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Re: Just wonderin' (fwd)
Ran some simplified Excel calcuations on the division of load current
between a 12 kV, 60 ma NST and a 15 kV, 60 ma NST. The Q's were
identical, and the assumed transformer resistance was 5500 ohms for the
12 kV unit and 6875 for the 15 kV. The outputs were connected in
parallel to an 0.0243 ufd capacitor (so-called matched capacitance, for
whatever that really means) and a shunt resistor to simulate the effect
of a gap and TC primary circuit. The higher resistance values
correspond to large gap spacings. The results are:
Load R Vo I(12 kV) I(15 kV) I(total)
(kohms) kv) (ma) (ma) (ma)
0 0 60 60 120
50 5.9 67 64 131
100 11.7 84 77 161
150 17.3 107 93 200
200 22.9 132 112 243
(That looks OK here, using Courier font. Hope it is at least
unscrambleable.)
Didn't calculate the power into the load, but should have.
These results looked strange, so simulated the same circuit in
Electronics Workbench, with identical results. (By the way, with no
resistive load in parallel with the capacitor the voltage goes way above
100 kV, as would be expected with a "matched" capacitor, which is tuned
for parallel resonance with the transformer leakage reactance. Clearly
shows why opening the gap up to increase the spark length can easily
wreck the NST.) I was surprised that the higher voltage transformer
took less of the load than the lower voltage one, but realized that the
difference was the lower leakage reactance of the 12 kV unit (200,000
ohms vs 250,000).
For what it's worth. Think it's right. If so, paralleling transformers
is a reasonable thing to do, at least if the voltage mismatch is in the
range given here.
Ed