High current brushes: VIII: Effect of electrical load

Abstract

Performance data are presented from controlled experiments with Ag-graphite brushes sliding on copper slip rings in a continuous-operating mode over a wide range of electrical loads (0.8 – 8 MA m −2) in a humidified CO 2 environment. The observed contact resistance, friction and wear characteristics are explained on the basis in part of past and recent contact models and in part of thermophysical property data acquired for the specific Ag-graphite brush material (mass fraction of silver in graphite, 0.75). The phenomenon of electromigration of silver is invoked to explain observed consistent asymmetry in contact resistance between anode and cathode brushes. Direct evidence in support of the models and observed brush performance is offered from results of detailed contact surface morphology and structure analyses.