The manufacturing process of power cables

2023-05-25 09:57:11

Every day, we produce power cables, with over 100,000 meters of cables and 50,000 plugs daily. Such massive production volumes require extremely stable and mature manufacturing processes.

1. Copper and aluminum single wire drawing for power cables

The commonly used copper and aluminum rods for power cables are processed through one or several drawing dies on a wire drawing machine at room temperature, reducing their cross-sectional area, increasing their length, and improving their strength. Drawing is the first step in the production process of most wire and cable companies, with die matching technology being the primary technical parameter.

2. Single wire annealing of Power cords

Copper and aluminum monofilaments are heated to a certain temperature to enhance their ductility and reduce their strength through recrystallization, meeting the requirements for conductive wire cores in cables. The key to the annealing process is to prevent the oxidation of copper wire

3. Stranding of Power Cable Conductors

To enhance the flexibility of power cables for easier installation, the conductive wire core is formed by twisting multiple single wires together. Based on the twisting method of the conductive wire core, it can be categorized into regular and irregular twisting. Irregular twisting further includes bundled twisting, concentric double twisting, and special twisting. To reduce the occupied area of the conductor and minimize the geometric dimensions of the power cable, the twisted conductor also adopts a compacting method, transforming the standard circular shape into semi-circular, fan-shaped, latticed, or compacted circular forms. This type of conductor is primarily used in power cables.

4. Insulation extrusion of power cables

Plastic power cables primarily adopt an extruded solid insulation layer, with the key technical requirements for plastic insulation extrusion being:

4.1. Bias Degree: The deviation value of the extruded insulation thickness is a key indicator of the extrusion process level. Most product structural dimensions and their deviation values are clearly specified in the standards.

4.2. Lubricity: The surface of the extruded insulation layer must be smooth and free from defects such as roughness, scorching, or impurities

4.3. Density: The cross-section of the extruded insulation layer must be dense and robust, free from visible pinholes and devoid of any bubbles.

5. Power cords are bundled together

For multi-core power cables, to ensure proper shaping and minimize the outer profile, the conductors are typically twisted into a circular form. The twisting mechanism resembles that of conductor stranding, but due to the larger lay length, most methods employ untwisting. The technical requirements for stranding include: first, preventing the reversal of non-circular insulated cores, which could cause cable kinking; second, avoiding damage to the insulation layer.

Most cables are accompanied by two additional processes during the cabling: one is filling, which ensures the roundness and stability of the cable after cabling; the other is stranding, which prevents the cable core from loosening.

6. Inner sheath of power cable

To protect the insulation core from damage by armor, proper maintenance of the insulation layer is required. The inner sheath is divided into: extruded inner sheath (isolating sleeve) and wrapped inner sheath (padding layer). The wrapped padding layer replaces strapping and is performed synchronously with the cable assembly process.

7. Power cable armor installation

Underground power cables should be capable of withstanding inevitable compressive forces during installation and may be constructed with internal steel strip armor. For power cables laid in environments subjected to both compressive and tensile forces (such as underwater, vertical shafts, or soil with significant elevation differences), a construction type with internal steel wire armor should be selected.

8. Outer sheath of power cord

The outer sheath is a structural component that maintains the insulation layer of the power cord to prevent corrosion of elements. The primary effect of the outer sheath is to improve the mechanical strength, chemical resistance, moisture resistance, water immersion resistance, and prevent the power cord from burning. According to the divergent requirements for the power cord, an extruder should be used to directly extrude the plastic sheath.