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Technology to the rescue

A few days ago I wrote about the fact that most Kiwis will have to pay an additional $600 a year for their power -- simply to cover the cost of investment in the national grid.

Presumably, this investment will be required to keep pace with the growing demand for electricity. It appears that our aging network of high-voltage distribution lines is no longer up to the task and must be enhanced.

Convenional thinking would mandate that more capacity would be added by stringing up more lines with the rationale that more lines equals more power carrying capacity.

However, that might not be necessary, thanks to newer technology.

The long spans of high-voltage cable you see strung between the power pylons that make up the national electricity grid are not as simple as they might appear from the outside.

One would assume that they'd just be lengths of stranded copper wire... right?

Well apparently not.

The problem with copper is that it's heavy and relatively weak. It's also prone to corrosion from the elements so even if you covered it in a protective layer, even the smallest breach of that protection could result in corrosion leading to both physical and electrical failure.

Instead, these "high tension" cables are a composite of aluminium, which is light and highly conductive -- and steel, which is strong.

Conductivity is essential to reduce the losses due to resistive heating of the cables and strength is also important because it allows pylons to be spaced further apart, thus reducing costs.

This setup is not perfect however.

Steel is still heavy, a limiting factor in the length of span that can be used.

Then there are the thermal issues.

Even though they're pretty thick, these cables still heat up under extreme load and unfortunately, aluminium has twice the thermal coefficient of expansion (COTE) of steel. This means that the aluminium part grows in length twice as quickly as the steel part and one would assume that the sheer stresses this creates will be a factor in determining what is a safe level of current that can be carried.

However, if we double the number of these hi-tension cables, we double the power capacity of the grid. Simple eh?

Unfortunately (again), it's not quite so simple.

The power pylons are built to carry a specific weight. Simply increasing the number of cables may not be practical in situations where they pylons are already carrying as much weight as their design limitations provides for.

Enter new technology!

I came across a very interesting article that covers the way the very same problem is being addressed in the USA.

Their "simple fix" involves replacing the steel/aluminium conductors with a composite of carbon fibre and specially shaped aluminium pieces.

Apparently this approach ticks all the boxes. It's cheap and effective, allowing more current to be carried and existing pylons to be used due to the lower weight and long spans that can be achieved.

Let's hope that our national grid engineers are going to opt for an approach like this and if so, that $600 a year may fall to a lower figure.

Only time will tell.

Carpe Diem folks!

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