Going from delta to wye?

[VernB]

Greetings all!
So here I am, plenty familiar with 120/208Y and what do they hand me to connect to? 208D *sigh*.
I see that most of the 208D in the building have been outfitted with 1P 208(240) to 120/240 transformers. This seems a bit inefficient to me (at the very least it looks like it would unbalance the heck out of the 3P).
Would someone gut check me that it would be more correct to use a 3P 208D to 120/208Y transformer in this app?

Vern

[George Stolz]

Vern, what is a 208 Delta transformer? :confused:

Delta transformers are generally 120/240....?

[VernB]

Vern, what is a 208 Delta transformer? :confused:

Delta transformers are generally 120/240....?

The incoming power is 208D. The current transformers are 1P 240 (primary, apparently tapped down to 208) to 1P 120/240 (secondary). What I'm talking about is using a transformer of 3P 240D (primary, tapped down to 208) to 120/208Y (secondary). I don't see Square D listing any transformers of 240D to 1P 120/240.

What I'm questioing here is the efficiency of using a single phase transformer from the three phase power vs a three phase transformer from the three phase power.

Vern

[e57]

:-? :-? huh? :-? :-?

[LarryFine]

The only thing I can envision as 208-D would be 208-Y without the neutral. Just out of curiousity, test your line-to-ground voltage.

[al hildenbrand]

Vern,

I'm just guessing here, . . .

But,

It sounds like you have a space in an existing structure with an existing feeder or branch circuit in it that used to supply something. It sounds like that "something" was a 208 Volt 3-wire 3 Ø load.

Now, that "something" is gone, the 3-wire feeder (or branch circuit) is still there, and you are being asked to put it to use for another purpose.

Still guessing here, but, are the new loads to be simple 120 Volt single phase loads like lights and receptacles in an office?

[winnie]

It would certainly be possible to wind a transformer with a 208V delta secondary. There are some weird wired systems out there. But I expect that this really is a 120/208V wye service where for whatever reason the neutral is not brought out. Though I believe that such would be a code violation, and that at this voltage a wye system is required to be grounded.

In any case, with a three wire three phase feed, a single phase transformer would load only 2 of the 3 lines. But if you are talking multiple transformers distributed around the building, with loads balanced amongst the 'distribution' phases, then I see no significant efficiency difference between using single phase versus three phase transformers. Remember that a three phase transformer is simply 3 single phase transformers sharing a yoke.

Are you considering changing out the single phase transformers and replacing them with three phase? Or are you considering additions to this system?

On the secondary side, the 120/240V single phase panels would have the _benefit_ of being insensitive to harmonics (which are likely not a problem anyway). If you were to change to 120/208V panels, all of the neutrals in any multi-wire-branch-circuits would become current carrying conductors, and you would reduce the supply voltage to any two pole loads.

I would not consider changing any of the transformers to three phase transformers.

I might try to hunt down the service neutral to see if transformers could be eliminated.

-Jon

[kingpb]

Would you guys quit using the wrong voltage designation..........geez

It is 208Y/120V, unless of course you really do mean a 120/208Y (single phase open wye derived from a 3 phase 4 wire system)

I feel better now, carry on!

[kingpb]

Greetings all!
So here I am, plenty familiar with 120/208Y and what do they hand me to connect to? 208D *sigh*.
I see that most of the 208D in the building have been outfitted with 1P 208(240) to 120/240 transformers. This seems a bit inefficient to me (at the very least it looks like it would unbalance the heck out of the 3P).
Would someone gut check me that it would be more correct to use a 3P 208D to 120/208Y transformer in this app?

Vern

Whay not put a zig-zag transformer on the 208V Delta connected side to create a neutral, then you don't need any of the single phase transformers at all (assuming they are for nothing other then deriving a neutral)

[winnie]

It is 208Y/120V

You are absolutely correct that this is the designation that is supposed to be used for three phase wye service with 120V line to neutral and 208V line to line.

Unfortunately the designation is totally arbitrary; some standards body decided 'wouldn't it be neat if 208Y/120V meant something different from 120/208Y'. As such, I can never remember which it is, and don't have a logical chain that I can follow to tell me which it is. So I keep getting this thing wrong. *sigh*

-Jon

[cpal]

Whay not put a zig-zag transformer on the 208V Delta connected side to create a neutral, then you don't need any of the single phase transformers at all (assuming they are for nothing other then deriving a neutral)


If this delta ??? supply is actually a 3 phase feeder or BC with out the grounded circuit conductor the zig zag may be an issue.

450.5 Grounding Autotransformers.
Grounding autotransformers covered in this section are zigzag or T-connected transformers connected to 3-phase, 3-wire ungrounded systems for the purpose of creating a 3-phase, 4-wire distribution system or providing a neutral reference for grounding purposes. Such transformers shall have a continuous per-phase current rating and a continuous neutral current rating. Zig-zag connected transformers shall not be installed on the load side of any system grounding connection, including those made in accordance with 250.24(B), 250.30(A)(1), or 250.32(B)(2).

[al hildenbrand]

I think we need more info from Vern, first.

If all he's connecting is single phase, and he has load that is 120 V and/or will accept 208 V (as opposed to 240 V), then he might just be able to reassign one hot supply conductor to use as a neutral. . .assuming he can get into the supply side of his source feeder or branch circuit and actually make the alteration.

[jim dungar]

Unfortunately the designation is totally arbitrary; some standards body decided 'wouldn't it be neat if 208Y/120V meant something different from 120/208Y'.

Jon,

I am sure that IEEE will be glad to hear that it made an arbitrary decision to use ANSI-C84.1-1989.

[winnie]

I am sure that IEEE will be glad to hear that it made an arbitrary decision to use ANSI-C84.1-1989.

Standards are necessary.

Most standards are arbitrary, at least in part. For most standards, you have some arbitrary components, and then logic and physics dictate the rest.

I accept this standard, and will try to remember it and use it.

But the numbers could just as easily been the other way around.

-Jon

[jim dungar]

But the numbers could just as easily been the other way around.

Jon,

How often have you ever heard anyone say 277/480? My guess is most people learned the bad habit of saying 120/208 just because it sounds like 120/240.

Yes standards are necessary. Just in this forum, there have been many tangential answers to questions because the two parties did not understand what each was describing.

ANSI C84.1 contains the US nominal voltages and how to describe them. I believe this standard has been in existence at least since the 1920's with the only major recent change being the nominal voltages in the 50-60's. The order of the voltages, the seperator (/ or X), and the location of the letter Y all mean something.

[VernB]

The only thing I can envision as 208-D would be 208-Y without the neutral. Just out of curiousity, test your line-to-ground voltage.

The power entrances are all aerial so it's easy to see what's coming in. There's a 208Y entrance with 4 conductors in the drop and one side of the secondaries of the three transformers is tied to a common conductor (the neutral). On the entrance in question, there's only 3 conductors in the drop and there is no common connection among the 3 transformers, so I'm sure it's a delta configuration.

Also the main entrance breaker is also marked "208 Main Supply".

Vern

[George Stolz]

Jim, I ask these questions as a student, not as an adversary:

The order of the voltages, the seperator (/ or X), and the location of the letter Y all mean something.

Can you elaborate? I've never seen an "X" as a seperator. What does it mean?

What is the significance of the location of the "Y"?

What is a zig-zag transformer?

It is 208Y/120V...
My apologies for offending your delicate sensibilities, I have miswritten nominal voltages in the past as well.

Incidentally, I hope this post is up to your quality standards (http://forums.mikeholt.com/showthread.php?p=668462#post668462). I'd hate to waste anyone's time. :roll:

[VernB]

Vern,

It sounds like you have a space in an existing structure with an existing feeder or branch circuit in it that used to supply something. It sounds like that "something" was a 208 Volt 3-wire 3 Ø load.

Now, that "something" is gone, the 3-wire feeder (or branch circuit) is still there, and you are being asked to put it to use for another purpose.

Still guessing here, but, are the new loads to be simple 120 Volt single phase loads like lights and receptacles in an office?

Yup, this is an old mill, all the original equipment was 208 3P and the lighting was all fluorescent with 220V ballasts so they never had any provision for anything else except 208V in the older areas of the building. Loads will be standard 120V.

Vern

[VernB]

Are you considering changing out the single phase transformers and replacing them with three phase? Or are you considering additions to this system?

I would not consider changing any of the transformers to three phase transformers.

I might try to hunt down the service neutral to see if transformers could be eliminated.

-Jon

I've confirmed from visual inspection of the POCO transformers, this is definitely delta, not wye. There's only 3 phase conductors in the drop from the pole, no neutral.

Vern

[VernB]

I think we need more info from Vern, first.

If all he's connecting is single phase, and he has load that is 120 V and/or will accept 208 V (as opposed to 240 V), then he might just be able to reassign one hot supply conductor to use as a neutral. . .assuming he can get into the supply side of his source feeder or branch circuit and actually make the alteration.

Al, that's a confirm, 120V for most of it and anything that needs 240 will be just fine with 208.

Vern

[jim dungar]

Can you elaborate? I've never seen an "X" as a seperator. What does it mean?
The slash (/) means that both voltages are available. The cross (X) means that either voltage is available. Notice on a standard transformer the primary is often listed as 240X480 which means you can wire it for either 240V input or 480V. The transformer secondary is listed as 120/240 which means it can supply 120V and 240V at the same time.

What is the significance of the location of the "Y"?
It defines the connection of the transfomer windings. I apologize that I can't remember all of the options other than a standard 4 wire connection like 208Y/120.

What is a zig-zag transformer?
This is a special autotransformer connection used to effectively turn a 3 wire delta system into a 4 wire wye. This is not 100% accurate but it explains the concept.

My apologies for offending your delicate sensibilities, I have miswritten nominal voltages in the past as well.
I don't know if I am supposed to answer this one, but. I too have been miswritten electrical terms and as a result have been able to strecth many topics into mega-length discussions. One of my personal improvements goals is to be more correct in my term usage even if it is at the expense of appearing pompus at times.

[LarryFine]

Also the main entrance breaker is also marked "208 Main Supply".Maybe the address is 208 Main St. :D

[George Stolz]

Jim, thanks for the explanations. :cool:

I don't know if I am supposed to answer this one...
No, it wasn't directed at you, but I do appreciate your comment. :)

[brian john]

For years I wrote 208/120 (not sure why, I think it came from my business partner) anyway last year I had an engineer trash a load survey I did using this nomenclature and I had to redo the report (easy enough). You'd have thought I slapped him for the lecture the contractor told me he received (I never met any was only on a 3 way phone conversation with him. This was not the only issue he had with my report but it was major to him...Need to check my standards next time.

[George Stolz]

I'd say the way the subject has turned is definutely relevant to the OP, but we're not applying what we're saying to what Vern is saying. I'm gonna try.

Terminology is key to the discussion, because I think Vern is saying things that mean things other than what he intended.

I've confirmed from visual inspection of the POCO transformers, this is definitely delta, not wye. There's only 3 phase conductors in the drop from the pole, no neutral.
(Coloring mine)

Vern, if you're saying that the sentence in blue is the basis for the conclusion in red, then you're not saying what you intend to say.

The sentence in blue is saying that this is an ungrounded system. An ungrounded system can be delta or wye, physically speaking.

Yup, this is an old mill, all the original equipment was 208 3P and the lighting was all fluorescent with 220V ballasts so they never had any provision for anything else except 208V in the older areas of the building. Loads will be standard 120V.
I'm thinking what you intended to say is that the ballasts were all wired "Line-to-Line" at 208V. Is that correct?

Basically, I think you are dealing with a 208V ungrounded wye system.

[winnie]

On the entrance in question, there's only 3 conductors in the drop and there is no common connection among the 3 transformers, so I'm sure it's a delta configuration.
Vern

George, did you see the above? If you can see the pole pigs, you can often identify wye and delta connections.

Vern, my bias is similar to George's; I also expect that the service is really from a wye bank but with no neutral supplied. The 'common' interconnection between the transformers can be 'hidden', via what looks like the 'grounding' terminal on the can.

Can you see the primary bushings on the cans? One or two primary bushing per can? Is the primary connected wye or delta?

-Jon

[e57]

While off on the topic of voltage and system designation. (Which is the way I was always taught them - Voltage to ground/system voltage.) What is 220? And where does it come from? And why wont it go away!?!? :grin:

[LarryFine]

What is 220? And where does it come from?Did you ever see Mr. Mom? ;)

[jim dungar]

While off on the topic of voltage and system designation. (Which is the way I was always taught them - Voltage to ground/system voltage.) What is 220? And where does it come from? And why wont it go away!?!?


In the early days of electrifying the US the nominal supply voltages were 110, 220, 440V. During the '40s-50's these were moved up to 115, 230, 460V. By the mid 60s they reached their present and official (as listed in the NEC) of 120, 240, 480V.

Why they won't go away is purely due to bad habits. I have no problem with three phase voltage systems but when it comes to residential I tend to slip into the "220" world. In fact this bad habit caused me to get an answer wrong on a test back in 1975. I can't forget the test but I also can't break the habit.

[e57]

Did you ever see Mr. Mom? ;)

Is this the "210-220 - whatever it takes" quote that is often heard? I have no memory of the movie....

[Smart $]

Al, that's a confirm, 120V for most of it and anything that needs 240 will be just fine with 208.
Vern,

I think you need to look at just having the service "upgraded" to 208Y/120, 3Ø, 4W. Currently it sounds as though you have a 208V, 3Ø, 3W service (it doesn't matter whether it is delta or wye as loads do not "know" the difference). To consider using sub-transformers is just "dancing" around the problem.



Question for others on nomenclature:
Is the term "open wye" a technically correct terminology by IEEE standards? It seems to me wye transformation is open by its very nature. So "open wye" is a nothing more than a redundancy. If it is a legit term, would someone please supply the "legit" definition?

[VernB]

(Coloring mine)

Vern, if you're saying that the sentence in blue is the basis for the conclusion in red, then you're not saying what you intend to say.

The sentence in blue is saying that this is an ungrounded system. An ungrounded system can be delta or wye, physically speaking.


I'm thinking what you intended to say is that the ballasts were all wired "Line-to-Line" at 208V. Is that correct?

Basically, I think you are dealing with a 208V ungrounded wye system.

Correct, the ballasts are all wired line to line for 208V. I've actually spoken to some former employees of the mill when it was operating as a mill and confirmed the delta configuration. Of course, I'm looking at the POCO transformers from the ground, but as far as I can see, it's definitely delta. I'll try to get a cell phone pic when I go back in tomorrow.

Vern

[VernB]

George, did you see the above? If you can see the pole pigs, you can often identify wye and delta connections.

Vern, my bias is similar to George's; I also expect that the service is really from a wye bank but with no neutral supplied. The 'common' interconnection between the transformers can be 'hidden', via what looks like the 'grounding' terminal on the can.

Can you see the primary bushings on the cans? One or two primary bushing per can? Is the primary connected wye or delta?

-Jon

Jon, I'll try to get a couple of pics with the cell phone tomorrow when I go back, I've confirmed with former employees of the mill that these entrances were definitely delta and what a pain they were to deal with because they were very unusual and most of the electricians didn't understand them. Gives me a lot of confidence having to deal with them now :).

Vern

[VernB]

Vern,

I think you need to look at just having the service "upgraded" to 208Y/120, 3Ø, 4W. Currently it sounds as though you have a 208V, 3Ø, 3W service (it doesn't matter whether it is delta or wye as loads do not "know" the difference). To consider using sub-transformers is just "dancing" around the problem.


That of course would be the optimal fix, that's for sure, there's a few roadblocks to it. First is that nobody really wants to disturb the working service because nobody's really comfortable messing with it. Second problem is opening up a can of worms with local code enforcement by having to rebuild/replace existing grandfathered facilities up to "modern". As it is, local AHJ is leaning on them to rip out all of the aerial power and replace it with pad mounted transformer and centralized meters. Lovely idea, but it means major disruptions to the building operations and the cost of it would be phenomenal.

For better or for worse, I'm stuck dealing with what I've got in place (isn't that the way it usually works?).

Vern

[LarryFine]

Is this the "210-220 - whatever it takes" quote that is often heard? I have no memory of the movie....Yep:

"Are you gonna make it all 220?" - Martin Mull

"Yeah. 220... 221, whatever it takes." - Michael Keaton

[brian john]

Larry WHAT MOVIE?????

[LarryFine]

Larry WHAT MOVIE????? Sorry. Mr. Mom.

[brian john]

Larry:

My brain does not function that far back GOOD PULL

[al hildenbrand]

Is the term "open wye" a technically correct terminology by IEEE standards?An open wye transformer bank has two transformers.

The classic application for an open wye exists when the PoCo, for whatever reason, only has two of three primary conductors (phases) coming to the transformer bank, and the PoCo wishes to supply 3 Ø to a customer.

The PoCo will put two transformers on the pole and connect the primary windings in an open wye. The third wye connected primary winding is not there.

The secondary windings of the two transformers will be hooked up in the classic open delta. The customer will receive, typically, 120 / 240 V , 4 wire 3 Ø with a wild leg.

[VernB]

Correct, the ballasts are all wired line to line for 208V. I've actually spoken to some former employees of the mill when it was operating as a mill and confirmed the delta configuration. Of course, I'm looking at the POCO transformers from the ground, but as far as I can see, it's definitely delta. I'll try to get a cell phone pic when I go back in tomorrow.

Vern

I'm back on site, I've measured the voltages as 245/248/250 between phase conductors and 132/142/157 from each phase to ground. At this point, I'm guessing that this is properly 240D, not the 208 that it's marked as.

Vern

[Smart $]

Is the term "open wye" a technically correct terminology by IEEE standards?
An open wye...
I understand what the term "open wye" implies. That was not the question. Should I assume you're response to mean "Yes, it is a technically correct terminology by IEEE standards" ...and your description to be the one published in IEEE reference documentation. I have never seen the term "open wye" used in any reference documentation. The only place I have seen it used is here on these forums...

[Smart $]

...At this point, I'm guessing that this is properly 240D, not the 208 that it's marked as.
I would say confirmed as ungrounded 240V, 3Ø, 3W (delta) service.

[e57]

Wow, spooky.... High for delta or wye, and there are transformers on all of the equipment in the building???? All of those transformers may have been a way to deal with that excessive voltage. From what I understand this is an older industrial building that is going to be re-purposed? And use primarily 120 loads?

From the sounds of the voltage you measured (What were they measured with?) but you just may have a wye system that is tapped >10% too high. Or an open delta, only slightly high, but OK... You might think about getting the POCO to replace or re-tap them, but sounds like you need something else..

But reading back you say you have no neutral drop??? (If this is true, any measurement to ground is questionable) Either way you need to become more familiar with your POCO rep as you need something else (Like a neutral) for what you want - with 120 loads... Sounds like your are going to basicaly starting over for this building. And sounds like you want a wye....

Edit to clarify...

[al hildenbrand]

IEEE reference documentationMy 7th edition of the Authoritive Dictionary of IEEE Standards and Terms doesn't include "open-wye", while it does include "open-delta".

The 13th edition American Electricians' Handbook shows, in Figure 5.55, a "Y-delta connection with one transformer missing."

The 4th edition of the Electrical Engineers' Handbook, under the heading THREE-PHASE CONNECTIONS WITH TWO TRANSFORMERS, has a paragraph titled "Open Y-open Delta Connection."

[augie47]

Are they POCO transformers ? If so, what can they tell you. I agree with e57, "spooky numbers".... my vote would be Wye tapped high.

[jim dungar]

Are they POCO transformers ? If so, what can they tell you. I agree with e57, "spooky numbers".... my vote would be Wye tapped high.

The numbers are actually okay for a 240V ungrounded delta system. In fact I am suprised that the L-G voltages are so balanced.

[e57]

I'm surprised he got line to ground numbers.... (That high at least) Why I found it spooky is that he has no neutral from the transformer and it sounds as if it is an ungrounded system. We cant see it from here and there was some initial confusion over what exactly it was that he had.... For a delta it's not very high phase to phase, but ???? whats with the L-G numbers???? Thats darned good and strong for a non-referanced potential differance, from an ungrounded 'anything'... No grounded conductor connection back to the transformers from apparently an ungrounded system. Does that strike anyone else as odd? Would he not be measuring to outside of the system? (The Line to Ground numbers that is) If its just me I'll shut up...

[e57]

Wasn't there some other discussion that mentioned something like this - I think by Charlie B?

[Smart $]

The 4th edition of the Electrical Engineers' Handbook, under the heading THREE-PHASE CONNECTIONS WITH TWO TRANSFORMERS, has a paragraph titled "Open Y-open Delta Connection."
Who authors this publication? To what degree does the industry consider this publication authoritative in comparison to the others mentioned?

I also have the A.E.H. 13th Ed., considering it and the first you mentioned as very authoritative. To this point I'm still leaning towards "open wye" as being coined terminology.

[kingpb]

The secondary windings of the two transformers will be hooked up in the classic open delta. The customer will receive, typically, 120 / 240 V , 4 wire 3 Ø with a wild leg.

Great, just after it was decided that 208Y/120V was correct, now the 120/240V versus 240/120V pops up.

Al, from what you said above, a 3-ph, 4-wire system is correctly stated as 240/120V. which, is not to be confused with your standard single phase service of 120/240V.

As far as "open wye" it is mentioned in Note d) to Table 1 in ANSI C84.1. that should be authoritative enough.

It is a single phase service provided by the utility, from a 3-ph, 4-wire system. Hence you have a single phase service with 208V line-line, and 120V line-neutral. This would be differing in that the line voltages are still 120 deg apart, versus a 120/240V service with a line-line voltage of 240V, and a phase difference of 180 deg.

[LarryFine]

I'm surprised he got line to ground numbers.... For a delta it's not very high phase to phase, but ???? whats with the L-G numbers???? Thats darned good and strong for a non-referanced potential differance, from an ungrounded 'anything'... Does that strike anyone else as odd?
That points out why the type of volt-meter (high or low input impedance) to use depends on what you want to know. In this case, the numbers are what they are because of capacitive coupling between the lines and the earth.

If one connected a relatively low impedance load between any one line and ground, that line's measured voltage would drop to near zero, and the other two would zoom up to near line-to-line voltage, like a corner-grounded Delta.

[Smart $]

As far as "open wye" it is mentioned in Note d) to Table 1 in ANSI C84.1. that should be authoritative enough.
It is. :D

[al hildenbrand]

Great, just after it was decided that 208Y/120V was correct, now the 120/240V versus 240/120V pops up.Mea culpa.

Pounding of chest.

I am still striving to be rigorous.

[al hildenbrand]

Note d) to Table 1 in ANSI C84.1. . .should be authoritative enough.Thanks, Bob.

[e57]

That points out why the type of volt-meter (high or low input impedance) to use depends on what you want to know. In this case, the numbers are what they are because of capacitive coupling between the lines and the earth.


Low or high impedance - I usualy come up to half of those amound measuring an ungrounded system - usually the tell-tale that it is ungrounded. Maybe its got rods right next to each other in extremely conductive soil or some other parralel path through a water line or such?? :rolleyes:

[kingpb]

Thanks, Bob.

Thanks Bob? Who is Bob?

[al hildenbrand]

Thanks Bob? Who is Bob?Well, evidently not you.

Thankyou, kingpb, for the ANSI reference.

[VernB]

Ok, kind of wrapping this sucker up, I have the following:

This is actually a 240D ungrounded delta (not 208 as marked).

The options for dealing with this are 240 to 240/120 transformer, delta to wye transformer, or a zigzag transformer.

Optimal solution appears to be a zigzag transformer to supply an artificial neutral.

Thanks guys!

Vern

[jim dungar]

Optimal solution appears to be a zigzag transformer to supply an artificial neutral.

This artificial neutral will provide a system of 240Y/138. This is fine if all you want is a refence voltage of <240V. This is not good if you want 120V for loads.

If you think there are a lot of electricians that have a hard time diagnosing ungrounded deltas, just wait until they see 240Y/138.

[VernB]

This artificial neutral will provide a system of 240Y/138. This is fine if all you want is a refence voltage of <240V. This is not good if you want 120V for loads.

If you think there are a lot of electricians that have a hard time diagnosing ungrounded deltas, just wait until they see 240Y/138.

Crud, thanks for reminding me of that :). Looks like the only real option is a 240D to 208Y/120 transformer.

Vern

[dbuckley]

Looks like the only real option is a 240D to 208Y/120 transformer.
Which will be on the customer's side of the meter, and so will use paid for power every day for years to come... You ought to do a calculation to make sure thats cheaper than whatever an upgrade to a 4W supply would cost, including the prohibitively expensive upgrades. It probably is, but its worth making sure.

[Smart $]

Crud, thanks for reminding me of that :). Looks like the only real option is a 240D to 208Y/120 transformer.

Vern
Sounds like all you need is to supply 120V loads. I was wondering if perhaps a 240 to 120/240, 3W autotransformer would suffice...???