Shaft Riding Brushes To Control Electric Stray Currents.
Electric discharge causing bearing and seal damage may occur in any nonelectric machine as a result of static electricity, accidental electromagnetic self excitation of casings, rotors, piping, foundations, galvanic effects, faulty grounding, etc. . In addition, electric machines may develop very high shaft currents (order of 100 amp in large generators) because of inherent electrical characteristics. Shaft riding brushes can help detect problems and neutralize the currents by shaft grounding. Conventional brushes (carbon, graphite, solid metals, braids, and combinations thereof) have proved to be unreliable. They also develop excessive amounts of conducting dust, require frequent maintenance (cleaning, replacement), and it may be necessary to shut the unit down for servicing. Other problems include intolerance to oil, water, dirt, other types of environmental contamination, and high surface velocity, and high or low temperature. Some brushes require special slip rings. The development, testing, and application of a patented line of wire-bristle brushes is described along with their electrical characteristics, life expectancy, specification parameters, maintenance and maintainability, etc. Design features, and over 12 years of field experience, especially with turbomachinery and for ship propeller-shaft grounding, are also described. Results of an ongoing three year comparative test program (laboratory and operational) by a major user are described. Hardware will be available for inspection at presentation of paper.
Sohre, John S. (1991). Shaft Riding Brushes To Control Electric Stray Currents.. Texas A&M University. Turbomachinery Laboratories. Available electronically from