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secondary coatings,sealing and breakdown


> > 
> Point taken, but...
> Can anyone explain why sparks would prefer to travel down the inside 
> of the former (winding) rather than the outside ?
> 
thppppppth! Oh, sorry, had to dust off some neurons. I'd guess that the 
magnetic flux density tends to be greater inside the secondary, and 
without the added dielectric of the end caps, arc form more easily.
Anyone else?

Stan Harle
Alamogordo, NM

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Magnetic fields do have an effect on electrical discharges in that they 
help retain electrons in the regions of high magnetic field- but I think 
the magnetic field effect is not big enough to make a difference for tesla 
coils.

However, if one looks at the electric fields in and around a coil above a 
ground plane (my program shows this), one sees that the fields inside the 
coil are relatively uniform like in a parallel plate capacitor. But, just 
as for a parallel plate capacitor, if you stick a conducting object 
in between the plates the previously uniform field becomes very distorted 
and the electic field is very high near the conducting object ( especially 
if it is long and thin).

So, if you run wires or anything inside the coil form, they will distort 
the electric field and cause discharges...

I'm still confused by the advantage of hermetic sealing, though. Perhaps 
Richard can provide some more insight. A guess is that the closeed 
secondary prevents motion of the slightly ionized gases to regions where 
they can become concentrated enough to cause a breakdown....?


-Ed Harris


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