On Sat, 16 Feb 2008 18:37:16 -0500 krw wrote: | In article , phil-news- | snipped-for-privacy@ipal.net says... |> On Fri, 15 Feb 2008 22:34:43 -0500 krw wrote: |> | In article , phil-news- | | | |> |> | Specifically, the six-phase "star" and three-phase center-tapped |> |> | wye. With any two phases any number of others is a few transformers |> |> | away. |> |> |> |> I don't know which you mean by "three-phase center-tapped wye". Maybe you |> |> can pick it out from this police lineup: |> |> |> |> * * * * * * |> |> \ \ / * * * | \ / \ |> |> \ \ / / \ / | | \ / \ |> |> N---* *---N---* / \ / | *---N---* N * |> |> / / \ / \ / | | / |> |> / / \ *---N---* *---N---* *---N---* | / |> |> * * * * * |> |> |> |> 1 2 3 4 5 6 7 |> |> |> |> If you don't see the guilty party, maybe you can draw a picture :-) |> | |> | #2 be the culprit. Your "split-phase" three-phase from another |> | post. |> |> That is the same as the six-phase "star" or "6 star". So if you can't |> see any difference, that's because there isn't any. I would not have |> called this a "wye" of any sort since it doesn't look like a "Y". But |> it could be TWO Y's interleaved. | | No, not "interleaved" but split. Invert each phase, as in a center- | tapped transformer (I.e. split) and you're there.
You mean like having 2 three phase 208Y/120 transformers, one fed 180 degrees out of phase from the other, and combining their outputs with neutrals tied together? That's what I meant by interleaved. If that's not what you are saying, then I don't understand what it is you are saying.
|> To make this derived system, you need either: |> |> 1. 3 single phase transformer cores | | Kinda like they do now on the pole.
Yes. Except instead of using 120-volt-only transformers (there are such things ... just 2 lugs on the secondary), they need to use the 120/240 volt transformers (plenty of those around) and understand the concept to know how to wire it up.
Metering that could be an issue. In the case of the apartment building, individual tenants would be metered at 120/240 so it's not an issue. But if this needs to be metered in its "6 star" configuration, it can be done with 3 CTs, each carrying the 180-degree-opposite conductor pairs running in opposing directions just as a single CT would be used for single phase power.
|> 2. 1 three phase tranformer E-core | | Kinda...
It could be done. The manufacturing just has to provide a pair of 120 volt windings, or a series 120/240 tapped winding, and sufficient terminal board space to deal with it.
|> Then you need to wrap these cores with 3 primary windings and 3 secondary |> windings. Usually the secondaries go on the inside and the primaries go |> on the outside, so the secondary at lower voltage and higher current has |> less winding resistance. | | Ok, I'm confused. This is different how?
The difference is that a traditional E-core 208Y/120 transformer would have only ONE 120 volt winding per core bar (times the 3 core bars). Two such windings at 120 volt each, or a 120/240 volt series winding (connected in series inside the winding instead of at the terminal board) would be needed for the "6 star" configuration.
|> Each of the 3 secondary windings needs to be either: |> |> 1. a pair of 120 volt windings which you can wire in series |> 2. a single 240 volt winding with a center tap right in the middle | | Exactly (is there a difference?).
Yes, there is a difference. In #1 you have 4 wires coming from the secondary winding to the terminal board. In #2 you have 3 such wires because the winding is series connected, possibly a continuous single wire, inside the winding itself, and just tapped at a mid-point.
It's a difference in construction. Some people might be more familiar with one over the other.
|> All of the center points of these windings are wired/bonded together and |> grounded. Then each of the three phases will have two poles 180 degrees |> apart. Some people will call this six phases. | | Right; split-phase "wye".
Keep the "wye" in quotes, then; it's not really wye. I would never call it a wye at all. It's a 6 pointed radial star.
|> |> Note that drawings are NOT to scale (relative to voltage). |> | |> | Close enough for government work. |> | |> | |> | |> |> |> Can you describe an electrical system configuration which is capable of: |> |> |> |> |> |> 1. Supplying 120 and 240 volts (not 208 volts) in single phase to all |> |> |> single phase loads. |> |> | |> |> | Look harder at a center-tapped wye. There is only 60degrees between |> |> | the "negative" of phase-A and Phase-B. |> |> |> |> I don't know which I need to look at. |> | |> | #2 |> |> Let me relabel the terminals like so: |> |> C' B |> \ / |> \ / |> A----N----A' |> / \ |> / \ |> B' C |> |> Between A and A' you have 240 volts. |> Between B and B' you have 240 volts. |> Between C and C' you have 240 volts. |> Between A and B you have 208 volts. |> Between B and C you have 208 volts. |> Between C and A you have 208 volts. |> Between C' and A' you have 208 volts. |> Between A' and B' you have 208 volts. |> Between B' and C' you have 208 volts. |> Between A and N you have 120 volts. |> Between B and N you have 120 volts. |> Between C and N you have 120 volts. |> Between A' and N you have 120 volts. |> Between B' and N you have 120 volts. |> Between C' and N you have 120 volts. |> Between A and C' you have 120 volts. |> Between C' and B you have 120 volts. |> Between B and A' you have 120 volts. |> Between A' and C you have 120 volts. |> Between C and B' you have 120 volts. |> Between B' and A you have 120 volts. |> |> Which connection pair do you need to ask about? | | I don't. You seem to see a difference between this "star" and an | ordinary 3-phase "wye" that delivers residential 240V split-phase. | I don't see anything new or particularly interesting here, but am | trying.
A true WYE is not split phase. That makes a contradiction of terms. But if you know of a manufacturer that makes such a transformer AND calls it "split phase wye" or some such thing, please do point to their catalog reference. I've looked at a lot of transformer catalog info online and have never seen such a thing in a single transformer.
|> |> |> 2. Divides up the single phase load in three equal groups in order to |> |> |> maintain a balance on each of the three phases of the utility supply. |> |> | |> |> | How does it divide anything? An imbalance can still be placed on |> |> | any one (or two). |> |> |> |> Of course an imbalance can always happen, and likely will. But it is a |> |> statistical thing. If a building has 54 apartments, connecting 18 of them |> |> to phase A, 18 to phase B, and 18 to phase C, would be "balanced" enough |> |> for utility purposes. If the supply were coming in as 120/240DCT, then |> |> all of the apartments would be on just one of the phases and the phase |> |> loading would be as lopsided as if the entire building were supplied with |> |> single phase power. If the utility insists on balancing the phases and |> |> rejects single phase service for this reason, they will reject 120/240DCT. |> |> If the supply is 208Y/120, that would satisfy the utility (18 apartments |> |> supplied with phases A and B, 18 suppleid with B and C, and 18 supplied |> |> with C and A). But it would not satisfied the need to have 240 volts. |> | |> | Sure, but your "six-phase" is no different than the normal three- |> | phase "wye". At least I don't see it. |> |> The normal three phase WYE is just: |> |> B |> / |> / |> A----N |> \ |> \ |> C |> |> Between A and B you have 208 volts. |> Between B and C you have 208 volts. |> Between C and A you have 208 volts. |> Between A and N you have 120 volts. |> Between B and N you have 120 volts. |> Between C and N you have 120 volts. |> |> There aren't any other ways to connect, and no way to get 240 volts. | | That's funny, because that's exactly how I get the 240V for my house | off the 3-phases on the pole.
Which connections give you 240 volts? If you are getting 240 volts from A-B or from B-C or from C-A, and if the phase angles really are 120 degrees as a true three phase WYE would be, then you are going to get 139 volts at A-N, B-N, and C-N. I don't think that is what you want.
FYI, I did find one utility offering 240Y/139 service for some portions of their service area, as a replacement for 240D.
Maybe you are getting ONE phase of 120/240 via ONE split phase transformer tapped to ONE phase (connected L-N) or TWO phases (connected L-L) of the primary distribution lines. But just because there is three phase on the distribution does NOT mean you are getting it. You are most likely getting one of: 208Y/120 three phase (my grandfather actually did get this at his home), or 120/240 single phase, or that old 240DCT/120 setup.
|> |> |> |> ... that is not the "6 star" I described? |> |> | |> |> | I still don't see the difference between that and a center-tapped |> |> | wye. Again, I'm not a power jock, so may be missing something |> |> | subtile. |> |> |> |> Maybe you saw something I didn't see. Check the above police lineup. |> | |> | Nope. You saw it, just one of us isn't "getting it" (I could easily |> | be missing something - 65h work weeks do that after a while). |> |> OK, hope the above helps. | | Nope. I'm still wondering why you see your "star" as any different | than what we see on 90% of the poles in the country.
208Y/120 is _very_ different. 208Y/120 has THREE line wires coming out at 120 degree phase angle equal intervals. The "6 star" (maybe we can call it 240*/208/120) has SIX line wires coming out at 60 degree phase angle equal intervals.If I provide you with exactly 3 transformers which are wired up with one winding for the primary voltage and one winding for the secondary at 120 volts, it can be wired up by connecting the primaries in whatever they need for the type of service (delta or wye) and connecting the secondaries in a wye configuration. There, you have 208Y/120 just like 90% of the three phase poles in the country (I'll just accept your stats of 90% as I do not know the actual figures).
I have never seen, and never heard of, any "6 star" or 240*/208/120 setup anywhere. I have never seen any utility tariff (I've looked through a few dozen over the past few years) that offers such a service.
I HAVE seen a couple three phase setups where a 120/240 volt pole pig was used, and only HALF of it was wired up to get 120 volts. I HAVE seen one manufacturer detail that they do make cans with the 120 volt windings in parallel internally, and still have 3 lugs with one of them not connected. So these are not necessarily a case of wasting half the capacity. The 3rd lug may simply be there are part of the process of manufacturing only one set of empty cans instead of two different sets.