1. The electrical energy is generated at voltage 11KV and it is transmitted at 132KV/220KV/400KV/765KV.
  2. 765KV is highest transmission voltage in India.

Mechanical Design of Overhead Lines

  1. Conductors used for Overhead Transmission Lines
  • Copper
  • ACSR (Aluminum conductor steel reinforced)
  • ACAR (aluminum conductor alloy reinforced)
  • AAAR (all aluminium alloy reinforced)
  1. A steel conductor is placed in centre of ACSR conductor to provide additional mechanical strength.
  2. Galvanized steel is used to make stay wire and earth wire.
  3. Types of Conductor
  • Stranded Conductor (ACSR)
  • Hollow conductor (used for large current more than 1000Amp)
  • Bundle conductor (used for high voltage)
  1. Advantage of Bundle Conductor
  • Reduces the corona effect
  • Reduces the interference with nearby communication line.
  • Power system stability increases.
  • Surge impedance decreases.
  1. Line Supports
  • Wooden Poles (Span upto 50 meters, life 20-25years, impregnated with creosote oil to prevent the portion of the pole below the ground level)
  • Wooden poles used for distribution of power in villages.
  • Steel poles
  • RCC Poles (longer span 80- 150m, longer life)
  • Lattice steel tower (long span 300m or above)
  1. Types of insulators
  • Pin type insulator (used upto 33KV)
  • Disc insulator (capacity of disc is 18KV)
  • Suspension insulator (it is string of disc and it is used in high voltage transmission lines)
  • Strain insulator (it is used at dead end)
  • Shackle insulator (it is used in low voltage transmission line)
  • Egg or stay insulator
  1. Sag: – The difference in level between points of supports and the lowest point on the conductor is called sag.
  • With increase in span length the sag is increased.
  • With increase in weight per unit length of conductor the sag is increased.
  • With increase tension in the conductor the sag is decreased.