RE: Over-voltage at Synchronous Gap ? ? ?

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

HI Malcolm and Gary,

At 05:33 PM 9/16/2003 +1200, you wrote:
>Hi Terry,
>
>On 15 Sep 2003, at 20:08, Tesla list wrote:
>
> > 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.
>
>I would be interested to see that statement quantified by facts and
>figures. The ringdown time in the primary vs the cap charge time is ??
>
>Malcolm
.....

>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.

Yes!!


>Gary Lau
>MA, USA

Happily running LTR systems are very stable and it is difficult for the 
primary voltage to go beyond what we expect.  However, a missed firing, 
safety gap firing, miss-tuning, over coupling, bad quenching...  Can 
"upset" the fine train of events that normally control the LTR coil and 
send it into some rather chaotic modes.  These disruptions are brief and 
recover in a cycle or two, but higher than expected primary voltage spikes 
can occur.  When things get weird is when some random event triggers say a 
safety gap firing that triggers another safety firing on the next cycle... 
and suddenly the whole thing can get into a goofy mode of operation no 
longer controlled by the sync gap but rather the mistimed safety gap 
firings combined with proper gap firings.  In other words, it is running 
poorly...  Usually a slight adjustment of tuning will snap the coil back 
into the proper train of firings and suddenly it will all work great 
again.  However, it can be sort of difficult at times to get it running 
just right especially on a brand new coil with a number of adjustments far 
out of whack.

First of all, it really helps to insure that the SRSG gaps are set as close 
as possible.  This allows them to fire at minimal variac settings were the 
safety gaps will never fire and the SRSG is in total solid control.  Then, 
there is plenty of room to fiddle with adjustments to get the best 
spark.  Things like coupling, gap timing, tuning can all be adjusted 
easily.  Then the power can be cranked way up.  If one is at high power 
with the coupling, gap timing, tuning, and safety gaps all going 
bad...  You will never get it figured out ;-))

For modeling, insert a few random miss-timed gap firings.  I suppose one 
could add the safety gap to the model too.  Then you will see that the 
whole system can be shifted into poor running chaos rather easily.  Then 
throw the gap timing off 2 mS, put up the coupling and model the secondary 
racing arcs, put the tuning off 75%...  In other words, model how a really 
messed up coil works!  "Then" take a look at that primary voltage waveforms 
;-)))  They are tortured and unpretty!!  I don't have such a model or I 
would pass it on, but I have seen it trying to fix finicky coils.  Horrible 
things go on!!  I blew a hole through 3/8 inch G10 once with primary to 
secondary arcs (transformer action).  I was trying to stop 18 inch arcs 
over a gap that would normally be 2 inches!!  Coil out of tune - It was 
trying to blow up!!  Coil in tune - No problem at all...  Heavily 
miss-adjusted LTR coils are pretty frightening machines!!, even to myself 
that is suppose to understand them :oD

In a formerly well running coil, one can usually just adjust the primary 
tuning a little to allow for a new environment or turn the gap motor a 
little to get the timing right again (it can get bumped).  Easy for "me" to 
do I guess ;-))  but I have seen some new coilers that have been pretty 
perplexed with the adjustments since they don't really see or understand 
some of the finer points.  So it is best to work at very low power at first 
where at least the safety gaps are not messing things up and errors will 
not do any damage.  At low power, on can "fiddle" until the coil suddenly 
starts running obviously really good!!  "Then", you can crank it up to full 
power.  The simple rule is to adjust everything for the best sparks at low 
power first...

Cheers,

         Terry