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Re: [TCML] 50:1 "black Box" and Charging inductor(s) design. NOW: dode design and ground question.



Wow, this is turning into a major project for you, Jim! Unless you're just really enjoying the challenge of constructing a DC res system from the ground up, it seems that it sure would be a whole lot simpler to just incorporate a pig to run ASYNC with raw AC and just hold on to that Raytheon beast for a nice HVDC supply for charging HV caps or electrostatic experiments ;^) I mean, if big impressive sparks are really all that you're after?.... That's the main reason that I never took the step to convert my Green Monster over to a DC resonant system - gets really complicated with all of the diodes (+ d'Qing diodes), huge HV filter caps, and multi-Henry'd choke coils. I'm not trying to be a "wet blanket" for your project, just saying... Regardless of all that, good luck with your endeavor :^)

David


On Wednesday, July 16, 2014 6:29 AM, Jim Mora <wavetuner@xxxxxxxxx> wrote:
 




-----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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