The Quiet Line
You know the sound of alternating current--that sixty hertz hum that pervades the built world--it's the buzz made by old fluorescent bulbs and refrigerator compressors, and it's the crackle of corona discharge from high tension lines. Everything you plug into the wall runs on AC (unless there's a convertor in the plug, like those found on laptop and cellphone chargers). At most voltages, AC moves more efficiently through the line, and it's simple to kick the current up and down in voltage--power can leave the plant at quarter million volts, then be stepped down to the thousandth part where it comes into your neighborhood.
Direct Current is making a comeback, though--in addition to running every battery-powered device, from cellphones to Teslas, High Voltage DC can efficiently send great quantities of power over long distances at surprisingly high efficiencies. Despite the hassle of converting the power from and back to AC, HVDC can move more electricity through less wire (DC has only two poles--positive and negative--and requires only two lines. AC adds a neutral phase, necessitating a third cable. Also, for reasons I can't begin to comprehend, HVDC can literally put more current through any given piece of cable. A two-cable HVDC line can stand in for up to twelve AC cables and their attendant structures). The savings add up over long distances; the break-even point comes after about 500 miles.
Almost all of America's electricity is consumed within 500 miles of its production; HVDC lines are quite rare. Two of the largest can be found in Southern California, connecting coastal cities to copious sources of power far inland. In a typical Southern California duality, one is benign; the other, sinister.
The Oregon Bipole
The Oregon Bipole (aka, the Pacific Intertie & Path 65) should be celebrated as a visionary piece of infrastructure. It supplies Los Angeles with up to 3,100 MW of cheap, clean hydroelectric power from the Columbia River. Operating at full capacity, the Oregon Bipole can supply nearly half of LA's demand. The 800 mile line enables two giant dams on the lower Columbia to power Southern California.
 |
| The Oregon Bipole, north of Mojave, CA. The Bipole is on the left (note it only uses 2 cables) and a normal AC high tension line is on the right (3 cables) |
 |
| The Oregon Bipole entering Sylmar |
The Oregon Bipole runs from Celilo, Oregon (near the Columbia River) to the fabulous Sylmar Converter Station in northeast LA. In addition to housing the bipole's valve hall (where the DC is reconverted to AC), Sylmar is home to a giant conventional substation, and the massive water treatment facility next door is the downstream end of the Los Angeles Aqueduct. The city dump is literally across the road, making Sylmar the epicenter of LA's utilities. (It also smells faintly of garbage).
HVDC lines are typically built with a 'ground return', a loose end buried in the ground a few miles from the line's terminal. If a tree falls on one cable, the buried return enables the second line to run independently (although at reduced capacity), with the earth serving as the other 'pole' for the current. The Oregon Bipole allegedly has a ground return buried in the Pacific Ocean at Will Rogers State Beach, near Malibu. I was unable to see any sign of the ground return, although the beach is quite nice on its own merits.
 |
| High tension lines surround the Sylmar convertor station in the San Fernando Valley. |
The Intermountain Bipole
Southern California's other HVDC line is a sinister reflection of the Oregon Bipole. The Intermountain line connects LA to a distant and copious source inland power--but it isn't clean. This line (aka Path 27) draws its 2,400 MW's from a coalfired plant in central Utah. (not only is the coal mined in Utah, it's still legal to burn it in any quantity out there.)
Why do I call the Intermountain Bipole sinister? Worse than the fact that it sources the dirtiest power available, the Intermountain Bipole allows LA to ignore the cost of its air conditioners--Delta, Utah is 500 miles away, and the plant's pollution will never darken coastal skies. It also enables hypocrisy on a grand scale--local activists would never tolerate a coal burning plant in the city, but the public is less interested in what happens east of the state line. In fact, the state of California burns ten times more coal in Utah than it does within its own borders--and the Intermountain plant represents only a fraction of the imported coal power. Coal burned in New Mexico, Arizona and Nevada provides an additional 3,500 MW to the state. This allows California to pass strict emissions regulations without impacting utility rates--a convenient fraud.
 |
| Ruin and folly. |
The Oregon Bipole is a triumph of infrastructural engineering--bringing power to the people. The Intermountain Bipole is fundamentally a piece of political engineering--sweeping the dirt far afield, it allows people to pretend consumption doesn't have its price.
Things are looking up, though--LADWP is committed to replacing coal, and the Intermountain Bipole may one day collect its power from solar projects like Ivanpah.
The Intermountain Bipole's ground return is easily visible just east of Barstow. The line's 'shield wires' (used to protect against lightning strikes) are repurposed for ground return between the valve hall in Adelanto and the electrodes buried in Coyote Dry Lake. Every time this segment of line is struck by lightning, the surge travels to the Coyote Lake bed, where it dissipates into the earth. From space, the return looks like a medicine wheel a half-mile in diameter; up close, it looks like a dirt road and a shed.
 |
| The Intermountain's ground return splits off from the shield wires to run the last couple miles to the buried electrodes. Note how the shield wires are insulated from the tower on the charged side. |
If You Go:
Both HVDC lines are easy to visit--the Oregon Bipole runs north along the Eastern Sierra, paralleling US 395 from Antelope Valley to Bishop. The Intermountain Bipole runs parallel to I-15 from Adelanto to Barstow. The Intermountain ground return is located at Coyote Dry Lake, east of Barstow.They're just power lines--the only notable difference for a DC line is the lack of buzzing in its corona discharge. (but given the proximity of conventional high tension lines, the buzz prevails anyway).
The Sylmar substation is located alongside I-5, just south of the Antelope Valley interchange. Be circumspect--LADWP is sensitive about the entire complex, and you don't want to be a nosy fellow.
