grege@gold.gvg.tek.com (Greg Ebert) (06/06/91)
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.
luns@spocom.guild.org (Luns Tee) (06/10/91)
grege@gold.gvg.tek.com (Greg Ebert) writes: > [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] As far as tensile strength goes, I seem to recall that power lines are aluminum wrapped steel cables. The steel being there for tensile strength, the strength of the aluminum is unimportant.