Views: 0 Author: Site Editor Publish Time: 2022-04-15 Origin: Site
The overhead power line is erected on the ground, and is a power transmission overhead power line that uses insulators to fix the transmission wire on the tower erected on the ground to transmit electric energy. The erection and maintenance are relatively convenient and the cost is low, but it is easily affected by the weather and the environment (such as strong wind, lightning strike, pollution, ice and snow, etc.) . The main components of overhead electrical lines are:
1. Conductor. Wires are components used to conduct current and transmit electrical energy. Overhead bare conductors are generally one per phase. 220kV and above lines use phase-split conductors to reduce corona loss and corona interference due to their large transmission capacity, that is, two or more conductors are used for each phase. The use of split conductors can transmit larger electric energy, with less electric energy loss and better anti-vibration performance.
2. Lightning protection line. Lightning conductors generally also use Steel core aluminum stranded wire ACSR, which is not insulated from the tower but is directly erected on the top of the tower, and is connected to the grounding device through the tower or the grounding down-conductor. The function of the lightning protection wire is to reduce the chance of lightning strike the wire, improve the lightning resistance level, reduce the number of lightning strike trips, and ensure the safe power transmission of the line.
3, the tower. Pole tower is a general term for electric poles and iron towers. The purpose of the tower is to support the conductors and lightning conductors, so as to maintain a certain safe distance between conductors, conductors and lightning conductors, conductors and the ground and crossing objects.
4. Insulators. Insulator is a kind of insulation product, generally made of electrical ceramics, also called porcelain bottle. In addition, there are glass insulators made of tempered glass and synthetic insulators made of silicone rubber. The purpose of the insulator is to insulate between the wires and between the wires and the ground, to ensure that the line has reliable electrical insulation strength, and to fix the wires to withstand the vertical and horizontal loads of the wires.
5. Hardware. In overhead power lines, fittings are mainly used to support, fix and connect wires and insulators connected in series, and are also used to protect wires and insulators.
6, tower foundation. The underground installations of overhead power line towers are collectively referred to as foundations. The foundation is used to stabilize the tower, so that the tower will not be pulled up, sunk or dumped due to vertical load, horizontal load, accidental disconnection tension and external force.
7. Pull the wire. The pull wire is used to balance the lateral load and wire tension acting on the tower, which can reduce the consumption of tower materials and reduce the cost of the line.
8. Grounding device. The overhead ground wire is above the conductor, and it will be connected to the ground through the ground wire or grounding body of each base tower. When the ground wire is struck by lightning, the lightning current can be quickly spread to the ground. Therefore, the grounding device of the transmission line is mainly a leakage conductor. Lightning current, reduce the potential at the top of the tower, and protect the line insulation from breakdown flashover. It closely cooperates with the ground wire to shield the wire. The grounding body and the grounding wire are collectively referred to as the grounding device.
Common behaviors that endanger overhead power lines include:
(1) Shooting and throwing objects at line facilities.
(2) Fly kites in an area of 300 meters on both sides of the overhead power line conductors
(3) Climbing the tower without authorization or erecting power lines, communication lines, broadcasting lines, and installing broadcasting speakers on the towers;
(4) Unauthorized access to electrical equipment on the wire.
(5) Use pole towers and cables as lifting and traction anchors, or tie livestock, hang objects and attach crops.
(6) Borrowing soil, piling, drilling, excavating or dumping harmful chemicals within the specified protection scope of the tower and the cable foundation.
(7) Build roads within the tower (excluding between the tower and the tower) or between the tower and the cable.
(8) Disassemble the equipment on the tower or on the cable, move or damage the permanent sign or sign;
To stop the above behaviors, in addition to widely publicizing electrical safety knowledge, it is also necessary to deal with them in strict accordance with the law. Usually, it is necessary to strengthen the inspection of the line, and solve the problem immediately to eliminate the hidden danger of the accident.
Line icing hazards generally include the following:
1. Damage the tower. When the line is covered with ice too thick, the mechanical load of the tower will be overloaded and broken. When used in a straight tower, a large unbalanced tension or broken wire tension will be formed, which will be damaged or collapsed beyond the design conditions of the tower.
2. Line tripping. The icing on the conductors does not necessarily come off at the same time. For vertically aligned lines.
If the ice coating on the lower conductor comes off first, the conductor will quickly rise or jump and collide with the upper conductor. Causes a short circuit between phases and trips, and the power supply is interrupted. When the lightning conductor is covered with ice too thick, the distance from the conductor will be shortened, resulting in a discharge grounding fault.
3. The insulator string is inclined and the conductor sags seriously. When the thickness of the ice layer in each span of the line is not uniform, the sag of the conductor changes greatly, resulting in the insulator string being inclined. Pipe fittings are subject to large horizontal forces. When shaved ice has a large span, the conductor sags seriously and the safety distance is insufficient, which will cause an accident.
4. The insulation level of the insulator string will be greatly reduced after freezing. Snow and ice build-up on suspended insulator strings may melt to form icicles. The short circuit of the insulator string causes a grounding accident.
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