you have 48 volt frames, you have dual power supplies tied to dual transformers that supply current. Each of the frames is served by DC from a humungous battery center supplied by 2 (power company transformers) each on a different AC leg. That is good until power dies, then large generators kick in to assist the downage of AC power. All of this assumes the blueprints are correct. Sometimes they are not. That gets you a mention in the national papers.