Why phase shift is required in star-delta transformer between primary and secondary?

In star-delta transformer how the phase shift of 30 degree will be done, between primary and secondary?. Is this phase shift is must?Why phase shift is required in star-delta transformer between primary and secondary?The phase shift is a natural consequence of the delta connection. It is not an option.



The currents entering or leaving the star winding of the transformer are in phase with the currents in the star windings. Therefore, the currents in the delta windings are also in phase with the currents in the star windings, and also the currents entering or leaving the star windings. And obviously, the three currents are 120 electrical degrees apart.



But the currents entering or leaving the transformer on the delta side are formed at the point where two of the windings comprising the delta come together - each of those currents is the phasor sum of the currents in the adjacent windings.



When you add together two currents that are 120 electrical degrees apart, the sum is inevitably shifted by 30 degrees.Why phase shift is required in star-delta transformer between primary and secondary?Here phase shift is not a requirement. It is a natural result because of the particular type of connection.Why phase shift is required in star-delta transformer between primary and secondary?Having a 30degree phase shift is part of convertion from wye-delta.