-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Bert Hickman
Sent: Tuesday, July 15, 2014 8:08 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] 50:1 "black Box" and Charging inductor(s) design. NOW:
dode design and ground question.
Hi Jim,
There may be a fly in the ointment when trying to use a delta
configuration: can the secondary winding-core insulation system support
a delta connection? Your existing floating wye configuration places
virtually no voltage stress between the floating common connection and
the grounded core. If your transformer was designed to specifically run
ONLY in wye mode, the designers may have skimped on the insulation
between the winding and core. You may have the three-phase equivalent of
three one-eared pigs. You'll need to closely inspect the core-winding
insulation thickness and clearances to see if you can reliably run with
a delta configuration on the secondary side.
*** Yes I had considered that, considering how close they join to the
chassis in the back. I can only try to carefully expose where they come
from....
If you reconfigure to delta and then ground the negative DC rail, the
maximum winding-to-core voltage stress will be the full phase-phase peak
voltage (~13 kV). Whether your transformer can withstand this stress
depends on how your transformer is constructed.
*** copy that**
If you instead let both DC outputs float, the delta-connected secondary
windings will also float, and the voltage across any pair of phases will
be approximately centered on around ground. The maximum winding-core
voltage stress will be about half that for the grounded DC rail case
above. ** interesting!** However, toe better insure balance, you might need
to add HV resistors and three small-value HV capacitors, with one end
connected to the phase output and the other end to the core, to create a
wye-like "soft ground". And, you'll definitely want to add two HV bypass
capacitors (one from each DC rail to your RF ground) to bypass stray RF
currents or accidental streamer hits away from your transformer.
Bert
***Thanks Bert, always a pleasure hearing your wisdom. I have been
temporally called off construction but will advise and maybe take some
pictures of where the floating neutral actually goes... And I am starting an
arduous diode string job at night. I want to protect these if I need to
abandon the Raytheon donor as poor solution.
Jim Mora
Jim Mora wrote:
<snip>
>
> *** I have a question in the diode configuration design stage. My Wye
input
> neutral will see ground as will the transformer / diode tank case of
course.
> Can the negative side of a delta side 6p rectifier also share this ground
or
> do I need a two wire raw DC output? If so, grounded fault currents would
> more likely trigger primary breaker protection, true?
>
> Thanks, and its cool we are on the same kind of track Stephan. Smoke and
> misery enjoys company ;-^)
>
> Jim Mora
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