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A comment on Rolling blackouts in California have power experts stumped. Parent comment

Re:Rolling blackouts in California have power experts stumped by etimberg on Monday August 17, 2020 @01:25PM (#24189410)
The resistance is not constant and is in fact a function of temperature [0]. Line sag is a proxy measurement for line temperature, since things expand as they heat up. From [1], most materials have positive alpha coefficients so the resistance increases with temperature.

0. https://en.wikipedia.org/wiki/Electrical_resistivity_and_con...

1. https://www.allaboutcircuits.com/textbook/direct-current/chp...

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Re:Rolling blackouts in California have power experts stumped by ISL on Monday August 17, 2020 @02:16PM (#24190074)
The statement referred to heating driving sagging, which increased resistance.

The increase of resistance with temperature is well-known -- I was curious if there is some effect that is directly related to the wire sag (changing morphology, somehow-altered surface area/skin-depth, changing kinks at the connections, some subtlety with increased length (cross-sectional area also increases), etc..).

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Re:Rolling blackouts in California have power experts stumped by hanniabu on Monday August 17, 2020 @04:27PM (#24191642)
Theoretically I would thing the sag itself should increase resistance since resistance increases with both length and smaller wire diameter. When the line lengthens the diameter should decrease (similar to stretching a piece of gum or putty).
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Re:Rolling blackouts in California have power experts stumped by function_seven on Monday August 17, 2020 @06:16PM (#24192884)
It's not being stretched by an external force, though. It's expanding due to heat. The diameter would also expand some negligible amount I think.
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Re:Rolling blackouts in California have power experts stumped by leni536 on Monday August 17, 2020 @04:53PM (#24191933)
I don't think it should. Heat expansion should slightly increase the diameter.
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Re:Rolling blackouts in California have power experts stumped by mensetmanusman on Monday August 17, 2020 @07:19PM (#24193451)
Not if the length increases to counteract it.
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Re:Rolling blackouts in California have power experts stumped by sharpneli on Tuesday August 18, 2020 @02:04AM (#24195739)
It doesn’t ”counteract” it. All dimensions increase based on the same coefficient. Same percentage increase on all axis.

See https://en.m.wikipedia.org/wiki/Thermal_expansion and check the coefficient of expansion.

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Re:Rolling blackouts in California have power experts stumped by Scoundreller on Monday August 17, 2020 @03:36PM (#24190999)
My thought is that after each expansion/contraction cycle, contraction is never exactly back to its previous state.

Like bending a piece of metal back and forth, it weakens each time.

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