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Re: HV xray cable revisited



Original poster: "MIKE HARDY" <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" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, January 04, 2006 10:36 PM
Subject: Re: HV xray cable revisited


> Original poster: "Barton B. Anderson" <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 <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" <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" <tesla@xxxxxxxxxx>
> >>>To: <tesla@xxxxxxxxxx>
> >>>Sent: Sunday, January 01, 2006 6:27 PM
> >>>Subject: Re: HV xray cable revisited
> >>>
> >>>
> >>> > Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
> >>> >
> >>> > Bart,
> >>> >
> >>> > That's funny that you say that. Actually, my experience
> >>> > with x-ray power cable is to leave it on the ground. May-
> >>> > be I'm "messing up" doing it that way, but I've never had any
> >>> > problems using x-ray cable in this fashion. I simply strip off
> >>> > enough of the outer sheathing and insulation along with the
> >>> > semiconductive carbon tape for proper standoff of the 14 kV to 17 kV
> >>> > from the inner 3 conductors to the outer
> >>> > grounded braiding and leave the rest of the cable intact. I
> >>> > solder all 3 of the inner condcutors together on the end as one.
> >>> > X-ray cables are really overdesigned for the usual sub-
> >>> > 20 kV voltages used to feed  Tesla primary circuits since they are
> >>> > generally rated around 75 kVDC. The thin outer rubber
> >>> > sheathing seems to be fairly durable, too, and effectively protects
> >>> > the grounded mesh sheathing (yes, I do ground the outer-
> >>> > mesh, just beneath the outer rubber sheathing and I have NOT
> >>> > witnessed any significant Blumlein affects).
> >>> > David Rieben
> >>> >
> >>> >
> >>> >
> >>> > ----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
> >>> > To: <tesla@xxxxxxxxxx>
> >>> > Sent: Sunday, January 01, 2006 10:33 AM
> >>> > Subject: Re: HV xray cable revisited
> >>> >
> >>> >
> >>> > >Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
> >>> > >Hi Mike,
> >>> > >For a quick reply, "get the cable off the ground and your problems
> >>> > >are over". I never allow hv feeds to be tossed along the ground.
> >>> > >Take care,
> >>> > >Bart
> >>> > >
> >>> > >Tesla list wrote:
> >>> > >
> >>> > >>Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>
> >>> > >>
> >>> > >>Some time back I had a discussion on the list about stripping off
> >>> > >>the black conductive coating that remains after the shield is
> >>> > >>removed, for 8" or so on either end of my HV xray cable. It seems
> >>> > >>this black coating still arcs if it is in contact to ground, or th
e
> >>> > >>other xfmr lead (14.4 kV). Is this simply distributive
capacitannce
> >>> > >>causing coupling due to it's use on AC? Do you think this robs
alot
> >>> > >>of energy? Is it dangerous if layed on damp ground? I find running
> >>> > >>the leads thru pvc to the TC cumbersome, and time consumming, when
> >>> > >>I want to drag it outside for short runs. Since I want to run my
> >>> > >>coil tonight for new years a quick reply would be greatly
apreciated.
> >>> > >>
> >>> > >>HAPPY NEW YEAR!
> >>> > >>Mike
> >>> > >>
> >>> > >>
> >>> > >>