RE: Over-voltage at Synchronous Gap ? ? ?

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

Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com> 


That is where my safety gap is firing (and quite loudly too as its
discharging the capacitor through the safety gap - in series with the
primary coil of course).  I am finding that if the synch gap is set to
late, as Gary states below, that this condition occurs.

Dan



 > I've not scoped an off-tuned system and I have minimal
 > experience with
 > running in an off-tuned state to look for effects of this, but I have
 > scoped a system with no secondary, and the primary waveform is a very
 > straightforward nowhere-to-go-but-down linear decrement.  As
 > you say, since
 > the energy has no where to go, it must stay on the primary
 > side and be
 > burned off, mostly in the gap, and also in cap dielectric and other
 > resistive losses.  But I still see no mechanism that will
 > cause a resonant
 > rise at the primary tank frequency (as opposed to F-mains).
 > I'm not saying
 > that it doesn't or can't, but if it does, there is some
 > mechanism that our
 > simulation models and basic understanding does not yet address.
 >
 > I have seen a sync gap set too late and this causes
 > instability, where
 > firings are missed, which causes some degree of mains
 > resonant rise, which
 > may account for the safety gap firing.
 >
 > Gary Lau
 > MA, USA
 >
 >
 > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
 >
 > Hi Gary,
 >
 > Normally the primary system is "loaded" by the secondary system which
 > actually burns most of a system's power.  If the secondary is
 > miss-tuned,
 > or removed in the extreme case, the power will have no where
 > to go.  Thus,
 > it is possible for the primary voltage to resonate to higher
 > than normal or
 > expected values.  Nowhere near the 80kV of an uncontrolled
 > resonate system,
 > but enough to false fire safety gaps.
 >
 > In a sync rotary gap system, firing voltage is not controlled
 > by a fixed
 > spark gap voltage  but rather "timing" alone.  If the voltage increase
 > occurs when the gaps out of firing position, there is nothing
 > to stop an
 > increase in voltage other than the safety gaps.
 >
 > Sync LTR systems can be pretty sensitive to tuning, gap timing, and
 > coupling.  If the tuning is off, dramatic primary to
 > secondary arcs can
 > occur.  Poor timing can draw much more line current and blow
 > fuses that we
 > are supposed to be using.  Coupling can affect quenching,
 > racing arcs, and
 > primary voltage adding to the confusion.
 >
 > So....  Sometimes it is just best to work at say 1/4 or 1/2 power and
 > re-tune everything just right if odd things are going on.
 >
 > Cheers,
 >
 >           Terry
 >
 >
 > At 09:38 PM 9/15/2003 -0400, you wrote:
 >  >Hi Terry,
 >  >
 >  >Can you expand on your statement below, which I've highlighted in
 >  >all-caps?  I can't imagine a situation where the primary voltage
 >  >increases after the gap fires, regardless of tuning.
 >  >
 >  >Thanks, Gary Lau
 >  >MA, USA
 >  >
 >  >
 >  > >Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
 >  > >
 >  > >As Kurt showed, maybe you need slightly more MMC
 > capacitance.  If you
 >  >are
 >  > >not using a Terry filter and don't have some of the same losses
 >  >involved,
 >  > >results may vary a little.  I would just add a little
 > capacitance to
 >  >the
 >  > >primary cap till things quiet down.  If you are using a 0 - 140VAC
 >  >variac,
 >  > >that may over voltage things a bit too.  Tuning may be an issue as
 >  > >well.  IF THE SECONDARY SYSTEM DOES NOT USE UP THE POWER
 > >PROPERLY, IT
 >  >MAY TEND TO RAISE THE PRIMARY VOLTAGE UP.
 >
 >
 >