Re: Weird safety gap behaviour

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

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.
 >
 >
 >
 >