Thermal design and development of actively cooled brushes for compact homopolar generators

The thermal and hydraulic design of actively cooled current transfer brushes for compact homopolar generators (HPG´s) is described. The development of high-energy-density HPG´S at the Center for Electromechanics at the University of Texas at Austin (CEM/UT) requires brushgear capable of handling high current densities and large thermal loads. Platelet technology has been applied in the design of actively cooled brushes with coolant injection directly from the brush contact face into the brush-rotor interface. Coolant channels a few thousandths of an inch in diameter have been designed in brushes constructed of photoetched platelets of copper (0.020 to 0.005 in. thick) and then bonded to form the cooled brush. Platelet construction of brushes also permits the incorporation of internal instrumentation for temperature measurement. The brushes have been designed to provide data on the effects of rotor speed, current level, coolant flow rate, and coolant injection pattern. These brushes will establish the data baseline required for future cooled-brush designs.