Insulator is a special insulation control, which can play an important role in overhead transmission lines. In order to prevent floating dust and other contaminants from adhering to the insulator surface, a path is broken down by the voltage at both ends of the insulator, that is, creeping. Therefore, increasing the surface distance, that is, climbing distance, along the insulating surface discharge distance, that is, leakage distance is called climbing distance. Zero value insulator refers to the insulator whose potential distribution at both ends of insulator is close to or equal to zero in operation. The influence of zero or low value insulators: The insulation of line conductors depends on insulator strings. Because of manufacturing defects or external effects, the insulation performance of insulators will deteriorate continuously. When the insulation resistance decreases or is zero, it is called low value or zero value insulator.
　　On the other hand, the common classifications of insulators are:
1. Insulators are usually classified as breakdown type and non-breakdown type.
2. According to the structure, it can be divided into pillar insulator, suspension insulator, pin insulator, butterfly insulator, tension insulator, anti-pollution insulator and bushing insulator.
3. It can be divided into line insulator, power station insulator and electrical insulator according to the application situation. Among them, the breakdown insulators for transmission lines are needle, butterfly and disk suspension, while the non-breakdown insulators are cross-bar and rod suspension. Breakdown insulators for power plants and electrical appliances include needle-type struts, hollow struts and bushings, while non-breakdown insulators include rod-type struts and ceramic sleeves for containers.
4. Insulators used in overhead lines are needle insulators, butterfly insulators, suspension insulators, ceramic crossbars, rod insulators and tension insulators.
5. The commonly used insulators are ceramic insulators, FRP insulators, synthetic insulators, semiconductor insulators and so on.