Wow, thanks, all, for the insight. I am a bit confused because I found after making my post that the Blume text on transformers states that Percentage Impedance is approximately equal to 100x the ratio of KVA output vs KVA input. Maybe that's how it was in days of yore, and the newer NEMA TP1...
Is it possible for me to make a rough estimate of the loss that a three-phase 360 kVA power transformer would have just from the percent impedance listed on the nameplate? Any insight appreciated! Thanks, Fred