Three Phase Transformer with only Single Phase Input

Technically you can rewire a 3 phase transformer to accept a single phase input power and then produce a split phase output power. I do not recommend trying to do this. To do this you will first have to do a simple analysis of the magnetic field current paths to identify where the primary and secondary windings should reside. Then you will have to rewire the windings of the transformer itself. This might involve removing all windings because some transformer windings are potted to reduce mechanical noise. If you attempt to do this I'd expect that the core will saturate at a lower power than the three phase condition.

Unfortunately you have the wrong component to do this job. It will likely take less time acquiring the correct transformer than it will take to rebuild this transformer to make an inadequate transformer out of what you have.

To simplify, since the transformer I have received is oversized (KVA rating), would it be possible to use only one of the windings to achieve the 208 volt output?

Do yourself a simple but worthwhile favor.JUST RETURN THIS TRANSFORMER TO SUPPLIER AND GET THE RIGHT ONE WITH REASONS FOR DOING SO.

JS

After some more thought, I think my approach would be more likely to work if the transformer had the same configuration of windings on both primary and secondary, in other words, delta / delta or wye / wye.

My previous (and this) answer might be bad, but they are not off topic.

You can probably get 120 volt at 1/3 of the transformers rated KVA.

You can probably not get 208 volt.

Look at the wiring diagram for the transformer.

Send transformer back. That's the easy way.

Short of returning the transformer:

If your transformer 2ndary is 208V phase - Neutral (?), then supplying 600V to 2 legs on primary will give unequal voltages on the 2ndary: L1-N = 208V ; L2-N = 104V ; L3 - N = 104V or approximately. the numbering is arbitrary and you have to find out which is which.

Loading this way, will have unbalanced current in the transformer and you can use the single 208V leg. The trouble is that there will be poor regulation (Voltage will fluctuate dependent on load, to some extend).

If this is a small size transformer for a single user, less than few kW, you could try and see. But if it is a large one for multi-users, better let them change it.

In any case, if you are not familiar with electrical devices like this, better not take a risk of damaging other peoples equipments. Make sure that adequate protection (fuses, C.B.) are there.