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Re: Voltage determination
----------
> 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
>
>
>
> Tesla list wrote:
> >
> > Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov>
> >
> > in free air, uniform field (not the case with a TC), it is roughly 30
> > kV/cm. Needle gaps run about 1/3 that (or close to the 1 kV/mm from
> > Jeroen), but, OTOH, needle gaps are notoriously erratic, especially as
the
> > voltage gets high. They are particularly sensitive to surrounding
objects
> > that perturb the field, and to various other ionization effects (UV,
> > radiation, etc.)
> >
> > You could use the uniform field number as an upper bound..
> >
> > The voltage on a TC is more realistically limited by the radius of
> > curvature of the top load. If your top load had a radius of curvature
of
> > 10 cm (i.e. the "tube" of the toroid was 8 inches in diameter), and it
were
> > very smooth, the maximum voltage would be around 300 kV. Any bumps,
> > ripples, etc. will tend to reduce the voltage. The larger diameter
(i.e.
> > across the toroid) has very little effect on the breakdown voltage, but
a
> > lot of effect on the capacitance.
> >
> > When the field is nonuniform (and changing), you can produce very long
> > sparks in a very low overall field. The field before lightning strikes
is
> > typically less than 10 kV/meter, and that's a fairly long spark in a
field
> > that is 1/300th that for breakdown (3 MV/meter)
> >
> > ----------
> > > From: Tesla list <tesla-at-pupman-dot-com>
> > > To: tesla-at-pupman-dot-com
> > > Subject: Re: Voltage determination
> > > Date: Friday, July 21, 2000 4:32 PM
> > >
> > > Original poster: "J. Kooiman" <jkooi-at-wish-dot-net>
> > >
> > > Hi Tom,
> > >
> > > There is a standard to it, 1000 V (1kV) by 1 mm
> > > So for 40 cm that would be around 400.000 Volts (400kV), give or
take a
> > few.
> > >
> > > greetings from Jeroen Kooiman from Holland.
> > > web :
> > <http://www.crosswinds-dot-net/~jeroenk>http://www.crosswinds-dot-net/~jeroenk
> > >
> > >
> > >
> > >
> > > > Original poster: "TruckDrivingMan" <Tom.Ansorg-at-t-online.de>
> > > >
> > > > Hi all !
> > > > I just finished my first coil,and I was wondering how much kVolts
it
> > > > spreads.The spark length is ~40 cm,the NST needs ~1,7 kW.Any ideas
for
> > > > measure
> > > > methods ?
> > > >
> > > > Tom
> > >
> > >
> > >
> > >
>
>
>
>