How to supply electrical current to a motor-powered rotating shaft?
The obvious approach is to either use a slip ring 



or a roll ring. 



1000A at 1400 RPM is possible for either approach (do your own thorough search for commercial suppliers, the links are merely intended to be informative). 

The slip ring uses brushes, the roll ring uses spring rollers. 

There are other methods possible, but not so applicable for DC. There will be significant electrical noise generated by the moving contacts so if you have sensitive instrumentation nearby it can be affected. The roll ring will likely be quieter electrically. Roll rings are used in the ISS to transmit solar power across a rotating joint.