The Y-Y bond guarantees the transformation of electrical quantities without changing the phase-to-phase and line-phase voltage and phase lag, ie the primary line voltages will be in phase with the secondary line voltages. The same applies to phase voltages and phase currents for each phase.
It is not necessary for the tertiary terminals to be available for connection, being a built-in winding and another efficient measure is to originate the grounding of the neutrons n1 and n2 (fundamentally n1). gates 14/B56
Neutral grounding in transformers is important because it supplies a closed path for currents out of balance of the system and raises the possibilities of using the system because it is possible to connect three-phase loads, high power and different single-phase loads.
This connection causes the system to have some undesirable characteristics, such as distortions in the winding voltages caused by the third harmonic currents caused by the excitation phenomena of the transformer and the unbalance of currents in the case of feeding an unbalanced load.
Several times a way has been found to overcome the problem caused by the harmonic components: to add to the transformer a tertiary connected in D.