newbie

[lemonman]

How do you connect 3 single phase transformers to get 3 phase 4 wire secondary, 277/480v?

 

[infinity]

You would connect one side of each coil together to form a center point. This would be your neutral. I would look like the WYE version of this:

 

[infinity]

Here's a little better diagram that shows the voltages:

 

[tkb]

Does it matter which way the winding is connected?
If a winding is connected in reverse will there be a problem.

Let's say the delta is connected
H1 on winding 1 to H2 on winding 2
H1 on winding 2 to H2 on winding 3
H1 on winding 2 to H2 on winding 1

X1 on all windings are the phases
X2 connect together in the center of the wye

What would happen if one winding was connected backwards?

 

[winnie]

What would happen if one winding was connected backwards?

If one of the secondary windings is connected backwards, then the output phase angles and line-line voltages will be wrong. In what is supposed to be a 480/277 system, all of the phase-neutral voltages would still be 277V, and one of the phase-phase voltages would still be 480V, but the other two phase-phase voltages would be 277V. Additionally, neutral current would not balance.

If one of the primary windings is connected backward in a bank of separate single phase transformers, you would have the same result.

If one of the primary windings is connected backward in a three phase transformer with a common core, then in addition to the above problems, the core magnetization will be wrong.

-Jon

 

[Fulthrotl]

Does it matter which way the winding is connected?
If a winding is connected in reverse will there be a problem.

Let's say the delta is connected
H1 on winding 1 to H2 on winding 2
H1 on winding 2 to H2 on winding 3
H1 on winding 2 to H2 on winding 1

X1 on all windings are the phases
X2 connect together in the center of the wye

What would happen if one winding was connected backwards?

it'll smoke.

 

[tkb]

I knew that there would be a problem, but I wanted to get it out there for the OP.

 

[lemonman]

Follow-up question.
What is the lowdown if there are 3- 112.5 kva pole mounted transformers, at some undefined primary voltage, for the electric service? What is the total secondary current, if the secondary voltage is 277/480v Y? I'm confused as to how this differs from 1- 112.5 kva 3 phase transformer.
Thanks for the help.

 

[charlie]

In a wye configuration, the current in the coil is the same as the current in the conductor that attaches to the transformer. Therefore, the output current of a 480 volt wye is the same as the output current of a 277 volt coil. :smile: