Jim
Simplest way to derive generator safe operating limits
https://youtu.be/KsG6qERjvC0
Also look up generator protection, PQ stability limits. It’s entirely
possible by under excitation of generator (inductive source) you could
force system to have unity power factor (ie synchronous operation).
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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