Wire and cable insulation material selection

Jan 05,2018
Wire and cable insulation material selection

PVC plastic is based on polyvinyl chloride resin, adding a variety of complexing agent mixture. Its excellent mechanical properties, chemical resistance, no fire, weather resistance, good electrical insulation properties, easy processing, low cost, it is a good material for wire and cable insulation and sheathing.

Polyvinyl chloride resin

Polyvinyl chloride resin is a linear thermoplastic polymer made of vinyl chloride polymerization, from the molecular structure, PVC has a carbon chain as the main chain, linear, containing C-Cl polar bonds.

2. The main properties of PVC

1) Electrical insulation properties: PVC resin is a more polar dielectric, better electrical insulation, but slightly less than non-polar materials (such as polyethylene, polypropylene). The volume resistivity of the resin is greater than 1015Ω · cm; the dielectric constant ε of the resin at 25oC and 50Hz are 3.4-3.6, and the dielectric constant changes obviously when the temperature and the frequency change; the dielectric loss of polyvinyl chloride Tangential tgδ is 0.006 to 0.2. The breakdown strength of the resin is not affected by the polarity, the breakdown strength is relatively high at room temperature and power frequency conditions. However, PVC dielectric loss is large, and therefore not suitable for high voltage and high-frequency applications, usually used in low voltage 15kV and medium voltage wire and cable insulation materials.

2) Aging stability: From the molecular structure point of view, chlorine atoms are connected with carbon atoms, should have a high stability to aging. However, in the production process, due to the direct influence of temperature and the action of mechanical force, it is easy to release hydrogen chloride to cause degradation or cross-linking under the action of oxygen, resulting in brittle discoloration of materials, significant decrease of physical and mechanical properties and deterioration of electrical insulation properties, Therefore, PVC aging. To improve its aging, you must add a certain amount of stabilizer.

3) Thermomechanical properties: Polyvinyl chloride resin is an amorphous polymer, which has three physical states at different temperatures, namely glassy state, high-elastic state and viscous flow state. Polyvinyl chloride resin glass transition temperature of about 80oC, viscous flow temperature of about 160oC. At room temperature in a glass state, it is difficult to meet the requirements of wire and cable use. For this reason, it is necessary to modify the polyvinyl chloride so that it has high elasticity at room temperature while having both high heat resistance and zero-resistance. The right amount of plasticizer can adjust the glass transition temperature.

PVC insulated power cables

PVC plastic cheap, good physical and mechanical properties, the process is simple, is commonly used wire and cable insulation materials. Therefore, a large number of the manufacture of 1 kV and below low-voltage power cables for the low voltage distribution system.