Why do we use Aluminum to substitute Copper in transmission lines?

Aluminum is very close to the conductivity of copper, about 1.6 times as much resistance per foot for equivalent gauge. So in equivalent wire sizes, aluminum would lose 60% more power to I²R losses.

aluminium-copper-cable

But aluminum has two properties that make it worth using. Cost. Density.

In density it is about 1/3 the weight per same volume. So this gives a serious advantage mechanically since we can increase the cross section area by 2 (make it 1.414 times the diameter) and it will have 0.8 times the I²R loss of copper and still be 2/3 times the total weight making the towers cheaper to build because they don’t need to be as strong by a factor of .66 and they don’t need to be as closely spaced.

Second the cost of copper by weight is around 6 times as much for aluminum. That means even though we used 2/3 the weight above we are still at a 10% cost (.66 x 1/6) for the wire itself, not to mention the tower costs savings I explained above.

It should be noted that high tension power lines average cost is $285,000 per mile and that is probably for aluminum wires. If copper were used, the cost per mile would probably easily be double given the savings I outlined above plus the increased efficiency saves generation costs.

To recap presuming we use aluminum wire 1.4 times thicker than the wire we would use if it was copper:

  • we reduce 20% in resistance and hence I²R power losses from about 6% to 5%, saving 1% of all energy produced and transmitted for years to come.
  • we save 33% in construction costs - tower strength required is less as the wire is 66% of the copper weight
  • We save 90% of the cost of the wire itself due to material costs AL vs CU
In practice, it's not all so clear cut: aluminum wires for transmission lines usually have have a steel core for more strength. Skin effect comes into play, too. I am sure there are extensive tradeoff spreadsheets comparing the cost benefits for the various amounts of aluminum to use as to what makes the most sense and provides the quickest payback as construction costs are one-time but efficiency is continuous.

Why are overhead high voltage power lines not insulated?

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