[TowerTalk] Lighting

Jim Lux jimlux at earthlink.net
Tue Jul 6 18:54:00 EDT 2004


Precisely that, Jerry... 

They've collected gigabytes of data from field mills all over Cape Canaveral, and I'll bet they really don't have a real handle on what might make a strike one place rather than the other.  Sure they can predict that they'll get X number of hits within Y area over a given time span, but as to what might explain the phenomenon you mention.. 

There are folks seriously looking at storm electrification and the fine scale behavior of lightning storms, but, it's hard to get lots of data.  You CAN say that if you're the highest grounded thing for miles around, you're probably more likely to get hit, IF there is a strike, but as to whether the structure might affect the rate of lightning....

There are people looking to trigger lightning artificially to protect high value items (rockets sitting on pads?) using things like lasers to ionize the air, but I don't know that it works all that well.  It certainly doesn't work well enough for them to discard all the conventional lightning protection (i.e. strike damage protection) surrounding the gantry and launch facility.  If you've got a $100M box or a billion dollar shuttle sitting there, you'd have to have a LOT of faith in your lightning prevention widget to justify getting rid of the existing mass and hassle of EMP/Lightning protection stuff.
  ----- Original Message ----- 
  From: Jerry Keller 
  To: Jim Lux 
  Sent: Tuesday, July 06, 2004 3:19 PM
  Subject: Re: [TowerTalk] Lighting


  And so we are left to attempt to define the undefinable in terms of explaining its behavior. I refer again to the many instances described by guys in the midwest, that T-storms with lots of lightning seem to stop striking as they pass over their well-grounded tower farms, and resume striking after they have passed. I have seen some of this myself at a distance, and the only thing that makes any sense is that the ground under the towers is sometimes less attractive for a strike than the ground elsewhere. 
   
  I love a mystery!!  :-)  73,  Jerry K3BZ
    ----- Original Message ----- 
    From: Jim Lux 
    To: Tom Rauch ; Wilson Lui ; 'David Robbins K1TTT' ; towertalk at contesting.com 
    Sent: Tuesday, July 06, 2004 5:56 PM
    Subject: Re: [TowerTalk] Lighting



    ----- Original Message -----
    From: "Tom Rauch" <w8ji at contesting.com>
    To: "Wilson Lui" <wilsonlui at atitec.com>; "'David Robbins K1TTT'"
    <k1ttt at arrl.net>; <towertalk at contesting.com>
    Sent: Tuesday, July 06, 2004 2:07 PM
    Subject: Re: [TowerTalk] Lighting


    > Thanks Dave and Wilson.
    >
    > > Grounding does not prevent strikes. What a proper
    > grounding system does do
    > > is allow for any lightning strike that does happen is
    > condected safely into
    > > the surrounding soil and not arc through any
    > equipment/structure trying to
    > > find a lower resistance path to earth.
    >
    > That's my opinion also, based only on the physics involved.
    >
    > I notice a large group of people actually think lighting
    > does not hit grounded structures because grounding causes
    > the charges to bleed off or dissipate.
    >
    > I'm curious where that idea actually came from. Does anyone
    > know?
    >
    It might go back as far as Ben Franklin, inventor of the lightning rod.
    There is much "lore" (no better word for it.. anecdotal, not based on any
    sound theoretical basis, etc.) about one kind of air terminal or another.
    The problem is it's really, really, really hard to do objective tests.
    There were some researchers at Erico (in Australia) who designed a HV power
    supply that can recreate the E field time history before the strike to do
    the testing, but I think they ran out of funding or were transferred or
    found other jobs before they got any substantive results.  The usual HV
    testing deals with the "after the strike" currents (e.g. the classic 2
    microsecond rise time (10%-90%) and 50 microsecond fall (to 50%) double
    exponential used for lightning impulses) or for switching surges (much
    slower rise and fall times).

    As it happens, there's not much commerical market in validated lightning
    prevention.. Nobody has anything that's 100% guaranteed, so you'd have to
    have a afterstrike damage protection scheme anyway, and once you have that,
    you don't care as much about whether you do or don't get hit.  There's
    plenty of market for one sort of air terminal or another, but, it appears
    (to me) that the selection would be based more on speculation than any hard
    science.



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