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Old 01-13-2020, 11:41 PM   #1
xoxoxoBruce
The future is unwritten
 
Join Date: Oct 2002
Posts: 71,105
Subterranean Power Line Blues

We were talking about the CA fires and power shutdowns during those fires because of the Power Companies declared liable for $millions in damages after some of their high tension lines were blamed for starting some fires. One solution would be to bury the power lines but as the carrying capacity goes up so does the difficulty and expense. This story involves the repair of one of the really big main cables coming out of a generation station. Worst case example if you will.

Quote:
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. It shorted out. (Lotta watts!) It feeds (fed) power from the Scattergood Steam Plant in El Segundo to a distribution center near Bundy and S.M. Blvd.

To complicate matters 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 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. They also claimed the down time is costing the costing LA $13,000 per hour. How to fix it and fast?

That's where the LN-2 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. I was amazed.
At the Boardman, OR, generation plant the connection closet(size of my bedroom) is where the feeds from the generator connect to the 500,000 volt power lines going out. There was instead of a door a steel plate with half inch bolts every two inches around the perimeter. Somebody screwed up on syncing the phase of the generator to the power line and the explosion blew that steel plate 50 feet. Nothing to fool around with, but I digress.

You can read the details of the three month repair of that CA main here. It's a good read, not real technical.
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