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.