Re: X-ray HV cables

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>


----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, November 02, 2005 2:51 PM
Subject: RE: X-ray HV cables


> Original poster: "Carl Litton" <Carl_Litton@xxxxxxxxxx>
>
> Hello Mike,
>
> At lower voltages (below 30 kV), you will be fine if you remove all
> coverings down to the thick rubber layer for 8 " back and then strip and
> combine the center conductors.  We use a few layers of rubber splicing
> tape followed by electrical tape over the raw ends of the shielding
> material that has been stripped back.  The two insulated center
> conductors should have their insulation removed and the strands of all 3
> conductors twisted together and soldered.
>
Are you saying cover the entire 'black shield with rubber tape, or just a
few inches
where it starts?


> I am curious about the 150 kV cable and where you obtained it - I would
> love to get some!  Standard x-ray cabling is rated for 75 kV DC and must
> be derated considerably for AC use.
>
I think other replies to this comment were correct. It's probably 75KV. I
assumed it was 150 because the max potential on our xray equipment is
150 KV.

> We make extensive use of the 75 kV cable in our group projects.  At
> higher voltages (100 to 250 kVAC), with the cable laying on the ground
> and coverings stripped back 18", the current will arc completely through
> the insulation directly into the ground quite readily, necessitating
> frequent repairs.  Up to about 150 kVAC, this may be prevented by
> keeping the cables off of the ground on non-conductive supports.  We
> have used it at higher voltages (up to around a quarter Megavolt) by
> running the cable through an outer jacket of heavy wall 1-1/4" I.D.
> vinyl tubing and/or inside of PVC pipe.
>
> We just had to go through all of this for our Halloween Jacob's Ladder
> running at 215,000 VAC.   Here is a not-so-good PowerPoint slide show of
> it operating at about 175,000 volts using standard 75 kV rated x-ray
> cable prepared as above with 18" stripping on both ends and run through
> PVC for the greater part of the run:
>
> http://www.dawntreader.net/hvgroup/ladder.ppt
>
>
> Good luck!
>
>
> Carl
>
>
> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: Wednesday, November 02, 2005 9:45 AM
> To: tesla@xxxxxxxxxx
> Subject: Re: X-ray HV cables
>
> Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>
>
> I'll answer my own inquiry. On the surface of this remaining HV cable is
> a
> black hard plastic covering about 0.5 Mil thick. Then about 3/8 " red
> rubber-like insulation, and the center conductors. Seems the black
> plastic
> is what's conductive. I sanded off the black plastic, down to the red.
> The
> red doesn't conduct. If I remove say 8" of this black coating on each
> end,
> do you think I'll be alright? Will this conductive "shield" cause the
> same
> kind of  capacitive resonance problems a true braded shield might. I
> don't
> intend to ground anything, however the cables will be laying on the
> ground.
> ----- Original Message -----
> From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Tuesday, November 01, 2005 1:52 PM
> Subject: X-ray HV cables
>
>
>   > Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>
>   >
>   > I got a 150 KV rated xray HV cable. Per D.C.'s recomendations, I
>   > stripped the outer jacket, removed the braded shield, and cut off the
>   > 'candlestick' ends. I then reterminated to acomadate the connections
>   > as I needed. The outer jacket (what was under the shield CONDUCTS !!
>   > It nicely shorted the hv output of my PT! What's going on here? Is
>   > this normal? I placed the hv leads of a 15kv nst at 2 points on the
>   > insulation away from the conductor, and it happilly arced! Any
>   > thoughts would be apreciated.
>   >
>   >
>
>