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Reliability of underground power lines? - Page 2

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Posted by clare on July 27, 2010, 4:16 pm
 


wrote:


House feed was not the subject.


Posted by Josepi on July 27, 2010, 9:09 pm
 


My bad.

Reado error.

I totally agree with your comments concerning high voltage burial. Waterloo
is typically a little more advanced in using new methods than Kitchener, the
museum.

Thanx

House feed was not the subject.


wrote:



Posted by Another Dave on July 25, 2010, 7:10 pm
 

On 25/07/2010 19:20, N9WOS wrote:


Here in the UK underground power cables on newly-built housing estates
have been standard for at least 45 years and very probably longer.
They're always conduited but I've never heard of ANY being replaced.

Perhaps climate conditions in the US are more extreme but I don't see
how that could make any difference. Temperatures of -25 degrees Celsius
occur in Britain, though admittedly not often.

Another Dave

Posted by N9WOS on July 25, 2010, 8:56 pm
 



You are referring to something else entirely.

Most of the street level distribution in the UK is low voltage <600V. low
voltage lines do not have the insulation degradation problem. A large
portion of the medium voltage 600V to 60,000V was installed long before
extruded polyethylene lines existed. They are using fluid filled cables.
Fluid filled cables have proven reliability. I am not talking about those
installation.

I am talking about extruded polyethylene medium voltage cables used in
street level distribution. Extruded dry polyethylene cables were first used
in the 1960's. major reliability/water problems were finally solved and they
finally started seeing widespread use in the 1990's.

Extruded dry polyethylene is the main cable type used in rural/suburban
underground power grids.

The first generation of dry polyethylene installations across the country
are finally reaching the end of life stage. Most of those were installed
using direct burial, because they didn't know the cables would have such a
poor lifespan. That means all the underground systems that have been put in
place the last 20 years are coming up for removal. And they will be removed
the hard way.




Posted by John Gilmer on August 16, 2010, 6:14 am
 



The stuff that was installed (both "high voltage" and local service voltage)
about 35 years ago seems to be holding up.

We have houses in two separate developments that are 35+ years old.

The single worse experience was in the home we live in now.    The service
"drop" is over 400'.    Just before we bought the house, the folks putting
in a new septic system cut the wires.    The wires were repaired but  a few
years later we had a succession of failures.   The basic failure was a pin
hole leak in the insulation letting enought water in to initiate a
completely failure.   Another set of failures occured near where a neighbor
routinely burned "trash" wood.   God only knows whether this was the cause.

Anyway, the power company decided to replace the entire 400+ line and while
there were at it increased the conductor size.   The new line failed once or
twice within 50' of the locus of the earlier failures.    Some of that might
have been because the installtion was sloppy.   The installers pulled and
then removed the cable at least once.   Because of our frequent experience I
have a nodding acquaintance with the local repairmen and watch them locate
the fault and die down and patch the cable.

But for the last few years we haven't had any problems.

The other house only has about a 40' drop but other homes have up to a 100'
drop.   I haven't seen any signs of the "drops" having failed in the
extended neighborhood but I do know of one failure of the 38kv line.

Back to my own neighborhood, there haven't been any underground failures of
the 38kv but a neighbor lost her transformer.   The first replacement had a
"bushing failure" and had to be replaced again.   They were without power
for about 5 days because of the transformers.

Our neighborhood is served by overhead high voltage wiring up to the edge of
the development and underground thereafter.   These have failed so many
times that I have lost count.   The cause is always the same:   the wind
blows down a branch or an entire tree and that takes out the power line.

Thus, my experience is that the underground "system" may well have random
failures (or even "hot spots") but is generall sound and will not require
change out in the immediate future.   But 40 to 50 years ago, houses used a
lot less power.   Heat pumps were all but unknown and air conditioning was
hardly universal.    Just as with above ground distribution, the "solution"
seems to be to fragment the low voltage distribution and add more
transformers and, occasionallly, put in high voltage feed to the "pole
pigs."

Frankly, from what I have seen, water, gas, and sewer lines are as likely to
required general replacement as the electrical lines.





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