Effect of Ambient Temperature and Humidity on the Current-carrying Tribological Properties of Carbon Brushes/Collector Rings
The operational reliability of hydroelectric generator units is critically constrained by the current-carrying tribological performance of carbon brush/collector ring systems, which are highly sensitive to ambient temperature and humidity. This study conducted controlled-atmosphere experiments on a 45 steel/carbon friction pair under temperatures of 20–40 °C and relative humidity (RH) of 40–60%. Key parameters including friction coefficient, wear rate, contact resistance, and contact temperature were measured, and surface damage mechanisms were analyzed. Results show that at 35 °C and 50% RH, the average friction coefficient reached a minimum of 0.1297, a 46.6% reduction compared to the maximum of 0.2427 at 25 °C and 55% RH. The lowest average contact resistance of 1.52 Ω was obtained at 25 °C/50% RH and 40 °C/45% RH, representing a 49.3% decrease from the maximum of 2.27 Ω at 25 °C/40% RH. Wear rate was minimized at 50% RH. Contact temperature exhibited an 'N'-shaped variation with increasing temperature at constant humidity. Elevated temperature promoted oxidation but reduced water vapor and induced desorption of water molecules, hindering water film formation. At 30 °C, friction coefficient, wear rate, and contact resistance all reached relatively low values. Increased humidity reduced surface roughness and smoothed the brush surface. Water vapor is a key factor influencing abrasive and adhesive wear, with adhesive wear minimized near 50% RH. High temperature or high humidity environments degrade current-carrying tribological performance. These findings provide optimal environmental parameters for enhancing the operational reliability of hydroelectric generator units.