Re: Weird safety gap behaviour

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

Original poster: "Ed Phillips" <evp-at-pacbell-dot-net> 

Hi Ed,

Are you saying the equivalent inductance of the NST is decreasing as the
amplitude is increasing and thus at low voltage (Cp=2.5 Cres), the Fres
is
38 Hz and when Lnst decreases, the Fres moves up closer to 60Hz   If so,
is
this due to shunts saturating?

Gerry R."

	That's not what I intended to say.  At least in my experience the
inductance INCREASES as the voltage is raised from zero, so to get this
phenomenon the capacitance would be less than that required for
resonance at normal operating voltage (the mythical "matched"
capacitance). If you look at a typical B-H curve you'll see what happens
to the permeability as the flux density increases.

	The first time I encountered the effect was when I had a big 0.0062 ufd
transmitting mica capacitor connected to a 15 kV, 60 ma transformer.
That's a lot smaller than the "matched" capacitance of around 0.0106
ufd.  I hooked the capacitor and a Simpson meter on 5000V scale across
the transformer and brought the voltage up from zero with a variac.  At
somewhere around 30 volts, as I recall, the meter suddenly pegged,
taking out the 5000V multiplier.  Fortunately the rectifier and meter
weren't damaged.

Ed

P.S. This was one of those stunts which, right after things went wrong,
caused me to wonder "why did I have to do that!".