Design Aspects of Conductive Microfiber Rings for Shaft Grounding Purposes

Carbon brushes using electrically conductive carbon graphite have been used for shaft-grounding and current-conduction purposes for a long time. We present an alternative brush concept made from millions of conductive microfibers. If properly designed, such brushes can meet all the demands on carbon brushes but exclude the problems of excessive wear and hot-spotting/thermal wear commonly quoted with the first. These brushes have negligible frictional wear, are free of maintenance, and robust towards contamination. In addition, they are especially suitable for use with high-frequency currents and voltages, as they also allow current- conduction based on electric field emission. We develop the design criteria for such brushes both for prevention of voltage build-up and current-conduction of several 10s of Amperes with frequencies in the MHz range. We support the theoretical results with measurement results taken at different rotor shaft speed.