Before understanding lightning phenomenon, you should keep two things in mind.
- The ice crystals in an active cloud are +vely charged
- The water droplets are usually carry –ve charges.
Therefore, a thundercloud has a +ve charge center in its upper section and a –ve charge center in its lower section.
As –ve charge builds up in the cloud base, a corresponding +ve charge is induced on earth because opposite charges attract each other and that +ve charges are in our overhead cables (i.e 11kv,33kv,66kv, 132kv, 220kv, 550kv lines), as shown.
But How lightning Occurs?
when in the clouds there are -ve charges and on earth overhead lines there are +ve charges, they will attract each other and try to meet each other.
When voltage gradients within the cloud build up of 5 to 10 kV/cm, the air in the region breakdown.
This is how lightning forms and strikes on earth.
But have you ever notice that the formation of a lightning stroke is a progressive breakdown of the arc path instead of the complete and instantaneous breakdown of the air path from the cloud to earth !!!!.
And after the first successful stroke, a second stroke with much greater brightness and faster than previous (first stroke) occurs.
As the leader strikes the earth, an extremely bright return streamer, called “Return Stroke” propagates upward from the earth to the cloud following the same path, as shown in the figure.
In a sense, return stroke establishes an electric short circuit between the –ve charge deposited along the leader and electrostatically induced +ve charges in the ground.
Therefore, the charge energy from the cloud is released into the ground, neutralizing the charge centers.
Initial speed of the return stroke is 10ˆ8 m/s while the speed of leader stroke is 10ˆ5 m/s. the current involved in the return stroke has a peak value from 1 – 200kA lasting about 100 µs.
About 40 µs later, 2nd leader called “dart leader”, may stroke usually following the same path taken by the first leader.
This is How Lightning Strikes from cloud to cloud or from cloud to earth, and this all phenomenon is the lightning phenomenon.
Have you any other information about lightning?
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