Brush Shifting

Brush Shifting Points : Brush Shifting DC Generator When the armature of a D.C. machine (without interpoles) carries current, the magnetic and mechanical neutrals do not coincide. Sparking will occur at the brushes unless they occupy positions that short circuit coil sides in the neutral zone. The brushes therefore, must be shifted to the magnetic neutral. The effect of the armature reaction depends upon the value of armature current. The brushes, therefore, must be shifted back or forth continuously as the value of the load current changes or the brushes must be located in a compromise position that represents the best average load. Commutation The width of a brush is invariably greater than the width of a commutator segment and the mica insulation. Whenever a brush spans two commutator segments, the armature coil connected to these segments is short circuited.