[TowerTalk] Static, Lightening, and protection

[Tom Champlin]

No one can predict what lightning will do, regardless of whatever protective 
mechanism is used, or regardless of the theoretical prowess of the designer. 
I have observed many hams who have a yagi above their tower, but do not have 
the 20 foot 2 meter shaft above the yagi who have never had any lightning 
problems. I also know hams who did have this big lightning rod above their 
yagi who lost the whole station. After personally inspecting such an 
installation that had just been hit, I decided to never have anything above 
the yagi except maybe 5' of mast for the truss. In 13 years, I have never 
had a hit. I do use heavy solid copper radials and 3 ground rods under the 
tower to help dissipate a strike should one occur. I also use the Polyphasor 
coax lightning arrestor which may be of some value.

73, Tom W0HH


----- Original Message ----- 
From: "Tower (K8RI)" <tower at rogerhalstead.com>
To: "Jim Lux" <jimlux at earthlink.net>; <TOWERTALK at contesting.com>
Sent: Sunday, March 21, 2004 9:48 PM
Subject: Re: [TowerTalk] Static, Lightening, and protection


> I'm gonna stick with it just as I wrote it. <:-))
>
>
> >
> > ----- Original Message -----
> > From: "Tower (K8RI)" <tower at rogerhalstead.com>
> > >
> > > First, Lightening is a discharge of static electricity, just like the
> > spark
> > > from your finger to the door knob after walking across a carpet.  They
> are
> > > pretty much developed by the same kind of process which is friction
> > removing
> > > electrons from atoms.
> > Not exactly.. shuffling your feet across the carpet is a somewhat
> different
> > charging mechanism than, say, rain drops and ice crystals being carried 
> > by
> > up and down drafts.
>
> Not really,  Electrons are stripped by friction.
>
> >The exact mechanism for thunderstorm electrification is
> > the subject of a fair amount of research (made more difficult by the 
> > fact
> > that thunderstorms tend to kill probes inserted into them).
>
> True, but it's not the basics, but the actual mechanics for which we still
> search.
> Such as the amount of energy given off when hail stones are formed and the
> amount of energy
> They contribute versus the water and wind. One theory holds that only with
> hil forming is there enough energy to produce thunderstorms.
>
> >
> > >
> > > The lightening strike occurs when a low enough resistance path is
> > > established between two points be they cloud to ground or between two
> > > clouds.
> >
> > Resistance has very little to do with spark/arc breakdown in air.  It's 
> > a
>
> It has every thing to do with it. Just not in the way most people think in
> terms of resistance.
>
> > (not very well understood, in the details) ionization phenomena, with
> > cascading leaders proceeding in short jumps, with charge moving through
> the
> > leaders to the head end of the leader.
>
> How they proceeded is one thing, but the ionized air is a relatively low
> resistance compared to the sourrounding air.
> >
> >
> > >
> > > It can be, and has been shown using a Tesla coil, and Vandegraff
> generator
> > > that some pretty hefty sparks can be developed.
> > And, as well conventional capacitors... A Tesla coil has a v, ery
> different
> > spark propagation mechanism than lightning or a DC single shot spark 
> > (like
> a
> > Van deGraaff generator, or, more commonly in impulse research, something
> > like a Marx generator).  However, like lightning, these are all
> > characterized by extremely non uniform fields, at least at some point in
> the
> > process. (Tesla coils can make quite long sparks with relatively low
> > voltages because they are repetitive impulses and have high peak power 
> > in
> > the impulses)
>
> True, but lightening strikes consist of a number of relatively short 
> pulses
> with high currents and very high, or steep rise and fall times.
>
> >
> >
> > Add a couple Lenhide Jars
> > > (sp?) and they and give you a poke you won't soon forget. It has also
> been
> > > shown that a single *sharp* protrusion added to the static ball on top
> can
> > > completely eliminate the *big* spark.  A coronal discharge will 
> > > develop
> > > around the sharp point bleeding off the energy.
> >
> > Yes, indeed, having sharp corners will create corona, which will bleed 
> > off
> > charge, but that's a small scale effect.  On a Van deGraaff generator,
> where
> > you're basically charging a capacitor of a few tens of pF with a current
> of
> > microamps, a corona current of a microamp is significant.  When you're
> > looking at transferring 10's of Coulombs at kiloAmps, as in lightning,
> it's
> > another story entirely.  Corona is the bane of HV engineers everywhere
>
> Except the build up is not abrupt. It may take tens of seconds or even 
> more
> than a minute for the charge differential to build.  If the build up can 
> be
> spread out, or partially drained it should have a positive effect.  With 
> the
> sharp points the charge should start bleeding immediately while still low.
> That is not to say the lightening strike could be prevented.   Maybe so 
> and
> maybe not.
>
> > (except those making ionizers<grin>) for a bunch of reasons: Where 
> > there's
> > corona, there's ozone and nitrogen oxides and other reactive/corrosive
> > species, which tends to degrade insulation; Corona is often a precursor 
> > to
>
> You should see the top of my tower.  I have to replace the connectors 
> every
> couple of years.  The HF antenna switch looks like I'd mounted it near a
> chimney.  All of the connectors are badly corroded on the exterior.
> Likewise, electrical tape doesn't do well. So far the longest lasting
> insulation has been the UV protected heat shrink and the liquid electrical
> tape.
>
> > breakdown (by effectively reducing the total gap length)
> >
> > > This is the premise behind lightening rods, static balls, and static
> > wicks.
> > > How well it works in real life is the question.
> > >
> > > It should be noted that "Static wicks" are a requirement on most
> aircraft
> > > certified in the last 20 or 30 years.
> >
> > These wicks are designed to reduce P-static, not eliminate lightning
> though.
> > What they're really designed to do is to reduce the corona
> > inception/breakdown voltage, so that as the airplane body gets charged, 
> > it
> > discharges in lots of little zaps as opposed to a few big ones.
>
> Those things look like little running lights when in heavy rain near a
> thunderstorm. They become a steady corona.  Once they do that you are dead
> reconing on the gauges with no nav instruments.
>
>  Essentially
> > the same as putting a needle point on your Van deGraaff generator
> collector.
> > Charge still accumulates (from the precipitation particles (impact
> > charging)) at the same rate, but it dissipates more quickly. They also
> > provide a "preferred location" for the discharge to occur (i.e. the 
> > static
> > wick, as opposed to your Com or Nav antennas).
> >
> That is true, but once the corona becomes visible the Nav and Com antennas
> only hear the noise.
> > >
> > > OK, so we know lightening is nothing more than the release of a very
> > > powerful  "spark" of static electricity between two charged points
> >
> > Ooops.. the big problem with lightning is that it isn't a simple gap
> between
> > two points.
>
> Didn't say simple gap.
>
> >  At least one of the sides is a fairly large (km) scale diffuse
> > charged cloud, and the other is the earth.  Sure, there are rough and
> pointy
> > spots on the earth side, but in the context of the overall scale 
> > (several
>
> I think from what I've seen the main charges are more on the order of 
> rather
> localized spots a few hundred yards across (most of the time).  OTOH I was
> headed north at 5000. There was a thunderstorm over Gladwin MI (GDW). We
> were well to the east by probably 15 miles.
> He had just asked me how close we could get when the storm gave a very
> graphic answer. A lightening bolt came out of the storm at roughly our
> altitude. It came straight at us, parallel to the ground.  Then it
> gracefully curved down and struck the ground about 2 miles to the west of
> us.  That lightening bolt struck a good 10 miles ahead of the storm and 
> out
> in clear bright sunshine. Actually it was almost 10 miles of blue sky
> between the strike and the exit point from the storm.  I had the camera
> pointed at the cloud, but did not get the lightening bolt.  However I do
> have a good photo of the area within seconds of the strike.
>
> > thousand meters), a few tens of meter isn't going to make a lot of
> > difference.  And, you'd have a hard time using the "shortest distance"
>
> It's not the shortest distance. They call it the tallest object which
> doesn't mean the same thing.
>
> > argument to explain why golfers standing in open fields get hit.  The 2
> > meters or so isn't going to make a lot of difference in a gap of 1000
>
> You wouldn't think so.
>
> > meters.  Likewise, the field concentration from that golfer isn't all 
> > that
> > big, in the context of the 10kV/meter kinds of fields you see before a
> > strike.
> > >
> Again, you wouldn't think so.
>
> Yet they tell us that if your hair starts to stand on end (been there and
> done that)
> curl up on the balls of your feet and make as low a target as possible and
> with as small a foot print as possible.  I dove in a pickup (through the
> open windown) instead.
> The strike hit the tower behind the truck.
>
> The main thing is ... Lightening is unpredictable.
>
> I'd head of it being capable of striking as much as 10 miles out fromt he
> storm, but never thought I'd have a front row seat from a mile up to watch
> it happen.
>
>
> Roger Halstead (K8RI, EN73 & ARRL Life Member)
> N833R, World's Oldest Debonair (S# CD-2)
> www.rogerhalstead.com
> >
> >
> >
>
>
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