Re: some new ideas for the SSTC guys

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi DC,

At 08:58 PM 10/3/2004, you wrote:
>
>Problem --- Exploding IGBTs when they are hit with a sec - pri spark 
>(Terry Blake's coil terrible demise at our Teslathon).
>
>A few years ago I did some experiments with a flat spiral coil (18 dia. 
>sec.).  In the classic configuration with a .05 uF cap, RSG, and 4.5 turn 
>primary the sec sprayed out 8 ft long sparks.
>
>At the urging of a plasma physics guru from UW-Madison (Paul Nonn for 
>those of you who might remember meeting him at Ed's recent Teslathon), I 
>removed the sec coil and placed it on a stand 10 feet away.  I used a 7 
>inch corona ball on the bottom to prevent any corona and used a single tap 
>which I attached to the "normal" primary coil.  With some re-tuning it was 
>again spraying out 8 ft sparks.

High coupling is not required if the primary and such losses are low.  If 
there are nil losses, there is only one place for the power to go 
;-))  Even 0.03 CCs work in many cases!!

>
>What I'm getting at here, is, the SSTC experimenters, Dan M., Steve W., 
>etc, might try using a larger dia sec coil and then use a 15-20 turn test 
>primary coil while feeding the sec coil a few feet away.  If this works, 
>then the greatest danger to SSTCing, ie, blowing the IGBTs should become a 
>problem of the past.

My failed model was also trying to reduce coupling to "isolate the primary 
circuits from bad secondary effects.  Modeling always tended to show that a 
few amp streamer hits would not hurt much on a conventional coil.  Even the 
OLTC was pretty well protected with a few transorbs.  Dan's book shows that 
a ground strike can greatly increase IGBT current which certainly is a 
factor to be dealt with!!

>
>It will take some experimenting --- perhaps the best tap is "inside" the 
>normal classic tap location or perhaps it will be "outside", but either 
>way, getting the sec away from the primary to act as a series fed setup 
>should eliminate the IGBT explosion problem.  If it does work the primary 
>can be either a flat spiral or normal solenoid coil --- perhaps enclosed 
>in clear acrylic with a large "feeder" wire over to the sec coil.

I think they should reduce the coupling a bit and go with a flat 
spiral.  But what do "I" know :o))

>
>If someone DRSSTC tinkering wants to experiment with this idea on their 
>present or planned near future coil, please advise and I will send you a 
>nice 10 ft long chunk of #6 AWG for experiments --- with 125 kV BIL 
>insulation --- it's 1 inch thick and offers great HV feedwire 
>performance.  We use this "big Red" on all our HV power supplies to feed 
>the 14.4 kV HV over to the base of the oscillator.
>
>Might work, might not, but worth trying.

Ya always have to keep trying ;-)))

Cheers,

         Terry


>
>Dr. Resonance
>