Re: Weird safety gap behaviour

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

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi Dr Resonance,

Is this a different phenomenum than resonant charging (like at Cp = Cres)?

Gerry R


 > Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
 >
 >
 > At certain load dynamics, NST can be ferroresonant with the circuit and
 > develop higher than normal potentials.  This usually occurs for just
certain
 > values of cap and pri inductance.  You need to change one or the other and
 > recheck for ferroresonance.
 >
 > Dr. Resonance
 >
 > Resonance Research Corporation
 > E11870 Shadylane Rd.
 > Baraboo   WI   53913
 >
 >  >
 >  >
 >  > This is a follow on to the weird SRSG behavior and I thank everyone
that
 >  > responded to that post.
 >  >
 >  > I'm getting a safety gap behavior that I don't understand.  I got the
SRSG
 >  > removed from the system so that added complexity is gone.  I have two
 > 15/30
 >  > NST's (magnetek) in parallel connected to the terry filter that in turn
is
 >  > connected to a 3 terminal safety gap (center terminal grounded).  One
side
 >  > of the safety gap is connected to Cp (2.5* Cres).   The other side of
the
 >  > safety gap is connected to the primary.  Cp is in series with the
primary
 >  > (standard TC topology for a two bushing power source).  The safety gap
 >  > consist of brass heat sinks that are threaded for 3/8" carrage bolts.
The
 >  > carrage bolts are adjusted to just not fire when the unloaded NST is
 > driven
 >  > with a variac at 140Vac.
 >  >
 >  > I'm now measuring the total voltage across the hot terminals of the
safety
 >  > gap differentially (BTW getting the same answer as when measured single
 >  > ended between a hot terminal and ground and then doubling the
 >  > result).  Following are the measurements:
 >  >
 >  > I slowly raise the variac voltage from 0 to 90V.  The peak differential
 >  > voltage across the two hot safety gap terminals increases to about
 >  > 16KV.  With no further increase of the variac voltage, the 16KV starts
to
 >  > run away (exponentially it seems) and snaps to 30KV.  The safeties are
now
 >  > firing and healthy arcs are coming from the secondary top load.  The
 >  > safetys dont fire until after the runaway so don't seem to cause the
 >  > runaway.  It takes about one second to snap to 30KV.   In 30KV mode,
the
 >  > variac output voltage is still 90V so the variac doesn't seem to be
part
 > of
 >  > the runaway.
 >  >
 >  > The next interesting thing is that I start to lower the variac
 >  > voltage.  The safety gap voltage stays locked on 30KV until the variac
 >  > voltage is reduced to 70V.  At this point, the safety gaps stop firing
and
 >  > the voltage returns to normal.
 >  >
 >  > The safety gap spacings measured 0.21 and 0.26 inches.
 >  >
 >  > Next, I set both safeties to about 0.20 inches.  Results were the same.
 >  >
 >  > Next, I set both safeties to about 0.17 inches.  The runaway again
starts
 >  > at 16KV but the peak voltage after runaway is now about 26KV
 >  >
 >  > If the safeties fired first and didn't regulate that well, then I could
 >  > understand that a transient response would be superimposed on top of
the
 >  > steady state response.  But the runaway happens first and then the
 > safeties
 >  > fire.
 >  >
 >  > Any ideas what is causing the runaway??  (maybe an engineering
 > explaination)
 >  >
 >  > Also, could someone explain reverse voltage mode from an engineering
point
 >  > of view??
 >  >
 >  > Many thanks for any responses,
 >  >
 >  > Gerry R.
 >  >
 >  >
 >  >
 >  >
 >
 >