On Fri, 15 Feb 2008 22:34:43 -0500 krw wrote: | In article , phil-news- | snipped-for-privacy@ipal.net says... |> On Fri, 15 Feb 2008 19:02:44 -0500 krw wrote: |> | In article , phil-news- |> | snipped-for-privacy@ipal.net says... |> |> On Thu, 14 Feb 2008 23:00:47 -0500 krw wrote: |> |> | In article , snipped-for-privacy@ipal.net |> |> | says... |> |> |> On Thu, 14 Feb 2008 19:05:59 -0500 krw wrote: |> |> |> | In article , snipped-for-privacy@notreal.none |> |> |> | says... |> |> |> |> |> |> |> |> >> B C |> |> |> |> >> \ / |> |> |> |> >> \ / |> |> |> |> >>A----N----D |> |> |> |> >> / \ |> |> |> |> >> / \ |> |> |> |> >> F E |> |> |> |> >
|> |> |> |> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound |> |> |> |> >>on the second core. C-N and N-F are both wound on the third core. A third |> |> |> |> >>of the 120/240 loads would be served from A-N-D. A third of the
120/240 |> |> |> |> >>loads would be served from B-N-E. A third of the 120/240 loads would be |> |> |> |> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E |> |> |> |> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N. |> |> |> |> >|> |> |> |> >I always wondered if either any electric company offered such a service, |> |> |> |> >or if there was any such thing as a breaker panel that would support it. |> |> |> |> |> |> |> |> Are we not forgetting about the primary windings for such a scheme? |> |> |> | |> |> |> | ...and how does this "six phase" differ from a center-tapped three- |> |> |> | phase? |> |> |> |> |> |> When most or all of the loads are single phase, the "6 star" can keep the |> |> |> loading balanced over the 3 incoming phases, while also providing genuine |> |> |> 240 volts to those single phase loads. 240DCT or 240DVCT puts most of |> |> |> the loading on one phase angle (which might be 2 incoming phase lines). |> |> |> 208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich |> |> |> on the L-N circuits. 220Y/127 is sometimes a compromise. |> |> | |> |> | Maybe I'm dense, but I see *no* difference between the two schemes. |> |> | ELectrically, I don't see how you could tell one from the other. |> |> |> |> A saw a bunch of different schemes in this thread. Maybe you can list |> |> the specific schemes you think are alike but treated as different. |> | |> | 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.
To make this derived system, you need either:
- 3 single phase transformer cores
- 1 three phase tranformer E-core
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.
Each of the 3 secondary windings needs to be either:
- a pair of 120 volt windings which you can wire in series
- a single 240 volt winding with a center tap right in the middle
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.
|> 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?
|> |> 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 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.