Transformer connection

Here's what I think...

The magnetization of the transformer core from one half primary would cancel out the magnetization from the other half because the currents are flowing in opposite directions. Only the resistance of the wiring would limit the current.

You forgot to mention a critical point. Since no net magnetic currents exist in the core the secondary circuit will get no power.

Since there is no magnetic current, Can I expect that the core will not get hot? on the other hand, since there is no variation of flux and therefore there is no induced emf, can I assume that the coil will be heated up depending on the dc resistance of the coil?

The primary windings will still produce a modest amount of heat that will heat the core by thermal conduction. The core will have far less heat than a properly wired transformer transferring maximum power to a load.

https://testguy.net/content/274-Three-Phase-Transformer-Winding-Connections

"and both outer leads are connected to phase."

Both to one phase, or, to different phases?

Don't forget the possibility of a split phase connection.

Both to the same phase

The circuit protective device(s) will operate, thereby disconnecting the fault.

Is this what you mean?

No, I think he really means this:-

In that case,there will be current flow thru line side to the neutral,similar to two paralleled transformers.

Dear guru HiTechRedNeck,

i respectfully disagree. Two parallel connected transformers do not share a common core. In this case the windings are shared by the same core and the the current in each windings are such that the magnetic field generated by each winding will oppose each other and will have a field nullifying effect which does not happen in the case of two separate transformers connected in parallel.

Current will flow from line side to neutral as you indicated but will not be similar to that of in parallel connected transformers. The current in this case may be equal to the sum of current through each winding (line voltage / DC resistance of the winding).

Kind regards,

It may cause the circuit breaker to trip due to a possible high circulating current caused by twice as much voltage being fed to a few windings of the transformer..

"a few windings of the transformer.." -- Please explain why only a few windings.

The length of the turn by turn windings are normally not the same unless they used the special bifilar type of windings..

In the Bifilar type, two wires are wound together in parallel, side by side from the very start up to the finish end..

As the windings of transformers are wound, the circumference or diameter increases in proportion to the number of turns, which in turn also lengthen the magnet wires used to complete a designated number of turns..

The same reason why every winding layers differs in the length of wires together with the corresponding wire resistances..

Submit a simple drawing to show us exactly what you mean.

Your text explanation in ambiguous,and subject to various interpretations.

Or the OP could just simply identify which, if any, of the posted drawings is what they meant.

Please refer to Randall's drawing in reply # 13.

I would rather hear it form the original poster,otherwise,it is just another opinion.

If you look at Thankan's post#7: then it's fairly certain that he was the original poster.

You are right. My mistake.

Multi-tapped primary and secondary transformers are common to allow for voltage selection,both on input and output.

It is difficult to be certain.