Re: coax (grounding shield & AC?)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Hi Peter,

You wrote:

> Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>
>
> I really have to question Dr Res' explanation of his observed 125kV
> sparks from a 14.4 kV RMS line as being due to an 8 times multiplier
> from a Blumlein effect. Far more likely I feel, is stray HV from the
> TC itself.  If the ground was faulty or of higher inductance (perhaps
> even a few loops might do) or simply not connected (I've done it
> too), then an arc from base of TC to the primary occurs and has to go
> somewhere. It will then jump the easiest low inductance path to
> ground. Depending on the setup this may be across the bushing to ground.
>
> I must admit to having used thick coax forever on all my MOT and PT
> powered coils for both of the hot lines with the coax ground grounded
> to the MOT ground.  It does terminate in a Terry filter though with
> resistance, MOV's and resistors though.
> I do like the earthed surround as an additional safety feature from
> ground strikes and also from passing over other cables, conductive
> surfaces, grass, cars etc.  Persoanlly I feel this outweighs the very
> unlikely potential for a Blumlein multiplier which is actually quite
> complicated and involves more than one spark gap for any significant
> multiplication if I recall.
>
> I would advise that you DO use coax for safety unless and until there
> is some data to suggest otherwise. A suitable test setup might
> involve using a loaded primary circuit without a secondary which
> might generate spurious HV.
>
> I was going to make a Blumlein multiplier as one of many little
> projects I want to do. I would be delighted to get 125kV but I am sure I
wont.
> Perhaps using water as the dielectric like these guys.
>
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=IEESEM002001000156000P11000001&idtype=cvips&gifs=yes
>
> Peter

and I wrote:

>Hi all,

> Although I realize that the Blumlein effect has been documented
> in certain situations, I have personally been using x-ray cables as
> transmission lines from my pig to my primary tank circuit in my
> big coils for years and have NEVER experienced it to my know-
> ledge. X-ray cable is basically coax cable "on steroids" that is
> generally rated at around 75 kVDC. As a matter of fact, I use
> the "inside"conductor as the "hot" and the outer braided shielding
> as the ground return currently on my Green Monster system.
> http://www.teslauniverse.com/members/drieben/
> This means that I only have to run one HV line from the pig
> to the tank circuit. BTW, I wonder how are the utility power
> companies able to run miles of primary lines under ground and
> avoid any of the ill Blumlein effects since the lines for this
> are obviously shielded and grounded?

I'm really gald to finally see someone who agrees with my viewpoint
on this matter and was able to more eloquently explain the reasoning
behind their position than I could :^) IMHO, you have pretty well
summed up why coax is NOT bad to use for the transmission line
from the transformer to the coil's tank circuit.

David Rieben