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Re: Why does running an NST on an async gap kill it?
Original poster: "Gerry Reynolds by way of Terry Fritz <teslalist-at-qwest-dot-net>" <gerryreynolds-at-earthlink-dot-net>
That could be true depending on the layout. What I mean by this is that I
made a voltage measurement of the sparkgap firing and recovering. I had a
4500 Vrms transformer and had the SG set to fire at maybe 3500 to 4000V. On
my first measurement, I did get RV hash that went to 20 KV. I reduced the
measurement loop (loop formed by the HV probe and its measurement ground
lead) to minimize any magnetic field induced voltages picked up in the loop
and all of that hash went away. In the system, there was no Terry filter,
just the xformer charging the Cp and a 2 element static spark gap. The
scope was analog type with 300 MHz bandwidth. I can believe that if one
placed the safety gap remotely from the xformer and form a "big" loop with
the wiring, that H fields could couple into this loop. I don't think the
hash is conducted into this loop however unless there is a forced break.
The spark gap impedance is ~2 ohms and at a peak current of say 100amps,
only 200 volts would be generated at the sparkgap during conduction. My
improved measurements seemed to confirm this as this was the only time I saw
RF hash and it was about 200V if my memory is serving me correctly. I
suppose if there was a forced break, maybe this current would make it's way
back toward the NST and then the RC filter would help.
My understanding in this particular case is that the ARSG was not even
turned on at the time the NST was turned on which makes me think this was a
resonant charging failure. I do not know, however, how the safety gap was
set. I think the person said he had a safety gap and MOV's and the terry
filter, but layout is important too.
Please comment further, I may learn something.
> >I'm wondering, if the safety spark gap was moved to be directly across
> >NST bushings and ground, if the NST would be better protected. Since the
> >charging current is coming from the NST, the sooner this can be shunted
> >better. I have to think what this would do to the 1000 ohm power
> >resisters since any Cp energy would then be dissipated in the resisters.
> >Maybe this isn't such a good idea. Comments??
> While it is true that the charging current comes from the NST, It
> is the discharge current from the cap and hash in the oscillating tank
> circuit that kills the NST.
> Matt D.