Re: More Coupling...

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Paul, All,

At 11:22 AM 12/23/2000 +0000, you wrote:
snip...

>Terry wrote:
>
>> You will notice that the voltage dV/dL is greatest about 25-30% up
>> the coil!!  The old sine function for secondary voltage is long gone
>> now...
>> The current is like 40% higher in the lower section of the coil
>> than at the base!!
>
>Perhaps not quite so high up when a larger h/d ratio is used. But
>there is some theoretical and good experimental evidence (from Terry)
>that the highest voltage gradient occurs at a point some way above the
>base of the coil. Maybe 10% to 40% up. That's for the free resonance.
>Add to that the EMF induced from a driven primary and if there's
>going to be trouble, it will be in this region of the coil.
>
>Peter Lawrence  <Peter.Lawrence-at-Eng.Sun-dot-com> wrote:
>
>> What bothers me at the moment is all I've heard is "smaller K
>> required for the smaller TCs", but no explanation of why - 
>
>It may be that for one reason or another a higher coupling coefficient
>might be desirable, but to achieve higher k means raising the primary
>which puts its max induced EMF closer to the part of the secondary
>which already has the highest stress. Perhaps therein lies the benefit
>of a cone primary, spreading the induced EMF more evenly along a
>longer length of coil, thereby allowing use of a higher k or more
>power before somethings breaks.
>
>To illustrate this idea, I've plotted the profile of the induced EMF
>due to a primary current, for Bart's secondary with his flat primary
>at k=0.205, and for a hypothetical cone primary with the same k.
>
>   http://www.abelian.demon.co.uk/tmp/bart-emf-profiles.gif
>
>Remember that the profiles shown are the voltage *gradient* and is
>just the component of EMF due to induction from the primary. The free
>resonating secondary voltage gradient would need to be added to this
>(with account of phase) to get the actual voltage gradient of the
>driven secondary. It's clear that using the cone primary considerably
>reduces the peak EMF gradient in the secondary for the same amount of
>coupling. Compare the location of the induced EMF peaks due to primary
>drive, with that of the free resonating secondary gradient as measured
>by Terry in the second graph in 
>
> http://www.abelian.demon.co.uk/tssp/pn2510/
>
>Clearly the potential (excuse pun) for secondary breakdown is going
>to be increased if these two peaks coincide. 
>
>Note also that the cone primary in the example profiles has a 50%
>higher self inductance for the same k factor - of possible benefit to
>primary tank circuit efficiency.
>
>acmi has been modified to produce the above EMF data when given the
>command line option -profile, which also suppresses the normal output.
>eg
>
>  ./acmi -profile < bart.in > bart-gradient.data
>
>Data is output in two columns, turn and relative-voltage-gradient.
>
>Peter Lawrence  <Peter.Lawrence-at-Eng.Sun-dot-com> wrote:
>
>> However, I seem to have had the most racing sparks in the middle
>> of my secondary, not at the bottom.
>
>Does your secondary have a modest h/d ratio, say 3:1 or less?
>Is it positioned quite high up off the ground, say a third or half
>a coil length? Do you operate without a ground plane beneath your
>secondary - relying on the building ground? I suggest tentatively that
>each 'yes' answer will raise the point of maximum stress higher up
>the secondary, although not higher than the mid-point.
>

snip...

This is, of course, very significant!!  It appears that racing arcs are now
starting to be understood (finally!).  The effects of the conical
primaries, as opposed to the flat, are very interesting too.  We now try to
avoid cone primaries since the higher coupling is believed to help create
racing arcs.  However, perhaps we are wrong and the people who have
preferred cone primaries for that last 100 years knew what they were doing
after all ;-)))  If higher coupling can be achieved while avoiding racing
arcs with cone primaries, the efficiency of a coil can be improved.  There
are a lot of variables and details with all that but we are getting pretty
good at figuring these things out ;-)


>Finally, I should admit to an ulterior motive behind acmi. Next year
>the software model of the secondary as used by tssp will be extended
>to take account of the primary coupling. It is hoped to adopt the 
>current filament summing technique as used by acmi, therefore any
>experimental validation of this method will be of direct benefit in
>the calibration of this part of the model.

That would be super neat!  

Although an order of magnitude beyond that, it would also be neat to have
it do the full arc to ringdown transient responses of everything.  In
otherworlds, the voltages/current from the moment the gaps fires to when it
all rings down (maybe with a streamer load!?) as a function of time.
Perhaps theoretically not to tough in light of all this new data but the
computing power needed to do that would be "big" ;-))  Since it is
Christmas I figure I can ask for anything ;-)))  Next Christmas, I'll ask
for the 3-D real time visualizations 8-)

>
>Many thanks for your various contributions - from which considerable
>progress has been made thus far.

It is interesting that such work does not add to, but multiplies what is
already known!!  Thanks a bunch Paul for all this wonderful work!!

Cheers,

	Terry

>
>Regards All,
>--
>Paul Nicholson,
>Manchester, UK.
>--