The cable is usually a rope-like cable formed by twisting several or several groups of conductors [at least two each group]. Each group of conductors is insulated from each other and is often twisted around a center. The entire outer breadth has a height Insulating covering. Many are erected in the air or installed underground or underwater for telecommunications or power transmission. In 1832, the Soviet veteran Xu Linge buried the telegraph line underground. The six wires were insulated with rubber and placed in a glass tube. This is the earliest underground cable in the world.
An insulated wire composed of one or more mutually insulated conductive cores placed in a sealed jacket. A protective cover layer can be added on the outside for transmission, distribution of electrical energy or transmission of electrical signals. The difference between it and ordinary wires is mainly the larger cable size and the more complicated structure.
The cable is mainly composed of the following 4 parts. ① Conductive wire core: made of high conductivity material (copper or aluminum). According to the requirements of laying conditions on the softness of the cable, each core may be formed by twisting a single conductor or multiple conductors. ②Insulation layer: The insulation material used for cables should have high insulation resistance, high breakdown electric field strength, low dielectric loss and low dielectric constant. Insulation materials commonly used in cables are oil-impregnated paper, polyvinyl chloride, polyethylene, cross-linked polyethylene, rubber, etc. Cables are often classified by insulation materials, such as oil-impregnated paper insulated cables, polyvinyl chloride cables, and XLPE cables. ③ Sealing sheath: protect the insulated core from damage by machinery, moisture, moisture, chemicals, light, etc. For insulation that is susceptible to moisture, lead or aluminum extrusion seal jackets are generally used. ④Protective covering layer: used to protect the sealing sheath from mechanical damage. Generally, galvanized steel tape, steel wire or copper tape, copper wire, etc. are used as armor wrapped around the sheath (called armored cable). The armor layer also serves as electric field shielding and prevents external electromagnetic wave interference. In order to avoid the corrosion of steel belts and steel wires by surrounding media, they are generally coated with asphalt or wrapped with impregnated jute layer or extruded polyethylene or polyvinyl chloride sleeves.