Voltage Build Up Process in D.C. Generator

Voltage Build Up Process in D.C. Generator Points : Voltage Build Up Process in D.C. Generator Let us consider a D.C. shunt generator: Consider an unloaded shunt generator, straight line Oa is the graphical plot ‘of Ohm’s law for field circuit and it represents field resistance which is constant throughout. When armature is driven at a speed, it will cut the residual flux, and according to Faraday’s law of electromagnetic induction small emf will be induced on armature called as residual voltage (oc). This voltage circulates small field current od in the field winding which produces the flux, this flux adds to the residual flux. Hence more flux will cut and more emf will induced (de), this emf raises the current to “of” which further increases the voltage to “fg” and so on. This increase in voltage will be up to stable point “n”. Not this “n” point is determined by the intersection of field resistance line oa and magnetization curve. Beyond this point n, the generated emf given by magnetization curve is less than required to maintain the corresponding field current.