High-Current Brushes, Part V: Subdivided Monolithic Brushes at Very High-Current Levels

Considerable interest has been shown during the last decade in the development of high-power electrical machines of the homopolar variety. Inherent in such machines is the transfer of very large currents between the rotor and stator at high speeds. In order to successfully transfer the high currents (current densities of up to 7.75 MA/m²at speeds of 50 m/s) with desired Iow losses and high reliability, a number of different schemes have been proposed. Such schemes include improved materials for monolithic brushes, the use of liquid metal systems, and the use of fiber brushes. The approach described utilizes subdivided monolithic brushes, which are intermediate in size and number of contacts between conventional monolithic brushes and fiber brushes. A series of short-term steady-state tests of brushes with constant total load, but with varying number of brush subdivisions, has been made. Results achieved by testing such brushes at three different current levels in a humidified carbon dioxide atmosphere are presented and discussed.