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W6KWF > TECH 30.09.21 07:30l 49 Lines 2702 Bytes #999 (0) @ WW
BID : 2454_N0ARY
Read: GUEST
Subj: Scattergood-Olympic Line 3/7
Path: IW8PGT<LU4ECL<HR1PAQ<CX2SA<N6RME<N0ARY
Sent: <10930/0229 2454@N0ARY.#NCA.CA.USA.NOAM [San Jose, CA] $2454_N0ARY
Each of the three legs in the feeder carrys 600-800 Amps (depending on
demand) of 230KV three phase power. The ground return is the Santa
Monica Bay. Down at the Scattergood Steam Plant and up in Santa Monica
they have a giant copper anchors out in the bay.
They lay these things in 2000 foot segments. 2000' is the longest
segment they can pull through the steel pipe. The pipe is laid first and
then the internal cable(s) are pulled through. Tensile forces must be
enormous. At each segment joint (splice) there is a very large and
expensive ($100K) underground vault. Future technology may allow them to
go 3000 feet, reducing the number of vaults needed per run, thereby
saving money.
After the feeder was originally built (and the cable pulled) it was
thoroughly evacuated to both leak test and remove any contaminants. It
was flushed with dry nitrogen and then reevacuated. Golden Bear High
Tension Oil was then slowly added while still maintaining a vacuum so as
to "pull" any residual gas contaminants out of the oil and the cables in
the pipe. The pipe, full of oil, is then pressurized to about 200 PSI
for some period of time before it gets powered up. 200 PSI is maintained
during operation to keep any bubbles from forming and to drive
insulating oil into the paper.
At both ends of the pipeline they have 6000 gallon tanks of Golden Bear
lightly pressurized under a blanket of dry nitrogen. There are pumps at
both ends. There is about 100K gallons in the entire pipeline, not
including the 6K gal tanks. Every six hours they reverse the pumps so
the oil oscillates back and forth in the pipe. The pumps only run at 3
gallons per minute but that is enough, over 6 hours, to get the oil in
each 2000 foot segment to go at least a segment or two length in either
direction. This eliminates hot spots in the copper conductors and
spreads the heat out over several thousand feet. A little competitive
pressure is always maintained between the pumps to get the 200 PSI.
They learned the hard way that you simply don't reverse the pumps lest
you get the Golden Bear equivalent of water hammer. The last hour of
every 6 hour cycle is spent slowly reducing the oil velocity down to
zero before you reverse it and then slowly ramp back up in the other
direction.
In between segments, in the vaults, are temperature sensors embedded in
the pipe. These monitor the oil temperature. These are wired to a
computer downtown. Because the oil oscillates, the DWP can track the
temperature gradient along the pipe and get an early indication of the
location of any hot spot problems. They have regularly spaced flow rate
and pressure monitors for the same purpose - detecting and isolating
faults.
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