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Re: HV xray cable revisited



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Mike,

As I understand it, the coating arcs not at the ends, but when the black coating comes in contact to a grounded object (or the ground itself). I suspect the cable is not sufficient for AC applications at the voltage your running. Check around and you'll see DC ratings on high voltage cable. AC and pulsed DC specs are much lower, so I wonder if the cable is not sufficient for the application. But, we can only make our best guess. As the cable is in your hands, possibly you could find out it's DC and AC ratings.

Take care,
Bart

Tesla list wrote:
Original poster: "MIKE HARDY" <mailto:MHARDY@xxxxxxxxxx><MHARDY@xxxxxxxxxx>

OK. I have 8" of the black conductive outer layer stripped back on both
ends, all shield removed. I know the cable is good, because it was pulled
from a functioning xray system (we just redid the test cell for a different
system). I personally think it's capacitively conducting AC. A cap (the
cable) with DC applied (the way xray PS are) charges to its value and then
just remains that way. A cap with AC applied will conduct. I just want to
use this cable safely, and without going through the hell of stripping the
black coating. Mine is a solid continuous bonded sheath, not a tape I can
peel back. I hope I'm making myself clear.
----- Original Message -----
From: "Tesla list" <mailto:tesla@xxxxxxxxxx><tesla@xxxxxxxxxx>
To: <mailto:tesla@xxxxxxxxxx><tesla@xxxxxxxxxx>
Sent: Wednesday, January 04, 2006 10:36 PM
Subject: Re: HV xray cable revisited


> Original poster: "Barton B. Anderson" <mailto:bartb@xxxxxxxxxxxxxxxx><bartb@xxxxxxxxxxxxxxxx>
>
> Hi Terry,
>
> I understand the conductive layer technology for corona losses and
> the dielectric layer is around the conductor and then the main
> insulation followed by the jacket. But, as I understand it, only the
> outer jacket was removed so I don't think it will be a problem. The
> oddity is the cable arcing to the outer jacket before he removed it
> (which must have been observed from the ends where he striped back
> the outer insulation initially). I can only assume the cable
> insulation damaged or insufficiently rated. Regardless, if he's got
> the main insulation on the cable and routed through the pvc, it
> should be fine (that doesn't mean go grab it hot, but it should be
> arcing to anything).
>
> Take care,
> Bart
>
> Tesla list wrote:
>
> >Original poster: Terry Fritz <mailto:vardin@xxxxxxxxxxxxxxxxxxxxxxx><vardin@xxxxxxxxxxxxxxxxxxxxxxx>
> >
> >Hi,
> >
> >It is common for HV DC cables, like used in X-ray, to have
> >conductive layers inside them in what looks like
> >"insulation".  These layers are used to increase the conductor's
> >apparent radius to prevent breakdown (corona leakage) inside the
> >cable's insulation.  I would never go cutting the layers off and
> >expecting it to work!!  One should normally use the cable with the
> >outer grounded jacket well grounded just like they meant it to be used.
> >
> >The capacitance between the conductor and the shield "might" be a
> >problem in a given system.
> >
> >Even a perfect insulator can still carry heavy AC displacement
> >currents (at Tesla coil frequencies) and "glow" when near grounded
> >objects...  If they are not designed for it, they can easily fail.
> >Thus, a DC X-Ray cable might fry under AC...  Really good cables for
> >such things are teflon or polypropylene.  Not much else
> >works...  Note that insulators too have a breakdown voltage just
> >like air.  Although much higher, there is still a limit to how much
> >RF voltage you can have on a radius.  Thus is why HV cables tend to
> >be very "special"...
> >
> >Best just to not really too much on insulation in our sport.  Even a
> >small coil can happily punch though a 1/4 inch thick sheet of glass....
> >
> >Cheers,
> >
> >         Terry
> >
> >
> >At 06:34 PM 1/4/2006, you wrote:
> >
> >>Yes Mike, arcing is a problem. Hard to say why it is however
> >>without seeing it. The outer jacket/shield should have been
> >>stripped back several inches beyond an ability to arc. If it was
> >>still arcing, then that is odd. Anyway, stripping the entire jacket
> >>off is fine to (a lot of work though).
> >>
> >>Take care,
> >>Bart
> >>
> >>Tesla list wrote:
> >>
> >>>Original poster: "MIKE HARDY" <mailto:MHARDY@xxxxxxxxxx><MHARDY@xxxxxxxxxx>
> >>>
> >>>So you don't think the arcing of the black coating to everything robs
any
> >>>power? Or in your case to grounded shield.
> >>>----- Original Message -----
> >>>From: "Tesla list" <mailto:tesla@xxxxxxxxxx><tesla@xxxxxxxxxx>
> >>>To: <mailto:tesla@xxxxxxxxxx><tesla@xxxxxxxxxx>
> >>>Sent: Sunday, January 01, 2006 6:27 PM
........