Necessity of lightning protection system:

• Lightning is one of nature’s most powerful & destructive phenomena.
• It contains a huge amount of energy (several thousands of Amps)
• It is a short duration ( up to 200 µsec ) but is a real cause of damage & destruction
• Primary effect- Buildings damaged, trees blown, personal injuries and even death
• Secondary effect- Transient overvoltage- damage to electronic system
• It can also cause fire, explosion, chemical release or mechanical disruption within or around a bldg.

 

Lightning Protection System (LPS)

• The lightning rod (Rod is earthed by one or more conductors)
• The lightning rod with taut wires (stretched above structure)
• Lightning conductor with meshed cage/Faraday cage (numerous down conductors & tape                  symmetrically placed)

 

 

 

Standards:

• BS 6651
• NFPA 780
• BS-EN/IEC 62305
• In Aug. 2008, BS 6651 has been withdrawn
• Now IEC 62305 & NFPA 780 are the recognised standards for LPS

 

Elements of a Lightning Protection System (LPS)

         

1. Air Termination System (Arrestor)

• Arranged at or along upper points of a roof
• Used to capture lightning current
• Dissipate it harmlessly to earth
• Material- Copper, Aluminium
• It consists of base, air rods & multiple points
• 25*6 mm Al tape on surface interconnected through clips and clamps (fig. 1 to 3)
• Clamps will ensure a low resistance, corrosion-resistant connection between air termination and down conductors.

                                          

 

 

2. Down Conductors ( Steel rebar )

• Provides direct route from arrestor to earth
• Greater the no, better the current sharing
• Placed in concrete column (during civil work) or can be bare conductor
• Either copper or steel bars are used
• 2 reinforcement bars of 25 mm dia. Placed in the centre of the column along the periphery
• Rebar to rebar connection-20D to ensure secure connection & proper bonding

 

 

                                             

 

     Fig 1 shows Test links- Periodic disconnection & testing of the earth termination system

 

3. Earth Termination system ( Earthing )

• Vital for the dispersion of current safely & effectively
• It should have low electrical resistance & good corrosion resistance
• It consists of earth electrodes, plate, mat, pits, Bars, earth points, bonds & clamps

 

 

Earth electrode arrangement should be as mentioned below :

Type A  

Type B

                                                                                                                          

4. Lightning Equipotential Bonding

• Interconnection of all metallic parts e.g. cable armouring, gas, water piping
• So in the event of lightning, no metallic part is at a different voltage level w.r.t. one another
• Should be near to Main LT / HT Panel & closely connected to earth with short length conductor

 

Where to provide earth connection?

• Body Earthing
• Neutral grounding ( only at source end – transformer & Diesel generator )
• Earthing for lifts

Non-conventional methods of earthing are pile earthing (cost-saving) & Ashlok chemical earthing.

 

                         

Pile earthing chambers for body earthing.