Closed Delta 120/240V 3-phase service

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:

  1. 3 single phase transformer cores
  2. 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:

  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

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.

Reply to
phil-news-nospam
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| Except, there is no connection to one lug of the big can except to | the small can, so you get either: | | B | / | / | N-----A' | \ | \ | C | | or maybe | | B | / | / | A-N | \ | \ | C | | (trying to show a different voltage on A) | | or some combination. Not too useful IMO. | | There are quite a few of those things in inner city Philly, as well as | some other odd practices.

Curious-er and curious-er. It might need an investigation.

I wonder if maybe there might be a Scott-T inside that big can and the little can could be modifying it somehow.

Reply to
phil-news-nospam

In the situation under discussion were the only significant three phase load is the elevator a three phase auto transformer wired in boost configuration would solve the problem at a reasonable cost.

Reply to
Tom Horne

Tom:

Thanks for the suggestion. Could you elaborate a bit more on how this would be connected please...

Are you saying that you would have standard split phase 120/240V from one transformer... Then in addition to that, you would have 3 autotransformers (or one 3 phase autotransformer) for the 3 phase load?

I've never heard of anything like this. Aren't auto transformers not permitted (from the utility primary to customer secondary) because of safety concerns? Or if it is a customer provided transformer (perhaps a buck-boost XFR), wouldn't you need a utilility transfomer on the primary 3-phase line anyway?

It doesn't seem that you would be saving anything here.

Beachcomber

Reply to
Beachcomber

| In the situation under discussion were the only significant three phase | load is the elevator a three phase auto transformer wired in boost | configuration would solve the problem at a reasonable cost.

What if you don't have any need for three phase power at all? Suppose your building has elevators that work fine on single phase power. The building is so big, however, the power company doesn't want to drop only one phase into it; they want to have all three phases coming in, in some approximation of a balanced load. And you need to supply 240 volts, not 208, to each tenant. What would you set up?

Reply to
phil-news-nospam

On Sat, 16 Feb 2008 07:54:39 GMT Beachcomber wrote: | |>In the situation under discussion were the only significant three phase |>load is the elevator a three phase auto transformer wired in boost |>configuration would solve the problem at a reasonable cost. |>-- |>Tom Horne |>

| | Tom: | | Thanks for the suggestion. Could you elaborate a bit more on how this | would be connected please... | | Are you saying that you would have standard split phase 120/240V from | one transformer... Then in addition to that, you would have 3 | autotransformers (or one 3 phase autotransformer) for the 3 phase | load?

With just 2 extra small transformers, you can add a couple extra phases to a normal 120/240 split phase and end up with 4 lines, 3 of which are the same as 208 wye, if you use the original incoming three phase distribution to derive it.

Or you can do it with just 1 weird transformer. Using a single phase transformer with a 139/277 volt split phase, you wire it's primary B-C if the original single phase is A-N (or wire it C-N if the original single phase is A-B). Connect the 139/277 center tap to one line end of the 120/240. Voila, you now have a Scott-T emulating 277 delta.

  • | | N
Reply to
phil-news-nospam

Of course, the answer is D). That is why tower light monitors are required.

What is real fun is when you move to a different tower, and still have to monitor the lights at the old transmitter site. I had to do that at WACX. I used a 1.024 MHz crystal and divided it by 1024, then filtered it to get a fairly clean sine wave. A current transformer monitored the circuit. The sine wave was on, when there was at least one light out. That way, when the beacons flashed, the signal dropped for a second.

At the other end, I used a 567 tone decoder to detect the 1 KHz signal. There was a small, but bright LED in the mater operator's field of view. They logged when it started flashing, and when it stopped. If the light went out it meant there was no AC at the old site, and that was logged in and out, as well.

BTW: My choice would have been F). Find the idiot who wrote the test and make them re-write it so that all questions were closer to the proper answer. There should be no throw away questions on a test like that.

Reply to
Michael A. Terrell

WPFB. the local AM & FM station in Middletown, Ohio had several engineers with a first class ticket. The AM was a daytimer, and later, allowed low power nighttime operation. They ran a background music service they called Musiplex as a SCA service. In the early days there were no commercial SCA equipment, so they built tuners & receivers and leased them, with their music service. One of the engineers must have been in love with Nuvistors. There was about a dozen nuvistors, and each section was built on a steel plate that mounted between a coupe sets of rails. The RF sections looked odd enough, but the 20 W PA amp look really funny.

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Reply to
Michael A. Terrell

What makes you think that its up to you to chose? The utility company is going to tell you what is available. The elevator company is going to tell you what they need, as well. As usual, you're playing another of your long winded, and useless games of 'What if'...

Reply to
Michael A. Terrell

I took the exams for First Phone, Second Telegraph and Amateur, in New York City, shortly after I was discharged fron the Army in 1946.

The FCC exam proctor noticed I was doing well on the first couple of elements I handed in and told me to do just about 80% and turn them in. If I didn't get the required 70% to pass, he'd give them back for me to try a few more questions. Of course I'd pick the easy question to answer first.

He said I had the record for most elements passed in one day. Probably also the record for the lowest passing score!

Reply to
VWWall

No, not "interleaved" but split. Invert each phase, as in a center- tapped transformer (I.e. split) and you're there.

Kinda like they do now on the pole.

Kinda...

Ok, I'm confused. This is different how?

Exactly (is there a difference?).

Right; split-phase "wye".

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.

That's funny, because that's exactly how I get the 240V for my house off the 3-phases on the pole.

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.

Reply to
krw

What if Phil bought his own bigass transformer?

Reply to
krw

I "worked" at WPGU-FM (at the time the only network affiliated student station) for a while. Their transmitter was on a 12-story dorm building about a mile from the studios (in the basement of another dorm building). THe logs were taken remotely over a phone line with a contraption that consisted of a rotary phone dial and meter. One of dial "positions" ('9', IIRC) returned the antenna light current, which was logged every half hour along with all the rest of the stuff.

As far as I was concerned, the whole test was throw away questions like that. It was a waste of a day and a trip to Chicago.

Reply to
krw

On Sat, 16 Feb 2008 14:16:04 -0500 Michael A. Terrell wrote: | snipped-for-privacy@ipal.net wrote: |> |> On Sat, 16 Feb 2008 06:38:55 GMT Tom Horne wrote: |> |> | In the situation under discussion were the only significant three phase |> | load is the elevator a three phase auto transformer wired in boost |> | configuration would solve the problem at a reasonable cost. |> |> What if you don't have any need for three phase power at all? Suppose your |> building has elevators that work fine on single phase power. The building |> is so big, however, the power company doesn't want to drop only one phase |> into it; they want to have all three phases coming in, in some approximation |> of a balanced load. And you need to supply 240 volts, not 208, to each |> tenant. What would you set | | | What makes you think that its up to you to chose? The utility | company is going to tell you what is available. The elevator company is | going to tell you what they need, as well. As usual, you're playing | another of your long winded, and useless games of 'What if'...

Maybe you should read some of the tariffs. Most jurisdictions do have some requirements that certain services must be made available of so requested. The only "what if" here is "what if someone knew what they were allowed to really ask for".

Reply to
phil-news-nospam

I think that logically, the process goes something like this.

  1. The architect or building contractor responsible for the electrical system needs to research the utility tariffs and policies and determine what services are available.

  1. Further research may be necessary to see what services are available at the specific location of the building under construction.

This may be different then #1.

  1. Given the available choices, it is up to the person designing the electrical system within the building the most economical and useful service, given the specific needs of the building (elevators, HVAC, pumps, machine shop tools, etc.) That is, should it be 120/208,
120/240, volt single phase or three phase, open wye, or closed-delta, etc.

#3 is the most interesting and the most difficult, apparently, from the comments offered on this thread. It doesn't seem that there are any carved-in-stone rules for what is best, only tradeoffs and different opinions.

Have I got this right?

Beachcomber

Reply to
Beachcomber

Progress Energy, who bought Florida Power, wouldn't let you provide any transformers. They did the calculations, and set their own transformers. Three phase availability was determined by your location, but generally any building above a certain level was three phase. Even small convenience stores and gas stations are three phase around here. The only home I've seen with an elevator had three phase power, along with an Onan diesel three phase generator with an automatic transfer switch.

Reply to
Michael A. Terrell

I would have had to go to Detroit to take the test. In the mid '70s it would have cost me about $1000 to make the trip, including a several day stay. That was why I walked away from broadcast work for 15 years. I was tired of patching junk with no parts budget, zero downtime and idiot station managers who thought they could tune a TV transmitter like their ham gear.

Reply to
Michael A. Terrell

Obviously, you don't and you've been flogging another dead horse. You can take any simple subject and turn it into mind numbing drivel. You've flogged this one for a week and made zero progress. Even if you got answers, they would only be valid for one location, not the entire planet earth.

You bitch about no availability of 208 volt appliances. How many do you see that are marked 240 VAC only? I see a lot that are marked

208-240 VAC. So your water heater is a few volts low. It won't make much difference in the output. If you buy at the right places, 208 volt stuff isn't hard to find, even in the deep south. If you are in an apartment, it is up to the landlord to provide the major appliances, and repair or replace them when they quit. So, if the building is big enough, they are supplied three phase. no matter how much you want to yak about what ifs, no one really gives a damn, except the local power company, and the owner of the building.
Reply to
Michael A. Terrell

Power is a function of the voltage squared. So a 3kW heater at 240v becomes 2.25kW at 208v. It may not be significant if it's used for storage heating but as an instantaneous heater it would matter.

Reply to
charles

Gee thanks for that lesson. I've know and used it since the '50s. If you need that extra bit of heat, you can buy the proper heating element. Not at the over the counter type 'DIY' dumps, but at a real plumbing supply house.

Reply to
Michael A. Terrell

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