Aluminum vs Copper? [RE-wrenches]

[Hugh Piggott]

<x-flowed>

>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/


- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------




</x-flowed>