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Conductor materials for lines and cables

Short answer

Overhead line conductors include ACSR, AAC, hard-drawn copper, and galvanised steel; underground cables use annealed copper or aluminium. Selection bases: high conductivity, tensile strength, low weight, low cost, corrosion resistance, and large diameter to reduce corona for overhead lines; for cables, flexibility and insulation compatibility are also critical.

List out the materials used in overhead lines and underground cables. What are the bases for selection of conductors for overhead lines and underground power cables?

Materials used

UseConductor materials
Overhead linesHard-drawn copper; aluminium (AAC); ACSR (aluminium conductor steel reinforced); all-aluminium alloy (AAAC); galvanised steel (earth wires, short spans); cadmium copper (long spans)
Underground cablesAnnealed copper; aluminium (stranded, sometimes sector-shaped)

Cable insulation materials include paper impregnated with oil, PVC, XLPE and rubber. Sheaths are lead or aluminium, and armouring is steel tape or wire.

Basis for selecting overhead line conductors

  • High conductivity, for low I2RI^2R loss and voltage drop
  • High tensile strength, to take wind and ice loads and allow long spans with low sag
  • Low weight (density), so that towers are lighter
  • Low cost and easy availability
  • Resistance to corrosion and weather
  • Low coefficient of expansion, so that sag changes little with temperature
  • Large diameter for a given resistance, which reduces corona (an advantage of aluminium and ACSR)

Basis for selecting cable conductors

  • High conductivity, because cable cooling is poor and the conductor must be compact
  • Flexibility, for laying and bending (so stranded conductors are used)
  • Compatibility with the insulation, and ease of jointing and termination
  • Cost: copper gives a smaller size, while aluminium is cheaper and lighter

ACSR is the standard choice for overhead lines. Copper or aluminium with XLPE insulation is common for cables.

✓ Answer checked by Claude Opus 5.5 (high effort)

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