Which conductor is used in underground cables?

Explanation:

Construction of Underground Power Cables:

Conductor:

• Usually, 1 or 3 conductors (depending on the application) are used.
• These conductors are stranded to reduce skin effects, and proximity effects and to keep them flexible.
• Conductors are made from electrolytic-grade pure copper.

Conductor screen:

• It is a semi-conducting tape or an extruded layer of a semi-conductive compound.

Insulation:

• It is provided to withstand electrostatic stress.
• Various types (and thicknesses) of insulators like VIR (Vulcanized India Rubber), Impregnated paper, PVC (polyvinyl chloride), and XLPE (Cross-linked polyethylene) are utilized depending upon the applied voltage.

Insulation screen:

• A layer of semi-conductive material is generally used in MV (medium voltage) and HV (high voltage) lines.
• It serves a similar purpose as that of the conductor screen.

Metallic Sheath:

• It provides protection to the cable from moisture and other chemicals (acids or alkalies) present in the environment or soil.
• It’s usually made up of Aluminium or Lead.
• It also provides a path for fault and leakage currents as the sheath is earthed at one cable end.

Bedding:

• It is a low-grade insulator like Jute or Hessian which protects the metallic sheath from corrosion and from mechanical injury due to armoring.

Armoring:

• It provides mechanical protection from various stresses the cable may get exposed to during its installation and operational life.
• It’s usually a steel tape wound around the Bedding layer.

Serving:

• Another layer of low-grade insulators like Jute or Hessian or a thermoplastic compound like PVC is again provided to protect the steel from atmospheric contaminants and agents.