Lightning Protection - Rolling Sphere

[NAZ55]

Gentlemen,
I have been trying to figure out a way to calculate a rolling sphere lightning protection radius for two different masts of unequal height having a distance smaller than the radius of the sphere.

I could go with the lower mast to be more conservative, but I would like to calculate the actual protection radius.

Also, I didn't see anything about this in IEEE standard and pretty much any paper that I have read so far.

Any advice or suggestion will be appreciated

Thanks

 

[jghrist]

See the attached file.

 

[NAZ55]

Thanks. That's exactly what I was hoping for.

 

[NAZ55]

I am trying to create a spreadsheet for rolling sphere.
You wouldn't happen to have one of those as well would you? Your first post was very helpful.
Thanks

 

[jghrist]

Sorry, I used Mathcad. For two masts, a spreadsheet shouldn't be too difficult. When you get to three unequal height masts, things get tricky. You can take two masts at a time for the area outside the masts, but if the masts are far enough apart, the rolling sphere may intersect the equipment plane inside the three masts. I had to use a Mathcad Solve Block. See attached file.

 

[NAZ55]

It's been a while since I worked on this. What I was actually looking for was a way to calculated the protection radius, if you have a shield wire with two different attachments of unequal heights.

 

[jghrist]

You didn't mention the shield wire. That's a whole different ballgame. Now it's not a protection radius, but a protected area between two lines on either side of the shield wire. I haven't quite worked out shield wires with different attachment heights.

How about two non-parallel shield wires with different attachement heights? For grins, don't neglect sag.

 

[NAZ55]

Like I mentioned earlier, I don't think I have seen anything in the standard, which talks about attachments of different heights.