Re: A triggered-s.g. 1-turn primary

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "marc metlicka by way of Terry Fritz <teslalist-at-qwest-dot-net>" <mystuffs-at-orwell-dot-net>

While i see where your going with this principle, I would like to see a
magnetic profile while in action.
  i just don't see a strong  coupling to the secondary with this unit?
Marc

Tesla list wrote:
 >
 > Original poster: "K. C. Herrick by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <kchdlh-at-juno-dot-com>
 >
 > I take note of jimmy hynes/Terry Fritz's posting of 4/28 but submit this
 > posting anyway, which I had been preparing.
 >
 > In another periodic retreat from solid-state exasperations, I have come up
 > with a notional spark-gap design,
 > 
<http://hot-streamer-dot-com/temp/tspk13s2.pdf>http://hot-streamer-dot-com/temp/tspk13s2.pdf.
 > You will need Acrobat Reader for that.  (I note that gif format yields a
 > lousy image, derived using Photoshop either from my CAD program's exported
 > pcx or from a scanned print of the drawing.  The pdf image seems just
 > lovely--similarly derived from a print.  Computer mysteries...)
 >
 > Referring to the drawing, six "6C"s, six "1/6 L"s, six "1/6 R"s and six
 > spark gaps are connected in a circle on the secondary's nominal diameter
 > (in my case that would be 12").  Six 6Cs in series yield C and six 1/6 Ls
 > in series yield L.  L and C resonate at the secondary's Fr when the 6 spark
 > gaps fire.  Each 1/6 L is merely the sum of a 6C's internal inductance +
 > the spark gap's intrinsic inductance + the interconnection inductance of
 > that segment of the primary loop, as arrayed on the nominal 12"
 > diameter.  Each 1/6 R is the sum of spark-gap, 1/6 C and interconnection
 > resistances in its segment.  All of those elements constitute a 1-turn
 > primary.  The secondary is to sit right on top of it--resting, perhaps,
 > directly on the capacitors.
 >
 > Each 6C has applied to it switched AC-mains input, coupled via windings of
 > a T1 and a T2 operating as chokes.  The AC is a sine wave that is
 > interrupted using two power MOSFETs, two IGBTs or a triac, not shown.  The
 > switching circuit is turned on during each mains 1/2 cycle at the
 > approximate voltage peak, staying on for 1/4 cycle and thus delivering a
 > step-voltage via the T coils to each 6C.  The coils in the Ts resonate with
 > each 6C so that, a few milliseconds after each step, the voltage on each 6C
 > reaches about 275 V (as simulated with MOSFET drivers) with 160 V peak from
 > the mains.
 >
 > Phasing of the T1s and T2s is such that the resonant-charging currents'
 > induced voltages in their series-connected second windings are of opposite
 > polarity & thus the series connections exhibit 0 V during the charging
 > time.  All 6 second-winding pairs are connected to a bus-pair that is
 > driven via a break-over diode from one of the 6Cs.  Because of the phasing,
 > the break-over diode sees only the voltage on the 6C.  The Ts are to be
 > physically located close to the physical center, to minimize the Fr flux
 > intercepted by them and their interconnections.
 >
 > During charging, each gap sees twice the voltage on a 6C.  Just prior to
 > the resonant-peak (absent breakdown), the diode breaks down and applies the
 > 6C's voltage to all six T-winding pairs in parallel.  This action induces
 > voltages into the charging windings such as to momentarily increase the gap
 > voltages, sufficient to cause the gaps to break down.  Again, during the
 > spark event, the coil polarities are such that each pair of trigger
 > windings exhibits no induced voltage.  Note that alternating trigger-coil
 > pairs are connected to the driving bus oppositely.  Thus the trigger
 > voltages on alternating primary-loop segments are of opposite polarity,
 > doubling the trigger voltage seen by each gap.
 >
 > The turns ratio in each T might need be no larger than 1:2 for reliable gap
 > firing; 1:1 and perfect transformers would cause the gap voltages to
 > increase by a factor of 1.5.  Also, all the Ts could well be consolidated
 > onto just two cores with one trigger winding on each core.  The 20 mH (in
 > my simulation) is not critical; a whole lot smaller and the peak mains
 > current becomes excessive while a whole lot larger, the charging time
 > becomes excessive.
 >
 > As soon as the gaps break down, the damped sine wave loop-current at Fr
 > commences flowing.  The 6C-charging T-coils then act to isolate the mains
 > from the spark gaps during the firing event while a simple clipping network
 > at the MOSFET/IGBT/Triac output clamps the pk-pk voltage there to less than
 > ~+/- 250 V--again, as simulated.  I've added a small R-C damping network as
 > well, to soak up most of the Fr signal there.
 >
 > The gaps keep conducting until the Fr current becomes too low, which will
 > occur well before each following initiation of capacitor charging, ~8 ms
 > later at 60 Hz mains frequency.  They are to have extremely close spacing,
 > perhaps 0.02" or so and thus will dissipate relatively little power.
 >
 > Since the capacitor charges for each half mains-cycle are of opposite
 > polarity, any tendency for metal to transfer across the gaps should be
 > minimized because the DC component of the gap current will alternate from
 > one mains half-cycle to the next.
 >
 > I show 115 VAC input but 240 V could be applied just as well.  I've
 > simulated the circuit using 40 uF for 6C, 33 nH for 1/6 L, 5 m-ohms for
 > each 1/6 R and 20 mH for each charging-coil of T.  I've not simulated the
 > trigger scheme except for using a "switch" for each gap and turning those
 > on for 500 us after the delay time.  The scheme works just fine in that
 > simulation: Fr is about 125 KHz and the peak first-half-cycle loop current
 > is about 9 KA with no simulated additional switch voltage-drop.  At 120 V
 > in, the line current is about 15 A RMS, 30 A peak.  The Fr current
 > diminishes to 1 KA at the 4th cycle (no secondary present).
 >
 > A 30 m-ohm total loop resistance is perhaps too optimistic.  Higher
 > resistance will, of course, diminish the peak current and also the number
 > of Fr cycles that will occur prior to gap-extinguishing.  With 100 m-ohms
 > total, I get only ~7 KA peak Fr current and that diminishes to 500 A in
 > just 1 1/2 cycles; likely not enough excitation to produce much of a
 > spark.  Thinking that perhaps two rather than 1 turn would be better (if Q
 > = X/R, X would be 4x, R would be 2x, perhaps, so Q would be about
 > doubled--right?), I temporarily added 600 nH and 60 m-ohms into the
 > loop.  I got 4 KA peak diminishing to 500 A in 2 1/2 cycles & whether
 > that's an improvement, I don't know.  I didn't bother to alter the 6C
 > values to bring Fr to the same frequency.
 >
 > It does seem to me that with too-high a dv/dt in the first half-cycle,
 > there might be the risk of secondary turn:turn voltage breakdown.  Would
 > the lower dv/dt and higher Q be better?  Perhaps someone else has already
 > considered that kind of thing & I've not paid attention.
 >
 > Clearly more primary segments could be added for more power--but cramming
 > more capacitors& gaps into the nominal diameter might present a problem.
 >
 > I could use some informed comment on this.  Perhaps it's all too fanciful...
 >
 > I'd be happy to email my SIMetrix simulation-schematic file to anyone with
 > SIMetrix and a real interest in the design.  Or, perhaps someone would care
 > to simulate it otherwise, using the pdf drawing as the source.
 >
 > Anyone interested enough to consider building it??
 >
 > Ken Herrick