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Reliability of underground power lines?

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Posted by N9WOS on July 25, 2010, 6:20 pm
 


I was watching one of those discovery channel shows talking about the
crumbling of American infrastructure. One of the things they covered was the
power reliability problems in Deerfield IL. To the point that they sued the
power company. They talked about old power lines being the problem, and
showed pictures of old above ground poles. But I really think they missed
the actual problem with the system in Deerfield.

The primary cause of the outages in Deerfield is the underground part of the
system. Not the aboveground part.

Deerfield is on of those communities that went to the expense of having most
of the wiring put underground in a lot of the developments. It was direct
burial installation. The problem is, it is over 20 years since the power
lines were installed, and they are reaching end of life. The only answer to
fixing it is, you have to completely rip everything out and replace it.

There power company has already replaced several miles of underground line,
but that is just a fraction of what is there. If they do replace all of the
lines, it will keep everything running for about another 20 years, then they
rill have to repeat it all again.

End of life for overhead lines is 50 to 60 years. Some are still in service
long after that in dry areas. The industry is finding out that the end of
life for buried lines seems to be 20 to 25 years.

Some places I had read about were even more depressing. They stated that it
would take them 20 years to replace all the lines. Which, given the 20 year
lifespan, means that when they finish, they will instantly start back at the
beginning again. Or basically, continuous perpetual replacement of the power
system.

From what I have seen, power companies have seem to accept that fact,
because they are putting the power lines in conduit for most of the newer
installations. That allows them to pull the lines and replace them without
having to dig up the land in-between. But the idea of pulling and replacing
everything every 20 years is not hopeful in regard to power prices. Because
every customer pays for that work with their power bill.

And it will also mean more scheduled outages, because you can't relplace
them while the system is live, so when you pull the wires and replace them,
everyone is out of juice.

And that doesn't help the countless places that have already had their lines
directly buried over the last 20 to 30+ years. All those communities are on
a runaway train headed right for endless power problems, and major
excavation and replacement of their systems.

A lot of the people wanted underground lines so they could have trees
without fighting the power company, but in a round about way, they are going
to have to have those trees removed to replace the underground lines in 20
years. So there is no way to win.

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?



Posted by clare on July 25, 2010, 7:03 pm
 




You forget that in Deerfield, as in many areas of the northeast and
much of the rest of North America, wind and ice storms reduce the
lifespan of overhead wires significantly.

Where we have above-ground hydro services, lines come down every
couple of years - and sometimes more than once in a winter - as well
as every 10 years or so in the summer due to high winds knocking down
trees etc.

Where we have underground services and buried transformer vaults
problems start with water infiltration around year 20 - 25.
Where above-ground transformer vaults are used, most are still working
fine after 30 years - and the local utility is replacing the buried
vaults with pad-mount above-ground units.

The added advantage of not having 50,000 starlings sitting on the
wires crapping on everything in range also cannot be ignored.

When they replace the underground service wires here in Waterloo
Ontario, a 5 minute switch-over outage is a LONG outage.

Not nearly as much headaches as with the overhead wires exposed to the
elements, ice, wind, trees,etc - as well as the poles being knocked
down by cars that leave the road for any reason.

I think you are over-analyzing things and coming to faulty
conclusions.


Posted by N9WOS on July 25, 2010, 9:17 pm
 



Umm...5 minutes... Depends on where you are in relation to the line being
replaced.

If they replace the line, then it means they are replacing it for a reason.
What is that reason? If it is shorted out, then that means that everyone
down stream of that line has been out for... hours? Day?

It will take them a couple hours to find where the trouble spot is. It will
take them a couple hours to verify the cable is dead once they isolate it.
So, four to six hours after the event, you finally know you have to change
it. Do you have that size of cable in stock? Do you have enough? So,
depending on where the power company warehouse is, we are talking 2 hours to
get new cable and hardware to pull it, on scene. Cut ends off old cable, set
up puller, clip end of new cable to old cable, pull, cut and terminal new
ends. An hour or two. Shut the power off to the rest of the neighborhood to
reconnect the isolated section... 5 minutes....

We are talking 10 to 12 hours from lights out to lights on for an
underground cable replacement if it is in a conduit, and requires no
digging. If it does require digging, we are talking a day + of no lights for
the people feed by that line.

That is the general timelines that are given for underground problems around
here in Indiana.



Posted by clare on July 27, 2010, 2:23 am
 



Nope. When they decide to replace underground cabling here it is
generally PREVENTATIVE. They know a problem is developing, so tnhey
run the new line and switch uit over before catastrophic failures.

There were the odd power outages of up to an hour in some areas after
heavy storms when water got into the subterrainian transformer vaults
- which is what triggered the upgrades.

Mabee the way they do it in your neck of the woods - but not here. In
our subdivision, they generally located the wet line pretty quickly,
then re-configured the feeds to bypass the bad cable. This sometimes
took an hour or so. The cable replacements themselves have never
caused more than a 5 minute outage for the switch-over - even when
replacing the transformers. My UPS carried the computers through
without a hitch - often the only indication the power had been out at
all through the day was a couple of the clocks were flashing.

Like I said, here in Waterloo Ontario, MUCH shorter.

Posted by Josepi on July 27, 2010, 2:44 am
 

I doubt the boys at Wloo North would do the circuit changeover that fast.

They aren't going to dig up your old service wires without dumping the feed
to the house first. The offending house feed would be out for hours, at
least. If the wires need replacing they would typically be blowing the
transformer fuses anyway, or they wouldn't be there, in the first place.


Many times they can put a long lead jumper from your meter base to a
neighbours to keep your house alive.

In Kitchener they don't get into the submersible compartment until the 8kV
is out. Too many accidents have stopped that crap. I don't think Wloo North
uses too many submersibles for a long time.



Like I said, here in Waterloo Ontario, MUCH shorter.



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