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Re: HV coax? (fwd)



---------- Forwarded message ----------
Date: Tue, 12 May 1998 06:58:23 -0500
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: HV coax?

Tesla List wrote:
> 
> ----------
> From:  Bill the arcstarter [SMTP:arcstarter-at-hotmail-dot-com]
> Sent:  Monday, May 11, 1998 10:29 AM
> To:  tesla-at-pupman-dot-com; dr.resonance-at-next-wave-dot-net
> Subject:  HV coax?
> 
> It was written:
> >>From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
> >>Sent:  Friday, May 08, 1998 8:51 PM
> >>To:  Tesla List
> >>Subject:  Re: Pole pig HV wires (fwd)
> >>
> >>to: Brian
> >>
> >>Never use coax to transmit power from a pole pig to a Tesla
> oscillator.
> >>It's capacitance is just right to resonate with the secondary of the
> >>xmfr
> >>and will produce severe overvoltages on the order of 150 kV.  Best to
> >>use a
> >>single conductor wire such as spark plug wire or coax can be used if
> >the
> >>outer ground braid is stripped away and not used at all.  Ground one
> of
> 
> Can you go into more detail on this??  Is this a resonance between the
> cable and the xfmr, or is it s transmission line phenomenon??
> 
> Seems like the output impedance of a pig would be much less inductive
> than that of an internally-current-limited NST.  Thus this resonance
> would be less pronounced on the pig.  Am I deluding myself?
> 
> Recently we've been powering our coil remotely via two parallel 30 ft
> lengths of 100KV-rated x-ray coax hooked to the pig.  This stuff is
> nearly an inch o.d., and the insulation between the center lead and the
> outer ground is at least 1/4 inch.  We do notice some odd effects - such
> as thin wispy arcs off the far end of the cable...  We have the shield
> grounds attached to the frame of the pig (ground) on one end only.
> 
> BTW- modern commercial x-ray transfomers have a special circuit designed
> to dissipate the energy capacitively stored in the cable after the
> exposure is complete.  This is to prevent accidentally electrocuting the
> field service engineers...
> 
> Is the above resonance effect the "Blum Line" effect (which I've tried
> to research but can't find anywhere...)??
> Thanks for your assistance!
> 
> -Bill the arcstarter
> Starting arcs in Cinci, OH
> http://www.geocities-dot-com/CapeCanaveral/Hangar/6160
> 
> ______________________________________________________
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Bill,

It's actually spelled Blumlein (which is German for "one wild and crazy
kind of line"... :^) ). Blumlein Pulse Forming Networks or their
transmission-line equivalents are typically used to generate relatively
"square" voltage pulses (typically high voltage, low impedance) for
radar, high speed laser and flashlamp, or nuclear research. Under the
appropriate conditions, a pair of transmission lines charged to Vo and
then suddenly switched by a sparkgap can provide a pulse of amplitude
2Vo or more into a low-imedance load. This has significant advantages in
generating very brief, high voltage, high power pulses, and can also be
used to generate a high voltage pulse while needing to switch a lower
voltage. 

For Tesla coilers, the Blumlein effect can have the undesirable
consequence of inadvertantly causing high voltage peaks on the HV
transformer end of coaxial transmission lines when the far end is
terminated by a spark gap. This voltage increase is the phenomenon that
D.C described...

-- Bert --