Many disc-shaped insulators are hung at one end of the high-voltage wire connection tower to increase the creepage distance. They are usually made of glass or ceramic or rubber, which is called insulators. In order to prevent floating dust and other pollutants from adhering to the insulator surface and forming a path, it is flashover and breakdown at both ends of the insulator, i.e. creepage Therefore, increasing the surface distance, that is, the creepage distance, and the discharge distance along the insulating surface, that is, the leakage distance, is called the creepage distance Creepage distance = surface distance / maximum system voltage According to different pollution levels, the climbing distance is generally 31 mm / kV in heavily polluted areas.
Zero value insulator refers to the insulator whose potential distribution at both ends of the insulator is close to or equal to zero during operation.
Influence of zero value or low value insulator: the insulation of line conductor depends on insulator. Due to manufacturing defects or external effects, such as dirty insulator surface, lightning stroke, etc. When the insulation resistance of the insulator is continuously reduced, it is called zero or low insulation resistance. The insulator is smooth, which can reduce the capacitive reactance between wires and reduce the loss of current.
With the construction of UHV AC / DC lines in China and the continuous improvement of requirements for mechanical strength, the problem of pure porcelain post insulator is becoming more and more prominent, especially in UHV DC converter station, which is mainly reflected in:
① External insulation problem. With the deterioration of operating environment, the anti pollution flashover ability of porcelain post insulator is insufficient. For UHVDC, pure porcelain post insulators require large creepage distance and structure, while too high post insulators are difficult to achieve strong bending and seismic strength.
② Earthquake resistance. The high-voltage equipment with electric porcelain post insulator as insulating part is called electric porcelain high-voltage equipment for short. The seismic problem of this kind of equipment has been difficult to be solved well. In the 2008 Wenchuan earthquake, most of the damage of high-voltage equipment was due to the fracture of porcelain bushing. For UHV DC system, the post insulator used for smoothing reactor requires an overall height of 12m and a support mass of 40t, while the converter station is located in Chuxiong, Yunnan, an earthquake prone area. Obviously, it is very difficult for porcelain post insulator to meet the seismic requirements.
③ Manufacturing quality problems. Porcelain post insulator is very difficult to manufacture because of its complex process, equipment conditions, raw material quality problems and other limitations. On the basis of a large number of investigations, the accident investigation working group of high-voltage pillar porcelain insulators of the former generation and transmission operation Department of State Power Corporation counted the accidents of porcelain pillar insulators according to technical reasons, and came to the conclusion that the fracture of pillar porcelain insulators was caused by the majority of product quality reasons.
