A cable is usually a cable-like cable made up of several or several sets of wires [at least two in each group]. Each set of wires is insulated from each other and often twisted around a center. The entire outer bread has a height. Insulated overlay. Multiple erected in the air or installed underground or underwater for telecommunications or power transmission. In 1832, the Russian veteran Xu Lingge buried the telegraph line underground. The six wires were insulated with rubber and placed in the glass tube. This is the earliest underground cable in the world.
An insulated conductor formed by one or more electrically insulated conductor cores placed in a sealed jacket. A protective cover can be added to transmit, distribute, or transmit electrical signals. The difference between it and ordinary wires is mainly that the cable size is large and the structure is complicated.
The cable is mainly composed of the following four parts. 1 Conductive core: Made of high conductivity material (copper or aluminum). According to the requirements of the laying conditions of the cable for the softness of the cable, each wire core may be stranded by a single wire or a plurality of wires. 2 Insulation: The insulating material used as the cable should have high insulation resistance, high breakdown electric field strength, low dielectric loss and low dielectric constant. Commonly used insulating materials in cables are oil-impregnated paper, polyvinyl chloride, polyethylene, cross-linked polyethylene, and rubber. Cables are often classified by insulating materials such as oil-impregnated paper insulated cables, PVC cables, and XLPE cables. 3 Sealing sheath: Protect the insulated wire core from mechanical, moisture, moisture, chemicals, light, etc. For moisture-sensitive insulation, lead or aluminum extrusion seals are generally used. 4 protective cover: to protect the sealing sheath from mechanical damage. Generally, galvanized steel strip, steel wire or copper strip, copper wire, etc. are wrapped around the sheath (called armored cable), and the armor layer simultaneously acts as an electric field shield and prevents external electromagnetic wave interference. In order to avoid the corrosion of the steel strip and the steel wire by the surrounding medium, it is generally coated with asphalt or wrapped around the jute layer or extruded polyethylene or polyvinyl chloride sleeve.
Cables can be classified into power cables, communication cables, and control cables according to their uses. Compared with the overhead line, the advantage of the cable is that the insulation distance between the lines is small, the floor space is small, the underground is laid without occupying the space above the ground, and is not affected by the surrounding environment pollution. The power transmission reliability is high, and the personal safety and the surrounding environment are disturbed. small. However, the construction cost and construction are both cumbersome and the manufacturing is complicated. Therefore, cables are mostly used in densely populated and densely populated areas and in heavy traffic congestion; laying over rivers, crossing rivers, and undersea can avoid the use of large-span overhead lines. Cables can also be used wherever overhead line interference is avoided and where aesthetics or exposure targets need to be considered.