Transformer connections

[dparkersaltriver]

Transformer connections for wye wye transfromers. Connecting a 480v wye /277 to 400v wye 230v transfromer from a 3 wire 480 source.

 

[jim dungar]

Just ignore the wye connection point on the 480V side, let it float.
Ground/bond the neutral/wye point on the 400Y/230 side, just like any other 3 phase 4 wire transformer output.

 

[LarryFine]

Welcome to the forum.

Connect the wye primary as if it is a delta: allow H-0 to float - do not connect it to the supply neutral or to ground.

The wye secondary should have X-0 grounded as a neutral.

 

[winnie]

Does this particular wye:wye transformer have a tertiary winding? If not you may have poor line-neutral voltage regulation. I presume this is a three phase transformer with a common 3 leg core. If not, all bets are off.

See http://apps.geindustrial.com/publibrary/checkout/GET-3388B?TNR=White Papers|GET-3388B|generic

The problems of wye:wye transformers are described on the first page.

-Jon

 

[texie]

I'm curious why the OP wants to use a Y primary given the technical issues that it presents.

 

[LarryFine]

I'm curious why the OP wants to use a Y primary given the technical issues that it presents.

Yeah . . . wye?

 

[winnie]

To the op: Are you sure you have a wye:wye transformer, and not a three phase autotransformer with a wye coil arrangement?

 

[dparkersaltriver]

Makes sense to me thanks

 

[dparkersaltriver]

Yes it a wye wye

 

[dparkersaltriver]

Does this particular wye:wye transformer have a tertiary winding? If not you may have poor line-neutral voltage regulation. I presume this is a three phase transformer with a common 3 leg core. If not, all bets are off.

See http://apps.geindustrial.com/publibrary/checkout/GET-3388B?TNR=White Papers|GET-3388B|generic

The problems of wye:wye transformers are described on the first page.

-Jon

Looks like ho and xo are common

 

[dparkersaltriver]

To the op: Are you sure you have a wye:wye transformer, and not a three phase autotransformer with a wye coil arrangement?

member: 163595"]
Looks like ho and xo are common
[/QUOTE]

To the op: Are you sure you have a wye:wye transformer, and not a three phase autotransformer with a wye coil arrangement?

It is a autotransfromer

 

[dparkersaltriver]

To the op: Are you sure you have a wye:wye transformer, and not a three phase autotransformer with a wye coil arrangement?

Yes it is a autotransfromer

 

[winnie]

Do you need to use the neutral on the output? Or is the requirement to take 480V down to 400V?

 

[dparkersaltriver]

Yes need to use on the load side

 

[winnie]

I believe you have the wrong transformer for the job.

Remember that if you want to supply line to neutral loads from a wye system, you are required to ground the neutral.

In addition to the problems of poor neutral voltage regulation, your transformer neutral is electrically connected to both your input and output. This means that the transformer neutral is going to try to act as a neutral for your _entire_ supply system, not just your secondary loads.

You state that you have a 480V 3 wire source. You don't state if you have an ungrounded delta, a grounded delta, or 3 wires from a grounded wye supply. If you have an ungrounded delta, then this transformer is going to try to act like a grounding transformer for the entire system. If you have a grounded delta supply, then grounding the neutral of this transformer will result in a short circuit.

If you have a grounded wye supply, then you are going to need to bring all 4 wires to this transformer to provide the correct neutral reference.

-Jon

 

[dparkersaltriver]

member: 163595"]
Looks like ho and xo are common

It is a autotransfromer
[/QUOTE]

 

[dparkersaltriver]

It is a autotransfromer

[/QUOTE]

I believe you have the wrong transformer for the job.

Remember that if you want to supply line to neutral loads from a wye system, you are required to ground the neutral.

In addition to the problems of poor neutral voltage regulation, your transformer neutral is electrically connected to both your input and output. This means that the transformer neutral is going to try to act as a neutral for your _entire_ supply system, not just your secondary loads.

You state that you have a 480V 3 wire source. You don't state if you have an ungrounded delta, a grounded delta, or 3 wires from a grounded wye supply. If you have an ungrounded delta, then this transformer is going to try to act like a grounding transformer for the entire system. If you have a grounded delta supply, then grounding the neutral of this transformer will result in a short circuit.

If you have a grounded wye supply, then you are going to need to bring all 4 wires to this transformer to provide the correct neutral reference.

-Jon

 

[dparkersaltriver]

[/QUOTE]
I have 3wires from a grounded 480/277 wye system.

 

[dparkersaltriver]

Heres a pic

 

[dparkersaltriver]

I floated xo/ho and have 400v phase to phase 230 v phase to xo and 230v phase to ground