DELTA / DELTA transformer

GoldDigger

Moderator
Staff member
Why would a delta to delta transformer have an X0 terminal on the secondary side?
Because it is actually a delta to wye transformer (which could be used to feed a delta wired load as long as the neutral is brought out to the disconnect whether it is actually used by the load or not?
Or because it also contains a set of zig-zag windings to create a neutral point for the delta for some oddball reason?

There will still be a ground/bonding point for that transformer frame and other sheet metal whether it is connected to the secondary windings or not, but that should not properly be labelled X0 if not connected.
 

Flex

Senior Member
Location
poestenkill ny
Because it is actually a delta to wye transformer (which could be used to feed a delta wired load as long as the neutral is brought out to the disconnect whether it is actually used by the load or not?
Or because it also contains a set of zig-zag windings to create a neutral point for the delta for some oddball reason?

There will still be a ground/bonding point for that transformer frame and other sheet metal whether it is connected to the secondary windings or not, but that should not properly be labelled X0 if not connected.
Would the X0 affect a corner grounded system?
 

GoldDigger

Moderator
Staff member
Would the X0 affect a corner grounded system?
The X0 of a wye winding set should not be connected to anything if the secondary is supplying a corner grounded delta system.
But the code requires that in almost all cases where the wiring system has a neutral, that neutral must be grounded rather than one (or none) of the other conductors.) One could argue that as long as the X0 is not brought out of the transformer housing, you could choose to corner ground the delta.
 

texie

Senior Member
Why would a delta to delta transformer have an X0 terminal on the secondary side?
For lack of more detail, I assume this is a 480 delta to 240 delta.
It adds little cost when making a transformer like this to add the X0 terminal at the center point of one winding. This makes the unit more versatile in that you can use the X0 terminal to ground and bond the secondary as is required and you then have a 120/240 3 phase "high leg" secondary. Or you can leave the X0 not connected to anything and corner ground the secondary to be compliant (not usually the best choice).
Also if you use the transformer in reverse you just connect nothing to the X0, but then you have to run the 480 secondary corner grounded or ungrounded (neither is usually desirable but can be made compliant).
 

Smart $

Esteemed Member
Location
Ohio
For lack of more detail, I assume this is a 480 delta to 240 delta.
It adds little cost when making a transformer like this to add the X0 terminal at the center point of one winding. This makes the unit more versatile in that you can use the X0 terminal to ground and bond the secondary as is required and you then have a 120/240 3 phase "high leg" secondary. Or you can leave the X0 not connected to anything and corner ground the secondary to be compliant (not usually the best choice).
Also if you use the transformer in reverse you just connect nothing to the X0, but then you have to run the 480 secondary corner grounded or ungrounded (neither is usually desirable but can be made compliant).
I agree that it could be a 240V delta secondary... but the midwinding tap is usually marked X4.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
For lack of more detail, I assume this is a 480 delta to 240 delta.
According to ANSI standards:
X0 is a terminal that is only associated with the center point of a wye connection on the LV side of a transformer.
X4 would be the terminal associated with the center point tap of one winding in a delta configuration.

Delta and wye, have to do with the connection of the windings, not how many conductors are involved in the system or circuits.
 

texie

Senior Member
I agree that it could be a 240V delta secondary... but the midwinding tap is usually marked X4.
Yes, usually X4 (also think I have seen this as X6?) in this case. I took the OP to be just calling this X0, but maybe he really doesn't have a delta/delta?
I guess I need someone more versed in the correct terminal designations for all the more non usual stuff such as this.
 

templdl

Senior Member
Location
Wisconsin
For lack of more detail, I assume this is a 480 delta to 240 delta.
It adds little cost when making a transformer like this to add the X0 terminal at the center point of one winding. This makes the unit more versatile in that you can use the X0 terminal to ground and bond the secondary as is reqired and you then have a 120/240 3 phase "high leg" secondary. Or you can leave the X0 not connected to anything and corner ground the secondary to be compliant (not usually the best choice).
Also if you use the transformer in reverse you just connect nothing to the X0, but then you have to run the 480 secondary corner grounded or ungrounded (neither is usually desirable but can be made compliant).
This is typical texie. Just think how simple this would be should the NP information or a picture of the NP were to have been included in the OP.
But it is a lot more fun to guess what the OP's question is.
My "guess" would be a delta secondary with a lighting at between the A and C phase which would actually be a 240/120, 3ph 4w. Would not the centertap be identified as X0?
But, what I find interesting is the number of replies that are based on interpretations, assumptions and guesses which when it comes to electric power can extremely dangerous.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
A few days ago someone posted a picture of a transformer nameplate that showed the wiring diagram with the X4 designation. I would link to it if I could find it.
 

templdl

Senior Member
Location
Wisconsin
Not according the standards in the industry. The center-tap would be X4.
I stand to be corrected Jim. I guess I could be the only reason I could think of for an X0 termination on a "delta" which now concerns me. If it is in fact a delta where did they get an X0 from? Taking a wild guess they could have a 240y/138 which may be a drive transformer and they are assuming the 240v is a delta voltage. Simply asking just what the X1,2,and3 to X0 voltages are could explain a lot.
It would help a lot to have a picture of the NP of the transformer but it is a lot more fun to guess.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
If it is in fact a delta where did they get an X0 from? Taking a wild guess they could have a 240y/138 which may be a drive transformer and they are assuming the 240v is a delta voltage. Simply asking just what the X1,2,and3 to X0 voltages are could explain a lot.
I agree.

it is common that people 'automatically' associate winding configurations when only L-L or L-G voltages are provided.
For troubleshooting (e.g. identifying 3-phase systems) all 10 voltage measurements are often required.
 

Flex

Senior Member
Location
poestenkill ny
It's a 480v delta primary 240v delta secondary. The transformer is being used in a PV install. Beside the fact that inverter can only generate 3 phase 480wye it was hooked up anyway. The building it feeds is 240v corner ground delta. Voltage from the building read what it should for a corner ground system. Before we turned on the inverter I wanted to check the readings on the primary side just to be safe. H1 -G 520v H2-G 480v H3-G 208v. Didn't go phase to phase for fear of smoking my meter. The secondary is hooked up as X1-hot X2-grounded hot X3-hot. There is a terminal at the bottom of the transformer marked X0 but nothing is hooked to it. The taps on the primary side are all on the 480v tap. Why would I get such strange voltages? I thought it strange that there was an X0 on a delta and can't remember if it went to one winding or all of them.
 

templdl

Senior Member
Location
Wisconsin
It's a 480v delta primary 240v delta secondary. The transformer is being used in a PV install. Beside the fact that inverter can only generate 3 phase 480wye it was hooked up anyway. The building it feeds is 240v corner ground delta. Voltage from the building read what it should for a corner ground system. Before we turned on the inverter I wanted to check the readings on the primary side just to be safe. H1 -G 520v H2-G 480v H3-G 208v. Didn't go phase to phase for fear of smoking my meter. The secondary is hooked up as X1-hot X2-grounded hot X3-hot. There is a terminal at the bottom of the transformer marked X0 but nothing is hooked to it. The taps on the primary side are all on the 480v tap. Why would I get such strange voltages? I thought it strange that there was an X0 on a delta and can't remember if it went to one winding or all of them.
Please provide us with a picture of the nameplate of the transformer as that would make it very simple to answer a lot of question. Providing verbal description often are prone to misinterpretation, assumptions and guesses.
 
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