Re: Official air breakdown voltage?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Terry,

On 27 Nov 2005, at 11:35, Tesla list wrote:

> Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi Antonio,
>
> At 01:21 PM 11/26/2005, you wrote:
> >>....
> >
> >The 30 kV/cm figure for initial breakdown is valid for at least 300
> >MHz. (At least, this is what my "Reference Data for Radio Engineers"
> >says.)
> >
> >Antonio Carlos M. de Queiroz
>
> Interesting!!  We always worry so much about high voltage RF
> breakdown distances.  RF tends to arc rather easily compared to DC.
>
> However, "capacitive" leakage current is probably the real
> problem.  If we have say 100kV at 100MHz and there is just 0.1pF of
> capacitance to ground, the current is:
>
> 100000 x 2 x pi x 1e8 x 1e-13 = 6.2 amps!!!!  That will easily burn
> though any insulation!!
>
> Good insulators at say 1e10 ohms will leak only 10uA at DC, but if you
> start oscillating the voltage, the leakage currents can get bad very
> quickly.
>
> So I guess we should not worry so much about RF breakdown voltages,
> but should rather be concerned with high voltage RF capacitive leakage
> currents....
>
> Cheers,
>
>          Terry

I don't think the story ends there either. I've used 15kHz
frequencies to test the insulation breakdown of polyesterimide-coated
wire (my favourite :) and noted that at those frequencies, unlike DC,
there is a lot of corona heating of the insulation going on. It is a
rather brutal insulation test but a goody if you want to find the
best quality insulation.

Malcolm