Re: Tracking inside secondary former

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Clearspring1-at-aol-dot-com>

Bart and Mark,

Thanks for your explanations of the propagation of internal flashovers and 
the resultant carbon tracking.  I believe you have also helped answer my 
wonderings whether "more is better" when it comes to internal baffles 
intended to thwart such flashovers.  I am thinking an extra baffle in the 
middle of the former would be cheap insurance.  (To the inquiry that appeared 
earlier about how to place such a baffle: with a friction fit, merely pushing 
the baffle midway into the former with an appropriately-sized, squared-off 
pipe or piece of wood should work fine.)

Bart points out the basic rule of the increased arc distance found with 
"insulator"/air interfaces as one of the main dynamics, which makes perfect 
sense.  This leaves me wondering why David had such success with his Sonotube 
baffles which were a "snug" fit in the secondary former, but were not sealed 
to the former.  Perhaps a significant volume of air is required for this 
interface phenomenon to take place?

Thanks all!

Michael Tandy

>>Where
there are voltage nodes large enough to conduct along a surface body (from one
node to the other), it will surely do so. Causes of this might be the form
material itself or even from the form being dirty. Once there is an arc from
point a to b, there will be carbon. This creates a conductive path until the
carbon track acts as a short (that's when the burning starts). 

I see basic principles involved here: voltage potential between two points and
if anything between the two points has a low enough resistance to arc at that
potential (air included). 

Bart <<

>>  My rule-of-thumb SWAG is based on the fact that, generally speaking,
arcs like to take the shortest available path. And, if there are any
sharp conductive corners (like a less-than-perfect solder joint or the
pointy bits of a hex nut) on the inside of the form, and nothing but
smooth surfaces (like a nice toroid and a good ground) on the outside,
you'll get higher e-field intensities on the inside to start arcs with
in the first place.

  Once the arc starts it will rapidly heat the nearest material; the
core. Since the heat is very localized carbonization is inevitable.
Once a carbon track is started good external spark generation is
unlikely.

  OTOH that "generally speaking" above is mitigated by such things as
path heating and self-repulsion (writhing arcs).

  The above ignores form defects (holes, conductive inclusions, etc.),
uneven windings, and other possible causes of e-field inhomogeneties.

  Mark L. Fergerson<<