Wire sizing for Western North Carolina hydro project

[mojisimo]

Hello I live in Western NC and am working on a microhydro project. I am going to run 2200 ft of wire and would like to have a 3% or less loss. The hydro machine is producing 1200 watts(HV 1200 (3 phase) from Harris Hydro and HydroInductionPower.com) and will transmit at 480 volts. I am trying to figure out the appropriate wire size for this venture. I would like to keep loss to around 3% and would like to know the math process behind it. Here is one of the ways I have had it presented to me . . .

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From Table 8 of NEC resistance of #10 (7/19) wire is 4.070 ohms /1000' (times) 4400 ft (2200 doubled) = 17.908 amps times 2.5 amps (1200 watts) = 44.7 volts drop

Divided by 1.732 (correction factor for 3 phase) = 25! .84 Volts which is 5.3833%.

It requires that you double the distance and concludes that # 10 will give 5.8 %

loss of power due resistance in the wire.

This only takes in to account the DC resistance; this does no factor in impeadence which is dependent on the frequency. As this is wild AC this will vary somewhat but this is still a factor that has to be considered sue to the length of the run.

Like wise a # 8 wire has a resistance of 2.551 ohms/1000' and this comes to 3.7 % loss.

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I have had it presented another way which concludes with a #4 wire. Can anyone give me some verification of this method and/or suggestions related to it? Also any opinions about what level of loss to accept?

Thanks so much,

Mike d

[hydrosun]

I always thought 10 guage wire had 1 ohm per 1000 feet. So for 4400 feet you get. 4.4 ohms times 2.5 amps gives 11 volts drop. Someplace along the line you multiplied twice. I not familiar with the three phase factor but I'll take your word and divide by 1.73 and get a drop of 6.5 volts for a loss of less than 1 1/2 percent. You could probably even go with a 12 guage wire with less than 3 % loss. With hydro it's not as critical  to keep the line losses under 2% like solar. With solar you have a limited voltage  window, especially on hot days. With hydro you usually  have a surplus of power and can afford to lose alittle more.

Chris

[wooferhound]

This may help you out a lot . . .

Voltage drop calculator:

http://www.electrician.com/vd_calculator.html

[willib]

thanks woofer.

it looks like #3 gage will give you about a 4 percent loss given

480V three phase  @ 18 A , and 2200 ft. run of wire..

sounds like an interesting project !

got any more details?

[RP]

As long as neither of these is a typo, 480V at 1200 watts is less than 3 amps and that's for single phase.  You could probably run this through monster speaker cable with minimal loss.

[drdongle]

Where in West NC, Pyrocast is near Hendersonville and I am near Newport Tn.

[willib]

Hmmm i took his 18A figure as his load .

[mojisimo]

I am putting a micro hydro system in at Turtle Island and am learning about wire sizing.

It is less than 3 amps but the 1200w machine @ 480 volts produces 3-phase power. It is the hi induction power high voltage version of the Harris Hydro machine.

On the calculator suggested by woof it requests "load in amperes", I assume that is the amps from the machine ~2.5 (1200w and 480 volts). Doesn't really sound like a "load" to me, but I am in the learning process . . .

I really am trying to find some info on the math behind the calculation. I am teaching a class about microhydro and would like to have a well-advised process for determining this value. I understand to use the ohms per 1000' feet value to determine # of ohm's based on distance (mine is 2200 ft). But I was advised by an electrician to double that distance. Then multiply the ohms lost by the amps (~2.5) to get voltage drop. At this point I have been advised to divide by a correction factor for 3 phase of 1.732 for the final voltage drop. Then calculate the % of total voltage.

If someone (an electrician hopefully) could verify the doubling of the distance and also the correction factor and maybe a short description of why to do each of these things I would be greatfull.

Thanks,

Mike d

[drdongle]

Where is Turtle Island?

[ghurd]

Double the distance because the wire and the amps go out and back.  Many wire charts have the 'round trip' distance figured in.

G-

[mojisimo]

Boone, NC

Turle Island is a very neat place, you can learn about it at tutleislandperserve.com.

[mojisimo]

This is true for 3 phase? Round trip and back, what about the division factor for 3 phase power?

[drdongle]

Boone isnt so far, I go to Grandfather mtn every year and it's only a few miles farther out.

[scottsAI]

NO.

Use the link to the calculator. They know what there doing.

Play with it, try single phase then 3 phase. The line losses changes a lot.

For a given cross sectional area, you can send more power with 3 phase than single.

The difference is not huge, but significant. That is why the utility's use 3 phase.

Have fun,

Scott.