Re: [TCML] measure VDG voltage

[Jim Lux <jimlux@xxxxxxxxxxxxx>]

-----Original Message-----
>From: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
>Sent: Dec 22, 2007 5:53 PM
>To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
>Subject: Re: [TCML] measure VDG voltage
>
>Hi Bert,
>
>I measured a 1" ball gap back when doing TSSP measurements for Paul. I'm 
>at a very low altitude of about 100 ft above sea level here in a CA. I 
>measured 26kv/cm at that time. I think the 30kv/cm is a nice roundabout 
>number, but I think 26kv/cm is a more accurate number and not just from 
>my own measurements. I know where the 30kv/cm is from, but from my own 
>measurements and others who have measured (including papers on the 
>task), I've seen values between 26 and 27 and "never" higher. That 
>4kv/cm does make the terminal voltage little lower.


For how long a gap?  If the gap is much more than 1/10th the size of the spheres, it's not a uniform gap anymore (for which that nominal 30 kV/cm number applies).  The actual calculation for spheres is a pain (no exact analytical solution that doesn't involve infinite series), and, there's a lot of stuff that can affect the exact voltage (surface finish, dust, etc.)

Most people use the tables (which can be scaled, to a point), and trust that you get around 5% accuracy, when you're looking at multiple tests averaged.


There is a paper I ran across recently in the context of high power RF breakdown at 100 kHz kinds of frequencies which looks like the breakdown for CW RF could be half that for DC or line frequencies.

I can't remember the author, title, or journal, so I'll have to wait til after the first when I get back to work.. It's laying on my desk.


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