Insulators are insulators used to support wires and are often used for the insulation of external live conductors in overhead transmission and distribution lines, power plants and substations, as well as various electrical equipment. They are generally made of insulating parts (such as glass, ceramics) and metal parts (such as steel feet, steel caps, flanges, etc.) assembled with adhesive or mechanical clamps. The basic performance of insulators includes electrical, mechanical, and thermal performance. In addition, there are also properties such as environmental resistance and aging resistance. When the voltage level of the insulator increases, its size and weight also increase accordingly, but the electrical and mechanical properties do not increase proportionally, and the heat resistance performance decreases rapidly.

(1) Electrical performance: The destructive discharge that occurs along the insulation surface is called flashover, and flashover characteristics are the main electrical performance of insulators. For different voltage levels, the withstand voltage requirements of insulators vary, and their indicators include power frequency dry and wet withstand voltage, lightning impulse withstand voltage, lightning impulse cutoff withstand voltage, operating impulse withstand voltage, etc. To avoid breakdown during operation, the breakdown voltage of the insulator is higher than the flashover voltage. In the factory test, breakdown type porcelain insulators are generally subjected to spark testing, which involves applying high voltage to cause frequent sparks on the insulation surface and maintaining it for a certain period of time to see if they are broken down. Some insulators also need to undergo corona tests, radio interference tests, partial discharge tests, and dielectric loss tests. Insulators in high-altitude areas have a decrease in electrical strength due to a decrease in air density. Therefore, their withstand voltage should be correspondingly increased when converted to standard atmospheric conditions. The flashover voltage of polluted insulators when they are damp is significantly lower than their dry and wet flashover voltage. Therefore, in polluted areas, insulation should be strengthened or pollution resistant insulators should be used. The specific creepage distance (the ratio of creepage distance to rated voltage) should be higher than that of the normal type. Compared with AC insulators, DC insulators have a poorer electric field distribution, as well as adsorption of pollutants and electrolysis. They have a lower flashover voltage and generally require special structural design and a larger creepage distance.

(2) Mechanical performance: Insulators are often subjected to the gravity and tension of the conductor, wind force, icing weight, self weight of the insulator, conductor vibration, mechanical forces during equipment operation, short-circuit electrical force, earthquake, and other mechanical forces during operation. The relevant standards have strict requirements for mechanical performance regulations.

(3) Thermal performance: Outdoor insulators are required to have the ability to withstand sudden temperature changes. For example, porcelain insulators require several cold and hot cycles without cracking. Due to the passage of current, the temperature rise and allowable short-term current value of its components and insulation components must comply with relevant standards.