Re: Recent s.s.t.c work

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Finn Hammer <f-h@xxxx>

Ken,

Before you get to firing this coil up at full 
power, It is my duty to report my recent experience with internal primary`s.
I was amongst the crowd that reported troublefree 
operation of internal primary`s.
The coils that I based my recommendation on, were 
a couple of OLTC`s and a couple of SSTC`s, both 
running in short bursts of up to 20 discharges at 
a time. The SSTC`s were pulsed at 200µS and the 
OLTC`s had the usual ring down caracteristic with 
one noch quench at K=0.2 anf Fres=70kHz.

I later built a DR-SSTC prototype to run about 
1.2 meter streamers. K=0.23, Fres=55kHz and internal primary.
This did not work out for very long. I did not 
understand the fault mode very well to start with 
(wonder if I do now!) but this is what happened:
Running the coil, I soon noticed a lot of smoke 
from the inside of the sec. former, as well as 
light from it.(running in the dark)
I inspected the primary coil, which was hevy PVC 
insulated wire, and found burned insulation on 
the top turn. Just a point where it is bent back 
inside the primary to go back to the bridge.
On the sec. coil there was also a zoot mark.
Running the coil at length in this condition 
caused the sec. to form a long zooty track on the 
inside, the whole length of the winding, and the 
output got progressively shorter in the process.

Stripping the wire off the sec. former showed 
that there had not been any puncture in the sec. 
former, so the transfer from the sec. to pri. has been capacitive.

I started to understand this at the same time 
when Stephen Ward showed, that it is not possible 
to insulate one`s way out of a corona problem: If 
you stuff dielectric into the gap, and the 
gradient in the remaining air gets higher.
Another poster noted that at RF, there are no 
insulators, just better or worse capacitors.

I now think that to make an internal, or any 
primary in physical close proximity to the sec. 
work, the only solution is field controll. Since 
the pri. windings are inherently pointy in an 
electrostatic sence, I think the solution lies in 
introducing a smooth grounded shield btwn pri and 
sec. this shield has to be slotted, perhaps in 
multiple pieces, to avoid 1, shorted turn, 2, loop current heating.

The purpose of this shield is to shape the field 
btwn sec. and this shield, so that no corona is formed.

I hope this all makes sence, and that it will be 
of use to you. In the meanwhile, the coils that I 
ended up making got to aquire a rather dull, conventional look:
http://home5.inet.tele.dk/f-hammer/DSC00135.JPG


Cheers, Finn Hammer

Tesla list wrote:

> Original poster: "K. C. Herrick" <kchdlh@xxxxxxx>
>
> Here's what I'm designing into the delay circuit 
> that I need, to be interposed, in the overall 
> feedback circuit, between my "pilot oscillator" 
> and the rest of the IGBT-driving circuits:  4, 
> 74HC164 8-bit serial in/parallel out shift 
> registers in tandem, clocked at 5.0 MHz using a 
> free-running Vishay XO-52B5.0 clock module.  The 
> last 16 outputs of the S-R chain will feed into 
> a pair of CD4512BC data selectors, which will be 
> addressed by the 4 LSBs from a TLC0820AC A/D 
> converter.  The MSB of the address drives the 
> /OE inputs of the selectors, one of them via an 
> inverter, so as to alternate their wire-Or'd 
> Tri-state outputs dependent on the address.
>
> The A/D's 0-5 V input will come from a pot, 
> located15 ft away in the control box.  And the 
> converter will latch its output during spark 
> events, so that changes in delay may be made only between sparks.
>
> In this way, I will be able to control the delay 
> of IGBT turn-on/turn-off so as optimally to 
> align those events with primary current 
> zero-crossing, as my simulation indicates I can 
> do.  I suspect that I may be able merely to 
> watch the spark and tweak the pot for maximum, 
> thereby choosing the delay that produces the 
> minimum power wasted in IGBT turn-on and turn-off.
>
> Happily, it's all ICs except for a few bypass 
> capacitors and the pot, so layout & wiring will be relatively easy.
>
> Ken Herrick