Re: [TCML] BIG solid state

[Michael Twieg <mdt24@xxxxxxxx>]

So Steve, was there a specific goal in mind here, or at this point have you
just gone mad with power?

Anyways, very impressive.

My main question is about the primary control.  You're still using primary
current feedback, right?  Does each bridge have its own CT and detect its
own zero crossing?  Or is there one CT which controls all the bridges?
Sounds like it would be very important to have identical tuning on all four
primarys to avoid chaos.

Also please post some waveforms if you have some.

-Mike

On Tue, Jun 14, 2011 at 11:35 PM, Steve Ward <steve.ward@xxxxxxxxx> wrote:

> Hi Everyone,
>
> Just a post about a recent project of mine.  Many hands involved on this
> one
> (see credits later).  So far its just a prototype, but results are
> promising:
>
> http://www.flickr.com/photos/kickermagnet/5811280440/in/photostream
>
> This is, as far as im aware, the largest Double Resonant Solid State Tesla
> Coil built and working as intended.  The machine stands 15 foot tall (to
> the
> top of the toroid).  With breakout point at 16 foot above the ground, its
> made some 25 foot sparks.  Power input at 200bps was measured at 33kVA
> (480VAC 3 phase, about 40.5A RMS).  I estimate a power factor of .92 given
> the line reactor used to smooth the current peaks charging the 2kJ of DC
> bus
> storage.  The secondary is 24" diameter and wound to just over 8 feet
> length.  The toroid is 96" by 16", and is indeed very ugly.
>
> For now, i dont have many photos of the detailed construction (this is
> something i should get to soon) but you can sorta see whats going on here:
>
> http://www.flickr.com/photos/kickermagnet/5487415037/in/photostream
>
> <http://www.flickr.com/photos/kickermagnet/5487415037/in/photostream>On
> the
> lower level, you can see banks of white electrolytic DC capacitors, 3300uF
> 400V X 16 total, wired in series parallel banks, one per each of the 4 IGBT
> inverters.  The inverters consist of a full-bridge of CM300DY-24H
> transistors.  So each pair of half-bridge bricks (there are 8 total, 4
> H-bridges) drives its own .625uF 20kVAC capacitor, and 2-turn primary coil.
>  There are 4 MMCs and 4 primaries.  The mutual inductance between primaries
> and equal MMCs force current balancing of the 4 drives (each drive sees the
> same load impedance).  This was chosen to avoid some possible issues with
> directly paralleling modules, such as, what happens if 1 device fails?
>  Does
> it take out all the rest?  In this scheme, there is DC isolation between
> inverter outputs, so one inverter failure should not take out the other 3.
>  And, in fact, if i did lose an inverter, i should be able to short its
> tank
> circuit (using its energy storage of the MMC to maintain tuning) and
> continue operating at 3/4 power.  Hopefully it never comes to this!
>
> The coil has a natural resonance of about 45khz, but i found that de-tuning
> the drive down to 40khz or so was best to keep it in tune with large
> streamer loading.  The primary current peaks at 6000A after about 6 cycles
> of excitement.  The coupling coefficient of the system is fairly high, at
> about .19 (estimated by a 5 cycle beat period that didnt quite notch).  So
> detuning the primary seemed to work well at efficiently transferring energy
> to the secondary in the event of being detuned by streamers.
>
> The primary copper is 3/8" diameter to keep the surface area down (which
> happens to reduce AC losses as the eddy currents are lessened).  I pump tap
> water through the primary to keep it cool, as the RMS current is something
> like 80-100A per primary coil!  Me (tall guy) and friend Mike working on
> the
> primary coils:
>
> http://www.flickr.com/photos/kickermagnet/5487414563/in/photostream
>
> The MMC is made out of giant polypropylene snubber capacitors, rated 5uF,
> 2500VAC pk, 3600Apk and 80A RMS each.  They make the CDE MMC caps look very
> small indeed.  I think the whole MMC bank (32 of these caps) weighs
> something like 150lbs.  Total bank is 4 strings of 8 in series, 2.5uF
> 20kVAC
> effectively.
>
> RF grounding was primarily a 4x20 foot sheet of metal "cloth" (1/2" square
> steel mesh) laid on the parking lot, and also clipped to the building
> ground
> rod (about 40 feet away).  Would have preferred an even larger sheet of
> metal down there, but this was available and quick, and seemed to do the
> trick!
>
> Spark performance ended up being right on target, at 25 feet, with
> extrapolations from smaller DRSSTCs (that make 10-12 foot sparks).
>
> I gotta thank the help of many friends, Jeff Larson for his use of
> materials
> and labor on the secondary coil for this beast.  Big thanks to the guys in
> Arcattack, who stayed at my house for a week this january to help me crank
> out this prototype (we actually got it running by the end of a week!).
>  Terry Blake has been supportive in helping setup and teardown of this
> system, which isnt trivial, and for being the guy in the suit.  And
> recently
> Jimmy Hynes (who got me working with DRSSTCs originally) who visited and
> instigated the testing of this machine, and helped tune it up to almost
> perfectly match our expected outputs. And Dave (who isnt on the TCML) for
> being such an awesome host, letting us run and store this machine at your
> shop, and dealing with the city and fire department on issues that really
> dont concern them, thats a story for another time.
>
> Steve
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