Plastic in Common Use for Wire and Cable ( I )
Polythene, crosslinked polyethylene, polyvinyl chloride, polypropylene, polyolefin, fluoroplastics and nylon are commonly used in wire and cable.
Polyethylene is the most widely used and the largest quantity of plastic. Polyethylene has small dielectric loss, high resistivity, high breakdown field strength, weatherability and good technology, which is the best electrical insulating material at present. But because of its low working temperature, it is mainly used as the insulation of the communication cable. The strength and hardness of medium density and high density polyethylene are high, and its water permeability is low, and it is used as a cable sheath. However, polyethylene has the biggest disadvantage, that is, easy to burn and strong black smoke, so its application has brought many hidden dangers to the environment.
Crosslinked polyethylene (XLPE) is an excellent thermosetting insulating material formed by adding low density polyethylene to crosslinker. It improves the mechanical properties, weatherability and permissible working temperature on the basis of inheriting many excellent properties of polyethylene, and has become the best insulating material for power cables at present.
Different crosslinking agents have been added, so different crosslinking processes have been formed. At present, three kinds of chemical crosslinking, warm water crosslinking and irradiation crosslinking are the most used. Chemical crosslinking is mainly used in medium and high voltage cables (such as 10KV and above); warm water crosslinking and irradiation crosslinking are mainly used for low voltage cables (1kV and below).
The insulation property of XLPE has a close relationship with its purity. The insulation of high voltage and extra high voltage cables above 35KV must be super clean crosslinked polyethylene, which not only requires high purity of raw materials, but also requires high cleanliness of cross-linking process equipment and environment, and stable and reliable process.