Transformer/s used for voltage drop question.

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Strife

Senior Member
I'm looking at a job where the customer wants a single phase, 240V, 600A panel at about 800-900 feet. After playing with the voltage drop thingies, the best scenario seems to be using a transformer to up the voltage to 480V at the beginning point and another 480V to 240V transformer at the other end.
That would require 300A at full load and I can get away with 3 sets of 250XHHW AL. Without the transformers it's an UNHOLY AMOUNT of parallels(like 9 or 10, and I AM NOT PULLING 900 feet bigger than 250).
My question is: If I use a 100% neutral transformer at the far end(where I change back to 240V), do I REALLY need to run a neutral between the transformers? As far as I can tell the answer should be no, but I just wanna make sure. I mean we're looking at roughly 3000 feet, so even at a dollar a foot for AL it's still 3K dollars.
 

tgreen

Member
240v 600a, @ 900feet is 16.49% voltage drop. using (2) 250's copper per phase.

i was going to recomend a buck boost transformer on the load side end, but dont see one that is large enough. your best bet might be to step it up at 480.

you could use (2) 250 alum per phase at 480 an have a 4.95% voltage drop. and even make some tap adjustments if you need to.

best option i can see
 

Strife

Senior Member
That's the reason I'm definitely gonna use the up and down transformers.
My question was though, if I use a 100% neutral at the "down transformer" do I really need the neutral wire between the transformers?
And your post kinda brought to mind another question, I was looking at 3 parallels to keep it under 3%(5% max, 2% for subfeed or so). From the end panel, I'm running 300' going to a 200A panel, so I could up that to be no voltage drop, but the other 400A I DO NOT KNOW how far it'll be. The customer wants to build lotsa things around, could be 100', could be another 400 feet.
I guess I could go as high as 350 AL and have a voltage drop on the feeders of about 3.5%, play with the taps a bit, and play with the other 1.5 percent when I come to it.
240v 600a, @ 900feet is 16.49% voltage drop. using (2) 250's copper per phase.

i was going to recomend a buck boost transformer on the load side end, but dont see one that is large enough. your best bet might be to step it up at 480.

you could use (2) 250 alum per phase at 480 an have a 4.95% voltage drop. and even make some tap adjustments if you need to.

best option i can see
 

templdl

Senior Member
Location
Wisconsin
I would opt for a 240 1ph2w -480 1ph2w feeding a 480 1ph2w 120/240 1ph3w transformer. Because the secondary of the step up transformer is only 2w then you only need primary protection. Besause the secondary is only 2w you only need to run 2w. There is no neutral required.
The the step down is considered a new source where you have 1ph3w grounding the neutral as one would a service entrance.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I would opt for a 240 1ph2w -480 1ph2w feeding a 480 1ph2w 120/240 1ph3w transformer. Because the secondary of the step up transformer is only 2w then you only need primary protection. Besause the secondary is only 2w you only need to run 2w. There is no neutral required.
The the step down is considered a new source where you have 1ph3w grounding the neutral as one would a service entrance.

All is good except that the 480 part will need to be grounded where it is derived and you will need a EGC sized to 250.66 run to the far end xformer. I think I would do a center tap at the step up xformer to use as a grounding point.
 
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