1. Rated voltage (u0/u) of wire and cable products: 300/500V
2. The long-term operating temperature of the wires and cables is 70℃.
3. The ambient temperature during wire and cable laying shall not be lower than: -40℃ for fixed laying, and -15℃ for non-fixed laying.
4. Minimum bending radius of wires and cables: For unarmored cables, it should be less than 6 times the outer diameter of the cable; for armored cables, it should be no less than 12 times the outer diameter of the cable.
5. After being stably charged with a DC 500V voltage for 1 minute at 20℃, the insulation resistance of the wires and cables should not be less than 2500 mΩ·km.
6. There should be no disconnection between each twisted pair of the wires and cables, or between the twisted pairs and the main conductor.
7. The conductors of the wires and cables shall withstand a 50Hz, 2000V AC voltage test for 5 minutes without breakdown between conductors and between conductors.
Detailed introduction to the manufacturing process of wires and cables
1. Copper and aluminum monofilament wires and cables commonly use copper and aluminum rods. At room temperature, these are drawn using a wire drawing machine through one or more drawing dies to reduce their cross-section, increase their length, and improve their strength. Wire drawing is the first process for most wire and cable companies, and the key process parameter is die matching technology.
2. Monofilament Annealing: Copper and aluminum monofilaments are heated to a certain temperature to increase their toughness and reduce their strength through recrystallization, thus meeting the requirements of electrical wires and cables for conductive cores. The key to the annealing process is preventing oxidation of the copper wire.
3. Conductor Stranding: To improve the flexibility of wires and cables and facilitate laying and installation, the conductive core is made of multiple single wires stranded together. Based on the stranding method, it can be divided into regular stranding and irregular stranding. Irregular stranding is further divided into bundle stranding, concentric stranding, and special stranding. To reduce the conductor's footprint and minimize the cable's geometric dimensions, a compaction method is used during conductor stranding, transforming ordinary round conductors into semicircles, fan shapes, tile shapes, and compacted round conductors. This type of conductor is mainly used in power cables.
Extruded plastic-insulated wires and cables mainly use extruded solid insulation layers. The main technical requirements for plastic insulation extrusion are as follows:
Eccentricity: The deviation of the extruded insulation thickness is an important indicator of the extrusion process level. Most product structural dimensions and their deviation values are clearly specified in the standards.
Smoothness: The surface of the extruded insulation layer must be smooth, and there must be no defects such as roughness, burning, or impurities.
Density: The cross-section of the extruded insulation layer must be dense and solid, with no visible gaps or air bubbles.
Technical requirements for cable assembly:
First, it prevents the cable from twisting due to the flipping of irregularly shaped insulated cores; second, it prevents the insulation layer from being scratched. Most cables undergo two additional processes during cabling:
Secondly, filling is used to ensure the roundness and stability of the cable after cabling; the third is binding to ensure that the cable core does not loosen.
In order to protect the insulated conductor from damage by the armor, the inner sheath needs to be properly protected.
The inner sheath consists of two parts: an extruded inner sheath (isolation sleeve) and a wrapped inner sheath (pad). The wrapped pad replaces the binding tape and is installed simultaneously with the cabling process.
Armored cables laid underground may be subjected to a certain amount of positive pressure during operation; therefore, an inner steel tape armor structure can be selected. For cables laid under both positive pressure and tensile force, a structure with inner steel wire armor should be selected. The outer sheath is the structural part that protects the insulation layer of the wire or cable from environmental corrosion. The main functions of the outer sheath are to improve the mechanical strength of the wire or cable, resist chemical corrosion, prevent moisture, prevent water immersion, and prevent the cable from burning. Depending on the different requirements of the cable, a plastic sheath is directly extruded using an extruder.
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