Why you think flat conductor is better than round conductor despite permitted by codes for lightning protection? Any formula for skin effect for round conductors demonstrating their inferiority over flat conductors for lightning protection?
Simple. Flat conductor has more surface area than round conductor. Remember, current travels on both sides of flat conductor.
I don't have a formula, but I am sure there is one.
Also, I have worked on radio installations for years. Flat conductor is what is used on every engineered lightning protection system for towers I have ever seen. If it's good enough for someone that makes their living designing LP systems, it's good enough for me.
Think of it this way. A 2 inch flat strap has as much surface area as a round conductor with a 4 inch circumference. I am just guessing that would equal about a 1 1/2 inch diameter conductor.
So. If you had to choose between a .030 x 2.00 inch strap or a 1.4 inch round conductor and they both were equally effective, which would you want to pay for and install?
Also, if you look close at engineered LP systems for communications, any round conductor used in that system is solid, not stranded. Have you ever had to work with 2AWG solid bare tinned copper? I have, it sucks. (LP system for a Verizon site). I believe that it would be physically impossible to work with any larger solid wire. The round conductor is used to bond the inside of MESA cabinets together and is always 'inside'. Towers will have flat conductor, usually 6 inches wide, from the base and electrodes to the control room.
I notice that you seem to be interested in LP systems. I don't think you understand them, though. I have been lucky enough to actually help design and build them so I have a leg up on you in that respect.
Have you taken the time to visit the Polyphaser site and go through their technical info? It's good stuff and un-like NFPA 780, it's up to date. Polyphaser has a vested interest in being correct. If they lose their untarnished reputation, it could cost them millions. They supply surge and lightning protection to our government and large corporations, along with small, single site retail sales. They even have real live people give tech support over the phone.
I just tried to find the tech info at the Polyphaser site to no avail. Sorry, as it's great stuff. They changed their site so they have less tech notes, but better person to person service.
http://www.protectiongroup.com/PolyPhaser
I did find this rather non-technical discussion that may interest you on Georgia Copper's site:
Copper strap (or strip) is the conductor of choice for low impedance RF ground connections. Due to the skin effect, RF
currents tend to flow along the outside "skin" of a conductor. Copper strap has a large, smooth surface area to take full
advantage of this effect. For decades, copper strap has been widely used in the RF ground systems of broadcast sites.
Lightning - Assuming lightning current is strictly DC, any copper conductor of similar cross-sectional area should conduct
lightning current equally well. However, research has shown that lightning is a series of DC pulses with a fast rise time.
Conductors with lowest inductive reactance and largest surface area, such as copper strap, should be strongly considered
when choosing conductors to handle the fast pulses of lightning current.
There's one great benefit of copper strap that is seldom mentioned. In a typical ground system, multiple ground rods are
driven and interconnected with bare copper wire or copper strap buried just below the surface of the soil. If copper strap is
used for this purpose, the large surface area of copper strap in contact with the soil can enhance any system of ground rods
and help lower overall ground resistance. For example, an 8-foot length of 2-inch copper strap would have just as much
surface area in contact with the soil as an 8-foot, 5/8" ground rod! And that's only considering one side of the strap!
Copper strap's greatest disadvantage is that it is slightly more difficult to install and connect than wire - for example, to go
through a wall, one simply has to drill a hole for wire and push it through. Strap requires a little more effort.
Just curious, what it the weather like where you live? Do you have frequent thunderstorms? I live in an area that has many storms each year. Just last night a line of thunderstorms came through and took out power to homes about 8 or 9 miles from here. I stood on the back porch and witnessed some of nature's fury, it's incredible. We went from no wind and no rain to a moderate amount of precipitation and 50 mph wind gusts in about 45 seconds. I would say the lightning visible as ground strikes were happening ever 30 seconds or so. In less than 15 minutes the storm was over. It's now bright and sunny just like it was yesterday, a few hours before the storm.
I have a friend that takes pictures of lightning. He's really good. He was in his van when the van got struck just as he pushed the camera shutter and got a pic of a bolt of lightning from about 6 feet away. Luckily, he wasn't hurt, but some of the van's electronics, including his ham radio, got fried. Unless you know what you are looking at, the picture looks like an out of focused mistake. Here are some of his pics. The one of his van isn't there. It lacked his usual style of capturing the beauty of the moment.
http://photo.net/photodb/folder?folder_id=650040
Those pics are all from Michigan near Lake Michigan. That is what we have to deal with when putting up towers and we have hundreds, if not thousands of towers here. I am a licensed amateur radio operator and we have ham gear in our county's emergency operations center, all the hospitals, the Red Cross, several fire stations and the county's mobile command center so I have more than a passing interest in protecting radio systems (and the schmuck holding the mike) from lightning. I have also been in two weather radar stations, one as it was being built. The weather service prides itself on being able to take direct hits to their towers and flat strap at those locations is abundant.
