Say we have 3 single-phase pole mounted 75kVA transformers that together form a 3-phase Delta-Wye system. Would you model those separately? If you model it as one single transformer, what kVA do you use?

We have a disagreement in the office about what the equivalent KVA should be for 3-75kVA transformers connected to form a distribution system.
Should the equivalent be:
a) 75
b) SQRT(3)*75, or
c) 3*75

If you model those 3XFMR's separately in SKM, do you get the same result as your answer above?

A bank of single transformers is consider as a single three phase transformer, if they are all the same size and impedance.
(3) 75kVA units equals (1) 225kVA unit.

^^^^ This ^^^^

Also note that the %Z does NOT triple and will likely be much lower than a typical 3 phase transformer. Those single phase cans are more like 1.2%, not 4 or 5% or so. This means your secondary available fault current will be higher than it is with a typical 3 phase unit.