Characteristics of DC Shunt Generator


     A dc shunt generator, the field winding is connected across ( parallel ) the armature terminals and in which the armature supplies both the load current and the field current.



No-load Characteristics :


     The generator is rough up to its rated speed. Now we notice some voltage in voltmeter, though IF is zero. This is due to residual magnetism present in the poles. This voltage is known as residual voltage ( OA ). Now increase the field current, Ish in steps and note down the corresponding voltmeter reading.

Characteristics of DC Shunt Generator

     The graph is obtained by plotting ammeter reading i.e., Ish versus voltmeter reading. The OCC starts from point A but not from origin as earlier. 



Load Characteristics :


     It is found that after voltage building up, a shunt generator is loaded, then its terminal voltage drops due to armature resistance and armature reaction. The terminal voltage V and load current IL can be measured, the relation between these V and IL can be drawn like a - b, known as external characteristic curve.

Characteristics of DC Shunt Generator

     If armature resistance drop components are added to this curve ab we get internal characteristic curve a - c, as shown. If armature reaction drop components are added to this curve ac we get curve or line a - d, it can be called as no-load characteristics, but on no-load the IL = 0. Therefore it is  imaginary and hence shown with dotted line.


     It is increased beyond the rated value, the terminal voltage decreases rapidly due to increased armature reaction, represented by curve be. It is known as drooping characteristics.




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