Reply To: T-shirt designers unite and take over

[Brian H]

JimmyT wrote: I believe that long distance transmission lines are made of aluminum, not copper. They also often contain several strands of steel wire to strengthen then. While copper is a better conductor, it’s weight/conductivity ratio is higher than that of copper. Copper is used in the step-up and step-down transformers at either end. But the bulk of materials used is aluminum.

Not meaning to second guess ya’ Brian. Just trying to maintain accuracy in order to maintain credibility.

Surprising — world-wide, lines are being stolen for the copper. Must be a hell of a shock …
Actually, it depends when and where:
http://encyclopedia.jrank.org/POL_PRE/POWER_TRANSMISSION.html :

“On account of the cost and the difficulty of repair of such lines they are not extensively used, and cables have not yet been produced for the extremely high voltages desirable in some very long circuits, although they are readily obtainable for voltages up to 30,000 or 40,000. As to the material of the conductors, copper is almost universally used.

For very long spans, however,bronze wire of high tensile strength is occasionally employed as a substitute for copper wire, and more rarely steel wire; aluminium, too, is beginning to come into use for general line work . Bronze of high tensile strength (say 8o,0oo to 100,000 lb per square inch) has unfortunately less than half the conductivity of copper; and unless spans of many hundred feet are to be attempted it is better to use hard-drawn copper, which gives a tensile strength of from 60,000 to 65,000 lb to the quare inch, with a reduction in conductivity of only 3 to 4% . As to aluminium, this metal has a tensile strength slightly less than that of annealed copper, a conductivity about 6o% that of copper, and for equal conductivity is almost exactly one-half the weight . Mechanically, aluminium is somewhat inferior to copper, as its coefficient of expansion with temperature is 50% greater; and its elastic limit is very low, the metal tending to take a permanent set under comparatively light tension, and being seriously affected at less than half its ultimate tensile strength .

Joints in aluminium wire are difficult to make, since the present methods of soldering are little better than cementing the metal with the flux; in practice the joints are purely mechanical, being usually made by means of tight-fitting sleeves forced into contact with the wire . With suitable caution in stringing, aluminium lines can be successfully used, and are likely to serve as a useful defence against increase in the price of copper . Whatever the material, most important lines are now built of stranded cable, sometimes with a hemp core to give added flexibility . With respect to line construction the introduction of high voltages, say 40,000 and upwards, has made a radical change in the situation . The earlier transmission lines were for rather low voltages, seldom above 10,000 . Insulation was extremely easy, and the transmission of any considerable amount of power implied heavy or numerous conductors . The line construction therefore followed rather closely the precedents set in telegraph and telephone construction and in low tension electric light service . In American practice the lines were usually of simple wooden poles set 40 to 50 to the mile, and carrying wooden cross-arms furnished with wooden pins carrying insulators of glass or porcelain . “