Hello Will,
Thanks for info.
Use of the coaxial cables for HV is not a surprise.
Years ago, when I was servicing TV sets, I found coaxial cables
used for CRT anode connection for old B/W TVs, at 13 to 18 kV.
Only solid polyethylene insulation cables, never foam.
Some times they were used for helping filtering the HV also, the extra
length of the coaxial being coiled and fixed inside the TV set case.
The first RG58 labeled coaxial I saw was used inside a B/W TV!
The larger B/W TVs were using a RG59 like coaxial and sometimes
the type used for the HV was the same type as the one used for
the 75 ohm antenna input connection.
Was hard to find a damaged coaxial insulation, unless it was melted
because of touching (by accident) a very hot power resistor or vacuum
tube, or by HV discharge at the cable's end, but not because of the
cable's poor insulation quality.
73,
Traian
Will Matney wrote:
> While reading an add I received, I visited Spellman's website and found
> this interesting. It involves using RG8-U cable as a high voltage supply
> cable for remote power supplies up to 8KV. Spellman manufacturers
> supplies for X-Ray equipment, etc.. If I recall, a while back, someone
> was interested in doing this. Below is a quote from their website.
>
> Will Matney
>
> *AN-07* Application Note
> What's the voltage rating of RG8-U coaxial cable?
>
> Output cable and connectors are not trivial items for power supplies
> where output voltages can be 100,000 volts or higher. The cables and
> connectors used must function together as a system to safely and
> reliably access and provide the power supplies output for customer usage.
>
> In many high voltage power supply applications, a shielded polyethylene
> coaxial cable is used. Polyethylene cables provide excellent high
> voltage dielectric isolation characteristics in a small but robust form
> factor. The shield conductor provided in a coaxial cable functions as a
> "Faraday Shield" for the center conductor of the cable that is
> referenced to the high voltage potential. If any breakdown in the main
> insulator occurs, the high voltage current will be bypassed to the
> grounded shield conductor that surrounds the main insulator. This
> inherent safety feature is one benefit of using a coaxial high voltage
> output cable.
>
> RG8-U has long been used as a high voltage output cable in the high
> voltage industry. There is a variation of RG8-U that utilizes a solid
> polyethylene core. Specifications for this cable do not specify actual
> "high voltage" ratings, since this cable was not designed and fabricated
> with high voltage usage in mind. So the reality is, there are no high
> voltage ratings for RG8-U. Over the years others in the HV industry have
> used this cable at 20kV, 30kV and even higher voltages. Spellman does
> use RG8-U cable, but limits it usage to applications where the maximum
> voltage that will be applied to the cable is 8kV or less.
>
> For voltages above 8kV where a coaxial polyethylene cable is desired,
> Spellman uses cables specifically designed and manufactured for high
> voltage usage.
>
> These cables are of the same general design; as described above but the
> insulating core material diameter has been increased appropriately to
> obtain the desired dielectric insulating capability required. Frequently
> higher voltage versions of these cables utilize a thin semiconductor
> "corona shield". This corona shield is located between the metallic
> center conductor and the main polyethylene insulating core. This corona
> shield helps equalize the geometric voltage gradients of the conductor
> and by doing so reduces the generation of corona.
>
> A high voltage cable and connector system can only be as good as the
> materials used to make it. Using cables that are designed, specified and
> tested specifically for high voltage usage assures that these materials
> are used within their design guidelines.
>
> http://www.spellmanhv.com/tech/app_an07.asp
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