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[TowerTalk] Re: Static, Lightning, and protection

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Subject: [TowerTalk] Re: Static, Lightning, and protection
From: Didier Juges <didier@cox.net>
Date: Mon, 22 Mar 2004 10:40:02 -0600
List-post: <mailto:towertalk@contesting.com>
At 09:50 AM 3/22/2004, David Robbins K1TTT wrote:
>
> Good point. At higher altitude, the dielectric strength of air is
> less, so the voltage cannot build up as much before the strike
> starts, so the clouds cannot build as much energy as they
> can in Florida.

statistically the change is relatively small.  In a typical area of
central Florida the median stroke current is about 25kA, where in
central Colorado it is about 20kA.  In the highest current range
(200-300kA) there are actually more strokes in Co .03% vs .02% in Fl.

Maybe the generally dryer air in CO offsets the altitude's effect on dielectric strength. I agree that the change is fairly small. I design HV TWT supplies for, among other things, military planes (radar and countermeasures), and some of what I do is qualified up to 90,000 feet (most go to 65,000). I also do some commercial equipment. We typically consider 3,000 feet elevation to be ground level. Most commercial equipment is certified to 10,000 feet and does not require special precautions, considering everything we do is potted in silicone compound. Air insulated equipment is another story.


A note on observing single storms. I have also seen the phenomena
mentioned where lightning seems to stop before it reaches my station and
then starts again on the other side.

I agree. There are many documented examples of strikes in a valley between two ridges. Assuming the storm is a static thing that moves across terrain and only hits the highest point is a mistake.


A good analysis of strokes to
an area as small as a ham station would take many years of data,
probably much more than is available in the current u.s. dataset.  Even
for detailed studies of power lines the minimum size data block we
normally use is 10 minutes on a side (about 10mi) and we average the
data over a 10 year period.

There you go again, trying to confuse us with data :-)



David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

73, Didier KO4BB


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