Jim
Do you presently have 120/208 “house power? If you want 3 phase usually
horrible expensive from utility. Another out there house power option is
240 high leg delta (you get 120/240 from one Xfmr, 3 phase from all 3, and
no ungrounded system risks since 120/240 xfmr establishes N-G connection.
At really large powers I’m like you I’d love a really large MG set from 25
-2500HP and up. Flywheel action provides 2.5-5X momentary overload
capacity and who needs a stinking variac, when I can very simply control
output voltage by field control of generator at O.5-1% of output load.
The only advantage of a solid state voltage control like I’m working on
(IGBT across Full Bridge, PWM control) is SS can be EPO electronically in
simulated 2ms with fault detection. A large MG set even with vacuum bottle
CB technology will be an order of magnitude slower, AT BEST.
If your looking for a generator I’d insist on a brushed rotor so you can
manually adjust Vo. Most generators have on board regulators that will
shut down unit if you exceed compliance ranges of generator. Irregardless,
you have to stay within the PQ stability limits of your unit or you will
cause thermal damage to stator or rotor depending on under over excitation,
and reactive power tolerance and unit input output limits.
Best Regards
Dave “Sparky” Sharpe
On Wed, Jan 22, 2020 at 1:32 PM jimlux <jimlux@xxxxxxxxxxxxx> wrote:
> I'm looking at alternatives for powering a medium sized coil/coils. I'm
> thinking in the 10kVA and up range.
>
> I think I would like three phase power 240V from 10-25 kVA (I think), so
> I can do a simple rectifier for a DC bus.
>
> If I went to a single phase supply, I'd need filter capacitors with
> largeish stored energy. 8 milliseconds at 20 kVA is 160 Joules which is
> 0.8 uF at 20kV. Doable, but bulky. (not that a three phase transformer
> isn't heavy, but...)
>
> So here are some alternatives
>
> Run off single phase 240V at home (40A@240V is just 10kVA), rotary phase
> converter (which would be big.. something like a 15HP three phase motor)
>
> Buy a generator that puts out 3phase. New towables around 10kVA are
> around $10k, but maybe you can get a used one significantly cheaper?
> (assuming it hasn't been horribly abused, e.g. by some dude running a
> tesla coil with no HV suppression on the power line - more likely, some
> dude running it without changing the oil or without oil at all)
>
> You can get a fixed generator that's 25kVA (e.g. generac 25kVA 3 phase,
> 120/208) for $9k (but then I'd have to buy a trailer to move it around)
> - hmm maybe buy a cheap used pickup truck and mount it in the bed? A
> self propelled tesla coil system?
>
>
> Rent a generator that puts out 3phase (kind of a hassle to go down and
> rent the generator every time I want to experiment, but maybe it works.
> $260/day, $600/week, $1700/mo)
>
> Buy a collection of single phase generators that are lashed together and
> somehow synchronized (yeah, that's TCML hackery... ) 10 kVA (ish)
> generators are about $1000 on Amazon (e.g. Westinghouse dual fuel 9500)
> or a Harbor Freight for $800-900. Yeah, they're noisy, inefficient, but
> my usage duty cycle would be low.
>
> Speaking of synchronization, what about ganging up inverter generators.
> I've ganged two Hondas together but that was single phase. I think you
> could built a small phase shifter box, or a small rotary converter
> (something like a 1HP three phase motor) and gang three inverter gens
> together. I'd be a bit afraid of cooking the electronics with a TC.
> There's something robust about using technology that was matured 100
> years ago when Tesla and Westinghouse were still alive.
>
>
>
>
>
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>
--
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA
Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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