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 and hot-spotting/thermal wears commonly quoted with the first. These brushes have ultralow friction and negligible wear and are very robust toward contamination, when compared with conventional carbon-based brushes. In addition, they are particularly 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 buildup and current conduction of several tens of amperes with frequencies in the megahertz range. We support the theoretical results with measurement results taken at different rotor shaft speed.