In order to increase the flexibility or curvature of the cable, a larger cross-section cable core is formed by stranding multiple smaller diameter wires. The core twisted by a plurality of wires has good flexibility and large curvature, because when a single metal wire is bent along a certain radius, the centerline is stretched outside, and the centerline is compressed inside. If the core is composed of multiple wires placed in parallel, because the wires can slide between. Therefore, it is much less laborious to make the same bend for a single wire of the same cross-section. In order to ensure the stability of the shape of the wire core structure and reduce the deformation of each wire when the wire core is bent, the wire core composed of multiple wires needs to be twisted.
As shown in the actual case, when the parallel conductors are bent and then straightened, the plastic deformation of the conductors may cause projections on the surface of the core, causing distortion of the electric field distribution in the cable insulation and damaging the cable insulation. In the twisted cable core structure, since the inner and outer portions of the core center line can move and compensate each other, the plastic deformation of the wire is not caused during bending, so the flexibility and stability of the core are greatly improved, and the twisting section is greatly improved. The smaller the distance, the higher the softness and stability of the core. In addition, the twisted wire is different from a single wire with a large section, and the bending is more smoothly distributed on a section of the wire core, so that the cable insulation is not easily damaged when the wire is bent.
Different cable applications have different requirements for the curvature of the cable core. The requirements for higher curvature are mobile cables, which are mostly made of rubber or plastic as the insulating material. The oil-impregnated paper-insulated power cable has a low curvature. This is because the bendability of the oil-impregnated paper-insulated power cable is mainly determined by the sheath structure, and the wire core has less influence on the bendability of the cable. Generally, only the wire is required. The core will not damage the insulation during production, installation and installation.
In general, the twisted form of the cable core can be divided into two broad categories, namely regular twisting and irregular twisting.
The rules are twisted. The regular, concentric and contiguous strands of conductors in different directions are called regular strands. Regular stranding can be further divided into normal and irregular stranding. The former refers to the same diameter of all the constituent wires, and the latter refers to the regular twisting of layers with different diameters of wires between layers. In addition, there are simple and complex divisions of the regular stranding. The latter refers to the fact that the constituent strands are not single strands, but are made up of finer strands that are regularly stranded and then stranded. This structure makes the core more flexible, common in mobile rubber insulated cable, the general power cable is the most common simple and regular twisting. therefore? Unless otherwise specified, regular twisting generally refers to simple normal regular twisting.
Irregular stranding. Refers to all the components of the wire are twisted in the same direction, also known as bundles. Although the stranding process is simple, the cost is low, the fill factor of the core is high, the outer diameter of the same cross-sectional area is small, and the curvature can be high, but due to its poor structural stability, the power cable is generally not bundled and insulated. Flexible strands or rubber insulated cables with lower voltage ratings are often used for stranding.
The ratio of the actual area of ​​the core conductor to the area of ​​the outline of the core is defined as the fill factor of the core. The fill factor of the regular twisted wire core is not only related to the number of single core layers of the core, but also related to the number of core conductors in the core. As actually shown, when the center conductor is one, the fill factor of the twisted wire core decreases as the number of layers increases, and the core fill factor of the five central conductors increases as the number of layers increases, but The absolute value is less than the number of center conductors. From the viewpoint of improving the core fill factor and stability, the regular twisted structure with one wire at the center is the best. Therefore, the power cable generally adopts a regular twisted structure with a wire as the center.
In order to increase the cable core fill factor, save material, and reduce costs, many cable cores are pressed against the core structure. After the core is pressed tightly, each wire is no longer round, but has an irregular shape, and the original gap portion is filled with the wire deformation, such as the actual pressing of the circular core section.
As shown in the actual case, when the parallel conductors are bent and then straightened, the plastic deformation of the conductors may cause projections on the surface of the core, causing distortion of the electric field distribution in the cable insulation and damaging the cable insulation. In the twisted cable core structure, since the inner and outer portions of the core center line can move and compensate each other, the plastic deformation of the wire is not caused during bending, so the flexibility and stability of the core are greatly improved, and the twisting section is greatly improved. The smaller the distance, the higher the softness and stability of the core. In addition, the twisted wire is different from a single wire with a large section, and the bending is more smoothly distributed on a section of the wire core, so that the cable insulation is not easily damaged when the wire is bent.
Different cable applications have different requirements for the curvature of the cable core. The requirements for higher curvature are mobile cables, which are mostly made of rubber or plastic as the insulating material. The oil-impregnated paper-insulated power cable has a low curvature. This is because the bendability of the oil-impregnated paper-insulated power cable is mainly determined by the sheath structure, and the wire core has less influence on the bendability of the cable. Generally, only the wire is required. The core will not damage the insulation during production, installation and installation.
In general, the twisted form of the cable core can be divided into two broad categories, namely regular twisting and irregular twisting.
The rules are twisted. The regular, concentric and contiguous strands of conductors in different directions are called regular strands. Regular stranding can be further divided into normal and irregular stranding. The former refers to the same diameter of all the constituent wires, and the latter refers to the regular twisting of layers with different diameters of wires between layers. In addition, there are simple and complex divisions of the regular stranding. The latter refers to the fact that the constituent strands are not single strands, but are made up of finer strands that are regularly stranded and then stranded. This structure makes the core more flexible, common in mobile rubber insulated cable, the general power cable is the most common simple and regular twisting. therefore? Unless otherwise specified, regular twisting generally refers to simple normal regular twisting.
Irregular stranding. Refers to all the components of the wire are twisted in the same direction, also known as bundles. Although the stranding process is simple, the cost is low, the fill factor of the core is high, the outer diameter of the same cross-sectional area is small, and the curvature can be high, but due to its poor structural stability, the power cable is generally not bundled and insulated. Flexible strands or rubber insulated cables with lower voltage ratings are often used for stranding.
The ratio of the actual area of ​​the core conductor to the area of ​​the outline of the core is defined as the fill factor of the core. The fill factor of the regular twisted wire core is not only related to the number of single core layers of the core, but also related to the number of core conductors in the core. As actually shown, when the center conductor is one, the fill factor of the twisted wire core decreases as the number of layers increases, and the core fill factor of the five central conductors increases as the number of layers increases, but The absolute value is less than the number of center conductors. From the viewpoint of improving the core fill factor and stability, the regular twisted structure with one wire at the center is the best. Therefore, the power cable generally adopts a regular twisted structure with a wire as the center.
In order to increase the cable core fill factor, save material, and reduce costs, many cable cores are pressed against the core structure. After the core is pressed tightly, each wire is no longer round, but has an irregular shape, and the original gap portion is filled with the wire deformation, such as the actual pressing of the circular core section.
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