TSSP: List Archives

From: Bert Hickman
Date: Wed, 16 Oct 2002 14:07:30 -0500
Subject: Re: [TSSP] Top Voltage

Hi Paul,

Defining "true" breakout, in single shot mode, as the point where the DC 
voltage suddenly changes across the resonator base capacitor makes great 
sense. It's a straightforward measurement, it should be minimally 
affected by the (much smaller) corona currents, AND it doesn't require 
specialized equipment to perform or measure. Cleanly defining the 
criteria and also capturing the voltage when initial breakout occurs 
should provide a meaningful worst case breakout measurements.

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
"Electromagically" (TM) Shrunken Coins!
http://www.teslamania.com

Paul wrote:
> Hi All,
> 
> I've made up some code to output E-field profiles through the
> field around the coil.  It also does equipotential charts.
> 
> Plotting the normal component of the E-field as we rise above
> the top of the OLTC sphere terminal, we get
> 
>  http://www.abelian.demon.co.uk/tmp/tf1210ab.field.gif
>  
> The red trace shows the sphere in the low position, down close
> to the toroid, and the green shows the sphere raised high.
> 
> Both spheres have been set to a potential which gives 30kV/cm
> at the surface.
> 
> In both cases the initial drop of the field is the same, both
> act much like an isolated sphere when examined close to the
> surface. 
> 
> The fields become noticeably different beyond about 1cm above
> the surface.
> 
> By about 8cm above the surface, the E-field is asymptotic
> towards the background field from the toroid beneath, which for
> the low sphere (red) is higher because the it's not as far above
> the toroid.
> 
> I was hoping there might be a big difference near the surface,
> in the first cm or two, but appears not.
> 
> Something qualitatively odd with these breakout voltages:
> 
> We'd expect that as the sphere is raised above the toroid,
> it becomes more exposed and we would expect a lower breakout
> voltage.  Down near the toroid, the sphere is better shielded,
> and in accordance with the usual effect of shielding, the
> sphere breakout voltage would rise.
> 
> This is borne out by the model voltages, 175kV for the low sphere
> and 101kV for the high. 
> 
> Terry's measurements on the face of it, seem to be the other
> way around:
> 
> tf1210a: 12th Oct, medium sphere just above toroid,
>          http://hot-streamer.com/temp/OLTC10-12-04.gif
>          Observed: 4 in 64 shots @ Vfire=250, equates to 188kV
>          
> tf1210b: 12th Oct, medium sphere raised to 7.25" above toroid,
>          http://hot-streamer.com/temp/OLTC10-12-11.gif 
>          http://hot-streamer.com/temp/OLTC10-12-11.CSV 
>          Observed:  50% breakout @ Vfire=270, equates to 204kV
>          Observed: 100% breakout @ Vfire=300, equates to 226kV
>          
> Requiring what seems like an increase from 188kV to 204kV.
> However, the former is described as 4 breakouts in 64 shots while
> the latter is 50% breakout.  
> 
> Perhaps if the high sphere was set to a Vfire which gave a 4/64ths
> breakout, then it would be below 250 rather than above 250.
> 
> Therefore I think we must try to set a standard for saying that
> breakout has occured, in order to make relative comparisons.
> Perhaps we should raise Vfire in each case to the point where
> a DC component is detectable in the base current.  As in the
> recent tests with a base blocking cap.   
> 
> Chances are that when the coil is at 50% breakout, it is already
> well above the breakout threshold.  Perhaps we should fire at
> very slow BPS, raising Vfire each time until the first bang 
> that leaves a residual DC on the base blocking cap.  Then stop
> at that point and record Vfire.  Hmm, if the voltage across
> the base cap was fed to a scope trace, the residual DC would be
> clear, and the peak Ibase can also be read off at the same time,
> by taking the peak volts across the cap and calculating from that.
> --
> Paul Nicholson,
> --
> 






Maintainer Paul Nicholson, paul@abelian.demon.co.uk.