[TCML] Re:Pros and cons

[uhvsystems@xxxxxxxx]

John,
Good points.I'm not expert on this but I have impression that the concept of one and the same PPS rate which would be ideal for all TCs is an illusion.By "ideal" I mean the best one for power input-spark lenght relationship.Too many things affect spark growth.From the geometry (top load) and size of the coil, output voltage peak,voltage  wave form and frequency to enviromental and atmospheric cicumstances.

Dex,

I'm 99.99% certain there's no SGTC ( at sea level altitude) which can generate 8 m long sparks at 100 impulses per second peaking 750 kV.Perhaps,in a long run this is possible with 1000 PPS or more but I'm not sure about that.OTOH,I'm positive that TC peaking 1200 kV at 100 PPS has a high probability ,in a long run,to break 8 m long gap!

Jim,

200-300 kV is a very interesting remark.This is a voltage range where first appearances of so called *leader corona* and *leader flashes* are experimentally observed.That should have consequences to the  behaviour of the sparks in HV impulses machines like tesla coils.To illustrate,if 250 kV SGTC is in position to prolong sparks 3x their single shot lenght at typical PPS rates,with 100 kV and corespondingly smaller impulse energy it wouldn't do much better ,at typical break rates,than about 1.3x spark lenght  in 100 kV single shot discharge.


regards,
Fez Zaev
       
  
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John Freau <futuret@xxxxxxx>  wrote:
 
Steve, Dex,
I'm thinking that a coil which has a rather small bang size for the physical 
size
and toroid size, may need a higher break rate for best results, just to bring it
into the sweet spot.  At low break rates, the spark may be barely breaking
out, and barely coalescing, etc.  I do think that large coils tend to be 
somewhat
more efficient in general.  It would be interesting to greatly increase the bang
size of Greg's coil, and then see what breakrate is best, and if the spark
length still grows well with increases of breakrate.  The toroid size is a 
factor
in these issues too.  Once the spark length reaches 3 or 4 times the toroid
diameter, the sparks have a much harder time growing longer.  With a small
bang size, a higher breakrate is needed to grow the spark to 3 or 4 times
the toroid diameter.  At that point the spark length is maxing out pretty 
much anyway, based on toroid size.  Much of what we see regarding
the performance of coils at various breakrates may have a lot to do with
the toroid diameter.  For example if the bang size of Greg's coil was 
greatly increased, then his coil would probably give long sparks at a
much lower breakrate.  Then if the breakrate was increased, the sparks
might not grow very much.  However if a much larger toroid was installed,
then the spark length would again increase more as the breakrate was
increased.  It's a matter of matching the input power to the toroid size
basically (within some acceptable range of breakrates).  In a totally
optimized system, a lower breakrate around 120 to 150 bps is probably
still best.... at least that's my guess.   
Regards,
John

Dex Dexter <dexterlabs@xxxxxxxxxxx> wrote :
 Large SGTC:
 
 http://www.lightninglab.org/gallery/2008Teslathon/images/120L02.jpg
I was quite amazed when Greg Leyh (who designed it) told me it could
put out 25 ft long discharges during outdoor 25 kW /350 BPS operation.
Since the coil is  DC charger powered ,the bang size from bang to bang
is constant and is somewhere between 70 and 75 Joules (only).
As can be seen this is a big coil which probably has something like
140...150pF secondary effective capacity.With 100% efficiency and no loss
peak secondary voltage would be aprox 1 MV.Some Dr.Resonance's resarches
indicate that in reality most sparking SGTCs peak at about 65%-75% of
their max possible voltage without loss.
Therefore,max voltage for this coil is about 650..750 kV.
Greg also said the best BPS rates given input power are somewhere between
100 and 350 BPS (what you with your 250 PPS DRSSTC observation confirmed).
I suppose he has experimentally reserched such things in a great detail.
So,the questions like how good this coil would perform at say 1200 BPS
and fixed bang size of 75 Joules are quite interesting.
I wouldn't bet the arcs would be much longer.
They would be  thicker and bushier instead I think.
Too low output voltage and bang size despite great  power input.
Do you (dis)agree?
Dex


jimlux <jimlux@xxxxxxxxxxxxx> wrote:

I suspect that most coils are in this category. at 30kV/cm, 200-300kV (which is probably a typical topload voltage for a small NST coil) would only support a spark of 7-10cm, and sparks much longer than that are common. 
 
The difficulty is multifold: 
 
The field is very non-uniform, which tends to lead to longer sparks, even in a single shot environment (Bazelyan and Raizer's book talks about this a lot, in connection with EHV and UHV transmission systems and switchgear) 
 
you have multiple pulses which can successively extend the spark through a previously ionized channel. 
 
As an obvious indication of unusual behavior, a lot of coils have sparks longer than the distance from topload to base, without arcing over the secondary coilform. 
 


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