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RE: Over-voltage at Synchronous Gap ? ? ?



Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> 

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.