Main data on the power transmission line
Network circuits are intended for transfer and distribution of electricity. They consist of substations and transmission lines (power transmission line) of different tension.
At power plants always build the raising transformer substations and on transmission lines of high tension transfer electricity to very long distances. And in places of consumption build the lowering transformer substations.
The basis of the network circuit is usually made underground or overhead power transmission lines of high tension. The lines going from transformer substation to input distributing devices and from them to power distribution points and to group boards are called the power line.
The power line is usually made by underground cable lines of low tension. For power supply of consumers the air or cable power transmission lines of 6 (10) kV for the power supply of substations and high-voltage consumers, the cable power transmission lines of 380-400/220-230V - for the power supply of low-voltage electroreceivers are used.
For transfer on distance of very high tension overhead power transmission lines are under construction. Wires highly rise above the ground, and as isolation air is used. The distance between wires is calculated depending on tension.
The air power transmission lines find broad application in rural areas and in towns. It can be explained them with smaller cost in comparison with cable lines, smaller density of building.
For wiring of air-lines and networks use different wires. One of the main requirements imposed to material of wires is the small electrical resistance. Besides, the material applied to production of wires has to be rather mechanically strong, to be steady against moisture and to chemicals which are airborne. At present use wires from aluminum and steel. It allows to save non-ferrous metals (copper) and to considerably reduce the cost of wires.
Copper wires are applied on special lines. Aluminum has small mechanical durability that leads to increase in the arrow of the dip, to increase in height of the support or reduction of length of flight between support.
For isolation of wires and their fastening to support linear isolation centers which have to have dielectric and mechanical strength serve. Depending on the way of fastening on the support, the pin (fasten on hooks or probes) distinguish insulators and suspended (they gather in the daisy and fasten to the support the special armature). Material of which they are made (porcelain, glass) also has to have durability.
Wires are suspended on steel concrete or wooden support by means of suspended or pin insulators. For the air power transmission lines use uninsulated wires. The exception makes inputs to buildings - the insulated conductors stretched from the power transmission line support to the insulators fixed on hooks directly on the building.
What it is necessary to pay special attention to?
Wires at which sections are are applied to the air power transmission lines up to 1000 V, under the terms of mechanical durability: aluminum - 16 mm2, steel single-wire - 4 mm2.
The smallest admissible height of the arrangement of the lower hook on the support (from earth level) is: at the power transmission line up to 1000 V for suspension towers - from 7 m, for transitional support – 8.5 m.
At the power transmission line more than 1000 V height of the arrangement of the lower hook for suspension towers - 8.5 m, for angular - 8.35 m.
On the air power transmission lines up to 1000 V install the grounding devices, and resistance of this device has to be no more than 30 Ohms.
Overhead power transmission lines consist of supporting structures, brackets, wires, insulators and the armature. Besides, the devices necessary for ensuring uninterrupted supply of consumers and the correct work of the line also enter: lightning-protective ropes, dischargers, grounding and additional equipment. And all this about air-lines.
Power cable lines are also applied to transfer and electric power distribution. Power cables are laid in the earth, water, in tunnels, on designs in the open air, etc. They are used generally for transfer of current on small distances and when construction of air-lines is undesirable or it is inadmissible. Damages to cable lines are not so dangerous as wire breakage of air-lines.
The power cable power transmission lines are applied to electric power transmission on high and low tension. The route for their laying gets out of conditions of the smallest expense of the cable and ensuring its greatest security from mechanical damages. The cable power transmission lines lay in trenches. The cable should not pass under the buildings and constructions existing or assumed to construction, under the drives saturated with underground communications.
In places of crossing with different pipelines or other communications power cables lay with observance of all rules which are stated in Regulations for electrical installation, and when passing cables through walls and overlappings cables lay in pieces of nonmetallic pipes.Top