120/240 Y transformers.

[Rocketir]

I had a customer request a 3phase 4 wire 120v l-n, 240v l-l wye connected voltage transformer. 120 l-n on each phase and 240 l-l across each phase. I had never heard of this? Does any utility use these? We currently have the 120/208 with three 120 l-n's and the 208 l-l. We also have the 120/240 with two 120 l-n. Never heard of whay he wanted and almost think its not possible unless you center tap the tx's somehow. Any information available on these? He mentioned that they were being used in the midwest. thanks.
Jess

 

[davidbeach]

They don't, can't, exist. You could have a 240Y/139V transformer, or you can have a 208Y/120V transformer, or you can have a 240/120V delta where the 120 is derived from the center tap of one winding. In all cases of a wye connected transformer the two voltages will be related by the square root of 3.

 

[Rocketir]

Thank you for the sanity check.
ps. enjoyed the NeqSeq paper.

 

[davidbeach]

You're welcome, and thanks for the comment on the paper.

 

[waross]

I agree with davidbeach.
Your customer is probably confused with the four wire delta connection.

or you can have a 240/120V delta where the 120 is derived from the center tap of one winding.

This may be open delta or closed delta, and will supply 240 volts three phase, and 120/240 volts single phase.
In open delta, the main, center tapped, transformer supplies the single phase loads and supplies line current to the three phase loads. The second transformer supplies line current to the three phase loads.
In closed delta, the three transformers support the three phase loads. The two untapped transformers supply approximately 1/2 of the 240 volt single phase load current. The center tapped transformer supplies approximately 1/2 of the 240 volt load current.
respectfully