Pacific DC Intertie

Secondary information, mostly from wikipedia.

The purpose of the intertie is to use the on/off flow of power from the Columbia river hydro system to help load-level Southern California. California runs baseload coal plants, and the intertie ships power north to the Pacific Northwest and British Columbia off-peak and south to SoCal on-peak. The hydro system was optimized by BPA in the 1960s to match annual water production in the Rockies, mostly stored in Lake Kinbasket, sending it south during the summer in daily boluses (timed to hit the regularly spaced dams), as opposed to a smoother and more spread-out flow.

The Columbia and Peace River hydrosystems, managed by the Bonneville Power Administration, are running river systems downstream from their top-end reservoirs. They cannot be used as pumped storage, there is not enough room for larger impoundments, and protecting salmon from superoxygenated water from big spills is BPA's principal mission. California's damaged ecosystems and massive appetite for water and electricity are no justification for destroying northwest riverine and offshore ecosystems.


1362 km

Conductor Cross Section

1171 mm2

?? are these "circular mm2" ??


3100 MW

Voltage (bipolar)

±500 KV

assumed at transmit end

Aluminum density


Resistivity of Aluminum


at 20C, varies with temperature

temperature coefficient


W.A.G. estimates

Resistivity at 50C


2.65E-8 * (1 + 3.8E-3*(50-20))     temperature is wild guess

Current (bipolar)


3100 MW / 1MV

Resistance per kilometer


3.15E-8 * 1000 / 0.001171

Voltage drop per km


0.027 * 3100

Power dissipation

260 kW/km

84 * 3100

Total voltage drop/leg

114 KV

84 * 1362



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 diameter 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 peaking power long distances; it is this or nothing! Perhaps there is an unmet business need. Or perhaps moving power very long distances ( > 2000 km ) 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!

PacificDCIntertie (last edited 2014-09-03 13:40:39 by KeithLofstrom)