Chris...
The attachment that WesR provided 10-19-12 is informative!
I would consider a good start gettign answers to the following questions:
A) 3-single phase bank?
B) If 3-phase is it core-type or shell-type construction!
C) If 3-phase was a 3rd winding provided?
D) Capacity, and voltages?
E) Is neutral of prmary-side connected to supply neutral (i.e., 4-wire)?
F) Is load mixed i.e, 3-ph, ph-ph, and ph-neutral?
G) Balanced or unbalanced supply?
Phil