8000' 460 volt run.

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copper123

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Hi,
My company i work for has been asked to look at doing some work for a job and I can't seem to make the numbers work at all.

They want to put power to a remote area facility. The distance is 8000 feet from the electrical distribution. At the electrical distribution they have some power quality issues. Not sure what that is. Anyhow, they want to take the existing 460 volt power at the distribution area and put it into a buck/boost transformer. They don't however want to change the voltage. 460 primary, 460 secondary. I have heard that you can use a buck/boost to stabilize the voltage, but this is a little odd for me. On the other end of the 8000 foot run, they want to install a 460 primary, 208/120 secondary transformer. I know I am not the sharpest tool in the shed, but these numbers just dont add up.
8000' run
3 phase power
200 amps
3 runs of 350 MCM
1 run of #2 for nuetral
I guess the the?fella that designed this is a Engineer, but it doesnt work in my calcs.
At 100 amps at 8000' 460, I still get a voltage drop of 10.6%
At 200 amps its like 14.9%
Am I missing something?
Also why would you have the 4 wire and not just a 3 wire in between. Why the neutral, and why would it still be so small?
I have found that the best way to learn about these things is to dig into the calcs and try to figure out why they do what they do. It's just in this case, I can't figure it out!
Thanks
 
Re: 8000' 460 volt run.

The buck boost transformer isn't going to do anything except use energy unless it is boosting the voltage. The reality is that it can't boost the voltage enough to make a difference.

It is time to install two transformers, one to jack up the voltage to about 4.16 kV and the other one to step it back down. Now you can use small wire and just adjust the taps on the transformers to get the voltage you need (you will normally get 2 - ? 2?% on each end).
I guess the the fella that designed this is a Engineer
Click to expand...
I wouldn't put any money on that. :D
 
Re: 8000' 460 volt run.

I agree with Charlie. Load of 200 amps at 4.16 kv using #2 AL 15 kv cable the voltage drop is negligible. You would spend a fortune to try to do it with 480 volt system. Some one does not know what they are asking (or doing) :confused:
 
Re: 8000' 460 volt run.

I also agree with Charlie, except I think I'll go a little further, I'd suggest that whoever's in charge of coming up with this idea isn't qualified to be doing it.

_____________________________________________________________________________________

And Bob, How'd you get in while I was typing? I see you down there in the posting page. :D

Edit: I see, another incident where your post was already there but the site was holding off on telling my machine about it. :D

[ July 11, 2005, 08:22 PM: Message edited by: physis ]
 
Re: 8000' 460 volt run.

If it was me, I would try to get the power company to put up another transformer near your new building and put another meter there. Your metering cost would be a lot less compared to all your cost going the other way. 8000' is a long way.
Jim
 
Re: 8000' 460 volt run.

Jim, I assumed that someone who is planning on going 1? miles down the road that they would be behind a primary meter. There are not too many subdivisions with lots that size. :D
 
Re: 8000' 460 volt run.

Thanks guys,
That is kind of what I expected also. It's good to see that my voltage drop calcs are close to what you guys have figured out as well. Ok, so here is another question. How do you figure out the size of wire that you would be need to pull in for your load? This is way over my head, I would imagine that 310.16 does not apply! volts x amps = watts so where do you go from here? Do they even have a table in the NEC for higher voltage installations. Everything I have seen is just installations over 600 volts. This is what I have thought about and you guys can laugh at me if you want. At the other end you are looking at 200 amps at 208 volts, 3 phase. 200 x 208 x 1.73 = 74,880 VA. So if our watts are 74,880 and our volts are 4160, our amp draw would be 18 amps. Heck, we could run this with a #12 wire! So where did I go wrong. You guys are saying #2 AL high voltage cable, is that in the NEC?
Thanks, I really love learning about this stuff!
 
Re: 8000' 460 volt run.

Ohm's law works for high voltage as well as it does for low voltage.

It's kind of funny but #6awg will work for 8k feet at 12 amps @4160 with a 3.7% voltage drop,
Unless I got my numbers crossed. but much cheaper than 2awg.

And you can not use a buck/boost to boost a load that is not constant, if you do you will be over voltage at loads still on as other loads are shut off!

I'm a little rusty at voltage drop as I'm spoiled with my voltage drop calculator in my truck. :D
 
Re: 8000' 460 volt run.

You might get a package deal from Square D for two 75kva 480/4160 transformers for under $5k at 480 your wire alone will cost over $100k to get a 3% VD Kind of dumb huh!

Of course that price depends upon how good you supply house deals with Square D, I use All Phase Electric Supply.

[ July 12, 2005, 12:15 AM: Message edited by: hurk27 ]
 
Re: 8000' 460 volt run.

Assuming this is an underground installation, #2 is just easier to handle. By the way, follow the instructions exactly or you will have cable failures. Also, use splice kits and elbow terminators. You will also want to ground the cable four times per mile and use #2 AL jacketed concentric neutral cable. The neutral will only be used for grounding but it is important for dig ins. I also recommend that it be EPR cable instead of the cheaper cross linked poly. :D
 
Re: 8000' 460 volt run.

copper123,
As Charlie gave good advise, I would add that if this is way over your head, why not bring someone on board who is familiar with this type of work?

Especially when it comes to the terminations. They do have instructions, but if you've never seen them installed, the instructions might not make sense.
They are also costly, and doing one wrong could fail and be a costly fix.
 
Re: 8000' 460 volt run.

Hi Warm water, Thanks for the advice, but no need to worry, i would never try to do any high voltage terminations like this. I am just trying to understand the calcs of how it should be done.
 
Re: 8000' 460 volt run.

Charlie,
(Jim, I assumed that someone who is planning on going 1? miles down the road that they would be behind a primary meter. There are not too many subdivisions with lots that size.)I was just thinking if you could get the power company to let you put in a 3 phase 277/480v 4-wire self-contained meter socket it could save him money and time. Anyway way Charlie thanks for the infor.
Jim
 
Re: 8000' 460 volt run.

Sorry Jim, I didn't intend to say that you were wrong. My intent was to say that I wasn't on the same page that you were on.

Actually, you are 100% correct unless they are behind a primary meter. :D
 
Re: 8000' 460 volt run.

So if our watts are 74,880 and our volts are 4160, our amp draw would be 18 amps. Heck, we could run this with a #12 wire! So where did I go wrong. You guys are saying #2 AL high voltage cable, is that in the NEC?
Click to expand...
Your caculations are ok. However the mfg has a minimum size for HV cable. Rome Cable has a minimum size of #2 AL good for 163 in the ground and 119 in duct. This is the typical URD cable with a PVC jacket. EPR Is the better cable but the new URD cable will last a long time.
By the way why does Charlie get all of the hi fives? :confused:
 
Re: 8000' 460 volt run.

I just got this funny image of a guy walking back through a crowd of his team mates after a touch down with all the slappin' fives and bootie pats,......... and it's Charlie. :D :D :D
 
Re: 8000' 460 volt run.

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