Thanks for the additional information. I have a model in EasyPower that I am looking at. When I run a 1500 KVA system with a delta-wye, I get a certain short circuit rating and calorie rating for arc flash. When I run the same simulation but switch the system to a wye-delta, I get the same exact short circuit rating and calorie rating. Perhaps this may lead to a conclusion that there is much difference between the two. Perhaps they run the delta secondary on loads that they know they need to mitigate harmonics. Perhaps they use the wye secondary for 277V loads. Incidentally, some of the wye secondaries are grounded, and some are not. Some of the delta secondaries are grounded, some are not. Interesting single line for sure.