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From: grege@gold.gvg.tek.com (Greg Ebert)
Newsgroups: sci.electronics,sci.energy
Subject: Aluminum saves energy (was Re: Gold saves energy)
Message-ID: <2464@gold.gvg.tek.com>
Date: 5 Jun 91 20:44:38 GMT
References: <sehari.676081817@du248-12.cc.iastate.edu> <1991Jun5.163512.1314@zoo.toronto.edu>
Followup-To: sci.electronics
Organization: Grass Valley Group, Grass Valley, CA
Lines: 35


Lets get one point settled. Gold plating 60Hz conductors is silly and
wasteful. At 60 Hz, the skin-depth [depth at which amplitude falls to 1/e
of original value, or ~ 0.37] is of the order of 1 cm for all metals.
Even at higher frequencies (Ghz), skin-depths are roughly equal. So
skin depth is not an important issue when selecting conductors.

Gold has a *LOWER* conductivity (4.5e7 mho/m) than copper (5.8e7 mho/meter).
Aluminum is slightly less conductive (3.5e7 mho/meter).

Gold may exhibit high resistance to corrosion, but so does aluminum
oxide. [Aluminum develops a thin Al2O3 coating in the presense of O2].

Electrical transmission lines are sized based upon how much RMS current
they must carry. For a given conductivity, the relative cross-sectional
areas relative to gold are:

	Copper=0.78, Aluminum=1.29

Now consider weight. Because above-ground wires must be supported, and the
cost of the supporting structure is determined by the weight of the
conductor, you want to minimize weight for a given conductivity.
For a given conductivity, the weight/unit_length relative to gold is:

	Copper=0.36, Aluminum=0.18

Note: Al=2.7 gm/cc, Cu=8.9 gm/cc, Au=19.3 gm/cc

[tensile strength is another issue, too]

Gee wiz! Aluminum has the lowest weight/unit_conductance. Could that
possibly be why every utility company uses aluminum wire ? [sarcasm]

I havn't looked at the commodity market tables lately, but I still
think copper is more expensive per-pound than Aluminum.