The Artitec load is one piece. I suppose if one were careful they could be separated.
I am also aware of the old Bachmann one that comes on a depressed flat car.
Woodland Scenics also makes a substation with a transformer.
I know nothing of power transmission other than I don’t want to touch the wires, so I don’t know how accurate any of these models are. IMHO, the Artitec and Woodland Scenics products look acceptable. I believe the Bachmann load could be made acceptable with a little work.