Re: coax cable with AC pole xmfrs

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

On 7 Nov 2005, at 20:42, Tesla list wrote:

> Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
>
>
>
>
> A transmission line is essentially a capacitor, ie, plate,
> dielectric, and another plate.  Removing the shield of x-ray cable
> leaves the PE/PP and no second plate, so the normal xmission line
> effect is now missing.  Common example of xmission line would be a
> coaxial cable with its inner conductor and outer braided shield.  RF
> currents travel along a capacitvely equal balanced line.

I should point out that the national grid consists of open-wire
transmission lines. Inductance is the other part of the picture. In
fact any conductor behaves as a transmission line and needs to be
treated as one when one goes high enough in frequency. Reducing the
distributed capacitance raises the Zo of the line but a transmission
line it remains. I think some measurements are in order to arrive at
some useful figures for this one. It may be that by removing the
outer coax shell the Zo is pushed into a region where propagation
losses at the excitation frequencies become significant. It may also
be that coupling into lossy surroundings is increased. Unfortunately
those surroundings can vary considerably and the losses along with
them so a cover-all approach like that might or might not be the last
word in getting rid of significant reflections. I have seen
transmission line effects such as HF voltage elevation using stripped
coax - in fact the effect killed a NST of mine (the only one I lost).

Malcolm

> I used coax cable and noted the entire HV bushing on the 14.4 kV pig
> crawling with capacitive sparks --- that's why I mentioned beware
> using coax at all with pole pigs.  I don't have the pri cap size or
> lengths of cable because this was back in 1967.  I also didn't have
> the equipment back then to do precise measurements.
>
> This was posted only to be a warning to anyone thinking of using coax
> with a pole pig --- don't!  or else you may damage the pig.
>
> Dr. Resonance
>
>
>
> >Is the effect one of two I mention below?? or is it a third
> >mechanism?? If it is a transmission line effect, can you explain why
> >removing the shield fixes it and why proper termination doesn't???
> >If a resonant charging effect, can you descibe the L that the coax
> >capacitance is resonanting with, the resonant frequency, and how this
> >works???   If a third mechanism, I would like to challange you for
> >the benefit of all the readers here to give a quick synopsis of this
> >effect :o)).
> >
> >Knowledge is everything and sharing it is golden.
> >Gerry R.
> >
> >
> >
> >Also is it
> >>Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
> >>
> >>These effects are well documented in Sargent & Dolan's book -- Power
> >>Electronics.  Also covered are both strip line and circular HV
> >>generators. Very novel designs.  It's out of print but I believe
> >>that Bert Pool (Stoneridge Engineering) has some copies for sale.
> >>
> >>>Anyway, going to the intent of the original post,  I'm trying to
> >>>understand the mechanism of voltage growth when using a shielded
> >>>coax (not because I want to use shielded coaxes, but because I want
> >>>to understand). Is the phenominum transmission line effects being
> >>>underdamped while energy is feeding the line,  is it a resonant
> >>>charging effect (series LC) due to the capacitance of the coax, or
> >>>is it some other mechanism???  Also in the TC context, is the
> >>>blumlein effect the same as the transmission line effect I
> >>>described above or something else???
> >
> >
> >
> >
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