From: Bert Hickman
Date: Mon, 07 Oct 2002 22:39:34 -0500
Subject: Re: [TSSP] TOPV breakout threashoul
Marco.Denicolai@tellabs.com wrote:
>
> Hello all,
>
> > -----Original Message-----
> > From: bert.hickman@aquila.net [mailto:bert.hickman@aquila.net]
> > Sent: 7. lokakuuta 2002 14:45
> > To: tssp@abelian.demon.co.uk
> > Subject: Re: [TSSP] TOPV breakout threashoul
> >
> >
> >
> > The effect of space charges on RF breakdown is presented in Loeb
> > ("Fundamental Processes of Electrical Discharge, McGraw-Hill/Chapman &
> > Hall, 1939), reflecting the work of L. E. Reukema. Reukema used sphere
> > gaps
> > and relatively short gaps (0.25 - 2.5 cm). He found a progressive
> > lowering
> > of breakdown voltage, by as much as 17% (about 25 kV/cm), as the
> > frequency
> > was increased between 20 kHz and 60 kHz. However, no further breakdown
> > voltage reductions were seen between 60 kHz and 425 kHz.
> > -- Bert --
> > --
> > Bert Hickman
> > Stoneridge Engineering
> > "Electromagically" (TM) Shrunken Coins!
> > http://www.teslamania.com
> >
>
> I recall Reukema was cited on:
>
> Meek, Craggs (eds.), Electrical breakdown of gases, John Wiley & Sons,
> 1978.
>
> I think the 17% was for uniform field. For not-uniform one (e.g.
> point-plane) the breakdown lowering was about 50%. I haven't got the
> book here right now :(
>
> Just to have an idea, think to the Plank dissertation. If I got it
> right, they were counting corona pulses as a mean to detect gas
> mixtures. Humidity and applied voltage highly influenced the pulse
> frequency. By just adding a DC component to applied voltage they were
> able to change the breakdown characteristic and find a "plateau" where
> the counting was almost independent from the previous factors and much
> more usable for industrial purposes.
>
> Best Regards
Hi Marco and all,
You have an excellent memory! In chapter IX of Meek and Craggs ("High
Frequency Breakdown of Gases"), Reukema's studies are covered - air gaps
of up to 2.5 cm between 6.25 cm spheres showed about a 15% reduction in
breakdown voltage for the range of 60-425 kHz. Similar results were
obtained by other researchers for uniform and near uniform field gaps (9
other references).
Studies done by Misere and Luft for highly nonuniform (i.e.,
point-plane) gaps showed significantly lower breakdown voltages at 370
kHz versus 50 Hz - 46% lower for a 3 cm gap and 70% for a 25 cm gap.
However, this is most likely due to initial breakout initially occurring
at a low voltage at the point, followed by "long spark" streamer
propagation after a space charge was created. Although the surface of a
smooth toroid is admittedly nonuniform, I would think that (for a
reasonably large ROC) it's closer to the sphere-plane or sphere-sphere
case than the highly nonuniform point-plane case at least as far as
initial breakout voltage is concerned.
Best regards,
-- Bert --
--
Bert Hickman
Stoneridge Engineering
"Electromagically" (TM) Shrunken Coins!
http://www.teslamania.com
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.