From: "Terrell W. Fritz"
Date: Thu, 05 Aug 2004 18:10:58 -0600
Subject: RE: [TSSP] Secondary dynamic Efield
Hi Marco,
See the animations at:
http://www.abelian.demon.co.uk/tssp/pn040502/
I am not sure the waveforms would have very good uniformity along the
length of the coil as it was being fired. The harmonics and non-linear
effects can be pretty large.
The only way I know of doing it would be with a capacitive voltage divider
through the secondary that also has an electrostatic shield. That is how
the Jennings and Tektronix style probes work at high voltages and high
frequencies without nearby fields messing the reading up.
Here is a diagram of the Jennings 60kV vacuum probe:
http://hot-streamer.com/temp/Jennings-JP-325/Diagram.jpg
A bunch of pictures are at:
http://hot-streamer.com/temp/Jennings-JP-325/
Of course, the shield is grounded and needs some pretty remarkable
insulation.... But it could give the true high frequency top voltage of a
coil.
Cheers,
Terry
At 11:36 PM 8/4/2004, you wrote:
>Hi Terry,
>
>I mean a water column extending inside the secondary with its top
>electrode at the secondary top and its GND electrode at the secondary
>bottom. At any height there would be no potential difference. No
>insulation problems. No oil needed.
>
>But to have a usable bandwidth the divider has to be immersed in a
>constant Efield. Now, if the Efield inside the secondary is almost
>constant (from top to bottom) in a static simulation, what happens
>during operation?
>
>If I recall voltage and current were bumping up and down the secondary.
>Am I right? If so it would be senseless to place the water divider
>INSIDE the secondary. This is my real concern.
>
>Best Regards
>
> > -----Original Message-----
> > From: owner-tssp@abelian.demon.co.uk
> > [mailto:owner-tssp@abelian.demon.co.uk] On Behalf Of Terrell W. Fritz
> > Sent: 5. elokuuta 2004 01:39
> > To: tssp@abelian.demon.co.uk
> > Subject: Re: [TSSP] Secondary dynamic Efield
> >
> > Hi Marco,
> >
> > I was going to actually shield the darn thing and insulate it
> > all with oil... A long lost project...
> >
> > Stray capacitance is the real killer. But I was going to use
> > copper ground shields to protect the sensitive dividers with
> > a known stable capacitance to ground. Lots of copper sheet
> > and lots of oil...
> >
> > I can "conjure" up the details if needed... I just stole all
> > the ideas from a Jennings RF 60kV vacuum voltage divider I
> > got off E-bay....
> >
> > Watch out for voltage stresses that cause breakdown off sharp
> > edges!!! I think that is what got mine all bogged down...
> > Even under oil, voltage stress and breakdown is a real big
> > deal for a divider that works at say 500kV... Big radiuses
> > and all that are needed... I "giant" vacuum divider would be
> > super cool if you have a glass/vaccum shop...
> >
> > Cheers,
> >
> > Terry
> >
> >
> > At 02:21 AM 8/4/2004, you wrote:
> > >Hi Paul,
> > >
> > >I'm getting acquainted with HV resistive dividers. I tested my first
> > >one and got proof of its poor performance. What
>oiled it was
> > >its 10 pf stray capacitance to GND. I got a step response of
> > 30 us (!).
> > >Some would say easy to guess for a resistance of 1.2 Mohm.
> > >
> > >Hanging the divider at 3 m height will sure reduce its
> > capacitance to
> > >gnd. That was my original plan. But now I learnt that any
> > discontinuity
> > >in the Efield even AROUND its water column will result in unbalanced
> > >stray capacitance and, therefore, in slow step response.
> > >
> > >I'm reluctant to place the divider inside the secondary because it's
> > >difficult to mount it and service it there. But there the
> > Efield should
> > >be pretty constant. But... Now comes my question.
> > >
> > >If I recall you and Terry produced some nice dynamic plots of the
> > >secondary voltage and current. Wasn't it so that they were
> > varying at
> > >the secondary frequency? That would imply not constant
> > dynamic Efield
> > >distribution inside the secondary and make the probe placement there
> > >definitevely a bad idea. Am I right?
> > >
> > >Best Regards
> > >
> > >
> > >
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.