Characteristic of DC Compound Motor


     The compound motor can be of two types, namely, the cumulative compound motor and differential compound motor. In a cumulative compound-wound motor the series-field winding is connected in such a way that the flux produced by it helps the flux produced by the main field winding, whereas in differential compound-wound motor the series-field flux opposes the main field flux. The characteristics of compound-wound motors are combinations of shunt and series wound motors.  



Speed-Armature Current and Torque-Armature Current Characteristics :


     The speed-armature current characteristic and torque-armature current characteristic of differential and cumulative types of dc compound motors are shown. In cumulative compound motor where the direction of current in both shunt and series windings are in same direction the speed versus armature current curve is slightly a more drooping than that of a shunt motor as there is an increase in flux with load ( as the both series and main fields are added together ). As speed is inversely proportional to flux, increase in flux causes decrease in speed.

Characteristic of DC Compound Motor

     As seen in differential compound motor where the direction of current in both shunt and series windings are in same direction the speed versus armature current curve is slightly more than the shunt motor 



Torque-Speed Characteristics of Dc Compound Motor :


     The starting torque developed by a cumulative compound motor is more and as the load on motor increases torque will also increases with load, and at no-load where there is a constant speed. Cumulative compound motors are therefore suitable in application where there is need of high starting torque for heavy loads like in rolling mills, punching machine etc.

Characteristic of DC Compound Motor

     The speed of a differential compound motor doesn't changes accordingly to the increase in load but its torque decreases as the load increases. Since the shunt motor develops a good torque and its speed will be almost constant irrespective of the load, hence shunt motors are more better than the differential compound motors and therefore they used rarely. The speed-torque characteristic are shown.


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