In the early days, insulators were mainly used in electric poles. With the development and needs of society, they were gradually used in high-voltage power line connection towers, mainly used to increase the creepage distance (creepage distance refers to the short space distance between two conductive parts, or between a conductive part and equipment and easily accessible surfaces measured along the surface of the insulating material. In order to prevent dust and other impurities from adhering to the surface of the insulator, forming a path that is broken down by the voltage at both ends of the insulator, that is, creepage. Depending on the degree of contamination, a creepage distance of 31 mm/kV is generally used in heavily polluted areas.), usually made of glass or ceramics.

Insulators have two basic functions in overhead transmission lines: supporting the conductors and preventing current from returning to the ground. In order to ensure these two basic functions, insulators should not fail due to various electromechanical stresses caused by changes in environmental and electrical load conditions, otherwise the use and operating life of the entire line will be damaged.

According to different standards, insulators are classified differently, as shown below:

1. According to whether they break down, insulators are usually divided into breakdown type and non-breakdown type.

2. According to the structure, it can be divided into column insulators, suspension insulators, anti-pollution insulators and bushing insulators.

3. According to the application occasion, they can be divided into line insulators and power station and electrical appliance insulators. Among them, the breakdown type insulators used for lines include pin type, butterfly type, disc type suspension type, and the non-breakthrough type includes cross arm and rod type suspension type. The breakdown type insulators used in power stations and electrical appliances include pin type pillars, hollow pillars and bushings, and the non-breakthrough type includes rod type pillars and container porcelain sleeves.

4. The insulators used in overhead lines include pin insulators, butterfly insulators, suspension insulators, porcelain crossarms, rod insulators and tension insulators.

The insulators commonly used in industry are mainly: ceramic insulators, fiberglass insulators, composite insulators, and semiconductor insulators.