Re: Voltage determination

["Ed Phillips" <evp-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Tesla list wrote:
> 
> Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
> 
> ----------
> > From: Tesla list <tesla-at-pupman-dot-com>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Voltage determination
> > Date: Saturday, July 22, 2000 10:26 AM
> >
> > Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net>
> >
> > Hi Jim, All,
> >
> > Agree about the needle and ROC situation, but I'm not sure about the
> 30kV/cm.
> 
> 30 kV/cm is the (approximate) breakdown for air in a uniform field. It
> would be the BEST you could do with a TC.. that is, the 40 cm spark could
> be as much as 1.2 MV (but it isn't likely, for other reasons).
> 
>  I
> > have no idea what it is but I'm starting to wonder if this value varies.
> I've
> > seen this value used (and several others). In the archives, I read a 1998
> post
> > from Bill Wysock stating that 13M "may" be around 8kv/inch (or near) and
> that
> > the output voltage was about 1/3 less than originally thought. This was
> based
> > on an IEEE paper he was reading at the time which appeared to leave an
> > impression on him.
> 
> 8 kV/inch is quite low...  but wouldn't be unrealistic for a very high
> voltage in a very long gap with a highly non-uniform field.
> 
> For a sphere gap of 40 cm (but the spheres are fairly big, >1 m diameter)
> the breakdown is around 900 kV
> (http://home.earthlink-dot-net/~jimlux/hv/spherev.htm) (around 22 kV/cm).  The
> rod gap (1/2" square rods) shows anywhere from 225 to almost 400 kV,
> depending on the waveform, etc
> (http://home.earthlink-dot-net/~jimlux/hv/rodv.htm), for a breakdown of around
> 6 kV/cm (15 kV/inch)
> 
> >
> > I'm not sure if Bill remembers that one, but it did start me pondering
> that
> > possibly a volts/unit value may change with coil power, dimensions,
> > environments, etc. If it does change, then is it too much to use a
> standard?
> > Maybe it doesn't - I don't know.
> 
> kV/cm changes a huge amount, and is highly dependent on environment and the
> electrode configuration.  Particularly as the voltage gets above 500 kV,
> the field nonuniformity caused by the spark leader is probably the dominant
> factor.
> 
> For a fairly recent and fairly complete discussion of long sparks, Bazelyan
> and Raizer's "Spark Discharge" (CRC Press) would be a good reference.
> >
> > I'm curious if anyone else has insight on the subject. Is there a
> consensus?
> >
> > Thanks,
> > Bart

	There are very useful for [low-frequency] gap breakdown voltages for
several different electrode shapes in the Handbook of Chemistry and
Physics, also CRC press.

	Of course, once leaders/streamers begin to form all bets are off and
spark length has more relation to input power than voltage across the
coil.

Ed