Introduction to the basic performance of high-voltage post insulators
The basic properties of insulators include electrical, mechanical and thermal properties. In addition, there are properties such as environmental resistance and aging resistance.
①Electrical performance: The destructive discharge that occurs along the insulating surface is called flashover, and the flashover characteristic is the main electrical performance of the insulator. For different voltage levels, the withstand voltage requirements of insulators are different. Its indicators include power frequency dry and wet withstand voltage, lightning impulse withstand voltage, lightning impulse chopping withstand voltage, and operating impulse withstand voltage. To avoid breakdown during operation, the breakdown voltage of the insulator is higher than the flashover voltage. In the factory test, the breakdown type porcelain insulator generally undergoes a spark test, that is, high voltage is applied to cause frequent sparks on the insulating surface, and it is maintained for a certain period of time to see if it is broken down.
Some insulators need to go through corona test, radio interference test, partial discharge test and dielectric loss test. Insulators in high altitude areas have a reduced electrical strength due to the decrease in air density. Therefore, their withstand voltage should be increased accordingly when converted to standard atmospheric conditions. The flashover voltage of polluted insulators when they are damp is much lower than their dry and wet flashover voltages. Therefore, in polluted areas, insulation must be reinforced or pollution-resistant insulators must be used. The creepage distance (the ratio of the creepage distance to the rated voltage) should be longer. Normal type is high. Compared with AC insulators, DC insulators have poorer electric field distribution, and have the effects of adsorbing dirt particles and electrolysis, and have lower flashover voltage. Generally, special structural design and greater creepage distance are required.
②Mechanical performance: Insulators are often affected by the gravity and tension of the wire, wind force, ice weight, insulator weight, wire vibration, equipment operation mechanical force, short-circuit electric power, earthquake and other mechanical forces during operation. Relevant standards have strict requirements on mechanical performance regulations.
③ Thermal performance: Outdoor insulators are required to have the ability to withstand sudden changes in temperature. For example, porcelain insulators require several cycles of cooling and heating without cracking. Due to the current passing through the insulating bushing, the temperature rise and allowable short-term current value of its parts and insulating parts must comply with the relevant standards.