Protection Methods Of Lightning systems.
The highest point of the facility is, in general, the most vulnerable to a direct lightning strike. Lightning rods or air terminals are needed to capture the strike to a proffered point, and to safely conduct the energy to ground to minimize the risk of damage. The number of terminals required, and their placement, is determined by the chosen lightning protection design method.
The placement of the terminals, whether conventional or active, is a critical part of lightning protection design process. Since 1750’s the most popular methods of lightning protection have involve sharp vertical rods (Franklin), horizontal and vertical conductors. Or combination of both. Only if air terminals are placed in the optimum location on the structure makes it possible to achieve an efficient and reliable lightning protection system. Historically a number of methods have been employed, some of which are still in common use, such as cone of protection Mesh and rolling sphere methods.
Cone of protection
The cone of protection is a simple geometrical construction that assigns a zone of protection to a vertical conductor. On a structure protected by Franklin rods using this design method, it is not usual to find location where lightning has struck well with in the supposed zone of protection
The highest point of the facility is, in general, the most vulnerable to a direct lightning strike. Lightning rods or air terminals are needed to capture the strike to a proffered point, and to safely conduct the energy to ground to minimize the risk of damage. The number of terminals required, and their placement, is determined by the chosen lightning protection design method.
The placement of the terminals, whether conventional or active, is a critical part of lightning protection design process. Since 1750’s the most popular methods of lightning protection have involve sharp vertical rods (Franklin), horizontal and vertical conductors. Or combination of both. Only if air terminals are placed in the optimum location on the structure makes it possible to achieve an efficient and reliable lightning protection system. Historically a number of methods have been employed, some of which are still in common use, such as cone of protection Mesh and rolling sphere methods.
Cone of protection
The cone of protection is a simple geometrical construction that assigns a zone of protection to a vertical conductor. On a structure protected by Franklin rods using this design method, it is not usual to find location where lightning has struck well with in the supposed zone of protection
Mesh Method (faraday cage) 
The mesh or Faraday cage method consists of series of horizontal air terminations (Copper tape), which are bonded to vertically descending down conductors. The structural steel if bonded may also be used to conduct the lightning impulse.
The mesh or Faraday cage method consists of series of horizontal air terminations (Copper tape), which are bonded to vertically descending down conductors. The structural steel if bonded may also be used to conduct the lightning impulse.
The picture opposit shows a labortory demonstration of the method, ( DON'T TRY AT HOME !)
Rolling spare method
Rolling spare method
The rolling sphere method is undoubtedly the most common recommended method in codes of practice. It is based on the electromagnetic model, which released the striking distance to the peak current delivered by the lightning strike. To apply this technique, an imaginary sphere, typically 45 m in radius (the striking distance), is rolled over the structure. All structure surface points that contact with the sphere and deemed to be protected, as shown in the diagram.
In order to determine weather lightning protection system is necessary, the following should be considered.
· Prevalence of thunderstorms and lightning protection system.
· Construction of the building
· Height of the building
· Relationship with other building or structures.
· Utilization and contents of building
· Type terrain.
· Regardless of the location, all the buildings and structures higher than 50m should have a lightning protection system.
Elements of a Lightning protection system.
Air Terminal
The primary function of an air terminal or termination system is to capture the lightning strike to a preferred point, so that the discharge current can be safely directed through the down conductor(s) to the grounding system.
The Down conductor
The function of a down conductor is provide a low impedance path from the air termination to the ground system so that the lightning current can be safely conducted to earth, without the development of excessively large voltage.
In order to reduce the possibility of dangerous sparking (side-flashing), the down conductor route(s) should be as direct as possible with no sharp bends or stress points where inductance, hence impedance, is increased under impulse condition.
The Grounding System
The grounding system must have a low impedance to safely disperse the energy of the lightning strike. Because the lightning discharge consists of high frequency components, we are particularly concerned with the frequency dependent electrical parameter of a grounding system- impedance- as well as low resistance grounding.
A disconnect link should be fitted in each of the down conductors to facilitate testing. The disconnect link should be a bi-metal connector for aluminum networks.
All metalwork on, or around, a structure should be bonded to the lightning protection system. Metallic drainpipes, fire escape ladders, metallic fencing, etc. should be bonded to the lightning protection system at the top and the bottom.
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AXIS Lightning Protection Systems are designed to protect structures and systems against Lightning damage. Axis tests its lightning protection products in accordance with Major international standards such as IEC, BS EN, UL& IS.
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