Direct Lightening Strokes
- Basically, lightning strike is an electric discharge on a massive scale between the atmosphere and an earth bound object.
- Most of the lightning events are between the clouds to cloud where discharges only occur in the high atmosphere.
- Near about 25% of all the lightning events is ground to cloud.
- A lightning rod is a metal strip or rod connected to earth through conductors and a grounding system, used to provide a preferred pathway to ground if lightning terminates on a structure.
- The class of these products are often called as air terminal.
- The lightning rod is simply a metal rod and without being connected to the lightning protection system.
- Lightning arrester often refers to fused links that explodes whenever a strike occurs to protect the locomotive’s main and important equipments.
- Nowadays, arresters are constructed with metal oxides, are capable of safety shunting abnormally high voltage surges to ground while preventing normal system voltages from being shorted to ground.
- A lightning protection system does not prevent lightning from striking; it only provides a way for controlling it and preventing damage by providing a low resistance path for the discharge of lightning energy.
- There are various methods of providing protection against direct lightning strokes followings are some of the methods discussed below.
Guardian Air Terminal
- These are some of the devices which are used against the direct lightning strokes.
- It consists of a rod which is surrounded by an electrically floating medium. The rounded tips are proven more efficient as compared to the sharp points.
- It comprises of four separate electrically isolated panels arranged to allow the section facing the step leader to rise in voltage due to capacitive coupling effect.
- The initiation of advanced triggering results in the larger protective area around the guardian air terminal.
Lightning Warning System
- A lightning protection system provides a means by which this discharge may enter or leave the earth without passing through and damaging non-conducting parts of the locomotive.
- A lightning warning system is a non-directional lightning detection instrument designed provide indication of nearby lightning strikes and according to that a duty of care to employees, passengers and all related personnel.
Conventional Lightning Protection System
Switching Surges due to External and Internal factors
(a) Earthing screen
(b) Overhead earth wire
(c) Surge Dividers