Wire and cable commonly used plastics are polyethylene, polyvinyl chloride, cross-linked polyethylene, fluorine plastics, polypropylene, polyolefins, nylon and so on.

Polyethylene is currently the most widely used and largest amount of plastic. According to the data in the table, polyethylene has a low meson consumption, high resistivity, high breakdown field strength, good weatherability, and good processability. It is currently the best. Electrical insulation material. However, due to its low operating temperature, it is mainly used as insulation for communication cables. Medium density and high density polyethylene have high strength and hardness, low water permeability, and are mostly used as cable jackets. However, polyethylene has the biggest drawback, that is, it is easy to burn, and the black smoke is strong, so its application brings many hidden troubles to the environment.

Cross-linked polyethylene is an excellent thermosetting insulation material formed by adding cross-linking agent using low-density polyethylene. It inherits the excellent performance of polyethylene, improves the mechanical properties, weatherability and allowable working temperature, thus becoming the best insulation material for power cables.

Due to the different addition of cross-linking agents, different cross-linking processes are formed. At present, there are three kinds of chemical crosslinking, warm water crosslinking, and radiation crosslinking. Chemical cross-linking is mainly used for medium and high voltage cables (such as 10KV and above); warm water cross-linking and irradiation cross-linking are mainly used for low-voltage cables (1kV and below).

Cross-linked polyethylene's insulation properties are closely related to its purity. The insulation of high voltage and ultra-high voltage cables above 35KV shall be ultra-clean cross-linked polyethylene, which not only requires high purity of raw materials, but also requires high cleanliness of the cross-linking process equipment and environment, and the process is stable and reliable.

It should be particularly pointed out that the insulation properties of polyethylene and cross-linked polyethylene have a "strange" that is suitable for AC insulation, but not suitable for DC insulation, in particular DC high voltage will reduce its insulation life. Therefore, DC cable insulation is more than rubber insulation or oil paper insulation. Furthermore, polyethylene and cross-linked polyethylene are insulated from "hydrophobia", and their breakdown is often associated with the presence of water, ie, the formation of "water branches" at high voltages, resulting in damage to the insulation. Therefore, when polyethylene and cross-linked polyethylene are used as insulation for high-voltage and extra-high-voltage cables, they are particularly "escaped from water" in their processing, storage, and insulation extrusion processes, and the cable insulation shield must have a water-blocking structure such as metal. jacket.

Compared with polyethylene, polyvinyl chloride and paper insulation, one of the greatest advantages of cross-linked polyethylene insulation is that the operating temperature is increased by 20°C, which improves the safety of the cable and reduces the input cost of the cable. For example, when the line flow is the same (such as 300A), the cross-sectional area of ​​the copper conductor of polyethylene or PVC insulated cable (such as YV or VV type) needs 120mm2, and the cross-sectional area of ​​the copper conductor of the cross-linked polyethylene insulated belt is only required. 70mm2 is sufficient. It can be seen that the advantages of cross-linked polyethylene insulated cables are so remarkable.

PVC has excellent physical and mechanical properties and excellent process performance. It is the most commonly used plastic in the 20th century, and it is also the main insulation material and sheathing material of low-voltage wire and cable. However, in the 21st century, PVC will gradually shrink or even fade out in the cable market. There are two reasons for this. On the one hand, people's awareness of safety has increased, and they hope to use halogen-free materials. Therefore, many halogen-free materials have emerged. It will undoubtedly become the new darling of the cable industry in the 21st century and squeeze the market.

On the other hand, polyvinyl chloride has five disadvantages:

First, the density is about 1.5 times that of cross-linked polyethylene, and the insulation cost is higher;

Second, the working temperature is low;

Third, the dielectric loss is high, more than 100 times higher than cross-linked polyethylene;

Fourth, poor cold resistance (-15 degrees becomes brittle);

The fifth is the release of toxic gas (HCL) during combustion.

In recent years, the development of cross-linked polyvinyl chloride mechanical properties, electrical and thermal properties, insulation resistance has been greatly improved, some small cross-section cables use the irradiation process to enter the market, in the device device wire, high voltage lead wire, automotive wire and building wiring aspects Application, but its disadvantage of having halogen is not changeable.

Fluoroplastics are widely used in wire and cable because of its high working temperature, small medium, insulation, weather resistance, acid and alkali resistance, oil resistance, and good flame retardancy. Among them, polyfluorinated ethylene propylene is popular because of its good processability. But its price is expensive and users have to think twice.

Low-smoke halogen-free polyolefins are new types of cable sheathing materials that have not been developed in the 20th century. His greatest advantage is that they are flame-retardant, and they are small and non-toxic when burned. They are increasingly used in important public buildings.

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