Re: Testing caps -> NST protection (fwd)

---------- Forwarded message ----------
Date: Wed, 29 Jul 1998 00:01:17 -0600
From: "D.C. Cox" <DR.RESONANCE-at-next-wave-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Testing caps -> NST protection (fwd)

to: Terry, Malcolm

This 2xErms value sounds very suspiciously like a blum line device ---
characteristic with cap value and very low inductance value producing 2E at
the other end --- pehaps at the safety gap area if the values are just
right for true blum line effects.


> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Testing caps -> NST protection (fwd)
> Date: Tuesday, July 28, 1998 9:02 PM
> ---------- Forwarded message ----------
> Date: Tue, 28 Jul 98 13:35:28 EDT
> From: Gary Lau  28-Jul-1998 1326 <lau-at-hdecad.ENET.dec-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Testing caps -> NST protection (fwd)
> >From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> >Subject: Re: Testing caps -> NST protection (fwd)
> >
> >Hi Gary,
> >         Since I said it (and have lived by it.....
> >
> >> Date: Mon, 27 Jul 98 09:07:53 EDT
> >> From: Gary Lau  27-Jul-1998 0854 <lau-at-hdecad.ENET.dec-dot-com>
> >> To: tesla-at-pupman-dot-com
> >> Subject: Re: Testing caps -> NST protection
> >
> ><snip> 
> >
> >> >Finally, I think I read that if the spark gap is close enough to the
> >> >transformer, secondary RF suppression isn't necessary. Is there
> >> >on this? 
> >> >
> >> >Thanks for your comments.
> >> >
> >> >Terry Perdue
> >> 
> >> Re. RF suppression, I've heard this suggestion too and I believe this
> >> misguided advice.
> >> 
> >> Terry Fritz has made some interesting measurements and discoveries
> >> the nature of primary gap/tank circuits, in that with each
> >> crossing, the gap extinguishes, each time exciting high frequency
> >> oscillations due to parasitic L-C components.  Measurements with his
> >> fiber optic voltage probe of Vgap show brief high voltage bursts of 2X
> >> Vpri at each zero-current crossing.  This is due to C-self of the
> >> inductor, fully charged at a zero-current crossing, resonating with
> >> primary inductor.  180 degrees into this VHF oscillation, the voltage
> >> across C-self reverses and since it is in series with the tank
> >> the two caps in series now present a voltage of  2X Vpri to the gap 
> >> AND TO THE NST POWER SUPPLY, causing the gap to re-ignite.  This
> >> is not influenced by lead length or inductance between the gap and
> >> supply (although other oscillations do arise due to this).  A train of
> >> Vpri (~40KV!!!) voltage bursts applied to an NST is not too healthy
> >> it.
> >
> >If there is that kind of voltage across the main gap, why does it not 
> >re-ignite? Why should a gap several metres downstream do so? I'm keen 
> >to know.
> >
> >Thanks,
> >Malcolm 
> But I said it does re-ignite.  Let's re-examine the gap dynamics.
> At each gap current zero crossing, the primary c-self is charged to the
> identical voltage as Ctank.  When the gap current is zero, it briefly
> conducting and Ctank is no longer in parallel with the primary, but
> instead in series.  The voltages across c-self and Ctank are equal but
> opposite, so the effective series voltage (Vgap) is zero, so it can't
> re-ignite.  Primary c-self is now free to ring with the primary.  180
> degrees into this ringing, the polarity of Cself reverses and being still
> in series with Ctank, the series voltage (Vgap) is now 2Vpri.  In a
> private exchange with Terry Fritz, he provided some scope traces of Vgap
> that indeed showed Vgap bursts of 2Vpri at each zero current crossing.
> Unclear is exactly when the gap re- ignites, at 180 degrees into the
> c-self/Lpri oscillation, or shortly thereafter.  But the important thing
> is that the 2Vpri bursts are real, supported by measurement and theory.
> I never suggested that a gap several metres downstream (safety gap?)
> fire while the main gap did not.  What I am suggesting is that NST damage
> being caused not by some effect due to inductance in power supply wiring,
> but rather from the 2Vpri bursts described above, and that damage from
> phenomenon is easily avoided with a simple RC low pass filter, and not
> just by using short power supply leads.
> Regards,
> Gary Lau
> Waltham, MA USA