This is the conductor of the power cableTypical twisting methodFrom the centerline or fromComposed of a core surrounded by one or more layers of spiral wires.Add an extra layer each timeJust need toCompared to the previous layerSix more wire coresExcept for conductors twisted in one direction, the twisting direction of each layer is opposite to the layer below. For the conductors of power cables,The core is a single wireAnd the twisted ones are allSame alwaysDiameter of wireAs shown in Figure 3-1, there are 6 wires in the first layer outside the core; Second layer, 12 pieces; Third layer, 18 pieces; and so on.The distance that a single wire of a conductor completes a complete spiral within one layercalledpitchThe requirements for pitch are specified in Part IV of the ASTM standard，The pitch should be between 8-16 times the outer diameter of the corresponding hinge layer.

The weight of C-grade and D-grade conductors is similar to that of B-grade conductors, with an outer diameter within a range of 3mil larger than that of B-grade conductors.

The following formula can be used to calculate the number of single wires in a concentric stranded conductor.

n=1+3N（N+1）  （3-3）

In the formula, n is the total number of single wires in the twisted conductor; N is the number of layers outside the central single line.

  3.6.2 Tight compression twisting

This concept describes the tight bonding of the layers through slight deformation of the layers. The conductor area has not decreased. The final diameter of the compressed conductor can be reduced by no more than 3% compared to the equivalent diameter of a regular concentric twisted core conductor. The general reduction is 2.5%.

Reducing the pitch of the outer layer of the conductor can solve this problem, but it can also lead to high impedance and require more conductor material consumption.

  Tight compression twisting is a more common twisting methodBecauseThe pitch set in concentric twisting results in the formation of small gaps between the layers in the conductorLow viscosity materials "fall" into these gaps formed after being extruded. This willCausing surface irregularities, increasing the voltage to be borne, and making it more difficult to peel off this layer.

 3.6.3 Twisted wires

This method is similar to compression twisting, except that the additional molding process reduces the diameter of the conductor by 9% compared to ordinary concentric twisted conductors. Causing the diameter of the conductor to approximate that of a solid conductor. But the air gap still exists as a migration channel for moisture. The main advantage of twisted conductors is to reduce the diameter of the conductor.

 3.6.4 Bundle twisting

This concept is used to describe the concentrated twisting of a single line in a uniform direction without considering geometric arrangement.

This structure is used for cables with flexibility requirements for small-sized conductors according to the American wire gauge, such as portable cables, and is applied in vacuum cleaners, lawn mowers, and other occasions.

In K-grade and M-grade conductors, the diameter of a single wire is constant. By increasing the number of single wires to meet the required cross-sectional area of the conductor.

  3.6.5 Bundle Wire Twisting

This concept is used forConcentric twisted conductorEach single wire is also twisted. It is a collection of concentric conductors and bundled conductors. The final conductor is composed of a concentric combination of bundled or coaxial twisted conductors. Each group is composed of a certain number of single wires, rather than a single wire twisted together. For the description of bundled twisted conductors, the number of twisted wire groups and the number of single wires in each group should be given.

G-grade and H-grade cables are commonly used for mining portable cables. I. L and M grade cables use twisted cables to form concentric cables with the same single wire size. The required cross-sectional area size is achieved by increasing the number of wires. Grade I cables use # 24AWG (0.020in) single wire, Grade L cables use # 30AWG (0.010in) single wire, and Grade M cables use # 34AWG (0.0063in) single wire. Grade I cables are typically used for railways, while grades L and M are used for more portable applications such as welding cables and mobile power cords.

  3.6.6 Fan shaped conductor

A conductor with an approximate fan-shaped cross-section is called a fan-shaped conductor. A typical three conductor cable has three 120 ° sectors, which form the basic shape of a circular cable. This type of cable has a smaller outer diameter than the corresponding concentric conductor cable, due toReduced proximity effect and can display lower AC impedance.

For paper insulated cables, most of the fan-shaped conductors are twisted and compressed to obtain the highest possible ratio of conductor cross-sectional area to cable cross-sectional area. The precise shape and size of products from different manufacturers may vary slightly.

Within a certain range, solid rather than twisted sector conductors have been used in low-voltage cables, and there have been attempts to use this conductor in medium voltage cables, but due to economic considerations at the time, it has not yet been realized.

  3.6.7 Dividing Conductors

Divide conductors into circles, consisting of three or moreTwisted together into strands，Separate the stock blocks with a thin insulation layerEach block carries a smaller current than the entire conductor, and the current is transmitted through the inner and outer positions of the entire conductor. this kind ofAdvantages of Structurelie inThe skin effect is relatively low, andSmaller skin effectenableThe AC impedance is lower than the traditional twisting method.

This form ofConductors should be considered for use inLike 1000kcmil（Corresponding to metric 507mm2）And in cables with larger cross-sectional areas carrying high currentsThe diameter of a quarter conductor is approximately equal to the diameter of a B-class concentric stranded conductor.

Note: GB/T 18890.2-2015 states that "conductors with a nominal cross-sectional area of 800mm2 or more should use segmented conductor structures"

 3,6.8 Circular conductor (hollow conductor)

A circular conductor is a twisted conductor in which each single wire is twisted around a central fiber rope, threaded metal tube, or I-shaped crossbeam. this kind ofThe advantage of conductors lies in，For conductors with a certain cross-sectional area, it is possible to eliminateSkin effectThe influence in the central position makes the overallAC impedanceshrinkUnder space constraints, for cables with a cross-sectional area of 60Hz, 1000kcmil, and above, as well as 1500kcmil under low-frequency conditions (such as 25Hz)（Corresponding to metric 760mm2）For cable conductors with cross-sectional areas above,Circular conductors are more economical.

  3.6.9 Stranded conductors in the same direction

As its name suggests, all single wires of a co directional conductor face in the same direction. Low voltage power cables are typically designed in the same direction, with a portion of the outer single wires being slightly smaller in diameter than other single wires. This twisting method can achieve an outer diameter similar to that of a twisted conductor. commonly usedConductors in the same direction are tightly compressedCommonly used for 8000 series aluminum alloys.

  Aluminum hydroxide is a white powdery material and a high-quality insulatorNowadays, manyTwisted aluminum conductorUsers are all affected by this reasonRequire the conductor to be water-resistant.Water blocking components such as water blocking strips, water blocking yarns, and other sealing materials are used as longitudinal water blocking materials to delay damage formationCopper conductors can also block water in the same way.

Regardless of the material of the conductor and the degree of compression, air will exist in the gaps of the conductor, which will become storage areas for water vapor and provide moisture for the production of water trees. In order to reduce the possibility of water tree production,Water blocking stranded conductorOften used for underground cables, of course, solid conductors are also used for conductors of size # 2/0 AWG and below for this reason.