>>From hullr-at-whitlock-dot-comFri Aug 16 13:38:33 1996
>Date: Fri, 16 Aug 1996 11:04:25 -0700
>From: Richard Hull <hullr-at-whitlock-dot-com>
>Subject: Re: Safety FAQ is here -- draft, asking for comments.
<major snipage of Skip Greiner's and Robert Stephens' comments>
Robert Stephens (I) wrote:
>> I don't see this phenomenon one of streamers building on previous
>> pulses, but rather a rapid succession of individual streamers,
>> occuring in sequentially increasing and decreasing lengths, each
>> with a differing length due solely and traceable to no other reason
>> than to the power level that created each individual one of them.
>> I had meant to post this earlier but have nor had time, I've noticed
>> in the meantime that the idea of employing a high speed streak camera
>> by Steve Roys has been suggested. If my hypothesis is indeed
>> correct, a fast enough camera will certainly be able to verify it.
>> Comments welcome as always.
>> Regards, rwstephens
Richard Hull responded:
>Robert, Steve, Skip, All,
>No streak camera is neaded! A common time exposure with a fan blowing
>vertically causing a continously drawn arc to rise will show 30 to 40
>seperate smaller arcs in a filmy web as the arc rose during the exposure!
> I mentioned on a previous post we have a number of photos with this on
>it which we dumbed the banjo effect.
>All arcs make it, though, to the full length of the channel!! Even the
>weak ones! The weak one images are of reduced brightness, though. The
>arc channel is definitely pumped with ions which rise with the arc. The
>recombination time, even in air, is much longer than 2.5 msec. (seconds)
>Thus, the arcs feed off of the previous arc channel's ions and zip
>readily out to distances which, individually, they couldn't reach due to
>Robert's comments about reduced cap energy along different parts of the
>input sine. As the arcs FIRST breakout, however, they are short, but do
>feed on the last arc's energy and cause the following arcs to reach ever
>greater and greater distances, until they either strike something or
>until the channel has reached the limit of what constant pumping with the
>limited energy of the system will support, in air. A question that we
>have never asnwered, is what causes the arc channel to hang on when
>striking and then break when the energy is still pourin' in. We have
>lots of theories on this, but no definitve answers. I think this is
>where the terminal capacity comes in and relates to having "shot its
>bolt" so to speak. The "storage well" is empty. Maybe the Ion load
>(impedance) of a constant long time arc reaches the impeadance value of
>the terminal load, and through voltage division, lowers the gap potential
>over which the arc is jumping. This would explain the FAILURE of new
>arcs following the break from a long hot, sustained arc to restrike along
>the same path, but look for another direction entirely! Still, there is
>no real proof of even this!
>We have studied the hell outta' this subject here in Richmond over the
>Richard Hull, TCBOR
Richard H., Malcolm W., Greg L., Bert H., Brent T., Steve R, Skip G., All,
This has become quite popular and I wish to address all of you in
general to save some time. Does anyone remember that Skip started
all this? :)
In my original post I achnowledged the long time existence of an
ionized path remaining in place after the light (energy) dissipated
from the previous arc. I didn't have a handle on the timeframe of
the existence of such lingering ionization. Richard Hull has helped
put it in perspective. I am certainly suprised to learn that pulsed
streamers created with less than a full capacitor charge along the
charging sine wave reach out just as long as the full charge
streamers, just less luminous.
I am certainly finding this exchange interesting and educational. I
do wish to say however that no one has yet given me evidence of
succeeding streamers 'building' upon their immediate forerunners. The
forerunners are gone by the time the next streamer comes along. Yes,
there is an ionization pathway that helps successive streamers to
propagate, but I think maybe the definition of 'building upon
preceeding streamers' is fuzzy or misleading, or subject to
As I see it there may be two major interpretations. Mine is: "O.K.
you've got a streamer (ionized, light emitting arc channel), next
you've got the same arc channel but it has suddenly grown in length
by some increment, then maybe again something happens and this arc
channel is suddenly longer again, its light output has not ceased at
any time during this cascade of growth". That is MY definition of a
streamer building upon itself. Some of you out there may define a new
streamer heading out along a non luminous ionization highway paved by
a previous streamer as 'a streamer building upon itself'. I ACHNOWLEDGE
THIS EFFECT, but do not support the definition.
Malcolm's comment that single shot coil experiments come no where
near to the streamer length achieved at regular system break speeds
certainly shows that the existence of this ionized spark highway make
succeeding pulsed streamers using that particular highway more
successful in the length business. No argument here! Bert, your
post went into the mechanics of this in excellent detail, and I agree
with much of what you said, but not the 'stepped leader' label.
Greg Leyh has also just suggested that we might compare
this effect to the stepped leader phenomenon found in nature's lightning
whereby the propagating , advancing arc channel actually stops and
pools energy for some 50 or so microseconds before leaping 50 or so yards
and then stopping and pooling again. I responded to his post suggesting that it
is not reasonable to draw this parallel. If a Tesla coil discharge
acted this way, we would see a streamer reach out, then while it was
still emitting light, the system break would add another energy
pulse, and we would see our existing streamer, make a jump in extra
length, the process continuing until a balance was achieved between
the system power and the loss load on the streamer. Perhaps this
would be observable with a system operating at ultrasonic break
rates, but I certainly haven't see it a modest typical rates of
400 PPS. And, if this WAS occuring, Richard Hulls 'banjo effect',
when the wind blows the arc channel sideways, would only be
observable at the outward ends of the streamer, not over
its entire length.
Please excuse me if I appear to be dragging this thread too far.
Richard's and Malcolm's most recent posts attempting to explain the
cause for a long time (relatively) connected super-hot streamer to
suddenly disconnect and look for other targets is certainly another
related phenomenon worthy of research and explanation.
Comments, flames, welcome.