On 5/10/19 3:56 PM, Gedas wrote:
Have a look at some of these cables.
https://www.awcwire.com/productspec.aspx?id=high-voltage-coax-15kvdc
At 15kV kinds of levels, the cheap solution is what is called GTO-15 -
it's used for wiring neon signs, and easily takes 15 kV RMS (so about
20kV peak). No shield. It looks and feels like RG-59 or RG-58 solid
dielectric with no shield (black outer jacket, PE insulation, stranded
copper core).
There's some much nicer silicone GTO-15 that is more flexible. There's
also a variety of HV cables used for applications like CRT anode
voltages back in the color TV days. Sometimes you can find a surplus
spool of 30kV or 45kV rated silicone insulated wire. You want to avoid
the old surplus synthetic rubber insulation - by now, it's almost
certainly got microscopic cracks in the dielectric, and tiny cracks in a
wire carrying 30kV can lead to "exciting" failures, especially if you've
got any stored energy in the system.
Shielded cables are a curse and a blessing - if the shield is grounded,
it can take more voltage because of the field control. On the other
hand, if you've got lots of stored energy, that shield can provide the
return path for an exciting energy dissipation event. Furthermore, the
coax itself stores significant energy - at 30pF/ft, a 10 foot length is
300 pF, and at 40 kV that's about 6 Joules - enough to make a nice snap
or burn something out.
If you're working with fast pulses, you also have to worry about
reflections from an impedance discontinuity inadvertently doubling the
voltage (or worse). There's a whole literature on HV pulse generators
using pieces of coax as transmission line capacitors. (see, e.g.
Blumlein) You can do some very cool stuff in terms of very fast, short
pulses with HV, coax, and spark gaps (or Krytrons and similar triggered
gap devices) as switches.
Gedas, W8BYA
Gallery at http://w8bya.com
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 5/10/2019 12:55 PM, Steven Katz wrote:
The mil spec rating for RG-213/U is 3700Vrms max; this is 5232Vpk.
I wouldn't use it at 7.7kVdc.
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Jim
Thomson
Sent: Friday, May 10, 2019 9:52 AM
To: towertalk@contesting.com
Subject: [TowerTalk] RG-213 Hi Pot ?
Does anybody know how much max V is on RG-213 ? Like what are the
results if a hi-pot tester used..
and say cranked up to the point where just a few ma occurs . I
have an application where I need a HV
cable, less than 10 ft, that will easily handle 5700 / 7700 vdc.
It will be hardwired at both ends, no HV connectors.
And with braid peeled way back from the center conductor, like 2-4
inches .
The plan was to also wrap some red electrical tape every few inches
along its entire length, to readily identify it as a HV cable.
Tnx.... JIm VE7RF
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