"Ian White, G3SEK" wrote in message
...
Ed Price wrote:

I would think that lightning protection should begin with the safe
equalization of charges.

Oh, how we all wish! But think what that implies...

If one could prevent localization of charge, there wouldn't be anything to
discharge.

That would require control over the weather - and again, oh how we all
wish!

I fully understand what I implied; this would be a technique well beyond our
current capabilities. OTOH, it would be a grand concept. And we wouldn't
have to "control the weather", just finesse one part of it, for a short
time, in a very local region, so it might be applicable to protecting
extremely valuable items and events, like maybe a shuttle launch or landing.


Failing that, if one could provide a controlled discharge mechanism, that
drains charge without a massive discharge channel, that would also be
good.

But again, we don't know how to do that. Starting from a weakly ionized
probe leader, lightning has a huge positive feedback mechanism. Once it
has started to go, it'll go all the way!


You don't know how and I don't know how, but that's a long way from knowing
that it's impossible. And I won't concede that there's no mechanism to
modulate a discharge.



Failing that, you fall back to a point g defense; first dissuading the
creation of a conductive channel to the protected area,

If an ionized leader has made it all the way down from the cloud into the
region of the protected area, we don't know any way to tell it "Wrong Way.
Not In My Back Yard".

If the leader has come so close, you absolutely cannot stop what's
probably going to happen next. All you can do is do is to design the
protection system to make the best of it.

or, failing at that, providing a specific, perhaps sacrificial path for
the massive discharge.

At last, we've come down to earth. All that lightning protection can
realistically aim to do is providing a specific path. The whole aim of
lightning protection is to provide a safe discharge path *past* the
structure that's being protected, as opposed to a damaging path *through*
the structure.

A "sacrificial" path is not an option to design for. The lightning
conductor *must* hang in there for the whole duration of the stroke(s), or
else protection will be lost before it's all over.


Sacrificial was a bad term; I didn't mean to imply that it wouldn't be
durable, just that it would be the path to take the hit and protect the rest
of the local area.



To keep the original discussion in perspective, all this stuff about
terminals at the top end of the conductor is about trying to achieve some
kind of "come here" effect in literally the final few feet of the entire
lightning path (or tens of feet, if we're really lucky) to make sure the
leader attaches to the terminal and not somewhere else on the structure.

The well known and most reliable way to do that is to make the terminal
higher than everything else, so it dominates the local electric field. But
that's still no guarantee that a leader won't come wandering down at some
distance off to the side, and then strike downward or even sideways from
there.


Bottom line: it's absolutely vital to be realistic about what lightning
protection can do - and also what it cannot do. A system designed out of
hopes and dreams will be the wrong system.


I HOPE I'm not there when it hits, and you're DREAMING if you think I'll
volunteer to hold the rod. That's being REALISTIC on my part. Seriously, if
all you can propose is a thick, conductive pole, then you are entering the
fight at your last line of defense. Think about the whole problem, not just
optimizing the existing solution.

And BTW, what would be so bad about having some way to create a conductive
channel from the charge to a place of YOUR choice? Even that modest goal
could vastly expand the "cone of protection" that existing masts provide.
Imagine being able to initiate safe cloud-to-cloud discharges. Imagine being
able to direct all charge for a one-mile radius to discharge (even
violently) to a designated lightning rod. One rod could protect an entire
building; several rods could protect an entire large airport. My speculation
about selection paths of ionization by RF excitation was just groping toward
one way to create those channels, and HAARP naturally came to mind.

Ed
wb6wsn