From: Bert Hickman
Date: Mon, 10 Jun 2002 07:49:23 -0500
Subject: Re: [TSSP] Re: Top V Probe Design
Paul, Terry,
Was just checking Sarjeant ("High Power Electronics") for insulating
oils used in high voltage air core tuned transformers for high voltage
pulsed power applications. On page 288 Sarjeant presents a chart
comparing dielectric strength versus electrode spacing for various
dielectric fluids that was originally generated by Sandia National Labs
for a 1.5 uSec dual resonant pulse shape. While not an exact match, it
should provide useful comparative data for the voltage divider.
The estimated impulse breakdown strength from the chart follows:
550 kV/cm R-Temp
500 kV/cm 20 weight motor oil(!)
400 kV/cm Water white mineral oil (Macrol 2930)
310 kV/cm Mineral Transformer Oil
The above is for single-shot impulse and assumes that any streamers or
gaseous byproducts have dissipated between successive impulses. Since we
want to run repetitively, significant derating should be applied - at
least a factor of 4-5. So, using a worst case design with a peak stress
of 60-75 kV/cm should do the trick. In addition to minimizing E-field
concentration via large radius electrodes and symmetrical geometry,
another thing to look at is closer matching between the permittivities
of the solid dielectric and oil to minimize E-field stresses at triple
points. For example, LDPE would be a better match than PVC or Mylar for
mineral oil and R-Temp (all above oils have an Er of ~ 2.2).
Best regards,
-- Bert --
--
Bert Hickman
Stoneridge Engineering
Coins Shrunk Electromagnetically!
http://www.teslamania.com
Paul wrote:
>
> Terry wrote:
>
> > For the Top-V Probe, here is the latest design:
> > http://hot-streamer.com/temp/HVProbe-2.gif
>
> I've been a bit busy with some other stuff for the last week or
> two, but so far I haven't been able to imagine any probe
> geometry that's going to be better than these coaxial cylinders.
>
> The tricky bit remains finding some dimensions that will
> stand up to the Vtop without breakdown. I'm not sure it's
> quite there yet. The wider secondary sure helps.
>
> > The 1 inch diameter rod has a breakdown at about 40kV in air
> > but I figure oil is 10X better so the diameter should be OK
> > to 400kV.
>
> Might only be 5 times better. Any idea what to use for oil?
> Bit outside my field this, so not sure what to suggest.
> --
> Paul Nicholson,
> --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.