Hi Jeff,
> In some modeling with a 4000V supply with 50 Ohms
> equivalent series
> secondary resistance and 20 uFd of capacitance, the
> single cycle
> peak capacitor current hit 21 amps compared to 80 amps
> if switched
> at the peak of the line. When drawing 1 Amp of plate
> current, peak
> diode current ran about 4.5 Amps.
I get about six amps peak current in the diodes with a 1 amp
load, and a start up current starting at zero of 23 amps
into the cap. That 23 amps has to come from the power line,
and is increased by the turns ratio. That's a lot of peak
line current on the primary Jeff to get 23 amps (or 21 amps,
who cares) on the secondary.
> Yes, 24 Amps on the plate side for a fraction of a cycle
> through diodes rated for at least 30 Amps. And yes, 240
> amps for a fraction of a cycle through the power line.
> What's the problem with those numbers?
The problem is it isn't a inrush limiter by any stretch of
the imagination, even though the solid state switch can
probably take the surge.
If we placed a 20 ohm resistor in series with the primary,
we be limited to 17 amperes peak in the primary. There is
a big difference between 17 amps and a few hundred amps. I
wouldn't call a few hundred amps the midway point or a
reasonable starting current.
If your breakers aren't jumping out of the wall then a
reduction between the "unlucky" worse case to always best
case (relying on your numbers) of four times is certainly
OK. It is a more reliable switch. That just isn't inrush
limiting by any means, and I don't think it could be
considered mid-way. I even know people who claim a zero
crossing switch works on filaments and limits inrush!
Myself, I start anything HV through 10-40 ohms. For
filaments I measure the long term excessive current, and it
takes dozens of cycles to get past the really high current
stuff that potentially does damage.
By the way, the power factor of a capacitor input supply
with a low ESR transformer is pretty bad, isn't it? Peak
current is six times the average current in the case you
gave! That sure isn't .8 or .9 true or real power factor. I
think someone confused displacement power factor (phase
error only) with true power factor (harmonic distortion
effects or ratio of peak to RMS included).
That very high but short duration peak current is the killer
for voltage regulation and true or real power factor.
73 Tom
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