China Zhenglan Cable Technology Co., Ltd Company News

  In practical applications, the design of compressed copper conductors needs to consider many factors, including compression coefficient, stranding structure, material resistivity, etc.   For example, for a 95 mm² compressed copper conductor, its kilometer resistance should not exceed 0.193Ω/km, which needs to be achieved through a reasonable stranding structure and single wire diameter.   The compression process will increase the resistivity of the conductor, so it is necessary to introduce corresponding correction factors during design, such as compression coefficient K3 and stranding coefficient K2, to ensure that the final resistance value meets the standard requirements.     The relationship between the cross-sectional area and DC resistance of compressed copper conductors can be summarized by the following points: 1. Inverse relationship: The cross-sectional area A is inversely proportional to the DC resistance R, that is, the larger the cross-sectional area, the smaller the DC resistance. 2. Compression effect: The compression process will cause the conductor to harden, thereby increasing the resistivity, which needs to be adjusted through the correction factor. 3. Design requirements: According to national standards (such as GB/T3956), the DC resistance value of the conductor is the key indicator to measure its qualification, and the cross-sectional area is only the basis for design and calculation. 4. Adjustment in practical application: In the production process, in order to reduce costs, the cross-sectional area may be reduced to the minimum value to meet the DC resistance requirements, but this practice may affect the overall performance of the cable.   Therefore, when designing and manufacturing compressed copper conductors, it is necessary to comprehensively consider factors such as cross-sectional area, compression coefficient, and material resistivity to ensure that the DC resistance of the conductor meets the standard requirements and meets the performance requirements in practical applications.   The specific calculation method of the compression coefficient K3 and twisting coefficient K2 of the compressed copper conductor is as follows: Compression coefficient K3： Compression coefficient K3 refers to the ratio of the actual cross-sectional area of ​​the conductor after compression to the theoretical cross-sectional area when not compressed. According to the evidence, the value of the compression coefficient is usually 0.90, which is empirical data based on production experience and process tests.   Twisting coefficient K2 ： The twisting coefficient K2 refers to the ratio of the actual length of a single wire to the length of the twisted wire pitch within a twist pitch. Other related parameters 1. Single wire diameter: For stranded conductors with a single wire diameter greater than 0.6 mm, K2 is 1.02; for stranded conductors with a single wire diameter not greater than 0.6 mm, K2 is 1.04. 2. Cabling coefficient: For single-core and non-cabled multi-core cables, it is 1, and for cabled multi-core cables, it is 1.02.   In summary, the specific calculation method of the compaction coefficient K3 and twisting coefficient K2 of compacted copper conductors is as follows: Compressive coefficient K3: Usually the value is 0.90.

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Flame-retardant wire refers to wires that are fireproof and flame-retardant. Generally, under test conditions, after the wire is burned, if the power is cut off, the fire will be controlled within a certain range and will not spread. It has the performance of flame retardancy and suppression of toxic smoke. As an important part of electrical safety, the selection of materials for flame-retardant wires is crucial. At present, the commonly used flame-retardant wire materials on the market include PVC, XLPE, silicone rubber, and mineral insulation materials. Material selection of flame-retardant wires and cables The higher the oxygen index of the material used for flame-retardant cables, the better the flame-retardant performance, but as the oxygen index increases, some other properties will be lost. If the physical properties and process properties of the material are reduced, the operation is difficult, and the material cost is increased, so the oxygen index should be reasonably and appropriately selected. Generally, if the oxygen index of the insulating material reaches 30, the product can pass the test requirements of Class C in the standard. If the sheath material and the filling material are both flame-retardant materials, the product can meet the requirements of Class B and Class A. Materials for flame-retardant wires and cables are mainly divided into halogen-containing flame-retardant materials and halogen-free flame-retardant materials;   1. Halogen-containing flame-retardant materials decompose and release hydrogen halides when heated during combustion. Hydrogen halides can capture active free radicals HO roots, thereby delaying or extinguishing the combustion of the material and achieving the purpose of flame retardancy. Commonly used materials include polyvinyl chloride, chloroprene rubber, chlorosulfonated polyethylene, ethylene propylene rubber, etc. 1) Flame-retardant polyvinyl chloride (PVC): Due to its low price, good insulation, and flame retardancy, polyvinyl chloride is widely used in ordinary flame-retardant wires and cables. To improve the flame retardancy of PVC, halogen flame retardants (decabromodiphenyl ether), chlorinated paraffin, and synergistic flame retardants are often added to the formula to improve the flame retardancy of polyvinyl chloride; Ethylene propylene rubber (EPDM): It is a non-polar hydrocarbon with excellent electrical properties, high insulation resistance and low dielectric loss, but EPDM is a flammable material. It is necessary to reduce the degree of cross-linking of EPDM and reduce the low molecular weight substances produced by molecular chain disconnection to improve the flame retardancy of the material; 2) Low smoke and low halogen flame retardant materials are mainly for polyvinyl chloride and chlorosulfonated polyethylene. Add CaCO3 and A(lOH)3 to the formula of polyvinyl chloride. Zinc borate and MoO3 can reduce the HCL release and smoke of flame-retardant polyvinyl chloride, thereby improving the flame retardancy of the material and reducing the emission of halogen, acid mist and smoke, but may slightly reduce the oxygen index.   2. Halogen-free flame retardant materials Polyolefin is a halogen-free material composed of hydrocarbons. It decomposes carbon dioxide and water when burned, and does not produce obvious smoke and harmful gases. Polyolefins mainly include polyethylene (PE) and ethylene-vinyl acetate (E-VA). These materials themselves are not flame retardants, and inorganic flame retardants and phosphorus series flame retardants need to be added to be processed into practical halogen-free flame retardant materials; however, due to the lack of polar groups on the molecular chain of non-polar substances, they are hydrophobic and have poor affinity with inorganic flame retardants, making it difficult to combine firmly. To improve the surface activity of polyolefins, surfactants can be added to the formula; or polymers containing polar groups can be mixed into polyolefins for blending, thereby increasing the amount of flame retardant fillers, improving the mechanical properties and processing properties of the material, and obtaining better flame retardancy. It can be seen that flame-retardant wires and cables are still very advantageous and are very environmentally friendly to use.

Shielded cable is a cable used to transmit signals. It has shielding properties and is used to prevent external electromagnetic interference from affecting its transmission effect. It usually has a conductive shielding layer to isolate or absorb the radiation of external electromagnetic fields. 1. Metal shielding Metal shielding is a shielding method mainly used for high-frequency signal transmission. It usually includes two forms: copper foil shielding and copper mesh shielding. Copper foil shielding is to wrap copper foil around the insulator and core wire to form a shielding layer around the entire wire. Copper mesh shielding is to weave copper wire into a mesh and put it on the outer layer of the wire. Its shielding performance is slightly inferior to copper foil shielding. 2. Aluminum-plastic composite shielding Aluminum-plastic composite shielding refers to the inner core wire covered with a layer of aluminum-plastic composite material, the outer layer is aluminum foil, and the inner layer is plastic film. Aluminum-plastic composite shielding can achieve a good shielding effect, and has the good electrical properties of the outer layer of aluminum foil and the protective effect of the inner layer of plastic film, especially suitable for low-frequency signal transmission. 3. Copper tape shielding Copper tape shielding is to wrap a layer of copper tape around the outside of the core wire, which can achieve shielding of external electromagnetic fields through grounding. Copper tape shielding has a better shielding effect and is suitable for occasions where both high-frequency and low-frequency signals are transmitted. In short, the application range of shielded cables is becoming more and more extensive. Its different shielding methods are suitable for different transmission frequencies and occasions. Users need to choose cables according to their specific application requirements. Different shield has different functions. Please choose as per your own situation.

1.1 The selection of cable insulation type shall comply with the following provisions: 1 Under the operating voltage, working current and its characteristics and environmental conditions, the cable insulation characteristics shall not be less than the normal expected service life. 2 It shall be selected based on factors such as operational reliability, ease of construction and maintenance, and the comprehensive economy of the maximum allowable operating temperature and cost. 3 It shall meet the requirements of fire-proof places and shall be conducive to safety. 4 When it is clear that it needs to be coordinated with environmental protection, environmentally friendly cable insulation types shall be selected. 1.2 The selection of insulation types for commonly used cables shall comply with the following provisions: 1 The selection of insulation types for medium and low voltage cables shall comply with the provisions of Articles 1.3 to 1.7 of this Code. Low voltage cables shall use polyvinyl chloride or cross-linked polyethylene extruded insulation types, and medium voltage cables shall use cross-linked polyethylene insulation types. When it is clear that it needs to be coordinated with environmental protection, polyvinyl chloride insulated cables shall not be used. 2 Cable lines in high-voltage AC systems shall use cross-linked polyethylene insulation types. In areas with more operating experience, self-contained oil-filled cables can be used. 3 For high-voltage direct current transmission cables, non-drip-impregnated paper insulation and self-contained oil-filled types can be selected. When it is necessary to increase the transmission capacity, it is advisable to select a type constructed with semi-synthetic paper materials. Ordinary cross-linked polyethylene cables should not be used for direct current transmission systems. 1.3 For mobile electrical equipment and other circuits that are often bent or have high flexibility requirements, rubber insulation and other cables should be used. 1.4 In places where radiation is applied, cables with radiation irradiation strength such as cross-linked polyethylene or EPDM insulation should be selected according to the requirements of the insulation type. 1.5 In places with high temperatures above 60°C, heat-resistant cables such as heat-resistant polyvinyl chloride, cross-linked polyethylene or EPDM insulation should be selected according to the requirements of the high temperature, its duration and the insulation type; in high-temperature environments above 100°C, mineral insulated cables should be selected. Ordinary polyvinyl chloride insulated cables should not be used in high-temperature places. 1.6 In low-temperature environments below -15°C, cross-linked polyethylene, polyethylene insulation, and cold-resistant rubber insulation cables should be selected according to the low-temperature conditions and insulation type requirements. Polyvinyl chloride insulated cables should not be used in low-temperature environments. 1.7 In crowded public facilities and places with low-toxic flame retardancy and fire protection requirements, cross-linked polyethylene or ethylene-propylene rubber and other halogen-free insulated cables can be used. When low toxicity is required for fire protection, polyvinyl chloride cables should not be used. 1.8 Except for the cases required by Articles 1.5 to 1.7 of this Code, polyvinyl chloride insulated cables can be used for circuits below 6kV. 1.9 For 6kV important circuits or cross-linked polyethylene cables above 6kV, the type with the characteristics of inner and outer semi-conductive and insulating layers co-extrusion process should be selected.   The difference between polyethylene, polyvinyl chloride, cross-linked polyethylene, and ethylene-propylene rubber materials： The difference between the four materials 1. Polyethylene. English abbreviation PE, it is a polymer of ethylene, non-toxic. Easy to color, good chemical stability, cold resistance, radiation resistance, and good electrical insulation. 2. Polyvinyl chloride. English abbreviation PVC, it is a polymer of vinyl chloride. It has good chemical stability and is resistant to acids, alkalis, and some chemicals. It is resistant to moisture, aging, and flame retardant. The temperature when it is used cannot exceed 60°C (polyvinyl chloride will release toxic HCl smoke when burning), and it will harden at low temperatures. Polyvinyl chloride is divided into soft plastics and hard plastics. 3. Cross-linked polyethylene. XLPE in English is an important technology to improve the performance of PE. PE modified by cross-linking can greatly improve its performance, not only significantly improving the mechanical properties, environmental stress cracking resistance, chemical corrosion resistance, creep resistance, and electrical properties of PE, but also significantly improving the temperature resistance level, which can increase the heat resistance temperature of PE from 70°C to above 90°C, thereby greatly broadening the application range of PE. At present, cross-linked polyethylene (XLPE) has been widely used in pipes, films, wire and cable materials, and foam products. 4. Ethylene propylene rubber (EPR). The full name is cross-linked ethylene-propylene rubber, which has oxygen resistance, ozone resistance and partial discharge stability; the dielectric loss factor is large, so it is only used in power cable lines with voltage levels below 138kV. Due to the good water resistance of EPDM, EPDM cables are suitable for submarine cables, and because EPDM has good softness, it is more suitable for laying in mines and ships.