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The speed versus armature current and torque versus armature current characteristics of dc motor

Torque versus armature   current characteristics of DC motor : The torque developed   by the motor would therefore be directly dependent upon the armature current as indicated by the torque equation ,T=K ΦIa. Increasing the armature current would increase the torque and vice versa.   Shunt motor : For the shunt motor shunt field is connected accross the line, the flux in the machine will remain essentially constant . So, for shunt motor, T=KΦfIa Compound   Motor: The current in the armature must also pass through the series field winding. The series winding may be connected comulatively were the flux due the series field will aid the shunt field flux. In cumulative compound motor the series field flux is additive with the field flux. But in the differentially compound motor the series field flux is substractive with main field flux. Total flux does not remain constant in compound motor as it does in the shunt motor. Cumulative compound motor T=k(Φf+Φs)Ia