Re: Official air breakdown voltage?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: William Beaty <billb@xxxxxxxxxx>

On Fri, 25 Nov 2005, Tesla list wrote:

> Original poster: "JT Bowles" <jasotb@xxxxxxxxxxx>
>
>
> I have read all over the net, around 25KV/inch  <<I use this one
> I read on one place,           around 30KV/inch

The e-field threshold voltage for air-breakdown is around 30KV/cm.  The
other values above are wrong.


> Now i have just been told    around 30KV / cm  !!!!   Thats 3 times
> the voltage I have been told

That's not a voltage!  You misunderstand.  The breakdown value for air is
a value of e-field, not a voltage.  It's the value of e-field located at a
point in the air.  It has little to do with the voltage between two wires,
or the voltage at a tesla coil terminal.


For example, if you put 30KV across two wires, then hold them an inch
apart, the e-field will NOT be 30KV/in in the space between the wires.
Instead the e-field will be very strong near the surface of the wires, and
very weak in the empty space between them.  The strong field near the
wires can trigger a spark, even though the breakdown field is 30KV/cm and
the wires are an inch apart.

>
> It is common sense that air pressure, humididty, current, and time of
> day all affect air breakdown voltage, but:
>
> IS there any official way to determine exactly what air breakdown
> voltage is? ( such as KV/distance )

Yep, but there are three things you need to know.  First, to eliminate any
tiny regions of strong field, use large, polished balls as electrodes.
Second, to create a parallel field, the
maximum distance between the balls must be at least 10x smaller than the
balls' diameter (meaning, use large balls with a tiny gap between them.)
And third, there is a voltage between the balls' metal surface and the
empty space.  If you simply measure the breakdown field by measuring
the breakdown voltage and measuring the gap distance, you'll be off by
about 1KV.

See Jim Lux' page on this:

  http://home.earthlink.net/~jimlux/hv/paschen.htm



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