Classification of line towers

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Line towers are rigid support structures used to erect 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 towers need to have a considerable distance.

The hydrogeological conditions along the transmission line vary greatly, so it is very important to choose the foundation form according to the local conditions. There are two basic types of line towers: cast-in-place and prefab. According to the type of tower, groundwater level, geology and construction method, the poured foundation is divided into undisturbed soil foundation, explosion-expanded pile and cast-in-place pile foundation, and ordinary concrete or reinforced concrete foundation. The prefabricated foundations for line towers include chassis for poles, chucks and cable reels, various types of prefabricated precast concrete foundations and metal foundations for towers. According to different foundation forms and different soil conditions, experts are currently researching and dealing with the theoretical calculation of foundation anti-uplift and anti-overturning to make it more reasonable, reliable and economical.

According to the structural material, the line tower can be divided into wood structure, steel structure, aluminum alloy structure and reinforced concrete structure. China has phased out wooden poles and towers due to low strength, short lifespan, inconvenient maintenance and limited timber resources. The steel structure is divided into truss and steel pipe. Lattice truss towers are widely used line towers and are the main structures for lines above ultra-high voltage. Due to the high cost of aluminium line towers, they are only used in mountainous areas where transportation is particularly difficult.

Reinforced concrete line towers are cast by centrifuge and steam cured, with short production cycle, long service life and simple maintenance, which can save a lot of steel. The concrete line tower with local prestressing technology can also prevent the rod from cracking and has reliable quality.

According to the structure, line towers can be divided into two types: freestanding towers and pull towers. A self-supporting tower is a pole tower that is stabilized on its foundation. The stay tower is to install symmetrical stay wires on the tower head or tower body to support the tower stably, and the tower itself only bears vertical pressure. This kind of utility pole saves nearly 40% of steel, but the cable distribution occupies a lot of land, which is not conducive to agriculture, forestry machinery and agriculture, and the scope of use is limited. Due to the good mechanical properties of the cable-stayed line tower, 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.


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