Re: the cure for racing sparks

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Paul and all,

Thanks for the very interesting simulations!! What model did you use for
the arc to ground? The huge voltage gradient that forms at the top of
the winding immediately after the arc is especially interesting, since
the full pre-arc voltage voltage, plus a bit of VHF oscillatory
overshoot, is now present across the top ~3% of the winding (~4.5 cm)
for a peak transient stress of about 70 kV/cm on Thor if the model is
simulating the behavior correctly... Ouch!

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
"Electromagically" Shrunken Coins!
http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> 
> I wrote:
> 
> > #8 Discharges to earth from the topload redistributes the coil's
> >  remaining stored energy into a 1/2 wave mode with a volts max
> >  around a third to half height. (RV) Cure: stay with streamers
> >  to air, or use wider toroid.
> 
> Antonio wrote:
> > The energy trapped in the self-capacitance of the secondary coil
> > is really not immediately available, and will usually oscillate
> > until dissipated.
> 
> Yes,
> 
> > The simple lumped model canīt predict what happens next in this
> > case. ...  Maybe those models that we discussed some time ago,
> > in a version (surely possible) including the primary circuit.
> 
> We just happen to have one of those :)
> 
> Modeling this situation, using dimensions for Marco's Thor system
> 
>  http://personal.inet.fi/atk/dncmrc/thor.htm
> 
> by way of an example, leads to the following time domain response.
> 
>  http://www.abelian.demon.co.uk/tssp/tmp/thor.wave.gif
> 
> with the animation
> 
>  http://www.abelian.demon.co.uk/tssp/tmp/thor.anim1.gif
> 
> This simulation assumes that there is no breakout until a certain
> topvolts threshold is reached.  At this point (40uS after firing)
> a discharge arc forms from topload to ground, and the arc is
> maintained for the rest of the event.
> 
> The resulting negative going transient propagates down the coil,
> rebounds from the bottom end, travels back to the top, where it
> again rebounds, and so on.   This is shown more clearly in this
> zoomed animation, which begins 100nS before the arc starts and
> shows the detail of the transient in slow motion,
> 
>  http://www.abelian.demon.co.uk/tssp/tmp/thor.anim2.gif
> 
> The transient seems to consist mainly of two modes: the primary
> resonance at around 68Khz and the secondary half wave at 226 kHz.
> All the other even-wave modes of the coil are also excited, roughly
> equally, at about 1/10th the amplitude of the first two.
> 
> The size and shape of the transient seems to depend on how much
> secondary energy escapes back into the relatively harmless primary
> resonance at 68Khz.  Most of the rest goes into the potentially
> damaging 1/2 wave component.  Obviously there's a lot more work to
> do on this, but there does seem to be the opportunity for primary
> tuning and coupling to affect how the coil copes with sudden
> topload discharges.  Much may depend on just where wrt the RF phase
> the arc discharge begins, which is obviously very sensitive to
> tuning and coupling.
> 
> Another thing which may affect the transient is how quickly it
> disperses, which occurs faster for shorter h/d coils.
> --
> Paul Nicholson
> --