Re: Breakdown Voltage Gradient and Paschen's Law - Doesn't make sense ?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

The equation isn't valid for "large gaps"  It's an approximation for 
smallish gaps (on the order of a few cm)

At 11:17 AM 7/18/2003 -0600, you wrote:
>Original poster: "Mccauley, Daniel H by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
>
>
>
>Something isn't making sense to me.
>
>I'm looking at some derivations of Paschen's Law in Lucas' High Voltage
>Engineering Book which states the following:
>
>**********************
>Under constant atmospheric conditions, it is found that the breakdown
>voltage of a uniform field gap may be expressed
>in the form:
>
>V = A*d + B*SQRT(d)       where d is the gap spacing
>
>For air under normal conditions:
>A = 24.4kV/cm
>B = 6.29kV/cm^1/2
>
>It then states that the breakdown voltage gradient is about 30kV/cm in
>gaps on the order of 1cm
>and about 6kV/cm for large gaps on the order of several meters
>
>**********************
>
>Using the above equation for say 1cm, I do indeed get approx. V =
>30kV/cm
>
>However, if I use d = 300cm (3 meters), i get about 24kV/cm, which is
>way off from 6kV/cm.
>
>Is there an error in the above equation, or am I missing something???
>
>Any help appreciated.
>
>Thanks
>
>The Captain