The basic structure of the wire

1. Single round wire The main varieties are copper single wire, aluminum single wire and copper-aluminum alloy wire. The diameter of the wire is used as the structural parameter, ranging from 0.01mm to 3.00mm. Except for some of the round single wires used directly as products, most of them are semi-finished products used by twisting single wires into multiple twisted wires.
In addition to the round single wire of a single material, there are also compound round single wires. Commonly used are bimetal round single wires, such as aluminum clad steel wire (high conductivity of aluminum, strong tensile strength of steel wire), copper clad aluminum wire (high conductivity of copper, light aluminum) and coated single wire, such as tinned copper wire, Nickel-plated copper wire.
2. The round stranded wire and cable are products of large length, which have to withstand many times of winding and unwinding during production, installation and use. If the wires with larger cross-sections are not used to twist small-diameter single wires into a certain cross-section Twisted wire, the product cannot be manufactured and used. Different use conditions and conditions require wires and cables to have different flexibility-that is, bendable or twistable. Therefore, the stranded wires used in various products have different requirements in terms of flexibility, etc. Therefore, 7 kinds of wire structures are specified in the wire standard. Table 1 is the wire structure specified by the standard.

Wires with the same material and the same cross-section can be composed of several structures, that is, the number and diameter of single wires are different. The more single wires in the same cross-section (the thinner the single wire diameter), the higher the flexibility of the wire.
The structural parameters of  round stranded wire are the cross-sectional area of ​​the wire (in mm2), the number of single wires and the diameter (mm), the stranded pitch diameter ratio, etc.
3. Derivative structure of round stranded wire
(1) Compact round stranded wire In the wire stranding process, the stranded wire is pressed tightly by means of a pressing wheel, etc., so that the conductor occupancy rate in the cross-section reaches about 90%. One is to flatten the protruding shape of the wire surface, which is beneficial to squeeze the thin (0.5-1mm), inner semiconductor layer (for uniform electric field) of the medium and high voltage XLPE cable, which is not easy to puncture. The second is to reduce the gap between the single lines.

(2) The diameter of the inner groove of the round stranded wire with inner hollow groove is generally 14-18mm. There are two kinds of product requirements, namely, oil-filled cables are used as oil grooves for oil flow, and high-current cables are used as channels for internal cooling through gas or liquid. (Can increase the energizing capacity). The conductor of the oil-filled cable is generally formed by twisting a Z-line or arc-shaped single wire to form a ring-shaped cross-section, and it can also be formed by twisting a round single wire into a spiral tube. As the internal cooling type forced cooling, the internal hole groove adopts a sealed metal tube.
(3) The sector conductor is the conductor structure used in the medium and low voltage 3-4 core oil-paper insulated power cable (1-10kv). It is used to make the insulated cores of the paper wrap insulation into three 120 shapes, which are twisted into a circle when the cable is formed. Shape (four-core cable is three 100, and the neutral wire 60 is sector-shaped), in order to save a lot of outer material. The line is rarely used.