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Size: 4361
Comment:
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Size: 4384
Comment:
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| Deletions are marked like this. | Additions are marked like this. |
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| Assuming a steel core with the same cross section of the outer aluminum, then the total cables cross section is 2340 mm^2^, for a diamter of 5.5cm and a surface area of 0.17m^2^/m . The cables would radiate/convect 1500W/m^2^ or 0.15W/cm^2^, which probably makes them hot but not terribly hot (which would cause them to sag a lot). | Assuming a steel core with the same cross section of the outer aluminum, then the total cables cross section is 2340 mm^2^, for a diamter of 5.5cm and a surface area of 0.17m^2^/m . The low thermal emissivity cables would radiate/convect 1500W/m^2^ or 0.15W/cm^2^, which probably makes them hot but not terribly hot (which would cause them to sag a lot). |
Pacific DC Intertie
Secondary information, mostly from wikipedia.
Length |
1362 km |
|
Conductor Cross Section |
1171 mm2 |
?? are these "circular mm2" ?? |
Power |
3100 MW |
|
Voltage (bipolar) |
±500 KV |
assumed at transmit end |
Aluminum density |
2700kg/m3 |
|
Resistivity of Aluminum |
2.65E-8Ωm |
at 20C, varies with temperature |
temperature coefficient |
3.8E-3/C |
|
W.A.G. estimates |
||
Resistivity at 50C |
3.15E-8Ωm |
2.65E-8 * (1 + 3.8E-3*(50-20)) temperature is wild guess |
Current (bipolar) |
3100A |
3100 MW / 1MV |
Resistance per kilometer |
0.027Ω |
3.15E-8 * 1000 / 0.001171 |
Voltage drop per km |
84V |
0.027 * 3100 |
Power dissipation |
260 kW/km |
84 * 3100 |
Total voltage drop/leg |
114 KV |
84 * 1362 |
Efficiency |
77% |
1 - 114 KV/500 KV, surprisingly high! |
Aluminum volume, cables |
3200 m3 |
2 legs * 1362 * 1000 * 0.001171 Not including towers, etc |
Aluminum mass, cables |
8600 tonnes |
2.7 * 3200 |
Assuming a steel core with the same cross section of the outer aluminum, then the total cables cross section is 2340 mm2, for a diamter of 5.5cm and a surface area of 0.17m2/m . The low thermal emissivity cables would radiate/convect 1500W/m2 or 0.15W/cm2, which probably makes them hot but not terribly hot (which would cause them to sag a lot).
These are estimates. I would love to see actual measurements or more accurate estimates, especially for the temperature.
It is surprising that they do not use much fatter wire, but Southwire doesn't offer anything larger, and existing designs for towers, construction equipment, etc will be scaled to off-the-shelf wire and spool handling equipment. My guess is the surprisingly low efficiency is evidence of the high value of moving power long distances; it is this or nothing! Perhaps there is an unmet business need. Or perhaps moving power very long distances in non-chemical form still isn't practical.
Why does this matter?
Moving energy from rectennas, or hypothetical solar arrays in New Mexico and Texas, will involve huge amounts of power transmission. Power Loop energy storage and transmission will be good in the long term (if we can dig the tunnels!) but for the next few decades the United States will be moving 1000GW peak demand power over wire. If we power with daylight solar, in the winter, and feed the power to some hypothetical energy storage system elsewhere (no pumped hydro in New Mexico!), then we will need to move perhaps 2500GW during peak times, almost 800 times the Pacific DC capacity, for 50% more distance to, say, Chicago. Estimate 1000x more aluminum in the wires, assuming higher voltage and efficiency improvements. Given that hypothetical pumped storage systems will be in huge mountain valleys, probably massively artificial ones in the Rockies far from the population centers on the East Coast, and will also add significant inefficiencies, this could be too low by a factor of 2. If we replace significant amounts of heat and transportation fuel with electricity, it could be too low by a factor of 5 or more.
The United States produced 1.76 million tons (2000 lbs) or 1.6 million metric tonnes of aluminum in 2010. We would need more than 5 years of current aluminum production to make 8.6 million tonnes of aluminum power transmission line. Assume this is rolled out over 10 years, for a production increase of 860 thousand tonnes per year, or an average of 10 extra tonnes per hour. Aluminum requires 15kWh/kg to produce (not including the coking electrodes) so that is 1.5GW of additional electric generation on average. We may be able to power the pot lines directly from solar cells without storage and limit production to daytime, for about 5GW peak load. Compared to the other big numbers, at least that is affordable!