insulators, bobbin insulators and wiring insulators. In addition, according to the different breakdown possibilities of insulating parts, it can be divided into two categories: type A, that is, non-disruptive type insulator and type B, that can be disruptive type insulator.