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Earthed lightning rods are provided
About the overhead lines
Above all tall buildings
At the substation
Near motor and generator terminals
Above all tall buildings
Earthed lightning rods (or air terminals) are primarily installed on tall structures to provide a low-impedance path to the ground for lightning discharges. By attracting the lightning strike to itself rather than the building, the rod conducts the massive current safely into the earth, preventing structural damage and fire.
Earthed lightning rods (or air terminals) are primarily installed on tall structures to provide a low-impedance path to the ground for lightning discharges. By attracting the lightning strike to itself rather than the building, the rod conducts the massive current safely into the earth, preventing structural damage and fire.
V=I├ЧZ тАФ Voltage rise across the conductor during a strike where Z is the surge impedance
RgтАЛ<10╬й тАФ Recommended resistance to earth for effective lightning protection
The principle involves creating a preferred path of lower electrical resistance between the cloud and the earth. As a storm cloud develops a high electrostatic potential relative to the earth, the lightning rod (usually a pointed metal rod) creates an intensified electric field at its tip, facilitating the formation of a leader towards the cloud. This 'captures' the lightning strike, channeling the current through a down conductor system with minimal impedance, effectively shielding the protected object within the rod's zone of protection.
Lightning rods must be connected to a low-resistance earthing system.
The 'Zone of Protection' is often determined by the rolling sphere method.
Materials used are typically copper or galvanized steel for high conductivity.
Frequent inspection of the down-conductor joints is mandatory.
Prevents structural damage from intense thermal heating.
Reduces risk of fire and explosion in tall buildings.
Protects electronic systems from induced transients.
Requires high-quality periodic maintenance.
May attract strikes that would not have hit the building otherwise.
Residential skyscrapers
Communication towers
Industrial chimneys and power plants
Lightning rods are also known as Franklin rods or air terminals.
Option A is incorrect because overhead lines use 'Earth Wires' (Shield Wires) specifically placed above the phase conductors, not conventional lightning rods.
Option C is partially true, but lightning protection in substations uses 'Lightning Arresters' (Surge Arresters) which are distinct from structural lightning rods.
Option D is incorrect as these require surge arresters, not air terminals, for protection against transient overvoltages.
B is correct тАФ Earthed lightning rods are installed above tall buildings to act as air terminals that safely discharge lightning strikes to the ground, shielding the structure.
Distinguish between 'Lightning Rods' (for building structures) and 'Lightning Arresters' (for electrical equipment/lines); the former manages current path, the latter manages surge voltage.