I need to carry some secondary 240V single phase about 1000' across the farm to a pole barn, and am concerned regarding voltage drop across that distance. In a perfect world I would have a 200A service, but can settle with 125.
I already have a spool of 3/0 aluminum wire which I'd like to use.
I'm wondering about using a pair of dry pack 3 phase transformers to bump the voltage up to 480 at the input, and then perhaps tapping off at 460 to 240 on the receiving end to reduce the voltage drop.
In essence I would be using the dry packs as a form of buck-boost transformer system, albeit at a higher KVA.
Is there any reason why this would not work? Also, because my transformers are not the center tap variety, is there any reason why I would need to run the neutral through the transformers as opposed to straight through?
Thx.
it has been many years since i worked in distribution, and with that i do not know anything about the dry pack transformers you are dealing with... did they come from an oilfield service or something.?
i doubt you can use the three phase transformers on single phase system.
are you just trying to get lighting out at the pole barn? or will you be using welders and such...?
if its only lights i would just run some underground out there and call it good.
Ely, a "dry pack" transformer is what is typically used inside a commercial building to step 480V three phase down to 240V 3 phase, and if it has a center tap you can also use it to step 480VAC down to 120/240 single phase.
If you look inside the transfomer, there are three individual transformer coils - one for each phase of the service. I'm wondering if two of these could be used to for the single phase legs.
i can definately tell you that i have no experience in that sort of thing... seems like a plant maintenence man would be a person to help.
3 phase will be 3runs of 3/0 pluse a run of ground @ about $5 a foot so about $5000 It would seem cost efective to see what the local electric supplyer would cost and have 240v and200amp service.a jury rig could work but I would have stepup xtmr at the barn,it will increase the voltage but the amps will not be close to what you seek.
Well if you want to figure it out here's the formula http://www.informationdestination.cengage.com/ReferenceContent/Electrical_Wiring/Voltage%20Drop%20Formulas.pdf
It's been ages since I actually had to figure voltage drop but it seems to me you can run for example about a thousand feet of number 10 copper and still be within the safe zone on a 30 amp circuit .
You might be able to Google the answer with the right search parameters .
You always have options .Say on a three phase transformer it might be possible to seperate the winding and parrallel the individual transformers to utilize the full capacity of the can . If you jacked it to 480 though you'd need another transformer on the load end to reduce it back to 240 .
It might be possible to find a 240 to 12,24 or 36 voltage control tansformer and use it as a booster .
On an auto transformer booster the transformer only carries the amount of the boost not the full load .Google will tell you much better than I can about that .
so your total load is going to be 125 amps? I hook up alot of dry xfomers, but the ones in factories. Im assuming your taking about the ones utility mount up on their poles. You could possibly bump up to 480. but you could only use 2 xfomers and you would then have 480 single phase. I would need to see a wiring diagram of the xformer to see how to tap it. Then as stated before you would then need a nother set of xformers to drop back down to your original voltage. I gotta watch the kid right now, but when i get some free time I can tell you what size wire you need to run. Are you going to be trenchin this in? or poles? Free air you can get a higher ampacity as well.
I did some figuring and at 125 amps using 3/0 aluminum you'd have about a 15 volt drop which would still give you 225 volts the source .
Voltage drop also depends on how much current you will be using.
You can use this http://www.southwire.com/support/voltage-drop-calculator.htm (http://www.southwire.com/support/voltage-drop-calculator.htm)
I think it's doable. But, can you post the model of the transformer?
If I figured right you will have the same voltage drop no matter what the voltage. The 480v transformer doesn't buy you anything that I can see.
What about putting a 208v buck boost at the pole barn? Depending on your actual input voltage that might put ya about right.
Except for the fact if you double the voltage you half the amperage and thus half the voltage drop .
I can't get it to come out the same for some reason .Evidently I lack the ability to punch buttons on a calculater or something .
On 240 no boost it's actually 31 volt drop ,far too much .On 480 it's 15.9 volts fairly close to a 3 percent drop figuring 480 volts .
But now if you fired it over the pasture field at 240 line and did use a 208 to 240 auto transformer on the load end you'd get around 245 or so which would do it under load .Only problem with that is if you only had a small lighting load of maybe only 20 amps those light bulbs would be pretty bright a least for a short while until they burned out .
Guys, as always thanks for the advice.
Whitman, I'm not planning to run a 3 phase service to the barn; what I'm wondering is if I can use some 3 phase dry-pack transofmers to step the single phase voltage up and down for the long wire run. As I recall, there are three individual coils inside a three phase transformer, so I'm thinking that this is doable.
Sparky, I'm thinking about using the in-building types of transformers that are used in factories (I already have a couple of spare ones); one on each end.
All, if I recall correctly, these transformers have multi-taps inside them to pull voltage off at 440, 460, or 480 volts. What I'm wondering is if I transform up from 240 single phase to 480 on the supply end, and transform down from 460 to 240 on the receiving end, if this will compensate for the voltage drop in the long secondary run that Al calculated.
If you have enough transformers you can get a lot of options .If my calculations were correct at 480 and 125 amps you only have about 3.6-3,9 percent drop over the thousand foot run of 3/0 aluminum .Play around with the tap connecters and you'll probabley get the load end voltage to something you can live with .Something maybe with in 230-250 volts . My shop has 248 coming in .
FWIW when I built my shop about 20 years ago I had 600 feet of number 6 tri plex just laying on the ground to supply 240 for my welder and power for the tools .If there was a voltage drop I certainly didn't notice it .
whats the KVA of the xformers? are the large enough to handle that amperage?
Re the KVA, one is 72 at 480 as I recall; the other one is smaller. They are sized large enough for 125A of 240 though.
Quote from: Al_Smith on September 28, 2012, 05:48:54 AM
If you have enough transformers you can get a lot of options .If my calculations were correct at 480 and 125 amps you only have about 3.6-3,9 percent drop over the thousand foot run of 3/0 aluminum .Play around with the tap connecters and you'll probabley get the load end voltage to something you can live with .Something maybe with in 230-250 volts . My shop has 248 coming in .
Al, thanks for the info; I'll give this a shot.
Scott
:D I once told a gent that if I had enough transformers I could build a bolt of lightning .I think he kind of questioned that until he saw my shop . ;)
Quote from: Al_Smith on September 28, 2012, 09:26:44 AM
:D I once told a gent that if I had enough transformers I could build a bolt of lightning .I think he kind of questioned that until he saw my shop . ;)
:D Wish that you were closer; I'd definitely be up for a shop tour!
Yeah it's kind of wild .240 volts 200 amps single coming in then it gets a little interesting .
480 3 phase from a home made rotary converter .Fed also through I think a 6 KA 480 to 240 for 240 delta .Odd ball europian 208/365 wye .240 to 276 via a 240 to 36 volt transformer hooked up auto for boost .Some place I've got a couple step downs from 480 to 200 Japanese but I've never used them .
So in a nut shell if you have enough transformers you can get just about any thing .
Yes Scott, it should work. You will actually get one fourth the voltage drop by halving the current because the voltage drop is proportional to the square of the current.
The only problem will be a higher voltage at low loads if you use different taps on the transformers. You may not even need to boost the voltage if the incoming voltage is relatively stable in your area.
Thanks Gary, Al and everybody else who responded. Now I just need to bury 1000' of wire and test this out...
I might suggest you just roll it out on top of the ground first to see if it works which most likely it will.