Re: Alternative capacitor materials

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

 > >Also, are there any readily available kinds of tubing that have a high
 > >dielectric rating to make HV wire with? I haven't found a listing for
 > >clear vinyl tubing's puncture voltage yet. If anyone knows this please
 > >tell me.
 >
 > Contact your local Neon sign repair shop. If you ask nicely he'll give you
 > plenty of HV rated wire that will withstand 15kV all day long. DO NOT
THINK
 > THAT THIS MEANS YOU CAN TOUCH IT WHILE IN OPERATION. A tiny pinhole leak
in
 > the side and you're in for an intersting experiance.

Since vinyl tubing is made to carry liquids and gases at fairly low
pressures, and, generally, to be food-inert, those are the properties that
are specified and controlled.  Dielectric withstand isn't spec'd, measured,
or tested for vinyl tubing.

That said, most plastics have a safe breakdown rating of around 150-200
kV/cm.  A tubing wall thickness of 1/16th inch, i.e. 0.159 cm, at first
glance would have a rating of around 20-30 kV.  However, it will actually be
a bit less: a) the field isn't uniform, but is higher near the conductor and
b) you're going to have air gaps/bubbles between the conductor and the
insulator, which leads to corona (and delightful phenomona like erosion and
"treeing", as it propagates through the insulator) and to field
concentrations, so the local field is somewhat higher than the average
field.