Insulators are generally made of glass and porcelain. It is mainly used to fix the conductor on the pole and insulate the conductor from the pole. Insulator is one of the key components of high voltage transmission line, its performance directly affects the operation safety of the whole transmission line. Glass insulator is widely used because of its zero value self breaking and easy maintenance. In the first few years of production and operation, glass insulator is widely used.

It is found that glass insulator has a series of advantages over porcelain insulator: due to the high mechanical strength of the surface layer of glass insulator, the surface is not easy to crack. Generally, the electrical strength of glass remains unchanged during the whole operation period, and its aging process is much slower than that of porcelain. Therefore, glass insulator is mainly scrapped due to self damage, which occurs in the first year of operation, but the defects of porcelain insulator are only found after several years of operation.

If glass insulator is used, regular preventive test on live line of insulator during operation can be cancelled. This is because each kind of damage of toughened glass will cause damage to the insulator, which is easy to be found by the operators during the line inspection. When the insulator is damaged, the glass fragments near the steel cap and iron foot are stuck, and the mechanical strength of the remaining part of the insulator is enough to prevent the insulator string from breaking.