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Re: NST TEST GRAPHS (was NST power test)
Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
> Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>"
> Does any of this testing show that a simple transformer model (leakage
> reactance, series resistance, magnetizing inductance, loss resistance)
> doesn't adequately describe the NST operating in it's linear (non
> saturated) regime?
> None of my testing indicates that this changes. However, the tests did
> that if the load is only a varying resistance the sec voltage is linear
> the sec wattage is non linear.
Which you would expect.. power transfer is a peak at matched resistance, and
zero with either a short or infinite resistance... Has to be nonlinear
> When the secondary VA is greater than the primary VA, it just means that
> there is reactive power circulating in circuit formed by the secondary
> leakage inductance, resistance, and the external capacitor. In fact, it's
> a good indication of resonant rise in the secondary, since that would
> nicely explain it.
> 0.01 uF at 60 Hz would be about +j265K ohms...
> 7.5kV open circuit with 30 mA short circuit output current would imply
> the leakage inductance has a reactance of about -j250K... (neglecting the
> iron and copper losses, which are probably around 5-10%)
> So, the 0.01 uF case is pretty darn close to resonant. What was the
> voltage across the capacitor in this case?
> Unfortunately, I did not have a variable uf capacitor to look for
> around .0106 uf. There was no voltage rise at .008 uf and the sec voltage
> was 5700 volts. There was also no voltage rise at .011 uf and the sec
> voltage was 6200 volts. If there is a voltage rise between .008 and .011 I
> would expect that the tuning would be very sharp.
Given the high resistance (secondary winding resistance, if nothing else), I
don't know that the Q is all that high. Ballparking it, I'd expect that the
resistance of the secondary is such that the loss in normal operation (i.e.
lots of current, low voltage) is around 5% of rated power. For a 7.5/30
(275VA) something on the order of 10W? At 30 mA, that's (R= P/I^2) around
11kOhm.. The reactance is (as calculated before) around 265K, so the Q( =
X/R) is going to be around 20. 5% might be optimistic.. 10% losses would
equate to a Q around 10.. To get a change in voltage of .707 (= 3dB) would
imply a change in C of around 20%...(say, from .01 to .012)
Perhaps Terry will make some current phase measurements (hint, hint) and
you'll see resonance clearly, as the phase flips through zero.