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Re: 3MV/meter



Tesla List wrote:
> 
> >From rwstephens-at-ptbo.igs-dot-netSat Sep 28 10:18:18 1996
> Date: Sat, 28 Sep 1996 09:24:16 -0500
> From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Re: 3MV/meter
> 
> >>From MALCOLM-at-directorate.wnp.ac.nzFri Sep 27 21:57:14 1996
> >Date: Fri, 27 Sep 1996 17:46:46 +1200
> >From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> >To: tesla-at-pupman-dot-com
> >Subject: Re: 3MV/meter
> 
>
> <snip>
> 
> Malcolm, All,
> 
> In John Kraus' book Electromagnetics, 4th edition, table 4-3, on page
> 149, lists a table containing common dielectric materials and their
> dielectric strengths.  Air (atmospheric pressure) is listed at
> precisely 3 MV/meter.
> 
> I guess that means any air filled meter that considers itself a  _real_ meter
> should be capable of measuring 3 megavolts. :-) Ha, ha.
> 
> Back to seriousity though, a very thorough treatise was done on using
> sphere gaps to accurately measure HF AC discharge voltages, as well
> as DC voltages in air by Clark and Ryan. Their work is used commonly
> in the industry as the authoratative standard for air breakdown
> values.  In order to get an accurate measurement it is imperative that both
> terminals have a smooth (polished clean) surface with a radius of curvature
> somewhat larger than that of the length of spark being measured.
> Large objects in the vicinity of the spheres can also cause
> perturbations in the extended field surrounding the spheres, and
> therefore ruin the accuracy of this test method.  I cannot find
> the reference where I have seen the exact figure for sphere size just now but a
> radius of 2X spark length seems to ring a bell.  The Clark and Ryan paper
> shows a chart tabulating the results of measuring sparking voltages between
> two 7 inch copper spheres with electrical current at 25 CPS and
> 123,000 CPS.  At 123 kHz, 1 inch of air was broken down at 48
> kilovolts.  At 25 Hz,  1 inch of air breaks at 52 kilovolts.  The
> breakdown values versus distance were perfectly linear up to the 50
> kilovolt range.
> 
> Malcolm, even your 35 kV/inch rule-of-thumb is slightly low, but may
> actually be more realistic when you factor in the common use of smaller
> radius or pointy terminals.
> 
> regards,
> 
> rwstephens

Robert,

I have seen papers where the Corums use 4KV/inch HF RF air breakdown 
potential.  Don't know where they came up with that value though!  There 
are as many thoughts on this as there are religious beliefs.

Richard Hull, TCBOR