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W6KWF > TECH 03.10.21 20:07l 45 Lines 2343 Bytes #999 (0) @ WW
BID : 09757_W1XSC
Read: GUEST
Subj: Scattergood-Olympic Line 5/7
Path: IW8PGT<IZ3LSV<I3XTY<I0OJJ<N6RME<W1XSC
Sent: 211003/1749z @:W1XSC.#NCA.CA.USA.NOAM [Santa Clara Co] #:9765 $:09757_W1X
Next came the X-Ray equipment. Sure enough, they can see the cable
shorting against the steel wall of the pipe.
Once all of the repair is done they still have to close it up. How do
you weld a steel pipe with paper insulation inside? Slowly. They have
special heliarc welding equipment and "certified operators" who take 8
hours to weld around one cross section of pipe. They are required to
keep their hand on the pipe no more than 3 inches from the tip of the
welder. If it is too hot for their hand they stop and let it cool. After
all, they can't afford another failure.
------
Oct 20, 1989 Update
I am getting all of these bits from a guy named Jim who is the project
manager. He looks kinda like a red neck RWK (Jesus in a hard hat with a
Harley belt buckle). [RWK is Bob Kerns, an ex-Symbolics person, 6'7"
tall, skinny, bearded. -- DLW] He is a really great guy. Jim was one of
the splicers on the project 17 years ago when he was working his way
through school. He is a now professional electrical and mechanical
engineer. After having worked his way up through the ranks at the DWP he
is now The Big Boss. He claims to be having the time of his life - back
in the field with one of the biggest challenges of his career. If we
ever recruit a VP of engineering I would hope its someone like him.
So, what went wrong? Varying load conditions in the three legs of the
3-phase circuit caused tremendously strong and dynamic magnetic field
changes. The electromagnetic forces between the three conductors and the
steel pipe (gack!) cause the conduit to wiggle around inside the pipe.
Over many years (and under the influence of gravity) the thing slipped
and wiggled every which way. Also, due to very slight diametric
temperature gradients, the differential thermal expansion of a cable
that big across causes bending and warping forces. Nobody ever thought
of any of this.
Wiggle alone may not have cause the problem, however. The spices between
cable segments are much larger in diameter than the cable itself. The
steel pipe at these points is much larger than the main run. So the
whole affair get fat and then shrinks down every 2000 feet or so. What
really screwed them was failure to put any sort of clamp at the splices
to keep the fat splice from getting pulled into the narrower main runs.
This is what cause the fault.
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