Description and test results of a current collection system for continuous duty HPG

A current collection system which includes a cooling system capable of operating at high velocities and current densities is needed before a continuous-duty compact HPG (homopolar generator) can be designed and built. The authors developed a current collection system that is capable of continuous operation at current densities of 40 MA/m/sup 2/ and a tip speed of 250 m/s. The current collection system is an integrated current collection/actuation/cooling system. The current collectors are solid copper leaves, 0.33 mm thick, that are mounted on a circular holder. The actuation system is a piston that actuates the collectors onto the slipring axially. Thin film evaporation cooling, at the interface between the collector and slipring, is used to remove the heat generated. Thin coolant films are wiped on the slipring. A slipring current density of 13 MA/m/sup 2/ at 175 m/s for 20 s was demonstrated. The system reaches steady state operation in 4 s. A heat removal capability of 15 MW/m/sup 2/ with the thin film evaporation technique was demonstrated. The contact resistance density was about 20n Omega -m/sup 2/.<>