Thanks for the replies. Yes, what I'm looking for is an explanation as to the mechanics of the underground power supply. How it worked, etc. Diagrams, pictures, explanations would be a tremendous help. I imagine it was a nightmare to maintain and probably severely limited speed also. That it worked at all is amazing.
New York also had the same underground power supply system and San Francisco was about to do the same until the earthquake of 1906 happened and the underground power system idea was abandoned in order to get the streetcar system back in operation as quickly as possible.
I've exhausted all ideas as to what to "Google", as everything I input returns everything but what I'm looking for. I'll admit, what I'm trying to find is pretty obscure, but DC's system was in operation up to the early 1960's so I'd think there would be info out there somewhere.
As for DC's NEW system, battery operation is probably what they will go with. I watched Seattle testing a new battery powered streetcar line close to Union Station.in November. Had both overhead and battery. Trains would go up and down the line first with overhead power then do a run off the overhead.
However, I read of a new system being developed in Germany and France that uses a n induction system for power.