Lightning Protection Systems

Lightning:

Lightning is an electric discharge between cloud and earth, between clouds.

In every second approximately 100 lightning strikes throughout the world. It has enormous energy having current ranges from 10KA to 90KA.

Lightning results in loss of life and property in every year, so each important building, structure should have effective lightning protection system.

Cause of Lightning:

There are various theories regarding the formation of lightning. I am not going into detail however there are two types of charges creates lightning such as:
1) Due to negatively charged cloud:

90% lighting strike is due to negatively charged cloud.

      2) Positively charged cloud:

This type may occur during winter season.

Diagram shows how creates lightning by Positive and negatively charged cloud . Here ground objects induced with opposite charge. Taller objects have higher density of charge so when cloud comes closer to the earth the upward streamer created.Lightning strikes when downward streamer and upward streamer joins.

Lightning protection systems dedicated to protect against

i)Direct lightning strike:

1. Early streamer emission lightning conductor

2. Simple rod lightning conductor

3. Meshed cage lightning conductor

4. Taut wire lightning conductor

ii) Indirect lightning strike:

Over voltage arrestor (surge suppressor) are used to protect electrical equipment's from momentary power surges caused by lightning. The indirect lightning generated by a lightning strike on the line  in question at far away from the equipment  and travel towards the equipment or by induction due to high intensity electromagnetic field caused by the flash.

How does early streamer emission lightning arrestor works

When lightning strikes an electrical field always created at ground level which increases the intensity of downward streamer. When the field intensity between 50 to 100KV/m, Corona effect started naturally at the tallest objects on the earth. This creates upward streamer and rise towards the cloud as shown in pictures. When distance between downward leader and upward leader such that breakdown of air occurs lightning continues to strike to the ground.

The principle of operation of  ESE is to create an upward propagating streamer earlier than conventional air terminal or other object on the earth such that greater the chances of  making contact between upward and downward leader causing discharge the lightning to earth.

The gain in lead distance of the spark over distance in mtr (ΔL) = V. ΔT  

Where

V (m/μs) : The average speed of the downward leader.

ΔT (μs) : Gain in spark over time of the upward leader.

Triggering Time Gain of ESE: The triggering time ΔT (μs) is defined as the gain at

the spark over instant obtained with an ESE terminal compared with a simple rod terminal exposed to the same conditions.

Triggering Time Distance Gain: The triggering time instance gain ΔT is associated with a triggering time distance gain ΔL.

For details study French standard: NFC 17 102C