What is Lightning?

Lightning is an electrical discharge in the atmosphere between clouds and ground. It's basicly a path for the current to flow down to ground and it happens in microseconds with enormous rise in heat, pressure and energy at strike point.

Lightning is the major threat for regions like Africa, South Asia, North America, Latin America and Australia

Lightning clouds are usually vertically developed (cumulative) type and large enough to contain different charge groups inside at different heights. CumuloNimbus (Cb) clouds are the ones where lightning is mostly observed. Bottom layer of this cloud is at around 500 meters above the ground and top layer may rise up to 8000 meters in the atmosphere. Cb clouds have different charge groups inside and bottom layer is usually negatively(-) charged where the top layer has positive(+) charges mostly.

 

Negatively charged bottom layer of Cb attracts the opposite charges from the structures on the ground, so the area under the cloud gets positively charged and all negative charges leave the area.

A
B

As the storm grows up, negative charges start moving downwards in the form of branches (A) and these are called “stepped leaders”. They move downwars step by step to a height of 200 meters above the ground and stop. At that moment, positive charges called "upward streamers" are emitted from any object, building or structure on the ground and march towards the negative charged branches (B) in the sky.

One of the upward streamers meet with one of the stepped leaders and this forms an “ionized channel” (C) which is called "Lightning". All current inside the cloud flows through this ionized path following the structure body which emitted the upward streamer. During this electrical discharge, “unsuccessful” stepped leaders disappear like all other upward streamers and they shrink back to the ionized path to support the charge transfer.

Lightning seems as if it strikes only once, however it repeats many times in microseconds until the cloud completely neutralizes itself. Any of these strikes can create massive pressure and explosion effect with sudden rise in heat up to 3000 C. This is why structural damage and fire can oftenly seen at the points of lightning strikes. Lightning also damages electronic equipment directly and/or by its electromagnetic field. Lightning bolts can cause injuries and even deaths with a strike on a humanbeing.

o

C

Lightning DAMAGE

The strike point of lightning is critically important. Depending on its path, any living creature on ground, any object and all structures can meet the damaging effects of lightning.  These effects are basicly; explosions by rapid rise in pressure, fire and burns by raise of heat up to 5 times of sun's surface, irreversible damage on electrical devices by high voltage up to millions of Volts and damage of electronics by sudden changes in electromagnetic field.

Lightning DAMAGE ON METAL TOWERS

Metal structures such as telecommunication towers, radio-tv towers, tower cranes, high voltage power transmission towers, wind turbines, security camera poles and weather station towers are primary targerts to lightning strikes because they are made of conductive materials and they are usually the tallest structures in a location.

When lightning hits the tower; lightning current flows down through tower body/legs and reach to ground. During this flow; lightning current damages any equipment on tower and/or in nearby shelter if exists and electromagnetic field of current damages sensitive electronics on tower body or inside shelter. Site goes off service, equipment has to be renewed and maintanence costs arise.

A proper lightning protection solution is a must for these kind of structures. In many parts of the world, metal towers are protected by lightning arresters with down conductors attached to them. Lightning arresters attract lightning on themselves and transfer the current to the conductor. However, since the conductor is attached close enough to the tower body, current finds the tower surface a better path to the ground and prefers to flow through tower body. This results with structural damage on equipment on tower and inside shelter.