Abstract
Metal fiber brushes were evaluated in a magnetic test fixture with variable speed, transport current and magnetic flux density. Silver alloy fiber brushes with a cross sectional area of 8.4 square millimeters were operated at a current of up to 90 amps, with a current density of 1070 amps per square centimeter. The brushes were operated in humidified air, at speeds of up to 15.5 meters per second and a flux density of up to about 0.6 Tesla. Significant differences between anode and cathode brush impedance characteristics were observed. The current-voltage curves of the cathode brush was approximately linear with current indicating constant contact resistance while the anode generally had higher impedance and in some cases its characteristic was non-linear with a diode like behavior. The magnetically induced circulating current losses were insignificant because of the small brush geometry and moderate magnetic flux density. Non-dimensional wear rates were on the order of 5E-11. Although operating temperatures in the brushes reached over 120 o C for the higher speeds and currents, thermal runaway was not observed at temperatures up to 120 o C.
Published Version
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