Classification of line towers
The line tower is a rigid support structure for erecting transmission lines. In order to avoid the danger of corona discharge and induced electrostatic field to people, the poles and towers used for high-voltage and ultra-high-voltage transmission lines must have sufficient height, and the transmission lines erected on the tower must have a considerable distance.
Tower
The hydrogeological conditions along the transmission line vary greatly, and it is very important to choose the foundation form according to local conditions. There are two basic types of line towers: cast-in-place and precast. According to the tower type, groundwater level, geology and construction method, the pouring foundation is divided into undisturbed soil foundation, explosive expansion pile and cast-in-place pile foundation, and ordinary concrete or reinforced concrete foundation. The prefabricated foundations of line poles and towers include chassis for poles, chucks and cable reels, various types of prefabricated precast concrete foundations and metal foundations for iron towers. According to different foundation forms and different soil conditions, experts are currently studying and processing the theoretical calculation of foundation anti-uplift and anti-overturning to make it more reasonable, reliable and economical.
According to structural materials, line poles and towers can be divided into wood structure, steel structure, aluminum alloy structure and reinforced concrete structure. Due to low strength, short life span, inconvenient maintenance and limited timber resources, China has eliminated wooden poles and towers. Steel structure is divided into truss and steel pipe. The lattice truss tower is a widely used line pole tower and the main structure of the line above the ultra-high voltage. Due to the high cost of aluminum alloy line towers, they are only used in mountainous areas where transportation is particularly difficult.
The reinforced concrete line tower is cast by a centrifuge and cured by steam. The production cycle is short, the service life is long, the maintenance is simple, and a lot of steel can be saved. The concrete line pole tower adopting local prestress technology can also prevent the pole from cracking, and the quality is reliable.
According to the structure, line towers can be divided into two types: free-standing towers and pull-type towers. A self-supporting tower is a pole tower that is stable on its foundation. The guyed tower is to install symmetric guy wires on the tower head or tower body to stably support the tower. The tower itself only bears vertical pressure. This kind of telegraph pole saves nearly 40% of steel, but the distribution of cables takes up a lot of land, which is not conducive to agricultural and forestry machinery and agriculture, and the scope of use is limited. Because the cable line tower has good mechanical properties, it can resist the impact of storm attack and line disconnection, and has a stable structure. Therefore, the higher the voltage, the more traction towers are used.
