Re: the cure for racing sparks

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Paul,

A local coiler here was tuning up his coil for the first time.  His coil is
very similar to my big coil (he was using mine as a model).  When the thing
was out of tune, he could arc 1+ foot long arcs from about 6 inches up the
secondary to the primary coil.  At the time, I could not possibly imagine
how he could be getting such high voltages so close to the base of the
secondary.  They were easily in the 150++kV range.  Not streamers, but hard
snap voltage arcs!!  I wish I had a picture...  I was thinking that it was
do to the turns ratios between the primary and secondary producing those
high voltages.  But as everyone explains to me, the coupling is too low for
that.

However, your animation shows just such an effect!!  The only thing wrong
with the coil was the tuning ws off, (it was very sharp).  Once the coil
was in tune, it ran perfectly.  The coil never showed signs of racing arcs.

BTW - I am a little behind on the top volts probe :o))  I had better get
that done...  I just got a couple 'more' Pearson 411 current monitors off
ebay today too :-))

Cheers,

	Terry



At 04:01 PM 7/13/2002 +0100, you wrote:
>Antonio wrote:
>> ...streamer formation? Maybe as lightning ...about 0.3 m/us? 
>> ...operating frequency of 100 kHz has 10 us. A streamer could
>> then move 3 m in the time of one cycle. The numbers look close
>> to what could cause problems, but not quite there yet.
>
>Yes, we're in the same ballpark, but as you say, the numbers don't
>quite agree unless we take it that streamer extension only occurs
>during quite small portions of the RF cycle, eg the bits marked #
>below, and it might even retreat a little during the o portions.
>
>      #  #                            #  #
>   #        o                      #        o
> o            o                  o
>o              o                o
>                o              o
>                 o            o
>                   #        o
>                      #  # 
>
>Perhaps we might gain a factor of 5-10 from this, thus forming
>circa 30cm per RF cycle?  I guess with racing arcs of case #2,
>the problem should manifest more with higher frequency coils. 
>Is there evidence of this I wonder?
>
>Streamers often seem to display a segmented structure - say 2-4
>distinct sections, brightest at the base near the topload, weakest
>at the extremities, with well defined boundaries between sections.
>Perhaps if an N section streamer forms over N half cycles it would
>account for this appearance.  Does anyone have a good photo of
>this effect?
>
>It'll be real nice to see topvolts scope captures from breaking-out
>coils because of lot of this stuff can then be checked out pretty
>quickly, I think.
>
>I'll just add another case to the list, 
>
>#A Rapid changes to topload boundary conditions during streamering.
>   Scatters energy into HF modes. (VC)
>
>Here's a little animation which illustrates the idea behind case #A
>
> http://www.abelian.demon.co.uk/tssp/pn040502/tfsm1-h1d2.anim.gif
>
>The time axis should be mS not uS as shown. This model is of a
>rather unnatural short discharge from the topload.  Not quite case
>#8 because the discharge arc is not maintained in this model, but
>similar to case #A.  We see the transient bounce along the coil a
>couple of times, dispersing as it goes, until eventually the coil
>is awash with random HF ringing.  Along the way, it can produce
>some pretty nasty voltages.  With case #A you'll have to imagine
>lots of small transients instead of the one big one modeled here,
>but the effect is to fill the coil with HF noise.
>
>Scope trace capture of the coil base current during streamering 
>would give enough data to say if case #A is happening or not.
>
>Case #8 might show discharges from near the middle of the coil
>occuring only in coincidence with discharges from the topload.
>
>Case #A might show thin weak arcs racing all over the coil, but
>only when the topload is issuing streamers.
>
>Does anyone have any examples of these cases?
>--
>Paul Nicholson
>--
>