Re: Transformers, Grounding, Cable questions.

To: tesla-at-pupman-dot-com
Subject: Re: Transformers, Grounding, Cable questions.
From: Tesla List <mod1-at-pupman-dot-com>
Date: Sat, 4 Oct 1997 22:05:34 -0600 (MDT)
Approved: mod1-at-poodle.pupman-dot-com


---------- Forwarded message ----------
Date: Sat, 4 Oct 1997 20:22:15 -0500
From: "DR.RESONANCE" <DR.RESONANCE-at-next-wave-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Transformers, Grounding, Cable questions.

To: Phil

You might wish to try a filter on each side of the variac, so
mains-filter-variac-filter-varisters progression.  The dual filters really
do help reduce any hash and make you a good neighbor.  An ounce of
prevention is worth a pound of cure.  Do not -- never -- use coax cable to
transmit the HV from the power supply to your oscillator.  Some strange
blum-line effects can occur with a capacitive feed and result in
overvoltages to your power xmfr.  Use a high quality 30-40 kv rated HV
cable and run a separate ground wire from the power supply to the
oscillator base.  We damaged a few xmfrs once and learned this lesson the
hard way.

DR.RESONANCE-at-next-wave-dot-net


----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Transformers, Grounding, Cable questions.
> Date: Saturday,October 04,1997 3:26 PM
> 
> 
> 
> ---------- Forwarded message ----------
> Date: Sat, 04 Oct 1997 22:12:17 +1000
> From: Phil Chalk <philoc-at-ozemail-dot-com.au>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Transformers, Grounding, Cable questions.
> 
> Hi all,
> 
> Due to a few lucky scores recently I am currently
> building a 'mains power box' for general service as
> well as TC work.  It will essentially be an isolation
> transformer, variac, voltage & current meters + optical
> current waveform metering output, filtering & MOVs,
> switching, fusing etc in a box.
> Later I will build a High Voltage box containing a few
> NSTs, filtering, safety gaps etc; & after that maybe a
> HV DC supply - I'd love to run a TC on DC.
> Then all future coils will be self contained with
> everything except power supply which will be connected
> by leads to the TC unit.  My first & only 'complete'
> coil had NSTs & everything in the box, making it one
> big heavy unit for a relatively small coil.
> 
> Anyway, I have a few questions.
> 
> 1.  Does anyone have any preference (& reason) for
> which order to connect the isolating transformer &
> (auto) variac ?  i.e. mains-isolation-variac-load, or
> mains-variac-isolation-load ?  Assuming the in-between
> connections are 'finger-proof' are there any pros &
> cons ?
> 
> 2. I'd like to have remote indication of safety-gap
> firing.  I'm thinking either some kind of optical
> detectors looking at the gaps, possibly hall-effect
> devices, or a small torroid as a current-transformer on
> the lead from the centre gap electrode to ground as
> sensing devices, followed by appropriate amplification,
> indication etc.  Anyone have any ideas, or ever tried
> to do this before ?
> 
> 3.  Those of you that use RG8/RG213 as high voltage
> connecting cable, what sort of connectors (if any) do
> you use ?  Surely not PL259s or 'N's ???  There seems
> to be varying opinion on whether or not to ground the
> shield. (& if so, I guess at which end ?)
> My spec for RG213 rates it at 5.5kv max DC & 3.7kv RMS
> max working voltage, but I'd be happy to push it.  The
> Uniradio equivalent UR M67 is rated at 40kv & 6.5kv
> respectively.  With the shield grounded, I think the
> 100pF/m capacitance would be a good thing with cable
> lengths of around a convenient 5 metres.  I'm still in
> two minds as to which end to ground it - i.e. unless
> I'm shot down in flames, the NST cases will be grounded
> to mains ground at the HV box. The safety gap & filter
> ground will have to connect by cable to the bottom of
> the secondary & to a separate RF gnd terminal at the
> 'TC box' end.  When an RF gnd is not available (I live
> on 3rd floor) it will have to go to mains gnd.
> Grounding shield at HV box end makes the cable like a
> giant feed-thru cap of a few 100s of pF & turns my
> L-section filter into a Pi-section, no ?  Grounding it
> to RF gnd at the TC end 'feels better' somehow though.
> 
> Any comments most welcome.  Thanx,
> 
> Phil Chalk.
> 
>