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Surface Temperature. Remote sensing

Does it work? And how?

I've read recently of Germany electrical Engineers pushing the spec for nominal peak operating temperature of high-tension overhead power lines to 210⁰C; so that they don't have to string so much extra for the "renewable" peaks. Up to now, nominal operating temperature is 80⁰C with a peak of 120⁰C when exposed "favourably" to the sun. Other than the lines sagging substantially further, it'd also increase the radiated heat substantially.

There are 22,000 km of high-tension electricity grid lines over Germany; presently humming along at about 80⁰C.

What do the satellites see? Do entire "pixels" become dazzled from the bright lines?

Re: Surface Temperature. Remote sensing

Er, and where does this heating come from?

OK, ambient air temp, direct solar radiation and. and.... Oh yes, electrical heating.

Does this mean that by upping the limit they can push more juice through and does this involve more energy loss?

I seem to recall that heat transfer rates are a function of the temperature difference. If so then operating at higher temperatures will also mean greater heat loss...... does this mean more energy losses and if so how significant?

Re: Surface Temperature. Remote sensing

The heating comes from having a resistance greater than zero and having an electrical current pass through it (I²R). By pushing more current through the same cross-section, the ohmic heating increases.

If the conductor maintains the same conductivity at higher temperature, then it's no less efficient than using several conductors to keep the temperature low. However, metals tend to exhibit decreased conductivity; i.e. increased resistance with higher temperature. So the specific losses increase. It doesn't usually matter in small quantities but when you're talking about thousands of gigawatt-hours being transmitted every day, and 10's of them not being available at the billable-consumer end, then minimization of those losses becomes important to be competitive.

The additional insolation (incident sunlight) heating pushes from 80⁰C up to a maximum allowed of 120⁰C. Hang some metal in the summer sun, away from a convective breeze and see how much it heats up all by itself.

Re: Surface Temperature. Remote sensing

Doing a quick bit of Googling it does look like these high temperature power lines do exist to a limited extent in Germany. This news story (date not given, but must be 2012 at the earliest) from RWE's website talks about the first ever high temperature power line, of about 12km length, to be installed in Germany:

link

The operating temperature is given as 175ºC rather than 210ºC.

With normal temperature power lines birds have no trouble, as far as I'm aware,in perching on them and may even be attracted by the warmth. It would be interesting to see the reaction of the German green movement if birds tend to get injured in trying to perch on these power lines that are operating at oven-like temperatures.