Re: Overcoupling?

To: tesla-at-pupman-dot-com
Subject: Re: Overcoupling?
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Thu, 06 May 1999 08:21:22 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Antonio,

> Original Poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> 
> 
> Terry Fritz wrote:
> 
> > >       The corona area you mention is probably a natural high field
> stress area
> > >that linear wound Tesla coils have about 2/3 up the secondary.
> 
> Why? 
> 
> Frequently I see the term "overcoupling" in this list, but can't see
> what it means. I don't see a reason for increased voltage gradients
> along the secondary just because the coupling coefficient to the
> primary is increased. A primary closer to the secondary would induce
> sparking between the two coils, certainly, but why sparks along the
> secondary? Would not this effect be due to tuning to a higher order
> resonance mode instead?
> 
> Antonio Carlos M. de Queiroz

Three things I can think of:
- the voltages do get higher at certain values of k as the energy is 
transferred much more rapidly giving the gap less time to lose it 
- closer proximity of the primary to the secondary encouraging corona 
formation around the secondary, particularly with raised primaries 
such as conical or helical (I've seen this in small systems)
- excitation of spurious resonances causing the secondary to be 
electrically shortened because of the presence of the upper sideband.
I finally had to accept that this is a possibility after Terry's 
current msmt results, much as I don't like the idea. Perhaps this is 
a field ripe for further measurement and exploration to see which 
of the above is correct.

Malcolm