Aluminum vs Copper? [RE-wrenches]

[Ron Young]

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Thanks Hugh, Jeff, Chris and others for leading me down this path. If I 
am understanding this correctly Hugh, and don't get too worried about 
greater than 5% line losses at max output, and use aluminum with proper 
precautions, then I can, say, use a 2/0 aluminum cable with a line loss 
of about 8% (based on the derated 40 amps instead of 52) or a #2 
copper, and not be too concerned? And if economics demanded I could 
even go to a higher line loss bearing in mind that: "As loss increases, 
the situation becomes much more complex, since more than 2 wires will 
start to conduct at once during the changeover." as you state in your 
answer to Paul Gipe on http://www.scoraigwind.com/CABLE/index.htm? 
Honestly I don't pretend to know what that really means but if I can 
get away with 8-10% without seriously compromising charging potential 
then the wire cost savings will very pleasant.

2500 watt turbine - 48v - 300' wire run - 3 phase

Ron Young

On 3-Sep-06, at 2:59 PM, Hugh Piggott wrote:

>
>> Hi Ron,
>>
>> Basic 3-phase formula:  P/V/1.73=I
>>
>> Or Power divided by Voltage divided my 1.73 = Amperage per leg (1.73 
>> is the square root of 3).
>
> This formula is true when we are talking about a star connected supply 
> with 48 volts on each phase relative to neutral.  If we are talking 
> about rms current in a wire feeding a rectifier with 48 volt DC output 
> then the answer is very different.  Rather than 1/1.73 (=0.58) it is 
> closer to 0.8.  The volt drop is therefore larger than a lot of people 
> would assume.  rms current in each of the 3 wires is about 0.8 (sq 
> root of 2/3) times the DC current after the rectifier. 2500/48 is 52 
> amps so I would reckon about 40 amps rms per wire.  And you lose power 
> in all three wires.
>
> There is some vagueness about the exact current factor because it does 
> depend on source impedance and waveform, but the variation in the 
> answer is not big.  Anyone interested in the nitty gritty, check out 
> http://www.scoraigwind.com/CABLE/index.htm
>
> Since most energy is delivered at less than 2500 watts it is not 
> necessary to get in a big panic about losses over 5%.  In high wind, 
> the wind turbine alternator will very likely deliver much the same 
> current anyway and become more efficient in the process so the loss is 
> less than you would assume.  (I guess the same reasoning applies to PV 
> in a lot of cases.)
>
> Isn't copper getting expensive?
> -- 
> Hugh
>
> Scoraig Wind Electric
> http://www.scoraigwind.co.uk/
>
>
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