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Reliability of underground power lines?

Discussion in 'Home Power and Microgeneration' started by N9WOS, Jul 25, 2010.

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  1. N9WOS

    N9WOS Guest

    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?
     
  2. Guest


    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.
     
  3. Another Dave

    Another Dave Guest

    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
     
  4. vaughn

    vaughn Guest

    Only true with direct bury construction. If they do the job correctly the first
    time by using conduit, there will be no need to dig new ditches to replace the
    lines; so your precious tree can stay in place. Further, the conduits will
    reduce (but not prevent) power outages caused by digging accidents. Once you
    have dug the trench for the direct bury cable, adding the conduit is a
    comparatively small incremental expense.

    Vaughn
     
  5. Dan Lanciani

    Dan Lanciani Guest

    | 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
    [email protected]*com
     
  6. N9WOS

    N9WOS Guest

    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.
     
  7. N9WOS

    N9WOS Guest


    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.
     
  8. N9WOS

    N9WOS Guest

    | With all the communities pushing for underground lines, are we, as a
    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
    animals.

    Some neighborhoods have buried low voltage going from poles to the house. I
    am talking about the neighborhoods that have the entire system underground.
     
  9. N9WOS

    N9WOS Guest

    Some neighborhoods have buried low voltage going from poles to the house.


    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.
     
  10. Guest

    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.
     
  11. Guest

    Up here they don't even trench to install new lines. The conduit
    follows the "mole" that theyshoot underground from point to point
    (transformer pad to transformer pad location, generally) and is
    similar to PVC water pipe that comes on a giant spool
     
  12. Josepi

    Josepi Guest

    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.
     
  13. Josepi

    Josepi Guest

    14kV circuits are typically run in duct banks of conduit, encased in
    concrete.

    The backyards are done like clare stated in many cases. Waterloo is still
    running 2.4kV in backyards until they get rid of their substations. With
    concentric neutral, direct burial cables the conduit is not needed and too
    costly.



    Up here they don't even trench to install new lines. The conduit
    follows the "mole" that theyshoot underground from point to point
    (transformer pad to transformer pad location, generally) and is
    similar to PVC water pipe that comes on a giant spoolOn Sun, 25 Jul 2010
    15:44:26 -0400, "vaughn"
     
  14. Guest

    House feed was not the subject.
     
  15. Guest

    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.
     
  16. Josepi

    Josepi Guest

    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.
     
  17. Josepi

    Josepi Guest

    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.
     
  18. EXT

    EXT Guest

    A lot of the people wanted underground lines so they could have trees
    Around here often the underground installation companies install natural gas
    pipes in a unique way. To install natural gas lines they use an air powered
    "torpedo" which will drag a cable underground over about 50 to 100 feet at
    a time. This cable is used to pull a cone to enlarge the tunnel and then
    drag a plastic gas distribution pipe without tearing up the entire route
    allowing them to go under trees. I am sure the same technology can be used
    to pull wires or conduit for wires.
     
  19. vaughn

    vaughn Guest

    The "torpedo" that I have seeen is an unguided device. It is a very useful
    device that can indeed be used to install conduit, but it does not have near the
    accuracy of directional boring. Also, there is always the chance that it will
    go "wild" and not emerge where you expect it to. It can even dive! In that
    case, you will have a hell of a mess before you finally manage to dig the
    expensive bugger out of the ground.

    Vaughn
     
  20. Josepi

    Josepi Guest

    The later units I have seen around KW used directional controls. I suspect
    the vibrators in the head do different planes of vibration to change
    directions. The guy driving it has a joystick and some method of feedback to
    know where it is going. Not sure how they do the feedback or actually
    control it. Like you said the older units could be dangerous and full of
    surprises.



    The "torpedo" that I have seeen is an unguided device. It is a very useful
    device that can indeed be used to install conduit, but it does not have near
    the
    accuracy of directional boring. Also, there is always the chance that it
    will
    go "wild" and not emerge where you expect it to. It can even dive! In that
    case, you will have a hell of a mess before you finally manage to dig the
    expensive bugger out of the ground.

    Vaughn
     
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