Wear Rates and Current Distribution of Carbon Brushes on Steel Slip Rings

This paper deals with brush wear and current distribution of carbon brushes on steel slip rings. Measurements of brush wear and brush current have been carried out both in generators in service and in a laboratory test rig. Wear rates increase with increasing brush current only for positive brushes on-site, whereas an evident correlation between brush current and brush wear was found for both polarities in the laboratory. The magnetizing current is, in general, unevenly distributed between the brushes operating in parallel, and the current shifts between different brushes during operation. The current distribution becomes more uneven with increasing mean current density and with increasing circumferential velocity of the slip ring.