Lightning Damage/Protection

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Lightning Surge Protection is NECESSARY !!!

Each year there are million and million of lightning strikes all over the world.The enormous energy of lightnings have inflicted huge damages to propertyand also endanger human lives, to avoid these damages, lightning/surge protection devices shall be installed.In present days, with the rapid development of electronic communicationdevices & much more sensitive operational voltages, these led to equipmentcan be easily damaged by lightning & surge.

Figure 1: Reason of electronic equipment breakdown, an average figure from different institution

Figure 2: Damages could occur in a radius of 1.5KM

Figure 3: Sources of surge and lightning discharge

Direct or close lightning strike

1a:Lightning strike at external lightning protection system, such as a processcontrol system (industrial installation), cables etc.

1b: Voltage drop at the earthing resistance ER caused by lightning current.

1c: Inductive surge voltage in close loop.

Distant lightning strike

2a: Strike in distant overhead lines.

2b: Inductive lightning impulse waves and surges on overhead lines caused by cloud-to-cloud lightning.

2c :Effected field caused by the lightning.

Sources of Lightning/Surge

Lightning strike includes direct lightning strike, close lightning strikeand distant lightning strike (Fig.3).The amplitudes and energy of theimpulse currents and voltages generated are especially dangerousto the electronic system to be protected.

Due to the existence of the earthing resistance, a direct or closelightning strike may cause a high voltage drop from earthing resistance to the distance surrounding, this is a great threat to theelectrical & electronic equipment in the building. Besides the highvoltage drop at the earthing resistance, the induction of theelectromagnetic wave caused by the lightning will also producesurges to the system & equipment (Figure 3: 1c).

Distant lightning strike is that the strike point is at a distance fromthe protected devices, or striking at the high voltage overhead linesand its vicinity, or the lightning discharge between the clouds(Figure 3: 2a,2b,2c).

Surge caused by switching operation

— Open or close electrical circuit on inductive load(e.g. Transformer, magnetic core, motor)

— Ignition or interruption of electric arc(e.g. arc welding Device)

— Operation of circuit breaker

Lightning discharge

All conductors may conduct lightning current(Figure.4).Such as:

1. Power supply lines

2. Data lines

3. Air termination devices (or earthing system)

4. Antennas

Figure 4: All conductors may conduct lightning current


Step voltage

When lightning occurs, the adjacent trees could become a conductorfor lightning current, if the lightning strikes the trees,a huge voltagedifference will be formed around the trees because of the largecurrent. If a man’s feet standing on the ground separately, a deadlystep voltage difference U will develop, this voltage difference could Obe life threatening(Figure 5).

Figure 5: Step Voltage

Lightning protection system is consisted of:

external lightning protection and internal lightning protection.

External lightning protection includes:

* Air termination device (lightning rod, belt and grid);

* Down conductor;

* Earthing system

Internal lightning protection includes:

* Shielding;

* Equipotential bonding;

* SPD installation

External Lightning Protection Mainly for Building & Structure Internal Lightning Surge Protection for Electronic Equipment