Ans: Step by step procedure of obtaining constant o/p using three brush generator
1) The field is excited from one main brush X and third brush Z fixed at 90° electrical with normal axis of brushes X and Y
2) As the load on the generator increases the armature reaction flux Øa increases .This is cross magnetising flux (crosses the main flux Øm)
3) Main flux Øm is is distorted .The resultant flux Ør at brushes 'ZX' reduces The effect is that the e.m.f. generated across them reduces .The effect is the reduction in field excitation .
4) This further reduces the emf generated across the main brushes XY The result is in controlling increased load and keeping o/p as far as possible as constant