What’s Up With That Weird Construction Project on Bernal Heights Boulevard?

There’ve been many questions and much speculation about the big construction project that’s gobbled up a whole lane of Bernal Heights Boulevard on the north side of Bernal Hill. It’s quite a scene:

The presence of several stainless steel vats on the job site has led some to surmise that, as part of this Golden Age for Beer in Bernal Heights, a new microbrewery is under construction there, with skyline views that will pair nicely with a full-bodied IPA. The frosty mist emanating from a pipe has caused others to wonder if the site will become a pop-up location for one of those trendy, liquid-nitrogen ice cream stands, like that popular place in Japantown.

Suffice to say, such rumors are false and unfounded. Instead, the project on Bernal Heights Boulevard is part of a PG&E effort to reposition a high-voltage electric transmission line that’s buried under the street.

Neighbor Sam wrote about this process a few years ago after spotting a similar operation underway in Los Angeles. Here’s his basic explanation:

It turns out they have a problem with an underground wire. Not just any wire but a 230 KV, many-hundred-amp, 10 mile long coax cable. […]

The cable consists of a copper center conductor living inside a 16 inch diameter pipe filled with a pressurized oil dielectric. Hundreds of thousands of gallons [of mineral oil] live in the entire length of pipe. Finding the fault was hard enough. But having found it they still have a serious problem. They can’t afford to drain the whole pipeline – the old oil (contaminated by temporary storage) would have to be disposed of and replaced with new (pure) stuff which they claim takes months to order (in that volume). The cost of oil replacement would be gigantic given that it is special stuff. [..,]

That’s where the LN-2 [liquid nitrogen] comes in. An elegant solution if you ask me. They dig holes on both sides (20-30 feet each way) of the fault, wrap the pipe with giant (asbestos-looking) blankets filled with all kind of tubes and wires, feed LN-2 through the tubes, and *freeze* the oil. Viola! Programmable plugs! The faulty section is drained, sliced, the bad stuff removed, replaced, welded back together, topped off, and the plugs are thawed.

That’s what’s happening on Bernal Hill right now. Only, the issue here isn’t a fault in the line. Instead, workers at the site tell Bernalwood that PG&E is re-positioning the underground electric line to bypass a sewer upgrade The City recently installed along Folsom Street.

So on Bernal Hill, a contractor is using liquid nitrogen to freeze a segment of the mineral oil that functions as an insulator for the high-voltage electric line. The frozen segment acts like a cork to seal off the mineral oil backed up in the rest of the very long electric line. There’s another liquid nitrogen site farther north on Folsom that corked the other end of the line, and in-between, a third crew is repositioning the power line to avoid the new sewer pipes.

So now you know.

PHOTOS AND VIDEO: Telstar Logistics

22 thoughts on “What’s Up With That Weird Construction Project on Bernal Heights Boulevard?

  1. Thanks, I was wondering about this. Thought it was strange that it goes 24 hours a day. Was thinking maybe the NSA was planting a device to monitor our tweets against POTUS. 😉

  2. OMG THIS IS SO COOL. I do wonder, though: if the city has already installed the sewer pipes, why does this electrical line need to be re-positioned after the fact? Is it just a proximity/safety issue?

    Also, is it really more cost-effective for PG&E to perform surgery on this fancy-pants electrical line than for the city to just install sewer pipes around it?

    • NB: I am not an engineer. This ignorance is why it’s not my job to plan these kinds of projects. 😛

    • I discussed this with the contractor. He basically said that the City trumps PG&E because of eminent domain, so it becomes PG&Es responsibility to move the power line. I can’t confirm if that’s entirely true, but that was his explanation.

  3. Thanks for the interesting post. The scientific and engineering complexity of this project absolutely amazes me.

  4. Thank you! Been wondering since Day 1 what the heck this was, especially since no one on site would say. And they were not the BATS traffic guys..

  5. What is the rush- why are they working 24 hours/day? And why is there always a police car there?

    • Keeping the freeze-plugs frozen is a complex and delicate process, and if the plugs were to fail, it’d be a huge, expensive mess. That’s why they work 24hrs… to minimize the amount of time required to complete the work on the electric line (and thus the amount of time the freeze-plugs are required). Presumably, the same logic also explains the police presence.

    • This is a matter of state law. . In CA, police are at either end of construction zones, day or night, with their lights flashing. The purpose is indeed to offer additional protection to the road workers. The construction company pays the wages while the police are on this duty.

  6. Wondering if the sewer project on Folsom is different than the last sewer project, and the Folsom sewer is being upgraded.

    Also this is the Martin-Embarcadero 230kv line, one of the 3 lines feeding power to SF. (I believe there are 3)

    My understanding is they couldn’t start work on this until the Pittsburgh- Potrero submarine cable was up and running reliably and the new Potrero to Embarcadero feeder was finished.

  7. That’s a fascinating engineering story; and it may even be true. Always remember, you can never take anything that PG&E says at face value.

  8. These days….no kind of wacky, or complex, or obscure story about a weirdness showing up in your face seems out of the ordinary.

  9. Finally got a vague response from PG&E:

    “As part of our commitment to provide customers with safe and reliable energy, PG&E is upgrading approximately 2,200 feet of underground electric cable along Cesar Chavez and Folsom Streets in San Francisco. Crews safely began the project in September 2016 and work is scheduled to be completed by the end of 2017. Prior to the start of construction, PG&E notified customers in the area, and a customer outreach specialist is assigned to this project.”

    While it is true they did send an email to neighbors about an “electric reliability upgrade” it was extremely vague.

  10. I was just talking to the foreman(?) at the site where today they were pulling new cable at Precita and Folsom. They had “frozen” the cable at the site up on Bernal, and the section of the cable that’s being moved (into a new pipe) is from Precita and Folsom to Folsom and 23rd. It’s being moved to make way for a new sewer. There was some conjecture that it was related to the C Chavez sewer replacement done a few years back but this portion was never completed, because they had to finish the Potrero – Embarcadero cable first to make sure there are redundant paths into SF.

    He thinks that after they complete their part, the city will come back to finalize some of the sewer work. I’d like to know more about that!

    This project has been in the works for 8+ years. PG&E acquired the cable 8 years ago, and it has been in their storage yard ever since until today when the big trailer with 3 giant spools on it fed it through the new pipes under Folsom.

    Trivia: That cable can handle up to 60,000 amps at 230,000 volts.

  11. Here’s some more info on that type of line:

    A high-pressure, fluid-filled (HPFF) pipe-type of underground transmission line, consists of a steel pipe that contains three high-voltage conductors. Figure 1 illustrates a typical HPFF pipe-type cable. Each conductor is made of copper or aluminum; insulated with high-quality, oil-impregnated kraft paper insulation; and covered with metal shielding (usually lead) and skid wires (for protection during construction).

    Inside steel pipes, three conductors are surrounded by a dielectric oil which is maintained at
    200 pounds per square inch (psi). This fluid acts as an insulator and does not conduct electricity. The pressurized dielectric fluid prevents electrical discharges in the conductors’ insulation. An electrical discharge can cause the line to fail. The fluid also transfers heat away from the conductors. The fluid is usually static and removes heat by conduction. In some situations the fluid is pumped through the pipe and cooled through the use of a heat exchanger. Cables with pumped fluids require aboveground pumping stations, usually located within substations. The pumping stations monitor the pressure and temperature of the fluid. There is a radiator-type device that moves the heat from the underground cables to the atmosphere. The oil is also monitored for any degradation or trouble with the cable materials.

    The outer steel pipe protects the conductors from mechanical damage, water infiltration, and minimizes the potential for oil leaks. The pipe is protected from the chemical and electrical environment of the soil by means of a coating and cathodic protection.

    Problems associated with HPFF pipe-type underground transmission lines include maintenance issues and possible contamination of surrounding soils and groundwater due to leaking oil.

    from https://psc.wi.gov/Documents/Under%20Ground%20Transmission.pdf

    Some other interesting reading at https://www.pseg.com/family/pseandg/powerline/reliability_projects/bpu_application/pdf/Exhibit%20JAW-2.pdf



  12. I just wanted to revisit this to conclude that the project is finally complete, the streets have been re-paved and re-striped.

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