"Dyn11" is not a mysterious code: it describes how the windings are connected and the phase shift they introduce. Here is how to read a vector group, and why this one is the distribution reference.
The vector group describes two things: how the three phases of each winding are connected together, and the phase shift the transformer introduces between the high-voltage and low-voltage sides.
Three basic connections exist: star (Y/y), delta (D/d) and zigzag (Z/z). By convention, the capital letter designates the high-voltage winding, the lower-case letter the low-voltage one. An "n" indicates the neutral is brought out (accessible).
The final digit is the clock number. It expresses the phase shift between HV and LV, counted as on a clock face: each "hour" is worth 30°. So 11 corresponds to 11 × 30° = 330° (that is, –30°), and 5 to 150°. This shift must be known, in particular to run transformers in parallel.
Which is why our configurator proposes Dyn11 by default, while leaving other groups open.
For standard distribution, Dyn11 fits the vast majority of cases. A different group is justified by specific constraints: paralleling with an existing transformer (the clock numbers must be compatible), heavy unbalance to manage, or an operator's requirements. When replacing a unit, you normally keep the existing group. In doubt, state your context in the configurator, or leave Dyn11, the safe default.
General educational overview; the final vector group must be validated against your network and protection constraints.
D = high voltage in delta, y = low voltage in star, n = accessible LV neutral, 11 = a phase shift of -30 degrees (11 x 30). It is the standard distribution group providing a neutral on the LV side.
It lets you distribute both 400 V phase-to-phase and 230 V phase-to-neutral, and it conditions the installation's earthing system (TT, TN). Without a brought-out neutral, no classic single-phase 230 V.
Not freely: the clock numbers (and other parameters) must be compatible. A Dyn11 and a Dyn5 introduce different shifts and cannot simply be paralleled. To be checked case by case.
Usually you keep the same group as the unit being replaced, to stay compatible with the installation, unless there is a specific reason validated by your design office.