So l have attached the question and my attempt to the solution. I think l answered all questions correctly....but for part c l do not know if l draw the phase angles of the winding currents and voltages with a 30 degrees phase shift between them ?

 

I would think the secondary windings are capable of carrying the full 543.5A at 460V line-line.

So the total load power would be √3*460*543.5=433kW.

Each transformer must carry half that power or 216.5kW.

The primary kVA per transformer with rated winding current & voltage is still 250kVA so each transformer is running with a power factor of 216.5kVA/250kVA=0.866

BUT ... the total 3-phase source power factor will be unity.

 

I would think the secondary windings are capable of carrying the full 543.5A at 460V line-line.

So the total load power would be √3*460*543.5=433kW.

Each transformer must carry half that power or 216.5kW.

The primary kVA per transformer with rated winding current & voltage is still 250kVA so each transformer is running with a power factor of 216.5kVA/250kVA=0.866

BUT ... the total 3-phase source power factor will be unity.

But wouldn't that damage the windings of the transformer ? Do we want that much current flowing into the windings of the transformer ?

 

But wouldn't that damage the windings of the transformer ? Do we want that much current flowing into the windings of the transformer ?

No since that value is the rated current for the secondary winding of each of the 250kVA transformers. One can draw the rated current without any damage.

 

No since that value is the rated current for the secondary winding of each of the 250kVA transformers. One can draw the rated current without any damage.

I am confused there. I thought the 250kVA was for three delta transformers connected. Which means when another phase is removed the power output decreases.

 

It's spelled out in the wording of the question which you might review ...

So two single phase transformers, individually rated at 250kVA are connected in open delta.