Brush Dynamics in Electrically Excited Synchronous Machines and their Influence on the Field Winding

This paper deals with the transmission of the field current in electrically excited synchronous machines (ESM) using brushes and slip rings. First, the theoretical principles related to brushes and sliding electrical contacts are presented. It is described how brush dynamics can lead to partial or complete lift-off of the brushes. We explain the possibility of predicting electric arcs arising when the brush is lifted and evaluate the usability of the developed models. Next, measurement results on brush slip-ring systems are presented and discussed. Finally, simulations using finite element method (FEM) are used to investigate the effects of brush dynamics on torque and iron losses in an ESM.