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Re: [TowerTalk] Lightning Damage

To: Jim Brown <jim@audiosystemsgroup.com>
Subject: Re: [TowerTalk] Lightning Damage
From: jimlux <jimlux@earthlink.net>
Date: Tue, 18 Aug 2009 10:36:51 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Jim Brown wrote:
> On Tue, 18 Aug 2009 08:13:23 -0700, Michael Tope wrote:
> 
>> BTW, I am not familiar with series suppressors 
> 
> Series-mode suppressors have been developed that are quite 
> effective on power line branch circuits. They work by storing the 
> strike voltage in a very large inductor, then discharging it 
> slowly once the strike event has past.






One example would be a series L followed by a shunt C (yes.. a low pass 
filter).. In a typical transient, the real problem is the high peak 
voltage, not necessarily the actual energy in the transient.  The low 
pass filter spreads the big sharp peak out into a lower longer one. 
Obviously, if you can set things up so the energy is dissipated, you're 
better off.

However, consider this.. say you have a "300 Joule" surge suppressor.. 
You're running your electronics which is say a few hundred watts..That's 
several hundred joules per second. Take that 300 Joule impulse and 
spread it out over a couple seconds, and you're not really talking about 
much.


NOTE... we're not talking about direct hits from lightning here.. that 
is up in the kilo or megajoule range, and needs totally different 
treatment.  This is line transients of a few kV (UL 1449 says 6kV @ 
500A, 1.2x50 uS for voltage, 8x20 uS for current)

By the way, a new version (3rd)  of 1449 goes into effect in a few 
weeks. It's now called ANSI/UL 1449-2006

For phone lines and similar things (a rotator control would probably fit 
this description), the appropriate standard is UL 497, 497A, or 497B, 
depending on the application. The B standard is probably the most 
appropriate for datacomm sorts of signals.


Eaton has a nice TVSS handbook on this sort of thing (googling might 
find it) which talks about the waveforms, the 3 location categories 
defined in IEEE C62.41 (branch circuits indoor receptacle, major feeders 
& inside service panes, and service entrance & outdoor long lines)


The standards call out both a voltage and a current, because the 
assumption is that the voltage will cause a breakdown or clamp and then 
the transient source can produce substantial current.  (i.e. testing 
from a 10kV supply with a 10 Meg resistor in series isn't a very 
realistic test...).  The test equipment needed is not trivial, by the way.

A 1999 IEEE paper by R. Siegert and O. Mohammed describes one approach 
(using a big capacitor, a triggered spark gap, and RLC networks for 
pulse  and impedance shaping)

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