A, general
There are hundreds of thousands of wire and cable products, applications in all walks of life. There are two kinds of their total use, one is the transmission current, one is the transmission signal. Current transmission cable is the main control of technical performance indicators is the conductor resistance and pressure resistance; signal transmission cable is mainly controlled by the technical performance indicators is the transmission performance, characteristic impedance, attenuation and crosstalk. Of course, the transmission signal is mainly by the current (electromagnetic wave) as a carrier, and now with the development of science and technology can be used as a carrier to transmit light.
Cable generally can be divided into six categories:
(1) bare class
(2) electromagnetic wire (wire)
(3) power cable
(4) wire and cable for electrical equipment
(5) communication wire and cable
(6) optical cable
Two, the basic structure of the cable
General cable the basic structure of a conductor, insulation layer and an outer protection layer, according to the requirements of add the structure, such as shielding layer, an inner protecting layer or armored layer etc., in order to cable are rounding of the auxiliary filler material. Conductor is the carrier of the transmission current or signal, and other structures are used for protection. Performance of the door according to cable products need generally has three, one is cable protection of the unit itself not to each other or to reduce the impact, such as pressure, heat resistant, anti electromagnetic field to produce a loss, communication cable preventing signal interference and so on. Another door is a protective conductor current closed to the outside influence, such as to prevent the leakage current, electromagnetic wave leakage etc.; finally a protection not to external cable internal impact, such as compressive strength, tensile strength, heat resistance, weather resistance, flame resistance, waterproof, anti electromagnetic wave interference.
The following is a brief introduction to the structural unit of the power cable.
(1) conductor (or conductor):
Its function is conduction current. Have a solid core and stranding points. Materials are copper, aluminum, silver, copper clad steel, aluminum, steel, etc., mainly used in copper and aluminum. The conductivity of copper is much better than that of aluminum. The national standard for the resistivity of copper conductor is not less than 0.017241.Mm2/m (20 C), the resistivity of the aluminum conductor is not less than 0.028264.Mm2/m (20 C).
2) refractory layer:
Only fire resistant cable has this structure. The effect is that the cable can withstand a certain amount of time in the fire, giving them more time to escape. Now used materials are mainly mica tape. In the fire, the cable will soon burn, because the mica tape mica sheet resistance to high temperature, and has the insulation function, in the fire can protect the conductor to run a certain time.
3) insulation:
Coated on the outside of the conductor, the role is to isolate the conductor, to withstand the corresponding voltage, to prevent leakage of current. Insulation materials in a variety of forms, such as polyvinyl chloride (PVC), polyethylene (PE), cross-linked polyethylene (XLPE), rubber (rubber many kinds, Ding nitrile rubber, chloroprene rubber, styrene butadiene rubber, ethylene propylene rubber, fluorine plastic, nylon, insulation paper. These materials are the main performance is the insulation performance is better, and other performance requirements according to the requirements are different, some requirements of dielectric coefficient is smaller, to reduce the loss, have flame retardant properties and can resist high temperature, and some require cable in burning or not produce less smoke and harmful gas, some requirements are tolerant of oil, corrosion resistance, while others require soft in cable.
4) shielding layer:
Outside the insulation layer, the function is to limit the electric field and the electromagnetic interference. For different types of cable, shielding materials are not the same, mainly has: copper wire braided, wrapping copper wire, aluminum wire, aluminum alloy wire) weaving, copper strip, aluminum foil, aluminum (steel) plastic belt, strip, etc. or longitudinally wrap around.
5) filling layer:
Filling the role of the main is to make the cable round the whole, the structure is stable, some cable filler also plays the role of water resistance, fire resistance and so on. The main materials are polypropylene rope, glass fiber rope, asbestos rope, rubber and so on, a lot of kinds, but there is a major performance requirements are non absorbent material, of course, can not be conductive.
6) inner protective layer:
The role of the inner layer is a protective layer or insulated wire core are not shield armor damage. The inner protective layer has several forms, such as extruding, wrapping, longitudinal, and so on. For the requirements of the high demand for the use of a packed form, the requirements of the use of low winding or wrap around the form. Now around the package materials also varied, such as the inner steel tape armored protection layer, using PVC tape wrapped, with PP belt (very thin, surface made of convex particles up together in thickness) around the package. Can not be used? Mainly is the quality of cable products market positioning. This is the use of the silane crosslinked insulation wire core or the use of color to distinguish, the nature of some of the same, but not all the same. Here, PVC tape and polypropylene tape are used to influence the quality of the product. Silane crosslinked insulation line core using color or color to distinguish, the product quality has little impact, mainly the needs of users.
The 7 armored layer):
Armoured role is to protect the cable without damage. The most common is the armored and steel armour, and aluminium armour, stainless steel tape armoured etc.. The main role is to use steel tape armored steel wire armour is mainly compressive, tensile with. According to the size of the cable armouring steel strip thickness is not the same, which are specified in the cable standard.
Outer protective layer 8: the protective effect of components in the outermost layer of the cable.
There are three main types: plastic, rubber and metal.
Among them, the most commonly used plastics are polyvinyl chloride, polyethylene and plastic.
