At lightning current densities and time scales the earth ionizes and rapidly
increases its conductivity. See equations by Weck and others:
http://www.ipstconf.org/papers/Proc_IPST2011/11IPST109.pdf
Note in the graphs how the effective resistance of the ground decreases as
the current increases.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
jimlux
Sent: Sunday, January 10, 2016 17:42
To: towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: [Bulk] Re: copper or galvanized ground
rods in red SC clay
On 1/10/16 8:56 AM, Roger D Johnson wrote:
>
>
>
> Another factor not usually considered by hams is that conduction
> through the ground is NOT the same as conduction through a copper
> wire! A copper wire has a copious supply of free electrons and will
> happily conduct increasing amounts of current until it melts. In soil,
> the conduction is by ions from metallic salts in the earth. The supply
> of ions is finite and when all are being used to conduct electric
> charges, the resistance rises sharply. The soil has gone into
> "saturation".
do you have a reference for this? I'm interested in a more technical
description of the phenomenon.
I'm familiar with some other soil and tissue conductivity phenomena relevant
to RF having to do with the ion mobility (e.g. the Cole-Cole model which is
used for all sorts of things at all sorts of frequencies:
prospecting for ore, measuring the ripeness of produce, and RF imagery of
human bodies)
A lightning ground system
> has to be designed to dump the current from a strike into a large
> "volume" of earth capable of conducting the strike current.
>
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