Insulating Materials Used in Underground Cables Construction

There is a big list, but the most common insulating materials used in underground cables construction are:
 
Poly Vinyl Chloride (PVC): It is a thermoplastic synthetic compound. It is generally used to insulate the cables. It has a good dielectric strength (17 kV/mm) and a maximum continuous temperature rating of 75oC. The PVC cables can be bent to smaller radii which makes them particularly suitable for laying in industrial places. Due to a high dielectric, mechanical strength, and exceptional resistance to moisture, the PVC cables have almost completely replaced the paper and rubber insulated cables in the range up to 11 kV.
 
Impregnated Paper: Paper is a very good and cheap insulating material. But it is hygroscopic in nature due to which its insulation properties get destroyed due to the ingress of moisture. To resolve this problem it is impregnated with some compounds such as paraffinic or naphthenic material. The ends of paper insulated cables should always be kept sealed to make them moisture tight. Moisture can also enter through small pin-holes and cracks in the sheathing which may not be visible to the naked eye. Therefore, these cables are invariably metal-seated to provide protection against ingress of moisture. It has high dielectric strength (40 – 50 kV/mm) and a continuous temperature rating of 80oC. It is used in high voltage power cable manufacturing.
 
Cross-Linked Polyethylene: The cables using cross-linked polyethylene as the insulating material is known as XLPE cables.

• It has high dielectric strength (20 – 40 kV/mm) and a continuous operating temperature rating of 90o
• It is non-inflammable, light in weight, flexible, mechanically strong, moisture absorption resistant, and has an extremely high melting point.
• These cables are directly laid on the soil bed and are used for voltages up to 33 kV.

 
Asbestos: Asbestos-insulated cables can withstand higher operating temperatures than paper, rubber, PVC, and varnished cambric cables. They are suitable for dry locations only as asbestos absorbs moisture. The operating temperature range is 100o – 200 degree depending upon the asbestos compound.
 
Glass, quartz, and silicon-rubber insulated cables are used where the operating temperature is above 105 degree