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Closed Delta 120/240V 3-phase service

Discussion in 'Electrical Engineering' started by Beachcomber, Feb 10, 2008.

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  1. charles

    charles Guest

    They stopped bothering about that years ago. Just before the problem, a
    whole group of 24 new bungalows was all put on one phase. And yes it was
    the one that kept tripping,
  2. Guest

    | In article <>, phil-news-
    | says...
    |> | In article <>, phil-news-
    |> | says...
    |> |> | In article <>,
    |> |> | says...
    |> |> |> In article <>,
    |> |> |> > obviously very different practices on different sides of the pond.
    |> |> |> > Virtually all residential distribution over here is 3 phase. The only
    |> |> |> > time I've ever spotted single phase is when an isolated property has its
    |> |> |> > own transformer.
    |> |> |>
    |> |> |> I just wish I had three-phase into my house.
    |> |> |
    |> |> | Different issue. My father wanted three phase into his house in the
    |> |> | late '50s. He argued that it was on top of the pole already so it
    |> |> | was a simple matter to bring it down to the entrance panel. They
    |> |> | told him that they would do it if he guaranteed a $100/month bill
    |> |> | (rather steep for the '50s).
    |> |>
    |> |> There is, afterall, a cost to keep 2 more pole pigs up there. Those things
    |> |> are not cheap.
    |> |
    |> | Try reading Phil. The pigs were already there! Three-phase was
    |> | already available on the pole; only the drop and meter were needed.
    |> Try getting a handle on business and economics. The cost of _using_ the
    |> equipment has to be paid for. There are costs of maintenance and replacing
    |> things that break. If the transformer blows up, the utility replaces it.
    |> If it is shared between two businesses, they share the costs. This is not
    |> a freebie ... except for the base level of service required for residences.
    | Phil, try getting a handle on reading comprehension; They're ALREADY
    | THERE!

    I can comprehend what you are saying. But it does not apply to how things
    like billing and tariffs are done. And the reasons and methods are quite
    logical and sound. If the three transformers are already there, then one
    of these conditions exists:

    1. They are already in use to full capacity by another customer and cannot
    be used. If you want to add three phase service at that location, either
    another set of transformers must be installed, or the existing ones must
    be upgraded to higher capacity. Either way, the existing customer does
    not need to pay more for this extra capacity. But the new customer does
    pay for it. That payment is both for the install work as well as the
    monthly costs (payback of purchase, or payment on lease, depending on
    how the utility got them). That payment usually is integrated into the
    delivery charges (see your local utility tariffs). To ensure enough
    payment for what is installed, there is a minimum usage charge to get

    2. They are in use at less than full capacity. The utility only charges
    existing customers for what they originally needed or actually need now
    depending on tariff requirements, and the minimum usage. The excess
    capacity the utility has to "eat". They can come along, if they wish,
    and trade out the big cans for little cans. But that costs money they
    cannot get paid for, so they have to decide which way to go, and usually
    it is to do nothing. But if things ever do need to be replaced, such
    as the transformers are damaged in a pole knock-down, they would have
    to replace them, and they will use the lowest cost materials they have
    consistent with the customer needs, tariffs, and NESC. Otherwise a new
    customer pays their fair share for the usage, for the capacity they
    need, according to tariffs.

    3. They are unused. The utility could just take them any time they need
    them for some other service. It's usually easier to take them from
    stock, so it might be a while (many years) before they recover them.
    If there is a new customer in the mean time, they might get a pass on
    part of the install cost. But the maintenance cost will be there in
    the form of a minimum usage in most cases.
  3. Guest

    | In article <>, <>
    | wrote:
    |> On Fri, 22 Feb 2008 20:49:29 +0000 (GMT) charles
    |> | In article <>, Stuart
    |> |> In article <>, charles
    |> |> > obviously very different practices on different sides of the pond.
    |> |> > Virtually all residential distribution over here is 3 phase. The
    |> |> > only time I've ever spotted single phase is when an isolated
    |> |> > property has its own transformer.
    |> |
    |> |> I just wish I had three-phase into my house.
    |> |
    |> | yes, very useful. A few years ago, the phase from which our house was
    |> | supplied kept tripping out. I seemed to complain more than others, so
    |> | the house was swapped on to phase 2 (Yellow, White, or whatever).
    |> And someone else's house got swapped over to the bad phase.
    | They stopped bothering about that years ago. Just before the problem, a
    | whole group of 24 new bungalows was all put on one phase. And yes it was
    | the one that kept tripping,

    There's a phase like that around here, and I'm on it. It's not too bad,
    but almost always when it goes out, the problem is in this one road up a
    narrow valley where only a single phase runs, and the MV lines are actually
    under trees well over twice the height of the poles that span all the way
    across the road. Tree clearing along this road (and many others like it)
    is pretty much limited to keeping the trees from getting near the lines.
    But they simply cannot avoid trees spanning over the lines some 20 or 30
    feet above them. Then in high wind or ice loading, branches break off
    and hit the line, sometimes breaking it. Many of these roads only have
    one phase. Some others do have three phases.
  4. Guest

    |> I've lived in some of these areas plus the south. I've never seen any kind
    |> of three phase service besides wye (either 208Y/120 or 480Y/277 and in one
    |> case 600Y/347) and delta (presumably 240D/120 since there was a center
    |> tapped leg on the few I've seen) for three phase and split phase (240/120)
    |> for single phase. I've also seen some 2-wire single phase feeding some
    |> highway lighting, but I did not know the voltage (could be any of 120, 240,
    |> 277, 347, 480, 600 as far as I know).
    |> You're sure none of these are in any abundance where you live?
    | In a residential neighborhood? Get real!

    So do you want to detail which of these systems are available to which
    classes of customer (residential vs. commercial) in the areas where you
    see them, and approximately what percentage of all service drops use

    1. single phase 2-wire 120 volt only
    2. single phase 3-wire 120/240 volt edison split phase
    3. single phase 3-wire 120/208 volt (2 poles of 208Y/120)
    4. single phase 2-wire 240 volt only
    5. single phase 3-wire 240/480 volt edison split phase
    6. single phase 3-wire 277/480 volt (2 poles of 480Y/277)
    7. single phase 2-wire 277 volt only
    8. single phase 2-wire 347 volt only
    9. single phase 2-wire 480 volt only
    10. single phase 3-wire 347/600 volt (2 poles of 600Y/347)
    11. single phase 2-wire 600 volt only
    12. three phase 4-wire 240 volts closed delta, center tapped at 120 volts
    13. three phase 4-wire 240 volts open delta, center tapped at 120 volts
    14. three phase 3-wire 240 volts closed delta
    15. three phase 3-wire 240 volts open delta
    16. three phase 3-wire 480 volts closed delta
    17. three phase 3-wire 480 volts open delta
    18. three phase 3-wire 600 volts closed delta
    19. three phase 3-wire 600 volts open delta
    20. three phase 4-wire 208/120 volt wye
    21. three phase 4-wire 240/139 volt wye
    22. three phase 4-wire 416/240 volt wye
    23. three phase 4-wire 480/277 volt wye
    24. three phase 4-wire 600/347 volt wye
    25. three phase 4-wire 1000/577 volt wye
    26. three phase 4-wire 120/240 volt Scott-T with 208 volt high leg.
    27. six "phase" 7-wire 240/208/120 volt "6 star"
  5. Guest

    | In article <>,
    | says...
    |> | In article <fpkv81$ate$>, says...
    |> |>
    |> |> >> Currently, the area around Vancouver BC. Other residential areas with
    |> |> >> single-phase service: near Waterloo, Toronto, and St. Catharines
    |> |> >> Ontario, near Montreal Quebec.
    |> |>
    |> |> >> Where do you live that has full three-phase MV on top of every pole on
    |> |> >> every street in a residential area? And three transformers on every
    |> |> >> pole that has a transformer?
    |> |>
    |> |> >The transformers aren't on every pole (every third), but the wires
    |> |> >are. I see it all over. All you have to do is look.
    |> |>
    |> |> I *have* looked where I live. I've told you what I see (a single MV
    |> |> wire on the top of the vast majority of poles in residential areas).
    |> |
    |> | Afghanistan?
    |> If I ever get there, I'll tell you what I see, if I make it back. But
    |> I have read some descriptions that would suggest something like 380Y/220
    |> for three phase.
    |> |> The next level up the distribution hierarchy is 3-phase, so 3-phase
    |> |> lines do pass through residential areas, but only one phase is tapped
    |> |> for the line of poles down each street or alley.
    |> |>
    |> |> Again, where do you see 3-phase on every pole?
    |> |
    |> | Illinois, New York, Vermont (haven't looked here in OH).
    |> Maybe you should. You'll find a LOT of 208Y/120, some 480Y/277 (larger
    |> buildings), and maybe some leftover 240D/120, as well as single phase
    |> service in 240/120. But do take your camera if you are convinced there
    |> are some "6 star" services around.
    | They surely wouldn't be called that because it's a stupid idea.

    I don't know what they would call it if they provided it. That name is
    one I made up just to have a way to refer to it until someone picks or
    reveals a better or already used name. You're the one that says it is
    already deployed; so you tell me what they call it in your area.

    |> |> Tell us some places.
    |> |> Even when there are 3 phases, do the transformers occur in groups of 3?
    |> |
    |> | Sure.
    |> And how many lugs on each are wired up? Does each transformer have the
    |> same number of MV bushings (whether that be 1 each or 2 each)?
    | Never climbed a pole, but all three phases are used for Edison 240V
    | service. How may lugs is that?

    That depends on the exact service. In the typical case there are three
    transformers forming a closed delta. The primary transformer will have
    3 lugs used. This transformer has a 120/240 volt secondary and provides
    the source of 120 volts. The other 2 transformers are wired to other
    phases on their primary, and have 2 lugs used at 240 volts. One is wired
    between one end lug of the first transformer and the high leg. The other
    is wired from the high leg to the other end lug of the first transformer
    forming the delta loop. The 2nd 2 transformers are not grounded. They
    may have (probably do have) an unused center tap lug. A total of 4 wires
    come off this setup to the service drop in question. These are the three
    phases plus the neutral from the center tap which is grounded.

    Other cases might be 240 volt delta without any Edison, or an Edison
    service that has no three phase at all.

    |> |> Or do you mostly get one transformer per pole, tapping only one of the
    |> |> 3-phase MV lines? (That's what I see when there does happen to be
    |> |> 3-phase distribution).
    |> |
    |> | One pig per pole, three wires going between poles, under the MV
    |> | lines.
    |> That's single phase 240/120 of the Edison split phase variety. No three
    |> phase services there.
    | Bullshit! The three wires were the three phases. You could see the
    | connections on the pigs.

    If the service is three phase, they put the three transformers on the SAME

    Sure, you could form three phase service by splitting the transformers up
    on different poles and interconnecting the secondaries between poles.
    In the extreme case, the middle pole could be getting 120/240 from one
    phase one an adjacent pole, and 120/240 from the other phase at the other
    pole, and merge them to have the full "6 star" at the middle pole. But
    is that actually wired that way for any service drop? The service drop
    would have 7 (SEVEN) wires if so.

    |> Look for cases of THREE transformers, each with the same number of MV
    |> bushings (either all have 1 or all have 2 each), and at least 3 LV lugs
    |> connected on all three. If only 2 lugs are connected on all three, then
    |> you have a wye system, usually 208Y/120 but 480Y/277 is possible (600Y/347
    |> is very rare except in Canada). If 2 lugs are connected on 2 transformers
    |> and 3 lugs are connected on one transformer, it is probably 240D/120.
    | Exactly!

    But that's not "6 star" at all.

    |> Other possibilities also exist. Be sure to get a number of photos at many
    |> different angles to get an unambiguous view of exactly how all the wires
    |> are connected. If you see one with 3 lugs connected on each of 3 separate
    |> transformers, where the middle lugs of each are connected together, and
    |> all the outer lugs, plus the joined middle lugs as one wire, supply 7 wires
    |> into whatever building is served, then be sure to get a LOT of photos.
    | I'm not in the business of supplying your curiosity.

    No, you are in the business of not knowing the difference between differnt
    kinds of three phase service configurations.
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