Structure Lightining Protection

[tin2779]

Hi,
I have this lattice incoming structure terminating a 69 KV line in to a small substation yard.

For the lightning and shielding analysis, I want to protect the equipment. Could you advise any link that could just guide me in this direction. the height of the structure is 8 meters and the yard is 10X20 m.

I think some kind of lightning rod will be required on the structure.
Thanks

 

[Inder76]

For typical substation, you might have to use either a spherical method if you use a mast or a shielding method if you use a shielding wire.


You can find these details at IEEE Std for shielding of substation.

There is another link that might help:

http://www.pserc.org/ecow/get/generalinf/presentati/psercsemin1/psercsemin0/sen_2001.pdf

but I wonder for a small substation, like you mentioned a kind of lighting terminal or rod that might work as well.

There are other Gurus here who might put a word. Mast or shielding wire might be to much specially if you have only one structure.

 

[jghrist]

IEEE 998-1996
IEEE Guide for Direct Lightning Stroke Shielding of Substations

Normally, you would have a shielding mast (just a steel pipe) mounted at the top of each column of the lattice structure. On a small substation, if you follow the method to calculate the probability of failure in IEEE 998, you will find that the probability will be very low without any protection. I'd say put a 10' pipe on each column (on top of a pyramid shaped top), do the IEEE 998 rolling sphere and probability calculations to show a lower than 1 in 100 year probability of flashover, and be done with it.

 

[peebee]

NFPA 780

 

[jgoebel]

Yeah, what peebee said.

The most helpful analogy for lighting protection (for me) was when someone talked me through the rolling globe analogy.

The lower limit of a sphere is positioned at air terminals. Any structure below the sphere is covered. Any structure or equipment that intersects with the sphere is in trouble.

I can't remember the diameter of the sphere off the top of my head -

 

[jgoebel]

looks like its covered in that IEEE 998 reference if you want to look further ..

 

[BJC]

Chapter 3 of TM5-690 has a few pictures of the 150'dia beach ball.

http://www.usace.army.mil/publications/armytm/tm5-690/