Re: Using HV COAX without stripping the shield

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>



I'm advising to strip the entire ground shield off of the entire 
length of the cable creating a HV lead wire, ie, PP or PE itself 
around the central conductor.

This eliminated the problem in our situation where the coax with 
ground shield was resonating so effectively it was sparking over a 
14.4 kV bushing --- the entire length of the bushing!!

Dr. Resonance



> It has been mentioned in the group in the past that there can be a 
> high frequency resonance when using a coax cable such as RG8U to 
> connect the HV from a PIG to the TC where the PIG is remoted from 
> the TC.  This resonance can cause a higher voltage standing wave on 
> the PIG end of the coax.  Dr R has suggested stripping the outer 
> braid of the coax to minimize the transmission line effect,  It 
> seems like to me that doing so changes the characteristic impedance 
> of the cable and doesn't really eliminate the problem.
>
> I was wondering if anyone has experimented with adding a series RC 
> termination to the pig end of the coax to effectively terminate the 
> coax. The C could be a string of C's to get adequate HV capabilities 
> and the R would be 50ohms if the shield wasn't removed or say 300 
> ohms if the shield was removed.  The RC time constant would be set 
> to be higher than the resonant frequency of the TC and yet low 
> enough to effectively terminate the coax for the high frequencies 
> where the coax length would resonant.
>
> Gerry R.