Characteristic of Shunt DC Generator

Characteristic of Shunt DC Generator Points : Characteristic of Shunt DC Generator Building up of Voltage of a Shunt Generator at No Load The curve plotted between the generated emf and shunt field current will be similar to that. The generator excites itself due to residual magnetism and develops the voltage as described below:
Line OP rep-resents the shunt field resistance. When the generator is started a small emf (represented by OA is induced due to residual magnetism. This induced emf causes a flow of current oa’ in the field circuit. This is obtained by drawing a horizontal line from point A meeting the field resistance line at point ‘a’ and then from point ‘a’ drawing perpendicular line meeting current axis at a’. When field current is Oa, the generated emf. is a’a” which produces a field current Ob’, which in turn produces a high voltage b’b”. This it is observed that effect is cumulative and value of induced emf and field current increases until these reach point D, the point of intersection of the shunt field résistance line and magnetic characteristic obtained. Instantaneous increases in induced emf and field current are shown but in practice flux increases gradually. OB is the maximum value of emf that can be generated and generator cannot generate more than this voltage.