I have a printing machine that needs to have (3) 100 amp, 3 phase feeds run to it. We have a 480 volt panel near by. The machine input needs to be 200-230 volt. Do we need three different transformers (one for each 3 phase feed) or can we put one large transformer to feed all three feeds. Would it make more sense to feed a bigger transformer that then feeds a new 120/208 panel?
Transformer
- Thread starter mgtack
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rcwilson
Senior Member
- Location
- Redmond, WA
Yes.
3- 208 V- 100 A circuits is 3 x 208 x 100 x 1.732 /1000 = 108 kVA. Standard transformer sizes are 112.5 and 150 kVA. Go for the 150 kVA.
150 kVA at 480V, 3 phase = 180 amps. Adding 25% bumps it to 225 A, the minimum size feed I would put in from the 480V panel. A 225 A breaker might trip on transformer inrush and a 250 or 300 A may be needed.
iceworm
Curmudgeon still using printed IEEE Color Books
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- North of the 65 parallel
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- EE (Field - as little design as possible)
mgtack-
This is more of an accounting problem than an engineering problem. There is no engineering reason to one xfm or three xfm.
Check the machine specs for the loading on the 3 circuits. Maybe they are not at 100%. Often the mfg pads their input specs to make sure they are not overloaded. Maybe they are ony loaded to 80%. If so a 112.5kva or 3 - 45kva will do just fine.
Put together a material list for each scenerio. Price it out. I suspect the issue will come down to ease of installation and how much room do yu have for the components.
Here are some issues you might think about:
Do you need non-ventilated transformers? This will have to do with the dust/moisture in the air. Some industrial processes are pretty bad. A non-ventilated 150kva weighs 2000 lbs. A 45kva non-ventilatied weighs 500 lbs. And if you do use a non-ventilated, don't forget the inrush is hellishly high. I would waste a call to mfg engineering dept to see just to check. I won't tell you how I know to ask this.
The single xfm uses one 400A primary disconnect, and 350kcmil primary conductors.
Each of the three 45kva will have a 70A primary. A 100A fused disconnect for each will work well.
I would not use a commercial panel board for an industrial process - unless that was the spec.An NQOD panel with a 400A main and 100A
QOB feeders just is not very robust. I'd pick a panel with a 600A main and can fit F-frame breakers or go with three separate 100A fused disconnects.
Each 45kva will require a 100A 3pole fused disconnect. Since these are dedicated xfms for each fedeer, there is no use to upsize the secondary disconnect or conductors.
Make some pencil sketches, figure out where the equipment goes. Makes some estimates for installation. Just use List prices, or pick a discount. Once you do this, you will know for sure. For me it is usually about ease of installation. But then I am an owners agent not bidding to a spec.
ice
This is more of an accounting problem than an engineering problem. There is no engineering reason to one xfm or three xfm.
Check the machine specs for the loading on the 3 circuits. Maybe they are not at 100%. Often the mfg pads their input specs to make sure they are not overloaded. Maybe they are ony loaded to 80%. If so a 112.5kva or 3 - 45kva will do just fine.
Put together a material list for each scenerio. Price it out. I suspect the issue will come down to ease of installation and how much room do yu have for the components.
Here are some issues you might think about:
Do you need non-ventilated transformers? This will have to do with the dust/moisture in the air. Some industrial processes are pretty bad. A non-ventilated 150kva weighs 2000 lbs. A 45kva non-ventilatied weighs 500 lbs. And if you do use a non-ventilated, don't forget the inrush is hellishly high. I would waste a call to mfg engineering dept to see just to check. I won't tell you how I know to ask this.
The single xfm uses one 400A primary disconnect, and 350kcmil primary conductors.
Each of the three 45kva will have a 70A primary. A 100A fused disconnect for each will work well.
I would not use a commercial panel board for an industrial process - unless that was the spec.An NQOD panel with a 400A main and 100A
QOB feeders just is not very robust. I'd pick a panel with a 600A main and can fit F-frame breakers or go with three separate 100A fused disconnects.
Each 45kva will require a 100A 3pole fused disconnect. Since these are dedicated xfms for each fedeer, there is no use to upsize the secondary disconnect or conductors.
Make some pencil sketches, figure out where the equipment goes. Makes some estimates for installation. Just use List prices, or pick a discount. Once you do this, you will know for sure. For me it is usually about ease of installation. But then I am an owners agent not bidding to a spec.
ice
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