Wire size and voltage drop for long run

[cardamon]

I have a 1kw, 240v three phase wind turbine that I will be mounting about 1350 feet from a transformer, rectifier and batteries.  I would classify the site as very good, 13-14 MPH average.  I have a bunch of 10-2 UF cable I would like to use for the wire run, and according to my calculations, that should be a reasonable size for the run, but I would like to know what others think and if I would gain much by going up a size.  I am also a bit confused as to why the conventional three phase voltage drop formula gives mush less of a loss as compared to hugh's method.  I assume this is because of how the rectifiers 'use' a given two phases when they are near their peak as opposed to continuously for a conventional load?

Thanks and regards

Ethan

[tecker]

Your good for 15 to 18 amps and would drop around 42 volts at 240 full load  .

[RUFUS]

Hey Dude

#10 wire is a 20% loss over that distance 191v.

#8 is 12% at 209v.

#6 is  8% at 220v.

#4 is  5% at 228v.

#2 is  3% at 232v.

You'll have to decide what you are hapy with

Try to stay under 10% loss imho, gona cost ya,

All values are approxamate

Have fun with it

                            Rufus

[cardamon]

Thanks Tecker,

Are you saying that with that wire size and system voltage I could push up to 15-18 amps?  Could you elaborate on how you got this answer?  That is a significant loss at max power, of course most of my power will come from less than max power but this begs the question: what is the rule of thumb for calculating acceptable drop?  Use current at average wind speed and keep that less than say 3%?

[DanG]

1000 watts at 240VAC three phase is about 4.1 amps current - wishful thinking but that is your 1kw so using 208VAC 3Ø on 3-wire per voltage drop calculator gives less than 5% loss at full output if you are running on copper 10awg.

http://www.powerstream.com/Wire_Size.htm

[spacejunk]

Thats using the "new math" right?

What about using ohms law....an oldie but a goody.

240V at 1000W would be 4.16A single phase , ~2.8A 3Phase I think.

I've uploaded an XLS file for calculation of voltage drop.

You might need to go to the link to download it.

[cardamon]

Thanks everyone for the replies.  I think there were numerous errors in some of the figures that were quoted.  I just double checked myself by spending an hour going over the formulas, using a VD calculator, and doing some examples.  Here is what I get:

wind turbine is 1kw, 240v three phase

wire is #10

distance is 1350 feet (one way not circuit length)

Three phase VD=1.732 x K x Q x I x D/CM

K=12.9 for copper (resistance constant)

Q= alternating current skin effect correction factor for large conductors.  NA here.

I= current

D= distance

CM = circular mills of conductor

Note that line current for three phase is found by Watts=V*A*1.732 (ignore power factor) thus solving for our values gives I= 2.4A

So VD= 1.732 x 12.9 x2.4*(1350/10380)

thus VD=~7 volts or about 3% AT MAX POWER

But note the VD is not what I am looking for, I know how to get VD, I just thought I would go over that because there were some conflicting answers.  I have two questions:

1.  How does one estimate the average voltage drop given that the turbine will of course not be operating at max power all the time?  would calulating the VD at average wind speed correspond to average vd drop (and thus average loss) or doesnt it work out that way?
   
2. Why does Hugh get twice the drop with his "2/3rds method" (http://www.scoraigwind.com/CABLE/index.htm) than I do using the above formula?  Of course that is a good question for hugh directly, I'll email him if he doesnt jump in and nobody else knows.
   
   

Best regards to everyone and have a good weekend.