Re: Using HV COAX without stripping the shield

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi David,

Yes, this run-away effect is because there is no termination at 
either end of the coax and nothing to dampen energy from the coax.  I 
believe you didn't experience it because you got lucky and the high 
freqencies in your system didn't excite the natural resonance due to 
the coax length.  If the coax is properly terminated at the pig end, 
then no reflections can be returned to TC end and this resonance is 
effectively "killed".  I believe Dr R when he said that stripping the 
insulation fixed his problem (being flashover at the HV bushing of 
the pig).  I continue to think that transmission line effects can 
still happen because even without the shield there is still 
distributed capacitance to earth ground in the coax and the 
distributed inductance got changed somewhat but still exists.  Bottom 
line, is a transmission line still exist where the characteristic 
impedance of the shieldless coax got changed and the propagation 
velocity got changed (probably because of the addition of air in the 
dialectric).  The resonant frequency of Dr R's given length of coax 
probably changed as a result of stripping the shield.  Anyway, this 
is my thinking.

Gerry R.

> Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
>
> I realize that there is the
> possiblity of run-away resonant voltage due to the Blume-
> line (spelling?) effect, but I have never personally noticed
> this problem when using my x-ray cables with the shielding
> intact.