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Re: [TCML] large DC coil power supply


Since I am working with switchgear on a daily basis, I can give a little
guidance from the power side...


> This is sort of like the power supply for Electrum, but Electrum was
> designed for permanent installation, and so some of the design decisions
> might be different.  Technology has also marched forward.
> Various issues and alternatives for discussion:
> How to get prime power in.. You're not going to use 16 gauge cheap extension
> cords here.
> if you want to run off 240 single phase, that's 100A.. bigger than one
> normally plugs into the old dryer socket.
> In show business, at this kind of power level, you start running 4 wire
> banded (4 separate wires with what are essentially fancy banana plugs on the
> end)
> Clearly, this is bigger than typical residential loads, so that means
> probably using a standalone generator, and in this class, that means 3 phase
> too, which is nice.  So, does one start with 240 or 480?
120/208 wye is a standard secondary voltage for three phase medium
voltage dry type CPT's.  30kVA is smallest size, however it weighs as
much as 3 oil filled pole pegs ( ~ 700 lbs).  Primary (HV) has +/- 7.5%
or 2.5% taps.


Another point, stay away from 480V single or three phase.  Available fault
currents and arc flash/shock hazards are significantly higher with 480
then 240V or less.  125kVA transformer or smaller @ 240V with available
bolted SC of 10kA or less has a AF HRC of '0' (street clothes, cotton;
voltage rated gloves).  Would be excellent if the generator you select
has field control adjustability, then you simply adjust generator output
reactive power via field excitation.  Field excitiation DC power
requirements are approximately 0.5-2.0% of machine output
(construction, speed/poles dependent).
> My gut feel is that 240:14400 transformers are more common (cheaper) than
> 480:14400. And 240V (or 208V) generators are going to be more common too
> (and so cheaper to rent.. in the $100/weekend category, it appears).
Yep, also three phase DC excitation power supplies are either 125/250VDC
for machines up to megawatt class.  208 will handly give you 250VDC, 6 pulse
> But, 2 or 3 transformers is a "big" package.. (but then, a 25kW coil is a
> big pile o' stuff anyway), and they're oil filled which makes transportation
> a bit more of a hassle.  Do you put them in separate road cases? or just one
> big 1000 pounder?
1-1000 lb case with dry type transformer shown above would work.
> But maybe there *is* some sort of industry that uses up 20kV 1 amp DC power
> supplies?  (yep.. buy 20 1kW class inverter microwave ovens, work out the
> non-trivial primary isolation issues, and run them in series/parallel)
Perhaps industrial microwave generators in the 50-100kW range?
> And then, once you've got your DC power.. how do you get it to the coil?
> It's fairly obvious that the power supply is big and bulky, and you're not
> necessarily going to want to stash it under the coil.. so that means running
> a few amps at 20kV around.. RG213 coax should do nicely for that.
Resonant DC PS would require charging inductor, de-Qing diode stack
and would provide up to 40kVDC.  Don't know if '213 would hold off that.

Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA

Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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