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Reliability of underground power lines? - Page 6

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Posted by Josepi on July 27, 2010, 9:07 pm

It definitely has taken off in popularity.

I watched, a few years back,  as they pulled five conduit tubes (for fibre
optics later) about 2" diameter, different colours, throught the ground over
200m in a stretch. I was quite impressed as they tunnelled right past the
local high tension station...LOL

Lincoln Village all the cable is in the boulevard, and they changed
ALL the high voltage undergrounds and ALL the transformer vaults over
the last 2 years. It was virtually all done without a trench. A couple
holes here and there, the rest all done with the "mole" - even accros
(under) streets, driveways, and sidewalks. And there are trees along
all the boulevards.

Posted by Dan Lanciani on July 25, 2010, 8:29 pm

| With all the communities pushing for underground lines, are we, as a country
| setting are selves up for a lot of power related headaches in the future?

I replaced the direct burial laterals for a house built in the late 50's in
(IIRC) 2003.  The lines were still working but I was upgrading the service
from 100A to 200A.  We looked at the wires and I would guess they were good
for another decade, though the insulation was starting to show a little
deterioration.  Over the same period the wires on the poles had been broken,
replaced, and otherwise maintained (with requisite power interruption) more
times than I can remember.  My new laterals are in conduit and absent some
as yet undiscovered plasticizer incompatibility I expect them to last even
longer.  So, it may well depend on local conditions, but if the wires on
the poles are subject to any kind of storm damage I think buried conduit
wins easily.

                Dan Lanciani

Posted by N9WOS on July 25, 2010, 9:22 pm

I am not talking about the low voltage 120/240 underground lines that are
after the transformer. I am talking about buried primary lines. 2.4 to
14.4kV that feed pad mounted transformers. They are totally different

Some neighborhoods have buried low voltage going from poles to the house. I
am talking about the neighborhoods that have the entire system underground.

Posted by news on July 25, 2010, 10:36 pm

The feed to our underground wiring (~35 yearsold) is aerial until it
gets to the subdivision.  All the distribution transformers are above
ground (pad mounted).  I've not seen the specific area of the
aerial-to-underground transition, but it has to be less than 1/4 mile
away from my house (based on the location of trees downed in a storm 2
weeks ago).

Had the HV feed been underground all the way to the substation (about
1.5 miles), we would have had uninterrupted power instead of 16 hours
of no power while overhead lines were repaired.  Our area was the last
restored out of about 10,000 customers without power.  I'm prepared
for a few days without power (small generator, Coleman stove, kerosene
heater, etc,) but most of the people here are not, prmarily because
the power is rarely out and the few outages we've had in the past 5
years were usually measured in minutes - longest was about 1.5 hours.

As far as I know, no one in the subdivision has experienced any
problems with the underground wiring (either the house side [120/240 @
200 amps] or the HV feed to the distribution transformers).

The in-ground coax that the cable company used is very different story


Posted by N9WOS on July 25, 2010, 11:00 pm

Yea, that is normal fair for around here too.

The local REMC will generally install a maximum of a 1000 feet or so
underground to transformer. What ever the length is on the small spools.
That is what they keep in stock, so, in a worse case scenario; they will
have the stuff on hand to replace it from scratch.

A company pushing newer stuff for mainline usage was trying to sell them on
higher reliability cable, so for grins and giggles they installed about a
quarter mile section feeding one of the major branch circuits. The branch
circuit can be feed from both ends, so if it fails, they can switch it back
to the other side in a mater of hours.

Beyond that, they have a general rule against installing any part of the
mainline underground.

I have about 200 feet of primary cable behind the barn that they ripped out
of a neighbors place down the road. It was only five years old and died a
painful death.

In Bloomington, where they are ripping up and repairing a few intersections,
duke energy is abandoning all the underground sections of line and are going
full overhead. Places that haven't had overhead lines in decades are getting
a line of new poles.

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