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Re: [TCML] large DC coil power supply

Also GE/ITI makes a 15kVA version of previous transformer, only saves you 50lbs
in weight however...


Looks like 1000 lb gang box is about right....

Dave S.

On Sun, Aug 15, 2010 at 5:26 PM, David Sharpe <sparktron01@xxxxxxxxx> wrote:
> Jim
> Since I am working with switchgear on a daily basis, I can give a little
> guidance from the power side...
> <SNIP>
>> 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.
> http://www.gedigitalenergy.com/products/specs/3CPT3-60-30.pdf
> 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
> unfiltered.
> ---------------------------------------
>> 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!"

Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA

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