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Date: Tue, 31 Oct 89 13:04:47 PST From: brian%cyberpunk@UCSD.EDU (Brian Kantor) Message-Id: <8910312104.AA04094@cyberpunk.ucsd.edu.UCSD.EDU> To: tcp-group@UCSD.EDU Subject: high power Something to read while waiting for your compilation to finish. The story is from Tom McMahon, hardware wizard at (and general manager of) the Symbolics Graphics Division in Los Angeles. \- ---------------- Date: Wed, 27 Sep 89 10:27 PDT From: Thomas L. Mc Mahon Subject: Cuts and jumpers (on a different scale) [Not quite the right mailing list but close. If you don't care about megawatts, bus bars bigger than your wrist, things that cause ground loops out to Hawaii, or big hairy construction projects hit D now.] ************ Several days ago a very large number of trucks and men from the Los Angeles Department of Water and Power descended on my neighborhood. They removed large sections of Pershing drive to a depth of 15 feet or so over a stretch of about a city block. I assumed they had a problem with a water main or something. When they started building semi-permanent structures over the holes I knew something really big was up. When the large trucks full of strange power tools, mega-welding machines, breathing equipment, and racks of test equipment came I started wondering. Driving by a couple nights ago (11 PM), I noticed that the pace hadn't slowed - they were at it 24 hours a day. My curiosity got the best of me yesterday when they brought in the giant tanks full of liquid nitrogen. LN-2 for the DWP? I parked my car and played the lookie loo. 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 1freeze0 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. \- ------ The next day: Last night the DWP held a curbside chat to allay the neighborhood's fears that they were going to accidentally blow us all up. Apparently all the vapor clouds from all the LN-2 blowoff had caused a great deal of concern. Interesting bits: The feeder was laid 17 years ago and was designed to have an MTBF of 60 years. There are other similar feeders in use around California, in the Pacific North West, and some on the east coast. This was the first failure in the western US. No one out here had any idea how to fix it so they brought in experts from the east. (NYC has had some faults.) This link is a very critical part of the LA power grid. Last night the city engineers verified the $13,000 per hour power cost figure quoted the day before. (I guess that means they are being forced to buy power off the grid somewhere else.) There are actually three center conductors (they had a cross sectional model to show us). Each is about 3" in diameter with a one inch solid copper core. Each is wrapped with hundreds of layers of a special paper. That, in turn, is sheathed with co
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