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Re: Sparks to ground
Tesla List wrote:
>
> >From hullr-at-whitlock-dot-comMon Nov 18 20:06:15 1996
> Date: Sat, 11 Mar 2000 02:35:50 -0800
> From: Richard Hull <hullr-at-whitlock-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Sparks to ground
>
> All,
>
> It has been stated on this list that one an arc contacts ground that the
> resonator Q goes into the hamper to near zip.
>
> I was reviewing some frame by frame video hits of maggey #11-E and note
> that the arc channel develops over an extended period of time!
>
> I note a spark approaching the heavily grounded aluminum siding on my
> house. The contact occurrs, let us say, at t0, in frame, f0. The arc
> channel is fairly dim, but contact is made and the arc channel is 115"
> long point to point. In the next frame, f1, (1/30 second later) the
> channel doubles in brightness.(as measured by my light meter (spot
> reading). In frame f2 the arc channel increases in brightness by another
> 40% or so over the preceeding frame. In frame f3, the channel retains
> about the same brilliance (white hot) as in f2 frame. In frame f4, the
> channel starts to reduce its brightness and is about 65% of f2s level.
> Frame f5 shows a greatly reduced channel intensity and is just about 10%
> below that of f0s level. In frame f5, The channel is just a faint mist
> of ionized vapor. Frame f6, shows the channel to have disappeared.
>
> Assuming 400 BPS (which is my normal break rate), This means that the
> system has energy pops at the rate of about 13 pulses per video frame. so
> we see that from time of contact to max brighness,(more or less), we
> actually sent in about 52 energy pulses. Is the electronic Q of the
> resonator system this slow to respond?!! Energy delivery to the arc
> channel was consistently on the increase over this long period
> (~120,000 usec).
>
> The rise to max channel current is rather slow, compared to the
> extinguishing of the channel which never takes more than 2 video frames
> (1/15 sec-60,000usec).
>
> I am making no judgments here, only reporting observational fact.
>
> Richard Hull, TCBOR
Richard and All,
Very interesting! Although my experience has only been with 2-coil
systems, and maximum arc length only in the 60-65" range, I suspect
that fundamental arc behavior is probably not much different. Storage
scope measurements I've taken seem to suggest that Q declines
dramatically during heavy arcs to ground. Are these measurements and
Richard's videotape analysis inconsistent?? I really don't believe they
are...
Q may be defined as the ratio of stored energy divided by the amount of
energy lost per radian. Resonator Q is a dynamic, real-time, reflection
of energy losses from all sources. While total resonator energy
typically changes very little over 1 radian, the denominator can change
instantly (and dramatically), particularly if the rate of energy loss is
large. For example, prior to breakout, resonator Q is typically quite
high (say 150 -200). However, once active streamers form, Q declines
significantly; I've measured "effective" secondary Q's of about 10-20 on
my system, depending upon power level, BPS rate, and streamer
variations. In general, the heavier the streamers, the lower the Q.
Once we initiate a heavy toroid-ground discharge, the rate of energy
loss climbs dramatically. In previous measurements, virtually all of the
energy in the resonator/toriod was lost in about 1.5 uSec, or about 1/8
of one cycle at Fo, This translates to an effective Q of less than 1
while the ground arc was firing. In effect, the arc became a
prodigious energy sink for all the energy the resonator could deliver! I
have little doubt that if we were still transfering energy to the
resonator at the time of the discharge, the additional energy would
_also_ get unceremoneously dumped into the arc.
So what does all of this mean when we get to the NEXT bang?? For a
disruptively excited system, not much at all! Once the previous bang's
ground-arc is extinguished, resonator Q returns to its high pre-breakout
value as though nothing had ever happened. Q only begins dropping during
the next bang once we resume losing energy to streamers or another arc
to ground.
In my view, the videotape observations of Maggie #11-E and the above
discussion of Q are not inconsistent. I did not mean to imply in an
earlier post that resonator Q stays low, only that it abruptly
transitions to a very low level during the time we are arcing to ground.
During the arc, Q doesn't go to zero, but it does appear to go below 1.
This very low value simply reflects the fact that virtually _all_ of the
resonator's energy is being removed during a brief, but powerful,
discharge.
I've tabularized the above videotape observations below with some
comments to the right:
Relative
T Lightmeter
(mSec) Reading: Comments
------- ------- --------
f0 33 1.0x Arc initiated
f1 67 2.0x Arc channel strengthening
f2 100 2.8x Arc at full strength
f3 133 2.8x Arc at full strength
f4 167 1.8x Arc weakenning
f5 200 0.9x Visible arc remnants almost gone, no re-strikes
f6 233 <x Arc completely extinguished, no re-strike
There are a couple of things that may be occuring in the above
sequences.
One _could_ assume that arc currents are increasing on successive
re-strikes, This is very plausible - If a heavily ionized trail
has been blazed and not had time to fully deionize before the next bang,
the successive discharge may further increase the supply of ions,
thereby lowering arc losses. When reignited during the next bang, larger
peak currents might flow, making subsequent discharges brighter (albeit
briefer). Richard, I seem to remember an earlier post where you provided
some evidence for this in a videotape analysis of streamer intensities
(discharging to air only) in the presence of variable "bang" energies.
Its also possible that the camera was integrating an increasing number
of
successful ground hits per frame. As a previous arc-path leaves its ion
trail ghost, there may be greater opportunity for lower-energy "bangs"
to
fully bridge the path blazed by their larger predecessors. The
progression from frame 1 could reflect only the "bigger" bangs
connecting at first, followed by more/all successive bangs connecting in
frames 2 and 3, until the discharge path begins to be disrupted in frame
4. This situation might occur as ground arc length approaches the
maximum sparklength for the coil. Once the channel begins breaking up,
only the larger bangs still connect (but just barely). In any case, I
don't see anything in the above scenarios that conflicts with the
changes in Q I've measured versus type or strength of discharge. Food
for thought! :^)
Why does arc breakup seem to take a shorter time than the buildup to
full strength? This may be related to turbulence which may be more
prevalent around a higher temperature, fully formed, multiple-strike arc
channel. In the power industry, turbulent mixing between the arc plasma
and a cooler media is used with great effectiveness to rapidly
extinguish arcs in high power/high voltage circuit breakers. Another
area for future TC research! :^)
My best wishes to you Richard, and safe coilin' to you all!
-- Bert --
P. S.
Richard, could you provide a little description of how you made the spot
lightmeter readings? The "brightness" of a videotaped arc image should
be related to the sum of the individual strokes. The more strokes/frame,
or the greater the current/stroke, the brighter the resultant image.
However, this would seem to presume that the camera tube's target isn't
saturating from the brilliance of the discharges...