EXTERNAL PROTECTION against lightning provides protection to structures against physical damage and injuries for contact voltages and contact with human beings.
The elements of a lightning protection system are the following:
Earth Termination System.
A correct surge protection installation
Other measures minimizing the destructive lightning effects (equipotential bonding, screening, etc.)
A Lightning Protection System (LPS) can be executed through Early Streamer Emission (ESE) arresters or through Rods or Meshed Conductors. These products are manufactured in accordance with the relevant international standards: IEC serie: EN 62.305, EN 50.164.
The functioning of ESE arresters is based on the electric characteristics of lightning formation. Lightning initiates with a downward leader, propagating in any direction. Once it approaches objects placed on the ground, any of them can be struck. The objective of an external lightning protection system is to control the lightning striking point thus providing the lightning current a path to the ground without damaging the structure.
The main feature of ESE arresters is the emission of a continuous upward leader before any other object within its protected area. The standards define this characteristic using a parameter called advance time (Δt): “Average gain in upward leader triggering compared with a reference point having the same geometry. It shall be obtained by laboratory tests. It is measured in microseconds.”
The advance time determines the protection radius of each lightning conductor. If the triggering occurs earlier, then the distance where the downward leader is intercepted increases, thus avoiding the lightning strike in a wider area. The advance time must be measured in a High Voltage laboratory, following the test procedure described in the standards of lightning protection using ESE Air Terminals.
Lightning protection using rods and meshed conductors is used to share and dissipate the lightning current through a network of down-conductors and earth terminations.