Mechanical Stability of Solid Brush Current Collection Systems

Conventional methods for designing mechanically stable solid brush current collection systems are sometimes found inadequate when developing state-of- the-art electrical machines. These methods rely primarily on the brush angle relative to the rotor as a complete stability parameter. This paper shows that brush angle is not a complete dynamic stability parameter; other parameters are important also. Stability boundaries are shown as functions of brush angle and system damping for various typical values of the other system parameters. The analysis indicates that brush stability improves with increasing trailing brush angle, decreasing slope of the friction- velocity curve, decreasing brush load, increasing brush radius of curvature relative to rotor radius, and increasing supported brush length.