Effects of Simulated Ambient Dust on Current-Carrying Tribological Characteristics of Carbon Brushes/Collector Rings

To elucidate the influence of ring-chamber dust on the current-carrying tribological behavior of the carbon brush/collector ring system in hydro-generators, D172 carbon brushes paired with 45 steel collector rings were employed as the research subjects. Current-carrying sliding friction tests were systematically conducted under varying concentrations of carbon powder, iron powder, and carbon–iron mixed powders. The evolution of friction coefficient, wear loss, wear rate, and contact resistance was analyzed in detail, while the worn carbon brush specimens were characterized using three-dimensional profilometry, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The results demonstrate that different wear debris powders, serving as third-body media, exert significant regulatory effects on both interfacial tribological and electrical conduction behaviors. Under the carbon powder condition, a relatively stable carbonaceous third-body layer readily forms at the interface, maintaining low friction coefficient and wear rate—both reaching their minima at 120 mg/min—thus demonstrating effective friction reduction and wear resistance. In contrast, iron powder conditions promote pronounced abrasive action induced by hard particles, which increases the friction coefficient, accelerates carbon brush wear, and deteriorates the interfacial contact state. For carbon–iron mixed powders, the friction and wear levels lie between those observed for pure carbon and pure iron powders; meanwhile, contact resistance decreases steadily with increasing powder supply rate, indicating relatively superior current-carrying stability. The study reveals that carbon powder primarily contributes positively through lubrication and interfacial protection, whereas iron powder exacerbates damage via particle plowing and contact disruption. The synergistic interaction between the two determines the evolution of the interfacial film layer and the resulting changes in electrical contact performance. These findings provide a theoretical basis for wear control and operational maintenance of carbon brush systems in hydro-generators.