Conventional Vs Structural Earthing Analysis of Lightning Protection in Structures

 

Lightning protection of structres are being done in 2 ways ,both confirming the indian standard.The first method is isolated protection(for convenience called as conventional method in this paper)and the second one is to use the naturally available steel in building as part of LPS such as down conductor and earthing (for convenience called as structural earthing in this paper)
in conventional method down conductors are outside the building and generally isolated form the strucure.vertical earthing electrodes are used which are also outside the building.generally the Lps is not connected to Equipotential Bondind bar,but in some cases earth electrodesare connected to other earthing system.
in structural earthing method,continous conductors super imposed inside columns and foundation which runs along with construcion steel will do the job of down conductors and earthing .Analysis on injury to living being by electric
shock due to a direct lightning strike in the
structure
IS/IEC 62305-2 Explains the risk assessment and probabillity of damages in a building during a lightning.probability of injury to living being due to touch and step potential(PTA)as well as the external LPS provided (PB)
PA=PTA X PB

Electrical Safety and Power Frequency
Fault Voltage Industrial / IT and commercial establishments generally use TN-S network for L.V electrical distribution with in
the facility. For establishments with number of electronic
systems, TN-S is the recommended network by every latest standards . The method is explained and recommended in IS 3043 as PME (Protected Multiple
Earthing). Properly implemented structural earthing ensures easy implementation of PME and there by reduce the power frequency fault voltage between electricity using equipment and extraneous conductive parts in a building during a fault. Equipotential bonding thus created avoids dangerous spark over and fire during a fault.

 

Protection of Electronics

Modern day electronic installations are highly sensitive to Transients. Transients in a building are created due to radiated Electro Magnetic Pulse (EMP) due to various reasons. Future electronic installations will be smaller & faster which means more sensitive to EMP. Electro Magnetic Shielding plays a major role in protecting modern day electronics.A properly installed Structural Earthing system mean a large volume shield created by natural components of the structure such as the metal reinforcement in ceilings, walls and floors, the metal framework, the metal roofs and metal facades. These components together create a grid-like spatial shield (faraday cage). The current injected into th reinforcing rods is assumed to flow through a large number of parallel paths. The impedance of the resulting mesh is thus low and, as a consequence, the voltage drop due to the lighting current is less. The magnetic field generated by the current in the reinforcing steel mesh is weak due to the low current density and the parallel current paths genrating opposing electromagenetic fields. Interference with neightboring electrical conductors is correspondingly reduced.With out any doubt, structural earthing provides the best equipotentialisation and protection of electronic systems.

 

Corrosion and Associated problems

Steel inside concrete have the advantage that, if the concrete is of adequate construction and covers the steel by at least 50 mm, they are reasonably protected against corrosion, throughout the life of the building.
Where as a conventional LPS is subjected to corrosion theft, vandalism etc hence need periodic inspection and maintenanceA properly installed Structural earthing system is permanent in the building well shielded provided welded iron reinforcing bars are used for concrete outer walls. Note that a good electrical bond is necessary. In several situations the steel reinforcing bars may not represent an adequate shield. An well-designed and implemented lightning conductor with conductive connections to
structural steel is an alternate method. Some tips about this conductor are
1. Galvanised steel inside concrete may create problem
to concrete and hence avoid GI inside concrete.
2. All penetrations of steel in reinforcement to an outer
area need careful design and installation. Use only
Copper, Copper coated steel or SS material for this
application.
3. Use only copper, copper coated steel or SS in
soil if connected to steel in reinforcement as
recommended in IS/IEC standard.

Cheap and Best in long run

To achieve a cost-effective and efficient protection system, the design should be carried out during the building conception stage and before construction. This allows one to optimize the use of the natural components of the structure and to choose the best compromise for the cabling layout and equipment location.for retrofit of Shielding measures in conventional LPS the cost is generally higher than the cost for new structures.

 

Structural earthing and Bonding system

  • More safety for human beings during lightning
  • More safety for electrical installations during fault &
    lightning
  • Protect Electronic systems against EMP
  • No Corrosion and Less Maintenance
  • Cheap and Best in long run
  • Structural Earthing is a standard construction practice in
    developed countries.
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