Re: Kelvin water dropper (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 20 Feb 2004 12:38:25 -0300
From: Antonio Carlos M. de Queiroz <acmq@xxxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Kelvin water dropper (fwd)

High Voltage list wrote:

> From: John Pepper <jspepper@xxxxxxx>

> I have actually wondered about this fact myself.  If one were to use
> interconnects with a .25 dia the effective corona radius is .125 in one axis
> only.  The other axis has a near infinit radius (being a long rod).  Perhaps
> then, the "virtual" radius would be some comprimise largely bias towards the
> smaller radius but still effectively lareger than a simple .25 dia corona
> ball.  Thoughts?

Thin wires can sustain surprisingly high voltages. The charges move to
the ends, leaving little electric field at the wire. The ends
must be rounded. But if the ends are simply formed into loops, again
the wire can sustain quite high voltages.
A good example is this electroscope that I have built:
http://www.coe.ufrj.br/~acmq/nichol4.jpg (the strange machine is a
"doubler of electricity").
The two small balls are suspended by thin wires, but the maximum
voltage that the electroscope can sense is practically determined
by the diameter of the balls (5 mm -> 7.5 kV. Measured: 5 kV).

I have a program that can calculate breakdown voltages for structures
with axial symmetry, as two balls interconnected by a wire.
See the Inca program, at:
http://www.coe.ufrj.br/~acmq/programs
(Trying to simulate what happens with two 5 mm balls with center to
center distance of 2 cm, interconnected by 0.1 mm wire, I get breakdown
in the center of the wire at 1.37 kV. The configuration, however, is
quite different from the one in the electroscope, and at these low
voltages, Paschen's law may be already working. Interesting.)

Antonio Carlos M. de Queiroz