Thermal Modeling of Continuous Duty Brush Gear

The operation of homopolar generator (HPG) contacts at current densities greater than 1.5 kA/cm2 and slip speeds greater than 180 m/s results in high wear rates in conventional contacts due to gross melting at the brush/rotor interface. High current levels also cause severe heating in the brush straps. The Center for Electromechanics at The University of Texas at Austin (CEMUT) is developing actively cooled brush gear for use in homopolar generators. Brush gear being designed for use in a multi-megawatt HPG is to be operated for at least 30 s at a current density of 2 kA/cm2 and slip speed of 200 m/s. Contact heating along with the heating of the brush strap and rotor was predicted by finite element analysis. The model takes into account heating due to contact resistance, friction, and the bulk resistance of the material as well as any cooling introduced to the brush, brush strap, or rotor. This paper describes the modeling and prefabrication analysis of the brush gear performance.