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I'm wondering just how cold it would have to be before electric power can no longer flow through overhead power lines. I know power lines generate a certain amount of heat just as a side effect from electric current, but I don't know if sucking off this heat will make them fail, or if very cold air will make them fail for some other reason. I'm looking for the reason and the approximate air temperature where failure will occur.

There are also transformers and metal pylons to worry about. Presumably wooden telephone poles would be fine, but the big metal pylons in long-distance lines might suffer too much thermal contraction.

I'm interested in overhead power lines only, which are exposed directly to air. Transformers and the metal pylons count too. I'm not interested in underground lines. I'm not interested in power plants themselves, which of course have their own vulnerabilities. Just the transmission infrastructure.

Also, I'm not interested in stormy weather either. I don't care about snow or ice accumulating on the cables, or rain short-circuiting something or wind blowing something down. All I care about is the cold ambient air affecting power transmission.

So how cold does it have to be before overhead power lines fail?

EDIT: For all I know there is no lower limit. Very low temperatures might actually be a benefit if they safeguard against overheating.

DrZ214
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Here are some pylons in Norilsk, Northern Siberia, where temperatures get down towards -50°C

enter image description here (source)

It's all a question of design and engineering: pylon spacing, the range of max and min ambient temperatures, and the range of currents carried on the cables - there will be whole design manuals that cover this, so a full answer would be way too long for this format. The short answer to your question is "it depends". Overhead electricity lines do exist in some of the coldest permanently-inhabited places on Earth.

So low ambient temperatures do not in and of themselves cause power lines to fail.

Poor engineering, inadequate maintenance, or conditions that are well outside the design range will cause them to fail.

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