Re: Strike Rail

To: tesla-at-pupman-dot-com
Subject: Re: Strike Rail
From: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Thu, 30 Mar 2000 18:33:47 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Bart,

> Original Poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net> 
> 
> 
> >
> > Original Poster: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz>
> 
> 
> Ok John and Malcolm, 
> This is interesting  - comment below: 
> 
> >
> > > There is some indication that in many coils, a strike to the primary 
> > > is unable to damage the cap because the low impedance of the 
> > > primary "kills" the voltage.  Also overvoltages will be shunted across 
> > > the safety gap.  I do not use a strike rail on my coils....I just let
the 
> > > sparks hit the primary. 
> > > 
> > > cheers, 
> > > John Freau 
> >
> > My reaoning exactly. I don't use strike rails either and the primary 
> > gets hit plenty. 
> >
> > Regards, 
> > Malcolm
> 
> 
> 
> 
> I was thinking that a high powered system may be better off with a strike
rail.
> Would either of you say a high powered (14.4kv/694mA pole pig driver)
strike to
> the primary have no ill effects on the cap? It just seems a 1.6MVp-p
strike may
> find it's way across the gap to the cap and possibly back to the transformer.
> Does the low impedance of the primary actually stop this from occurring
> regardless of power levels? 

The cap - unlikely as it can only climb back up to its original 
charged voltage if all energy from the secondary somehow  got 
transferred back into it - unlikely in view of transfer losses. This 
would happen with no breakout anyway so I can't see a problem 
there. The gap is essentially still in a conductive state when 
secondary sparks burst forth so the transformer terminals are still 
shorted by the gap so differential voltages don't seem likely if the 
transformer is electrically close to the gap (which mine always are 
these days).
       The only thing I could see happening is a high common mode 
voltage racing back towards the transformer terminals but I haven't 
seen any evidence of it in the systems I fired recently. If anything, 
pigs should be more immune to damage from that kind of event 
because of their BIL ratings.  I could always be proved wrong 
however so if in doubt, don't try it.

Regards,
Malcolm