Effects of Lightning
- Fire
- Mechanical Damages
- Injuries to people & animal
- Damages to electric & electronic equipment
- Explosions
- Hazardous to computer systems, control system, regulation system, power supplies etc.
Over voltage and current due to lightning
- The typical worst voltage is about 6,000 V for transient voltage in building power supplies.
- It causes a current typically greater than 3,000 A and no greater than 10,000 A in building power supplies.
- In communication systems, the worst voltage is about 5,000 V and current is in hundreds of amps.
Classification of Structures
- Common Structures
- Any structure utilized for commercial, industrial, farming, institutional or residential and less than 60 m in height.
- Special Structures
- Structures with confined danger
- Structures dangerous to their surroundings
- Structures dangerous to social and physical environment
- Miscellaneous structures such as,
- Tall structures (above 60 m),
- Tents and camp sites,
- Temporary sites and structures under construction
Construction of an external lightning protection
- Air termination system
- Protective angle method
- Rolling sphere method
- Mesh size method
- Down conductor system
- Earth termination system
Air Termination System – Protective Angle Method
- Suitable for simple structures or small parts of a bigger building
- Air termination conductors, rods, masts & wires should be positioned so that all parts of the structure to be protected are inside the envelop surface generated by projecting points on the air termination conductors to the reference plane at an angle to the vertical in all directions
Protective Angle Method
- Air termination mast
- Protected structure
- Reference plane
- Intersection between protective cones
- Separation distance according to IEC 61024-1
- Protective angle according to the IEC 61024-1
- The top of the air-termination rod shall not be higher than the value given in
- IEC 61024-1. The ground level is assume as reference plane.
- The design of a non-isolated LPS air-termination on a flat-roof structure using
- The protective angle air-termination design method
Rolling Sphere Method
- Suitable for complex shaped structures
- The sphere of radius R is rolled around & over all the structures until it meets ground plane or any permanent structure or object.
- Places where the rolling sphere touches the structure a strike could occur & at such points protection by Air termination Conductor is required.
Mesh Method
- Suitable for protection of plane surfaces
Down Conductor System
- If the lightning current is shared in several down conductors, the risk of flash & the electromagnetic disturbances inside the structure is reduced.
- Down conductors should be uniformly placed along the perimeter of the structure with a symmetric configuration
- Current sharing can be improved by quintessential interconnection rings
- Down conductors must be as short as possible
Earth Termination System
- In order to disperse the lightning current into the earth without causing dangerous over-voltages, the shape and dimensions of the earth-termination system are more important.
- Two Basic types of Earth Electrode arrangements apply for earth termination system
Type A
- Composed of radial or vertical earth electrode
- Each down conductor shall be connected to at least one separate earth electrode composed of either a radiating or vertical electrode
Type B
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