In this image what would be different if it were a Delta to Delta Trafo?????

[mbrooke]

That would imply a delta winding, but the winding could be wye.

It could, but not in this picture. The secondary neutral automatically disqualifies a primary wye under real world conditions.


And yes I know there is a wye ungrounded- delta- wye grounded 3 winding odd ball connection out in existence that "makes" its own primary neutral, but outside of a 115kv-13.8kv 60MVA POCO transformer I don't think one has ever been made for a 600 volt and under system.

 

[Smart $]

That would imply a delta winding, but the winding could be wye.

Three wires running to the primary of a 3Ø transformer implies neither a delta or a wye primary winding configuration.

 

[mbrooke]

Just an interesting observation: There are different ways to interpret and answer the original question. You take the angle of "this is the conductors we have, so if we keep those, what kind of delta fits that." I take the angle of "ok a delta, well erase the secondary stuff you have there and here are the options..." (as I did in post #6). Im am not saying one way of addressing the question is more right or wrong, just noting the difference. Similarly with the transformer designation in the drawing, I gave the OP words more weight and took into account that the drawing was not say drawn up in autocad. Others treated the drawing as gospel. Again, I am not saying one reading of the OP is more correct, just interesting to see how different people analyze and interpret things.

Regarding transformer designations, I'll retract the "industry standard" comment. I guess I dont really know if there actually is a specific "industry standard" in terms of the use of the words "delta" and "3-wire". I did do some digging though. I looked at a website that sells used transformers and they have photos of the data plates on almost every one. http://www.philipsbrothers.com/. About half of the delta primary padmounts just had a single voltage on the data plate. The other half had the voltage and the word delta. Of course they all had the phasor diagram on the dataplate. All of them said the voltage and the word delta in the verbal description. I didnt see any use of the term "3-wire"

Just today I came across an example of why I like to see the word "delta"/ 1.33 MW PV project plan set. Drawn/stamped by an EE. Also had third party review. Transformer shown as 12.47-480 volt, but its a wye-wye. You cant assume everything will denote a transformer correctly.

In the POCO world Y grounded primary wye grounded secondary is as common as water vapor and there are technical/operational reasons for that preference, however in the 600 volt and under world those concerns do not exist (or minimal) making wye-wye impractical never being used. The only time one will need a neutral for 480-208 conversion for an auto transformer (a few exist) and if such is present in the graphic, it would mean said graphic is incorrect.

 

[electrofelon]

Three wires running to the primary of a 3Ø transformer implies neither a delta or a wye primary winding configuration.

I think we agree, and that has been one of my major points. Perhaps "imply' is not the appropriate word. I'll rephrase: in the vast majority of cases in < 600 volt electrical construction, if the primary does not have a neutral, then it terminates on a delta winding. In theory, one could have a 3 terminal wye connection because the wye point is not accessible (not common in electrical construction but it happens elsewhere).

 

[Smart $]

.... In theory, one could have a 3 terminal wye connection because the wye point is not accessible (not common in electrical construction but it happens elsewhere).

In my experience, the wye point of a wye primary is accessible.

 

[roger]

In my experience, the wye point of a wye primary is accessible.

Same here, it's labeled "HO" and is common to "XO"

Roger

 

[Smart $]

Same here, it's labeled "HO" and is common to "XO"

If by "common" you mean directly connected, that is not my experience.

 

[roger]

If by "common" you mean directly connected, that is not my experience.

All the YY transformers I have used have had a factory installed removable jumper that ties the HO and XO taps together. I admit that my use of YY transformers has been Padmounts and dry types may be different.

Roger

 

[mbrooke]

All the YY transformers I have used have had a factory installed removable jumper that ties the HO and XO taps together. I admit that my use of YY transformers has been Padmounts and dry types may be different.

Roger

It depends. One some there is a separate HO and XO, on others a single HOXO bushing with both linked together and still on others both the HO is directly connected to the tank with no bushing accessible. Other than an isolated neutral, an HO serves about the only purpose of testing.

 

[roger]

on others a single HOXO bushing with both linked together

Not disputing that but please provide a link to one.

Roger

 

[Smart $]

All the YY transformers I have used have had a factory installed removable jumper that ties the HO and XO taps together. I admit that my use of YY transformers has been Padmounts and dry types may be different.

Service padmount (meaning MV to LV) that I've seen have jumpers from each terminal/bushing to the enclosure (ground)... not to each other, isolated from the enclosure. On services, both are typically grounded and thus the reason factory installs the jumpers.

I've only seen one dry type. IIRC it had an X0 to ground jumper but none on H0.

 

[mbrooke]

Not disputing that but please provide a link to one.

Roger

H0X0 linked and brought out via single bushing:

 

[mbrooke]

Not disputing that but please provide a link to one.

Roger

Separate H0 and X0 (grey bushing in the bottom of the HV compartment):

Schematic showing the separate bushings being independent of one another and not electrically connected:

Bonus; Ungrounded primary wye (as Electrofelon mentioned), but note the secondary delta:

I don't have any pics of the third kind, but I am mostly certain you can get a pad mount with the H0 bounded directly to the case as you would find with a 3 phase or single phase single bushing pole pig.

 

[roger]

Service padmount (meaning MV to LV) that I've seen have jumpers from each terminal/bushing to the enclosure (ground)... not to each other,

See mbrooke's post, notice they are linked together, not just bonded to the enclosure.

Roger

 

[Smart $]

See mbrooke's post, notice they are linked together, not just bonded to the enclosure.

Roger

I see that. Have never seen any of those up close in person. Learned something new today.

Also, note he show's the kind I mentioned.

 

[mbrooke]

See mbrooke's post, notice they are linked together, not just bonded to the enclosure.

Roger

I see that. Have never seen any of those up close in person. Learned something new today.

Also, note he show's the kind I mentioned.

I don't doubt you. Keep in mind it will vary greatly based on what each POCO specs during ordering as a result of project needs and established company practices. When ordering a utility transformer there are about a dozen different options for every possible spec imaginable, let alone the ability to order a custom odd ball. Hence IHMO where all the disagreement and confusion comes from.

FWIW these are the typical grounding options for an "off the shelf" padmount transformer, meaning if the money is green enough you can ask a manufacturer to cobble together just about anything outside the spec sheet.

Connections and neutral configurations

• Delta - Wye: Low voltage neutral shall be a fully insulated X0
bushing with removable ground strap.

• Grounded Wye-Wye: High voltage neutral shall be internally tied
to the low voltage neutral and brought out as the H0X0 bushing in
the secondary compartment with a removable ground strap.

• Delta-Delta: Transformer shall be provided without a neutral
bushing.

• Wye-Wye: High voltage neutral shall be brought out as the
H0 bushing in the primary compartment and the low voltage
neutral shall be brought as the X0- bushing in the secondary
compartment.

• Wye-Delta: High voltage neutral shall be brought out as the H0
bushing in the primary compartment. No ground strap shall be
provided (line to line rated fusing is required).

Page 5:


http://www.cooperindustries.com/con...es/library/210_3phTransformers/CA202003EN.pdf

 

[GoldDigger]

It is interesting to note the presence of the isolation link in several of the transformers with an H0X0 bushing.
Removing the link allows the wye primary to be operated as a wye with floating neutral point. That connection could be used with either a wye or a delta source if appropriate.
If the transformer had a delta secondary, the open wye point setup on the primary side would be more often used.

 

[mbrooke]

It is interesting to note the presence of the isolation link in several of the transformers with an H0X0 bushing.
Removing the link allows the wye primary to be operated as a wye with floating neutral point. That connection could be used with either a wye or a delta source if appropriate.
If the transformer had a delta secondary, the open wye point setup on the primary side would be more often used.

You know I do wonder about that. To my knowledge it can't be assessed from the outside but to be honest I don't even know where its located.

 

[electrofelon]

Mbrooke, great pictures thanks. I am used to seeing the common HO/XO terminal with removable bonding strap in the LV compartment as your pictures in post #52. The isolated HO bushing is interesting, never seen or heard of that.

So the Wye primary with no accessible wye point does exist! I am assuming from the phasor diagram that the wye point is not brought out. Would such a unit just be used equivalently to a delta primary?

 

[mbrooke]

Mbrooke, great pictures thanks.

Weclome, and thank you for starting this interesting debate

I am used to seeing the common HO/XO terminal with removable bonding strap in the LV compartment as your pictures in post #52. The isolated HO bushing is interesting, never seen or heard of that.

Some POCOs use them more than others. Personally (imo) it just "looks" right having the primary neutral separate from the secondary.

So the Wye primary with no accessible wye point does exist!

Yup, provided the secondary is delta (3 wire, no neutral).

I am assuming from the phasor diagram that the wye point is not brought out. Would such a unit just be used equivalently to a delta primary?

In that particular unit I believe it is not drawn out. (On some units it is brought out via insulted bushing in the HV compartment but you have the option of leaving it floating or not) An ungrounded wye primary functionally equivalent to a delta primary for that unit.