[TowerTalk] [Bulk] Re: [Bulk] Re: copper or galvanized ground rods in red SC clay

[David Robbins]

correct, on the time scales and current level of lightning the ionization of the soil rules.  I could see a saturation effect being possible for DC, perhaps in cases where you are using the soil return for a monopole DC transmission line.  I would not expect it for AC.


Jan 10, 2016 05:28:23 PM, jimlux at earthlink.net wrote:

On 1/10/16 11:40 AM, David Robbins wrote:
> 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.

Very interesting..
(and, of course, there's about a 3:1 difference among the various 
models, which I'd sort of expect)

That paper and the references it cites will give me a fair amount of 
reading.

However, I don't see any sort of "saturation" behavior: in fact, it's 
more of a negative resistance (i.e. resistance goes down as current goes 
up).


>
> David Robbins K1TTT
> e-mail: mailto:k1ttt at arrl.net
> web: http://wiki.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
>
>
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
> jimlux
> Sent: Sunday, January 10, 2016 17:42
> To: towertalk at 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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