Difference Between Overhead Lines and Cable Lines
一、The difference in product use
Overhead lines: Overhead lines mainly refer to overhead open lines, erected above the ground, and are transmission lines that use insulators to fix the transmission wires on the towers standing on the ground to transmit electric energy.
Cable line: The cable line is an electrical signal transmission system composed of communication cables and ancillary equipment.
二、Product features are different
Overhead line: low investment cost, convenient erection and maintenance, easy to find and troubleshoot in time, but overhead line will be directly affected by bad weather and environment, and failure will occur, and the entire transmission corridor occupies a large area of land, which is easy to damage the surrounding area. The environment causes electromagnetic interference.
Cable lines: Cable lines have the advantages of long service life, large communication capacity, stable transmission quality, less external interference, and good confidentiality performance, so they occupy a dominant position in wired communication lines.
三、 The structure is different
1. Overhead lines: Because overhead lines are easily corroded in the atmosphere, bare wires are generally used for overhead lines.
(1) Conductor: Conductor is a component used to conduct current and transmit electric energy. The lightning protection wire and the lightning protection wire are generally made of steel-cored aluminum stranded wire, and are not insulated from the tower but are directly erected on the top of the tower, and are connected to the grounding device through the tower or the grounding downconductor.
(2) Tower: refers to the pole and tower. The purpose of the tower is to support the conductors and lightning conductors, so that a certain safety distance is maintained between conductors, conductors and lightning conductors, conductors and the ground, and crossovers. Insulator, an insulator is a kind of electric insulation product, generally made of electrical ceramics, also called porcelain bottle.
(3) Fittings: Fittings in overhead power lines are mainly used to support, fix and connect conductors and insulators in series, and are also used to protect conductors and insulators. The tower foundation and the underground devices of the overhead power line tower are collectively referred to as the foundation. Guy wire, the guy 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.
(4) Grounding device: The overhead ground wire is above the wire, and it will be connected to the ground through the ground wire or grounding body of each base tower. When the lightning strikes the ground wire, it can quickly spread the lightning current to the ground. Therefore, the transmission line The grounding device is mainly to discharge the lightning current, reduce the potential of the top of the tower, and protect the insulation of the line from breakdown and flashover.
2. Cable line: The cable line is composed of wires, insulating layers, sheathing layers, etc.
(1) Wire: To transmit electric energy, single or multi-strand wires of copper or aluminum are used, usually multi-strand, such as household and building wires.
(2) Insulation layer: Insulate the wires and wires, the wires and the sheathing layer from each other. The insulating materials include rubber, asphalt, polyethylene, polyvinyl chloride, cotton, hemp, silk, oil-impregnated paper, mineral oil, vegetable oil, etc. At present, Most use oil-impregnated paper.
(3) Sheathing layer: It protects the insulating layer and has the function of preventing insulating oil from spilling. It is divided into inner sheathing layer and outer sheathing layer; Reliable, seldom damaged by external force, safe for personal safety.
四、Basic requirements for laying overhead lines and cable lines
(1) The cable specifications should meet the regulations, the arrangement should be neat, without damage, and the signs should be complete, correct and clear.
(2) The fixed bending radius of the cable, the relevant distance and the wiring of the metal sheath of the single-core power cable shall meet the requirements.
(3) The cable terminal and intermediate head shall not leak oil, and the installation shall be firm. The oil pressure of the oil-filled cable and the set value of the meter shall meet the requirements.
(4) Good grounding.
(5) The color of the cable terminal is correct, and the metal parts such as brackets are completely painted.
(6) There should be no debris in the cable trench, tunnel and bridge frame, and the cover plate should be complete.
(7) Steel-cored aluminum stranded wire or aluminum stranded wire should be widely used in overhead lines. The cross-section of the aluminum stranded wire of the high-voltage overhead line shall not be less than 50 square millimeters, the cross-section of the core aluminum stranded wire shall not be less than 35 square millimeters, and the cross-section of the empty wire shall not be less than 16 square millimeters.
(8) The wire section should meet the requirements of the maximum load.
(9) The selection of the cross-section should also meet the requirement that the voltage loss is not greater than 5% of the rated voltage (high-voltage overhead lines), or 2%~3% (lighting lines with high visual requirements), and should meet certain mechanical strength.