Re: [TCML] Re:Pros and cons

[jimlux <jimlux@xxxxxxxxxxxxx>]

uhvsystems@xxxxxxxx wrote:
> 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.


I sort of agree.  As a practical matter, tesla coils tend to have 
certain popular design sizes, based on the availability of HV 
transformers (may be less so for solid state), so for a "neon sign 
transformer" powered coil, of any configuration, there's probably an 
optimum pps, just because there's not a huge design space in terms of 
physical configuration that works at all.  Likewise for pole transformer 
based designs, which tend to run at 14-15kV rms and a few kilowatts 
(here the practical limit might be the mains power supply.. it's 
inconvenient to wire up something for more than about 50Amps at 240V)


> 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!

The latter is not much different from a transient on a EHV line 
triggering a long spark, and those, while not common, have certainly 
been observed. To a certain extent, the voltage at the electrode from 
which the spark starts isn't much different (in terms of spark growth) 
whether it's 100 Hz or 100Hz modulated 100kHz.

> 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.

In fact, lower voltage coils,like the very small ones using a 
electromechanical interrupter (buzzer), tend not to have long sparks, 
but more of the brushy discharge or lots of shorter sparks, say, 10cm 
long. So your observation is interesting about leader corona.

The maximum voltage at the top of the tesla coil is almost certainly 
limited by the radius of curvature of the electrode, and empirical 
evidence suggests that toroids are better than spheres, even though the 
max voltage is less for the same overall size.
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