Rolling Spheres

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electrics

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Hi, I want to learn about this method to prevent lightnings from destroying buildings. I could not figure out how this rolling and mounting the rods which catches the lightning are carried out wh,le designing. . I dont know if they are arresters and not rod. Can you explain me this method (We roll the imaginary spheres after mounting the rods or just roll them over the building without rods. İs this method used for checking or designing the functioning of the rods. ) and what is used to catch the lightning . A simple spiky rod or arrester which has special feature to attract the lightning. Thanks in advance buddies...
 
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The key to Lightning Protection is to understand how much of an area is protected. So in the simplest case, imagine a single air terminal (lightning rod) on a pole sitting in the middle of a field. Of course to be proper lightning protection, the terminal would be connected to a conductor that runs down to some sort of ground loop.

The old method would have said that you draw a cone with it's apex at the tip of the terminal, and with an angle of "X" degrees. "X" was variable depending on how important the structure was. Everything inside that cone is protected.

The new method - rolling spheres - has you take a sphere of some diameter (like 100 meters) and roll it around between grounded surfaces. So you would touch it to the air terminal and the ground and everything under that would be protected. If you roll that sphere around 360 degrees you would get something like a cone but with sides that are curved like the outside of your sphere rather than straight like a normal cone.

I've uploaded a screen shot that hopefully makes it a little more clear...

http://d.pr/bPea
 
For some more images and examples, go to Google Images and copy and paste the line below

"rolling sphere" lightning

into the search box.

There are at a least six good diagrams in this search.
One even talks about a "96% protected area" which suggest that the 46 meter radius sphere method protects you 96% of the time. To get 99% certainty takes a smaller [larger?] sphere.
 
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The 150' beach ball.

The 150' beach ball.

electrics said:
Hi, I want to learn about this method to prevent lightnings from destroying buildings. I could not figure out how this rolling and mounting the rods which catches the lightning are carried out wh,le designing. . I dont know if they are arresters and not rod. Can you explain me this method (We roll the imaginary spheres after mounting the rods or just roll them over the building without rods. İs this method used for checking or designing the functioning of the rods. ) and what is used to catch the lightning . A simple spiky rod or arrester which has special feature to attract the lightning. Thanks in advance buddies...
Click to expand...

It's the 150 beach ball. When the points are all located blow up the 150 diameter beach ball and roll it around the facillity. If it touches anything but a point do it over.
 
I would suggest you review Section B.3.2.2 in Annex B of the NFPA 780 - 2011 Edition. This will give you the best explanation of the rolling sphere method. From there, see section 4.7.4 for the prescriptive methods for using the rolling sphere model.
 
I want to learn only what is the logic of this method. My friend described it quite clear but I still have some doubts. For example the order of arranging the arresters and rolling the spheres. Which one is first? Also for an arrester which one is true? A cone or sphere shaped protection area? Are all these hypothetical or based on true assumptions. So if spheres method is true so why do we use classical cone protection method use? I need some basic explanations. I thank also my friends claster first, that they tried their best. But I am trying to understand and failed to do yet...
 
Everything associated with lightning protection should be considered best practices based on tested theories. There is no law of lightning protection. At best, an LPS is a mitigation tool against the effects of lightning and nothing more. Lightning is arbitrary, capricious, random, stochastic, and unpredictable.


Read the Annexes of the NFPA 780 and if you still have questions, consider purchasing a recent lightning protection book

Suggestion:

"The Art and Science of Lightning Protection" by Martin A Uman.
"Lightning Protection for Engineers" by NLSI.
 
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