Hi Bert,
My bad on corner delta grounding which is usually, but is rarely done these
days, on the "B" Phase. Clearly, this gives you only two phases... The
diodes may be another story but we are back to the design and windings of
the transformer standoff to the inner primary.
In a perfect world, I would wire this to be paralleled wye. I really have no
intention of removing interleaved silicon steel however! When I have time,
I'll take a much better look at it for options.
Jim Mora
-----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.
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.
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. 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
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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