High voltage post insulator basic performance introduction

The basic properties of insulators include electrical, mechanical and thermal properties. In addition, there are environmental resistance and aging resistance.

① Electrical performance: The destructive discharge occurring along the insulation surface is called flashover, and the flashover characteristic is the main electrical performance of the insulator. For different voltage levels, insulator withstand voltage requirements are different, its indicators are power frequency dry, wet voltage resistance, lightning impulse voltage resistance, lightning impulse cut-off voltage resistance, operation impulse voltage resistance. In order to avoid breakdown in operation, the breakdown voltage of the insulator is higher than the flashover voltage. In the factory test, the breakdown type of porcelain insulator is generally through the spark test, that is, the high pressure makes the insulation surface frequent sparks, maintain a certain time, to see whether it is broken down.

Some insulators also need to pass corona test, radio interference test, partial discharge test and dielectric loss test. Insulator at high altitude, due to the decrease in air density and the decrease in electrical strength, therefore, its withstand voltage converted to the standard atmospheric conditions should be increased accordingly. The flashover voltage of the dirty insulator when it is wet is much lower than its dry and wet flashover voltage, so it is necessary to strengthen insulation or use the dirt-resistant insulator in the dirty area, and the creepage specific distance (the ratio of the creepage distance to the rated voltage) should be higher than the normal type. Compared with AC insulators, DC insulators have poor electric field distribution, adsorption of dirt particles and electrolysis, and lower flashover voltage, which generally requires special structural design and larger creepage distance.

② Mechanical properties: the insulator is often subjected to the gravity and tension of the wire, wind, ice weight, insulator weight, wire vibration, equipment operation mechanical force, short-circuit electrical power, earthquake and other mechanical forces in operation. The relevant standards have strict requirements for mechanical properties.

③ Thermal performance: Outdoor insulators require the ability to withstand sudden temperature changes. For example, porcelain insulators are required to undergo several hot and cold cycles without cracking. Due to the current passing through the insulation sleeve, the temperature rise of its parts and insulation parts and the allowable short-time current value must meet the provisions of the relevant standards.