Abstract: A solid brush current collecting system for dynamo-electric machines which selectively uses compatible materials in different applications for the moving and stationary contact members. Brushes of different compositions are disclosed and the current transfer and collecting members are operated in an inert gas atmosphere, such as carbon dioxide, having either water or organic additives, such as alcohols, hydrocarbons, ketones, and the like, to achieve operation of the current collector system at higher temperatures, higher velocities and higher current densities than is possible with conventional systems. Low friction and low wear rates are in part achieved by operating the contact members in a low temperature environment.