Protection zones

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Power transmission lines

The line voltage, measured in kilovolts, can be determined by the number of plates forming the insulator garland on the line: the larger the number, the higher the voltage of the line. 
 
Line voltage Length of insulator garland  Number of insulators (plates)
110 kV About 1.5 m About 7-9
330 kV About 3.5 m About 17-23
The line voltage can also be determined by the distances between conductors of different phases and the number of conductors per phase. In 110 kV lines, there is one conductor per phase, and in 330 kV lines there are two and more conductors per phase.
 
Each tower is marked with the tower number and the abbreviated name of the power line; voltage (110 kV or 330 kV) can also be indicated. For example, “VE3-Vv” on the tower means a 110 kV power line “Vilnius Power Plant 3 – Vievis”. 330 kV lines can be marked also by the letters LN (line) and a three-digit number, e. g. LN-456 marking the line “Neris-Utena“.
 
Overhead lines can be single-circuit or double-circuit. Double-circuit lines are those lines where two separate lines are suspended on the same tower. Then one tower can carry 4 or 7 conductors. One of these conductors – the top one – is a wire installed for lightning-protection purposes. 
 
A 110 kV overhead power line
 
A 330 kV overhead power line
 
A 330 kV double-circuit overhead power line 
 
 
Components of an overhead power line:
  • Lightning-protection wire
  • Cap supporting the lightning-protection wire
  • Traverse
  • Insulator garland (plates)
  • Conductor
  • Tower
  • Markings
  • Tower base
  • Brace
  • Brace base
  • Grounding grid
 
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