Re: the cure for racing sparks

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

Original poster: "marc metlicka by way of Terry Fritz <twftesla-at-qwest-dot-net>" <mystuffs-at-orwell-dot-net>

Hello Antonio, 
Please excuse the long delay in replying to your comments.

Tesla list wrote:
> 
> Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>
> 
> Tesla list wrote:
> (sniped)
> 
> This only indicates that the material has very high resistivity, and so
> can retain static charges for long time. This is, in principle, a good
> thing. But I have wondered if charges accumulated over the insulation
> of the secondary may be one of the reasons of "racing sparks". These
> charges can be easily moved, and could be moved by the RF electric
> fields
> along the coil, producing the mysterious sparks.

 This seems to be what I have Wondered also, It only stands to reason to
me that if the coating has an ability to hold, and possibly gain a
charge, This might cause problems. Maybe as this charge builds it might
locate itself on a lump or bubble in the coating somewhere, this along
with the field strength of the coil itself, could be just enough to
cause a breakout? This would present a racing arc along the coils
length.
 In july I had one of the most amazing racing arc episodes i've ever
seen. I took my 3k coil to our company Party, I had changed out the two
1.5kva control transformers (3kva total) with two 4000 watt light
dimming auto transformers. On set-up I lowered the primary to 3" below
the bottom most turn of the secondary, when the main contactor kicked
in, the coil developed a very strong racing arc. This arc seemed to
start right at the upper turn that aligned with the lower edge of the
toroids  bottom curvature. This arc travelled 2" OUT FROM THE SECONDARY
FORM? 
 The arc travelled from top to bottom, but it was floating in the
secondaries field?
My secondary is coated with motor varnish and wrapped with 8 mill. pvc
tape. This gives it a healthy dielectric isolation from the primary, but
the racing arc from over current still presented itself.
 The difference was instead of running down the windings, it ran in the
field of the secondary without damage.


> 
> > I have found that by using a finer wire gauge, with more turns, In the
> > primary construction to achieve the required inductance,, Helps in the
> > energy transfer from primary to secondary, AND secondary back to
> > primary!
> >  I have tried too explain this in the past, many times, but have met
> > only resistance? I will state here that in the oscillations of an
> > operating TC, not only must the tank energy be transferred to the
> > secondary, BUT It must also be transferred back to the tank circuit
> > "via" the primary coil.
> >
> >  It has been argued by me and several renowned coiling theorists, That
> > though the coupling magnetic field from primary to secondary forms may
> > be a very efficient transfer, When the secondary tries to reverse this
> > charge, There is simply far too little windings! This is why i feel that
> > a thinner wire, wider primary form works far more efficiently.
> 
> This is not true. The Tesla transformer is linear and reciprocal, and
> the coupling coefficient measured in both directions is exactly the
> same, no matter how the coils are built. It has been proposed that
> primaries with higher impedance are less lossy, due to smaller currents
> in the gap, however.

 Again my problem of explaining myself comes into play, I do not doubt
that the coupling is the same. It stands to reason that if the primary
to secondary coupling = .025, then the secondary to primary would be the
same.
 My thinking is that the primary magnetic field, Being an air core
field, drains into the secondaries windings very efficiently, (when the
gap fires).
 But, the field of the secondary winding is in a different configuration
and it literally has to drain the power from the top of the secondary
winding, down the side of the coil, to the primary.
 This oscillation between primary, or tank, to secondary and back, could
promote racing arcs in itself?
 Or at least carry any winding breakout that may happen, along with it.

I will stand by the difference in field shape and intensity and/or the
concentration (to breakout) due to inclusions at close to threshold
voltages as the leading causes of racing arcs. 
 As in the above example, the toroid shielded as much as it could, but
the over currenting of this coil allowed a breakout from bellow the
shielding to the primary. Except it was totally supported by the power
of the secondary field being drained into the primary!
 It was a great learning experience, even if no one understood why i was
so excited at the time.

Marc M.


> 
> Antonio Carlos M. de Queiroz