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Re: Twin SSTC (fwd)
---------- Forwarded message ----------
Date: Sat, 07 Jul 2007 10:19:32 -0800
From: Greg Leyh <lod@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Twin SSTC (fwd)
The NLL twin prototype coils use a classic Tesla Coil primary circuit,
with an inductor, capacitor and a switch. There are no master
oscillators, or any type of feedback system as used in DRSSTC designs.
The switch is a single IGBT, which receives an ON signal for the
duration of the 1st envelope (exactly 2 cycles in this case.)
Later on, during the secondary ringdown and after the main arc activity
trails off, the primary switch is turned ON again, to recover the energy
remaining in the secondary. The timing and duration of this action is
not critical. It appears that up to 5-25% of the energy can be
recovered using this method.
The design of the NLL twin prototype coils attempts to incorporate and
test every feature that might be used with the final NLL 120ft coils,
including aspect ratios, coupling, primary drive topology and energy
recovery. The design is necessarily as simple as possible, in order to
scale to the final size with minimal risk.
Yes, each tower must have it's own independent drive system, as a 600ft
round-trip xmsn line operating at 50,000A pk would not be practical.
The phasing between the two coils is then adjusted by setting the time
delay between the two envelope command signals.
So far, we've had just two opportunities to run the coils; at the Maker
Faire and the Integratron. The coils displayed a wealth of unexpected
and unexplainable behavior, particularly in terms of how the two
secondaries interacted and coupled with each other.
For instance I had originally assumed that the streamers would repel if
the two coils were in phase, and attract when the coils were 180deg out
of phase. Observed behavior at Maker Faire was completely different.
The arcs would bridge as expected at 180deg, but adjusting the phase in
either direction would cause one streamer to *grow* in length while the
other streamer would almost disappear! The first 10 seconds of this
YouTube clip shows this effect, as I run the phasing from 0, thru 180 to
360, and back: http://www.youtube.com/watch?v=06hWFQSqJfI
Scope waveforms of both coils' Isec indicated that the phase was indeed
changing, and that the Isec amplitudes were remaining relatively
constant. However, Ansoft Simplorer simulations indicate that
substantial energy can couple between the secondaries through the
toroid-toroid capacitance. In the simulation, a mere 6pF (my rough
estimate for the actual Ctor-tor) will couple nearly all the energy from
one sec to the other in about 8 cycles. I plan to make a more refined
measurement of the secondary interactions when the San Francisco lab is
set up later this month.
One other odd bit of behavior occurred when the phasing was set around
180, and the primary voltage was decreased so that the streamers barely
touched. One could see the interaction point physically move several
feet back and forth between the coils, at a speed of about 1-2 Hz. This
movement was strongly reflected in the Isec waveforms, in the form of
their *Fres* alternately changing, at this 1-2 Hz rate! That is, the
start of both Isec waveforms remain locked in phase, but about 6 cycles
into the envelope the relative phases are shifting past each other by
over 90 deg, at this 1-2 Hz rate. I don't have any footage of this
effect, but it's fairly easy to replicate, and plan to do so as well
when the labspace is ready. My only theory at this point is arc loading
of Fres. GL
Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Fri, 6 Jul 2007 11:52:04 -0600
> From: S&JY <youngs@xxxxxxxxx>
> To: Tesla List <tesla@xxxxxxxxxx>
> Subject: Twin SSTC
> Greg Leyh recently demonstrated his large twin SSTC at the Make Fair, or
> whatever it was called. What was unique was that it was really two
> phase-locked SSTCs, each with its own power driver. This allowed
> elimination of a transmission line to connect the two primaries in series.
> Instead, I presume he controlled the drivers with a pair of fiber optic
> links from a master oscillator in his control box. He also had the ability
> to vary the phase relationship between the two coils, which could make for
> interesting effects. His power drivers apparently are something beyond
> DRSSTCs in that they can redirect unused energy back into the power supply
> or supplies for better efficiency (I don't know if he uses a common power
> supply, or one for each coil - I suspect the latter).
> I would love to know more details. My question is, would Greg or anyone
> else knowing more details about Greg's setup be willing to share them with
> Also, has anyone else built a twin DRSSTC setup using separate drivers for
> each coil? If so, would you please post some details?
> Finally, I believe a twin TC driven with two SISGs, each triggered with the
> same pulse ala Finn Hammer style, wouldn't work well because there would be
> no way to phase lock the frequencies of the two coils. Is that correct?
> Or, if the resonant frequencies of the two coils were almost identical,
> would they lock in phase via the streamer connecting the two toroids?
> All comments will be appreciated.
> --Steve Y.