Going from delta to wye?

[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, 3?, 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 documentation

My 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]

transformers

transformers

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 ? 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.

 

[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??

 

[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